Investigation On Different Salt Curing Methods In Quality And Storage Stability Of Salt Cured Hilsha

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1. INTRODUCTION
 
1.1. Status and importance of fish processing and preservation in Bangladesh:
 
Fish is one of most useful and easily digestible the protein source in the diet of Bangladeshi people. About 85 to 90 % fish proteins is digestible and contain all essential dietary amino acid (Nilson, 1946). In the agriculture based economy Bangladesh, fish and fisheries play an important role in human nutrition, employment, income generation and export earnings. Fisheries provide 63% of animal protein, contribute 5.3% to GDP and 5.77% to foreign exchange earnings (DOF, 2005). Fish is highly perishable food item especially in hot climate of Bangladesh where unsanitary environment and poor handling practice worsen the situation. And a high proportion of artisanal catches fails to reach the markets far from areas of production due to the poor handling practice and very often due to the high cost involved in transportation and due to poor storage facilities.
 
In Bangladesh as the transportation and the process of handling of fish and fish products are poor, a huge quantity is spoiled during transportation of product from one end of the country to the other. Moreover, fisherman does not get proper return for their harvest during the peak period of harvest due to the seasonal supply of fish and lack of preservation facility in Coastal area of Bangladesh. Even sometimes they just have to abandon the spoiled harvest, as it becomes unfit for human consumption The lack of adequate fish handling, preservation and processing methods and storage facilities contribute significantly to the low supply of fish to poor rural dwellers which form three quarters of the population in developing countries whatever may be amount of harvest, as it has got no value until it reaches the consumer as a food Therefore appropriate fish processing and preservation methods are very much essential in order to minimize the fish wastage due to spoilage and to improve the fish quality for proper consumption. 
 
 
1.2. Status and Potential of fish preservation and processing in Bangladesh:
Dry and dehydrated fish is one of the most important export items in Bangladesh. The demand for dried and dehydrated fish as an export item is increasing day by day. According to the Export promotion Bureau in 2003-2004 the quantity of exported dry fish and fish product from Bangladesh was 472 tons which valued 4.16 crores taka and in 2004-2005 it was 272 tons and valued 3.71 crores taka. On the other hand, in 2003-2004 the quantity of exported salted and dehydrated fish was 377 tons and valued 1.38 crores taka and in 2004-2005 it was 770 tons and valued 28.97 Crores taka indicating increased trend in the earning of more foreign currency from previous year exporting salted and dehydrated fish products. It is also clear that the demand of these fish product is increasing than that of the unsalted dried fish products.
 
1.3. Fatty fish is a potential candidate for preservation and processing:
From the time immemorial hilsa fish have been found to play very important role in the field of national economic development, employment and in the supply of protein enrich food to the people of our country. At present the country produces near about 2 lacks metric tons of hilsa fish which cost about 2000Crores taka. Chilled hilsa exported to India was 3584 metric tons and export earning valued about 51.95 Crore taka. Source for the year 2004- 2005 regular earning statement from certificate issued.(Jatiya Matsya Pakkah, ’05 ) hilsa fish alone contributes about 12% – 13% of the total fish production of Bangladesh and it also contributes about 1% to the GDP. It also earn 50-60Crores taka each year through Exporting of about 2000-8000 M. tons of hilsa fish to India and many other countries (Halder et al 2004)
 
About 4.5 lacks of fisherman are engaged on a full time and part time basis in harvesting. In the same way 20-25 lacks people are involved directly or indirectly in distribution marketing, transportation etc.
 
Hilsa fish is a very popular and tasty fish among Bangladeshi people living at home and abroad. It has been found to contain higher level of protein, fat and minerals. The fish has been found to contain specialized type of fat having about 50% of unsaturated fatty acids out of which about 2% w-3 fatty acids exists. This fatty acid reduce the human blood cholesterol level thereby reducing the level of heart diseases (Rao et al., 1977). Hilsa fish protein also contains nine different types of fatty acids which human stomach cannot synthesize. Moreover it contains higher quality of Ca, P, Fe and Vitamin A, D including trace level of Vitamin B. Hilsa fish liver contains 120 IU of Vitamin A (Halder et al., 2004)
 
1.4. Role of salt in fish preservation and processing:
Salting is a process of fish preservation where the water content is reduced by the penetration of salt, whereby the activity of moisture of the spoilage bacteria is stopped or reduced, Sodium chloride diffuses into the fish flesh by a dialysis mechanism and water is diffused outside due to the osmotic pressure between the brine and fish muscle solution. Two basic principles describe the mode of action as well as significance of salting:

 
Salting is done in combination with sun drying and smoking for variety of species. But in   case of fatty fish species like hilsa fish salting is the choice of traditional fish preservation.
 
1.5. Problem statement:
Salting is a suitable processing and preservation technique for country’s greatest harvest of fatty fish. There are however several problems found to be associated with the process as discussed below:

 
1.6. Activities and expected outcome
● Hilsa and sorpunti fish were collected in high fresh and extremely acceptable condition as raw material for the present problem study.
● Commercially salt cured hilsa fish were also collected from the local fish market for using it as a raw material to compare its quality and storage stability with that of the experimentally salt cured hilsa and sorpunti fish.
● Attempts were made to produce best quality salt cured hilsa and fish.by using different salt curing methods and to adopt the best quality product producing salt curing method for future use in the laboratory as well as in the industrial level.
● Our activities also includes to study the present problem on the basis of analytical, technological, chemical and physical aspect with a view to find out the best processing method suitable for salt curing of hilsa and sorpunti fish.
● We have also tried to evaluate the storage stability of all the salt cured products produced in the laboratory as well as commercially salt cured product collected from the local fish
market.
● All possible variable/ parameters related to quality, storage stability etc. were utilized as per facilities available in the fish technology laboratory IFST,BCSIR, Dhaka.
● We have also taken steps to make a comparative study on the technological and qualitative gradation among all of the salt cured products studied in the present thesis work.
● Attempts were made to compute and interpret all of the available results to give a crystal clear idea regarding the findings of the present study for its benefit with immediate effect and afterwards.
 
 
 
1.7. Research Needs
● To take research initiative for following regulation regarding public health and sanitation while producing salt cured hilsa and sorpunti fish in laboratory level.
● To ensure on the freshness and acceptable range of the raw material so that no spoiled or already spoiled fish taken for salt curing process.
● Research work are also needed in order to find out where there is any variation in quality and storage stability of the product if washing and cleaning of the whole fishes and cut fishes are ensured.
● Clean knives, containers or other tools used during the salt curing process have to be ensured to be clean and contamination free so that the raw material of the process may remain contamination free by bacteria and pathogens.
● Pure salt of standard quality, proper salt fish ratio are to be maintained in order to avoid the problems already faced by the existing system of salt curing of hilsa fish on commercial basis.
● During wet salting the salted fish are to be kept in the brine solution so that the fish cannot come in contact with the air in order to avoid development of rapid rancidity.
● Research activities are also needed in the field of proper packaging and storage of the finished product in order to ensure stable quality product during storage and marketing.
● Research works are also needed to avoid excess salting which are not favorable for producing a quality salt cured fish product of standard quality and storage stability.
● Research and development works are needed in order to verify all of the steps starting from collection of fresh acceptable fish samples and to the finishing of the salt curing process together with quality assessment and storage stability study. Simultaneously making comparison with that of the commercially salt cured hilsa fish product procured from the local fish market.
 
1.8. Scope and limitation
● There was a scope for analysis of the nature and category of free acid present in the lipid portion of the experimentally and commercially salt cured hilsa and sorpunti fish. We know that some of the free fatty acids are essential for maintaining sound health and preventing cardiac diseases.
But we could not work in this field of free fatty acid analysis due to lack of GLC in the fish technology laboratory.
●  We could compare between smoke cured and salt cured hilsa fish products during the present assignment, but due to time constrain we could not make such effort.
 
It was our limitation.
● In addition to find out the level of Fe, Ca, P and sugar there were scope for finding the level of Zn, Cu, I in the salt cured hilsa and sorpunti fish.
But due to lack of the required chemical we become unable to do this sort of analysis.
 
It was our limitation.
● There was a scope for field trial of the salt cured fish  produced in the laboratory together with the commercially salt cured fish to have an ideas about the consumer level of acceptance.
 
A field trial of the experimentally salt cured hilsa and sorpunti fish with that of the commercially salt cured hilsa fish collected from the local fish market were given in the fish technology laboratory and in the Food Quality Control Laboratory and the result of the trial goes infavour of the salt cured hilsa fish (mixed), two types of salt cured hilsa fish with sugar and preservative.
 
● There was a scope to see the amino acid present in all of the salt cured fish samples studied in the present thesis work.
 
But it was not possible for doing so due to unavailability of the amino acid analyser in the fish technology laboratory.
 
It was our limitation for the present thesis work.
    
1.9. Objectives:
No research activities can be carried out without any aims and objectives. As such we have considered all of the works already carried out in this field and we have also taken into considerations the problem statements mentioned above regarding salt curing of hilsa fish in Bangladesh. Having in mind all of the factors mentioned in the different paragraphs of the introduction chapter we deem it fit for undertaking the present thesis work with the following aims and objectives.
● To take an attempt for producing better quality salt cured hilsa and sorpunti fish the laboratory level.
● To find out and adopt the best method of salt curing especially for hilsa fish.
●To observe the quality as well as the storage stability of the salt cured experimental fishes with that of commercially salt cured fish collected from the local fish market.
●To give the suggestion and recommendation so that the fish processing personnels consumers as well as the academic professionals may be benefited economically, nutritionally and for academic fitness.
 
2. LITERATURE REVIEW
It is well known to all of us that just after harvesting the fish spoilage of fish is caused by autolysis, enzymatic and by bacterial action. As a result quality of harvested fish is reduced due to spoilage loss during post harvest period. To minimize the spoilage loss of the fish, various traditional and old methods as well as modern ad updated technique of fish processing and preservation have been introduced by the fish technologist, fish processors and by the academic professionals. As a ready reference we would like to sight some of the research work done in the field of fish processing and preservation those have already been carried out at home and abroad.
 
The literature reviewed here includes few works on salting and salted products of those species which are considered to have direct relationship with the present research work.
 

 

 

 
□ Wang et al. (1954) while working with characteristics of muscle tissue dehydrated             by fish drying techniques observed that reconstitution properties were influenced by six factors which were.

 
□   Von Loesecke (1955) reported that reconstitution means the replacing of water in dried foodstuffs though the process of reconstitution a large quantity of the water which was originally present is assimilated. The ability to reconstitute is one of the most distinctive qualities of dried fish products.
□ Wodicka (1958) while worked with texture of foods reported that the ideal type of dried foods are specifically processed products which have rapid reconstitution properties and closely resemble the freshly prepared good items.
□  Von Loesecke (1955) observed that not all products reconstitute to 100 % of their original state because of inherent differences in their chemical composition.
□ Connell (1957) reported that dried fish produced in a one current of air attain properties which is different from those of the fresh fish and understanding of  the difference in quality among various dried food products have been found to have a clear picture from the consideration of  reconstitution properties. Considering the fact Smithies (1962) observed that unsatisfactory processing condition or prolong storage may give a quality to a food product that will require periods more and will be difference from the tenderness and juiciness from the control.
□  According to Acker (1967); Rockland (1969) and Labuza (1972), the temperature, atmosphere, moisture and the relative nature of the components comprising the foods governed the chemical and physical reactions responsible for food alteration during storage.
□  Taylor (1961) reported that equilibrium relative humidity of a foodstuff determines whether it will gain or loss moisture in a particular environment and so this property is more relevant to storage behaviour than in moisture content.
 
□  Gur-ariech et al. (1965) showed that data on moisture sorption of foods are useful in the determination of techniques for processing and packaging of dehydrated foods and for the prediction of undesirable chemical, physical and microbial changes that might occur during storage of dehydrated foods.

 
 

 
3.1. Basic materials necessary for fish salting process:
Pure common salt, turmeric and two varieties of fatty fishes were used as raw material for the present research study.
 
3.1.1. Fishes
Introduction of the fishes:
The two varieties of fatty fishes were used for this comparative study of different salting process.  The fish varieties were:
                 
Hilsa (Tenualosa ilisha, Hamilton-Buchanan, 1976)
Sorpunti (Puntius sarana, Hamilton-Buchanan, 1822)
 
Collection of the fishes:
 
The raw fishes had been purchased from the local fish market of Dhaka city in the early hours of the day and the fishes were brought to the Fish Technology Section, IFST, BCSIR, Dhaka for conducting the research activities in the month of February, 2006.
The whole experimental period covered 10 months of duration started from February, 2006 to November 2006.
 
Feature of the External morphology of the fishes:
For each species, ten samples of fishes had been taken for the experiment. The length and weight of each sample of hilsa, sorpunti fishes were estimated and an average length and weight for each species were determined and recorded.
 
Table1: Showing average length and weight indicating the external morphology
              for each species.     
  

 
3.1.2. Common Salt:
Sodium chloride (NaCl), also called salt, common salt, and table salt, is generally recognized as a safe, antimicrobial and incidental food additive. Salt has been used as a seasoning and flavor enhancer as well as a preservative or curing agent, had been purchased from the local market.
Salt Purity:
For salting, the purest salt with the finest grain available had been used. Salt which are virtually chemically pure (less than 1% impurities) results in fish with a milder, more pleasant flavor, which do not need prolonged freshening. The finer the salt, the more rapidly the brine forms, and thus the more rapidly the flesh is penetrated with salt. Standard curing salt was collected from the local market.
 
                   
 
 
 
 
 
 
 
 
 
 
 
 
Plate 1 Showing hilsa fish in fresh and highly acceptable condition
                                  during taking measurement in the laboratory
 

 
 
                Plate 2 View of sorting of the pieces of hilsa fish for salt curing by 
                              application different salt curing methods in the laboratory
 
                                                                                                                                                                          
 
              Plate 3 Showing sorpunti fish in fresh and highly acceptable
                             condition  during taking measurement in the laboratory
 

 
                        Plate 4 Showing  pieces of sorpunti fish for curing by different
                          salt curing methods in the laboratory
 
3.1.3. Turmeric:
Fresh dried and powdered form of turmeric is used as a newly introduced element in salt curing method with a hypothesis that it would work as –

 
3.1.4. Sugar: Sugar, salt, preservative treated hilsa fish product were used as a research material in the present study with a view to introduce a new dimension in the salting process and extend its shelf life with the preservative action of the sugar itself. To confirm regarding the enhancement of quality of the quality of the sugar, salt, preservative treated hilsa fish we have produced this product in the laboratory so that we can control all the influencing factors for improvement of quality. The added sugar have been considered to act as a preservative along with added preservative.
3.1.5. Preservative: Addition of preservative actually slowed down the liberation of soluble amino compounds in the salted product. The amount of amino acid residues in peptides decrease strongly than that of the free amino acids. Addition of preservative during storage improve the taste. Added preservative actually slowed down proteolysis activity which is based on the retarded growth of enzyme producing bacteria. The effective action of the preservative was to a certain extent slightly different in its use for instance benzoate and POB-OMe were relatively stronger in preventing the liberation of peptides and sorbate was the least effective.     
 
3.2. Methods applied for the present experiment

3.2.1. Dry salting:
During this experiment the raw fishes were eviscerated, cleaned, washed, weighed and had been enrolled by dry salt (fish weight : salt weight = 3:1), stacked in containers and stored for a salting or curing period, at room temperature.
In this method, the extracted water of the fish due to salt action had been removed from the container. Thus the fishes are always allowed to remain in dry condition for the production of dry salt cured fish.
During this process of dry salting the change in weight, salt content, moisture content and physical acceptance of the fish have been determined and observed. Its quality was also observed by chemical method.
3.2.2. Pickle salting:
While applying this method, the raw fishes were eviscerated, cleaned, washed, weighed and had been enrolled by dry salt (fish weight : salt weight = 3:1), stacked in containers and stored for a salting or curing period, at room temperature.
The salt reacts with the fish and water is extracted out from the fish-body and a salt-solution is formed. Thus in this method, the fishes are always allowed to remain in such solution for the production of pickle-cured fish.
During this process, the changes of fish in weight, salt content, moisture content and physical acceptance of the fish have been determined and observed. Its quality was also observed by chemical method.
3.2.3. Brine salting:
During this experiment the raw fishes were eviscerated, cleaned, washed, and weighed. A 30% salt solution is prepared (30 gm salt in 100 ml water) which is called brine. The fishes are kept at this saturated brine solution stacked in containers and stored for a salting or curing period, at room temperature for the production of brine salted fish.
During this process of dry salting the change in weight, salt content, moisture content and physical acceptance of the fish have been determined and observed. Its quality was also observed by chemical method.
 
3.2.4. Mixed salting:
This method is a combined form of dry-salting and brine-salting method.
At first, the raw fishes were eviscerated, cleaned, washed, weighed and had been enrolled by dry salt (fish weight : salt weight = 3:1). Secondly, another 30% brine solution is prepared and added to that fish, stacked in containers and stored for a salting or curing period at room temperature.
Thus in this method, the fishes are always allowed to remain in such dense salt solution for the production of mixed-salted fish.
During this process, the changes of fish in weight, salt content, moisture content and physical acceptance of the fish have been determined and observed. Quality assessment was done by chemical method.
 
3.2.5. Preparatory salting:
Fish are scaled, eviscerated and soaked in dry salting vat for a duration depending on the types and size of the fish (2-8 days). Salted fish is soaked in freshwater tank and thus preprocessed for a sundrying.
 
Methods applied for the salting of hilsa fish
1. Dry salting
2. Pickle salting
     3. Brine salting                                           
      4. Mixed salting
 
Methods applied for the salting of sorpunti fish

2. Pickle salting
     3. Brine salting                                           
      4. Mixed salting
      5. Preparatory salting
 
A                                                                                                                      B
                                                                                   
 
 
 
Plate 5 Showing salted fish products A) hilsa B) sorpunti fish produced by different
              salt curing methods in the laboratory
 
 
3.2.6. A new dimension of preservation and processing of fatty fish by using salt, sugar and preservative
 
3.2.6.1. Pickle salting: In addition of the pickle salting method, 5% sugar and trace amount of preservative were added and the salted fish samples were kept them in refrigerator. The weight of the fish were taken after a certain time interval.  
 
3.2.6.2. Mixed salting: In addition of the mixed salting method, 5% sugar and trace amount of preservative were added and fish samples were kept in refrigerator. The weight of the fish were taken after a certain time interval.  
 
 
 
 
Plate 6 Showing the salted hilsa fish product treated with sugar and preservative
Salting of roe
1. Brine salting
2. Brine salting with sugar and preservative

 
Plate 7. Showing roe in fresh and highly acceptable condition
A                                                            B


 
Plate 8. Showing salt cured roe A) In brine salt curing method B) In salt, sugar and  
           Preservative
 
 
 
 

 
Plate 9. Showing commercially salt cured hilsa fish product
 collected from the local market
 

 
Plate 10 Showing salt cured hilsa fish product produced in the
                             laboratory by following commercial salt curing process
 
3.3. Fish storage
The processed and preserved sorpunti fish after completion of the salt-curing process have been found to attain a level of quality. But storage of the salt-cured product is very important to extend its shelf-life. Because in a high humid and high temperate weather of Bangladesh, the cured fish products losses its quality by adsorbing more water from the surrounding air and thus facilitating the growth of bacteria, moulds and so on. In order to verify extended shelf-life of the salt-cured fish product of the present study, three kinds of storage conditions were designed and developed in the laboratory which are mentioned as follows:

 
Procedure:
After 7 days, when the fishes become dry and crispy, each kind of salt-cured fishes are subdivided into 3 portions of amounts. Each portion are then weighed and kept into 3 different storage conditions into the laboratory. The stored products are observed at intervals to record the sensory scores.
In order to reduce the adverse effects of NaCl on lipid oxidation, color, and flavor of fish, fish and fish products are handled, prepared, and processed under refrigerated temperatures. Low temperatures reduce the rates of oxidative reactions and retard microbial growth.
 
A                                                                           B
 

 
 
                                                                       
 C
 
Plate 11 Showing different storage conditions of salted sorpunti fish
                 kept in

 
3.4. Biochemical composition analysis
 
3.4.1. Moisture determination:
Procedure:
Determination of moisture content of the raw as well as salt-cured fishes was conducted by AOAC method (AOAC, 1975). For this purpose, some washed and dried tarred porcelin basins of known weight were taken. Each type of salted fish samples were taken into each basin and weighed. The samples were dried into oven at 104°C for 24 hours in order to remove the moisture. Drying, cooling and weighing were continued until constant weight was established.
Calculation:
                                                 
% of moisture =                                                       x    100
                  
 

 
   Plate 12 Showing an electronic balance while taking weight of
                                    fish muscles samples.
 
3.4.2. Protein determination:
Micro-Kjeldhal method:
The crude protein of the fish was determined by Micro-Kjeldhal method. The basic principle of this method involves the converting of the nitrogenous protein into (NH₄)₂SO₄, when boiled with H₂SO₄. (NH₄)₂SO₄, on distillation with excess of sodium hydroxide (NaOH), gives ammonia (NH₃) which is absorbed in boric acid solution containing methyl red. The amount of N₂ absorbed in boric acid is determined by titration with N/70 H₂SO₄.
 
Procedure: the process involves the following steps:
Preparation of digested solution:
Some pieces of filter paper were taken and weighed in an electronic balance. The each type of fish samples were taken in each piece of filter paper and kept a record of the identification of the fish sample-type and they were also weighed. A mixture was prepared by adding 20 ml concentrated H₂SO₄ (20%) with the addition of digestion mixture (a white powder).This mixture was kept in the Kjeldhal flask Buchi-digestion unit. Then the weighed fish sample with filter paper also kept in that Kjeldhal flask of digestion unit until the mixture becomes clear. Thus a water-colored digested solution is prepared.
 
Preparation of sample solution:
      Water was mixed with the digested solution at an amount to make the total solution of 100 ml.  5 ml of sample solution was added with 10 ml NaOH and 150 ml water. The prepared sample solution was kept into Micro Kjeldhal distillation unit for 50 minutes and the distillate were collected in 5 ml of 2 % boric acid and were titrated with  N/70 H2SO4.The titration readings were recorded and calculated as follows.
 
Calculation:
The percentage of nitrogen in the sample was calculated by the following equation:
% of N₂ = (Titration Reading – Blank Reading) X Strength of Acid X                                                                                                            
0.0002 X 100/5 X            
     
 % of protein = % of total N₂ x 6.25
Table 7 (d). Showing variation in biochemical composition of the experimentally dry
                     salted product of sorpunti fish  produced in the laboratory
 

 
The result of biochemical composition of dry salted sorpunti fish has been represented in Table 7(d). It is evident from the result that the dry salted sorpunti fish contained moisture, protein, fat, ash and salt content ranging from 30.0 to 33.1, 33.2 to 35.0, 9.6 to 11.0, 11.5 to 12.1, 10.1 to 11.5 % respectively. Fe, P, Ca content of the product contain 1.8 to 2.6, 120.3 to 123.8, 442.8 to 445.2 mg/100g of fish sample respectively.
 
Table7 (e). Showing variation in biochemical composition of the experimentally
                    brine salted product of sorpunti fish  produced in the laboratory
 

 
The result of biochemical composition of brine salted sorpunti fish has been represented in Table 7(e). It is evident from the result that the brine salted sorpunti fish contained moisture, protein, fat, ash and salt content ranging from 45.0 to 47.8, 21.5 to 23.0, 9.9 to 11.5, 9.5 to 10.2, and 10.5 to 12.5 % respectively. Fe, P, Ca content of the product contain 1.2 to 1.9, 120.3 to 125.1, 402.1 to 405.2 mg/100g of fish sample.
The Pearson’s correlation (r) between ‘moisture and protein’, ‘moisture and fat’ and ‘protein and fat’ of the experimentally preparatory, mixed, pickle, dry and brine salted sorpunti fish samples had been computed and were represented in Table 8 (a), 8 (b), 8 (c) and 8 (d) and 8 (e) respectively.
 
Table 8 (a). Showing the computed Pearson’s correlation and ‘t’ value among
                     moisture, protein and fat of preparatory salted sorpunti fish
 

 
** Correlation is significant at the 0.01 level
 
Table 8(b). Showing the computed Pearson’s correlation and ‘t’ value among
                   moisture, protein and fat of mixed salted sorpunti fish
 

 
** Correlation is significant at the 0.01 level
 
Table 8 (c). Showing the computed Pearson’s correlation and ‘t’ value among
                    moisture, protein and fat of pickle salted sorpunti fish
 

 
** Correlation is significant at the 0.01 level
 
Table 8 (d). Showing the computed Pearson’s correlation and ‘t’ value among
                     moisture, protein and fat of dry salted sorpunti fish 
 

 
** Correlation is significant at the 0.01 level
 
Table 8 (e). Showing the computed Pearson’s correlation and ‘t’ value among
                     moisture, protein and fat of brine salted sorpunti fish 
 

 
** Correlation is significant at the 0.01 level
 
The negative “r” value between ‘moisture and protein’ and ‘moisture and fat’ refers to an inverse relationship that is with the increase or decrease of one of the two values, the corresponding value of the other nutrient will be decreased or increased respectively. On the other hand, the positive value of “r” between ‘protein and fat’ content of sample fish  cured by commercial salt curing process refers to a direct relationship between the two variables which indicates that the value of protein content increases with the increase of the value of fat content.
 
 
A                                                                                 B

 
 
C                                                                                   D

 
 
E
 
Fig. 3. Showing direct relationship between the ‘protein and  fat’ and inverse
           relationship between ‘moisture and protein’ and ‘moisture and fat’ content of                              
           the fish cured by
 

 
The graphical representation of the direct and inverse relationships among the nutrient contents of experimentally salt cured sorpunti fish samples had been shown in Fig. 3A, 3B, 3C and 3D and 3E. The line and bar diagram in this figure had shown the direct co-relation between ‘protein and fat’ content and inverse co-relation between ‘fat and moisture’ and ‘moisture and protein’ content.
The “t” value between percent of ‘moisture and protein’ and ‘moisture and fat’ content of experimentally salt cured sorpunti fish samples had been computed which were highly significant at 1 % significance level ( p < 0.01) and indicated a strong negative relationship between them,The “t” value between percent of ‘protein and fat’ content of experimentally salt cured sorpunti fish samples had been computed which was highly significant at 1 % significance level ( p < 0.01) and indicated a strong negative relationship between them. Fish organs like roe contain significant amounts of minerals Ca, P, Fe etc. depending on the state of spawning of the fish.
 
Like biochemical composition, the mineral composition of roe were found to be dependent on the mineral content of water where the fish grows, type of food eaten and state of maturation. The calcium content of roe have been found to be much less than in muscle whereas roe have been found to contain remarkably high amount of Fe and P. The higher amount of P and Fe content of is an indication that this organ acts as a reservoir of essential micronutrients required in different physiological function of fish tissues.
 
Salted roe is a very costly commercial processed food in USA. The market price of 1 kg. roe is 400 $ in UK. (Halder et al., 2004). But its cost in the local market is only 400 TK / kg. Taking in mind the cost difference of salted roe between Bangladesh and USA we have started the work of processing roe through salting and to observe its biochemical composition along with essential minerals like Ca, Fe and P. with a view
 
 
Table 9 (a). Showing variation in biochemical composition of roe in fresh
                     Acceptable condition after chemical analysis in the laboratory
  

 
 
Table 9 (b). Showing variation in biochemical composition of the experimentally
                     salted roe produced in the laboratory
 

 
 
to find out its effectiveness to meet nutritional requirement as well as financial gain through its marketing abroad, salting process of roe in the laboratory have been done.
 
The result of biochemical composition of fresh roe has been represented in Table 9(a). It is evident from the result that the roe contained moisture, protein, fat, ash ranging from 60.0 to 62.1, 29.0 to 30.5, 7.8 to 8.8, 2.1to 2.7 % respectively. Fe, P, Ca content of the product contained 6.5 to 6.9, 490.1 to 494.4, 37.1 to 40.7 mg/100g of roe sample respectively.
 
The result of biochemical composition of experimentally salted roe produced in the laboratory has been represented in Table 9(b). It is evident from the result that the salted roe contained moisture, protein, fat, ash and salt ranging from 35.3 to 36.3, 33.5 to 35.1, 11.4 to 13.3, 6.5 to 7.7, 9.9 to 11.4 % respectively. Fe, P, Ca content of the product contains 19.2.4 to 20.3, 480.5 to 493.8, 74.2 to 81.4 mg/100g of experimentally salted roe respectively.
 
Table 10. Showing the computed Pearson’s correlation and  ‘t’ value among 
                  moisture, protein  and fat of salted roe
 

 
** Correlation is significant at the 0.01 level
 
 
The Pearson’s correlation (r) between ‘moisture and protein’, ‘moisture and fat’ and ‘protein and fat’ of the experimentally salted roe had been computed which were represented in Table 10. and were found to be -.991, -.850 and .870 respectively. The test of significance indicated by “ t” of the experimentally salted roe samples were computed between moisture and protein , moisture and fat  and protein and fat were found to be -20.922, -4.560, and 4.995 respectively. That the relationship indicated by “t” value were found to be significant at 0.01 level. The negative “r” value between ‘moisture and protein’ and ‘moisture and fat’ refers to an inverse relation that is with increase or decrease of one of the two values, the corresponding value of other nutrient will be decreased or increased respectively. On the other hand, the positive value of “r” between ‘protein and fat’ content of salted roe cured by experimental salt curing process refers to a direct relationship between the two variables which indicates that the value of protein content increases with the increase of the value of fat content. 

 
 
Fig. 4. Showing direct relationship between the ‘protein and fat’ and
inverse relationship between ‘moisture and protein’ and
‘moisture and fat’ content of the salted roe.
 
The graphical representation of the direct and inverse relationships among the nutrient contents of experimentally salt cured roe had been shown in Fig. 4. The line and bar diagram in this figure had shown the direct co-relation between ‘protein and fat’ content and inverse co-relation between ‘fat and moisture’ and ‘moisture and protein’ content.
 
The “t” value between percent of ‘moisture and protein’ and ‘moisture and fat’ content of experimentally salt cured roe had been computed which were highly significant at 1 % significance level (p < 0.01) and indicated a strong negative relationship between them.
 
The “t” value between percent of ‘protein and fat’ content of experimentally salt cured roe had been computed and found to be which was highly significant at 1 % significance level (p < 0.01) and indicated a strong positive relationship between them.
 
The preservative used have a slowing effect on the liberation of amino acids and peptides in the salt cured product. They thus increase the shelf life of the product by preventing microbial decay and slowing down proteolysis.
The sugar added in the production of salt cured hilsa fish treated with salt, sugar and preservative reacts together for decreasing the pH 5.8 to reduce the autolysis or bacteriological putrefaction.
 
The protein content of fatty fish 15-20 % in raw condition and pH of muscle tissue 6.6 – 6.8 after catching goes down to 5.6 – 5.8 when it goes up again to over pH 6 it is generally a sign of autolytic or microbiological putrefaction.
 
Results of biochemical composition and process ingredients of the experimentally mixed salted hilsa fish product treated with sugar and preservative have been represented in Table 11 (a). The preservation process is a new approach in Bangladesh have been carried out in the laboratory for the first time. It is evident from the results represented in Table 11 (a). that the process ingredients such as (%) salt and (%) sugar varied from 6.2 to 7.9 and 2.1 to 3.1.    
 
Table 11 (a) Showing variation in biochemical composition and process ingredients 
                      of mixed salted hilsa fish treated with salt, sugar and preservative in the
                      laboratory.
 

 
Trace amount of preservative were added which were not detectable by analytical process and for this reason the content of preservative have not shown in the Table 11 (a).  Moisture, protein, fat and ash content of the product have been found to contain 35.3 to 37.3 %, 31.9 to 33.7 %, 10.7 to 12.1, 10.7 to 12.1 and 6.4 to 7.5 % respectively.
 
Table 11 (b). Showing variation in biochemical composition and process ingredients
                       of pickle salted hilsa fish treated with salt, sugar and preservative in the
                       laboratory
 

 
 
Results of biochemical composition and process ingredients of the experimentally pickle salted hilsa fish product treated with sugar and preservative have been represented in Table 11 (b). It is evident from the results of the Table 11 (b)  that the process ingredients such as (%) salt and (%) sugar varied from 6.1 to 8.0 and 2.3 to 3.1. Moisture, protein, fat and ash content of the product have been found to contain 36.1 to 38.3 %, 30.0 to 31.7 %, 10.7 to 12.3, 6.1 to 7.5 % respectively.
 
Table 11 (c). Biochemical composition of salted roe treated with salt, sugar and
                      preservative
                       

 
Results of biochemical composition and process ingredients of the experimentally salted roe treated with sugar and preservative have been represented in Table 11 (c). It is evident from the results of the Table 11 (c) that the process ingredients such as (%) salt and (%) sugar varied from 6.1 to 7.2 and 2.0 to 2.9. Moisture, protein, fat and ash content of the product have been found to contain 35.3 to 36.3 %, 33.5 to 35.1 %, 11.4 to 13.3, 6.5 to 7.7 % respectively.
 
Table 12 (a)  Showing the computed Pearson’s correlation and ‘t’ value among
                       moisture, protein and fat of salted mixed salted hilsa fish treated with
                       salt, sugar and preservative
 

 
** Correlation is significant at the 0.01 level
 
 
Table12 (b). Showing the computed Pearson’s correlation and ‘t’ value among
                      moisture, protein and fat of salted pickle salted hilsa fish treated with
                      salt, sugar and preservative
 

 
** Correlation is significant at the 0.01 level
 
Table 12 (c). Showing the computed Pearson’s correlation and ‘t’ value among
                      moisture, protein and fat of salted roe treated with salt, sugar and
                      preservative
 

 
** Correlation is significant at the 0.01 level
 
The Pearson’s correlation (r) between ‘moisture and protein’, ‘moisture and fat’ and ‘protein and fat’ of the experimentally mixed and pickle salted hilsa fish and roe treated with salt, sugar and preservative had been computed which were represented in Table 12 (a), 12 (b) and 12 (c) respectively. The negative “r” value between ‘moisture and protein’ and ‘moisture and fat’ shown in the same Tables refers to an inverse relationship that is with increase or decrease of one of the two values, the corresponding value of other nutrient will be decreased or increased respectively. On the other hand, the positive value of “r” between ‘protein and fat’ content of sample fish  cured by experimentally salt curing process also shown in Table12 (a), 12 (b) and 12 (c) refers to a direct relationship between the two variables which indicates that the value of protein content increases with the increase of the value of fat content. The computed of “t” shown in the above Tables have clearly indicated that all of the correlations were significant at 0.01 level.
 
 
A
                                                                                                                         B

                                    C
                                                

Fig. 5 Showing direct relationship between the ‘protein and fat’ and inverse
           relationship between ‘moisture and protein’ and ‘moisture and fat’
           content of the
A. Mixed salted hilsa fish product treated with salt, sugar and preservative
B. Pickle salted hilsa fish product treated with salt, sugar and preservative
C. Brine salted roe treated with salt, sugar and preservative
 
The graphical representation of the direct and inverse relationships among the nutrient contents of experimentally salt cured hilsa fish samples and roe had been shown in Fig. 5A, 5B and 5C. The line and bar diagram in this figure had shown the direct co-relation between ‘protein and fat’ content and inverse co-relation between ‘fat and moisture’ and ‘moisture and protein’ content.
 
The “t” value between percent of ‘moisture and protein’ and ‘moisture and fat’ content of salt cured fish samples and roe treated with salt, sugar and preservative had been computed which were highly significant at 1 % significance level ( p < 0.01) and indicated a strong negative relationship between them.
 
The “t” value between percent of ‘protein and fat’ content of experimentally salt cured fish samples and roe treated with salt, sugar and preservative had been computed and which were highly significant at 1 % significance level ( p < 0.01) and indicated a strong positive relationship between them.
 
4.2 Technological aspect and performance of different salt curing methods
Salt curing is one of the oldest and widely used processing and preservation method for preservation of fish especially fatty species of fishes throughout the world including Bangladesh. But with the advent of civilization and development of technologies with the advancement of scientific technological knowhow, the very old method of salt curing have been updated to solve some of the problems arises while processing the fish by this method. Our present work regarding technological aspects of different salt curing methods have been undertaken with a view to updating the salt curing method in Bangladesh based on the findings of our present study. It is expected that the outcome of the present study might be able to pinpoint regarding the way of application of the updated technology for proper utilization of the products in a highly acceptable condition in order to meet the nutritional requirement and thereby contributing in terms of financial need.
 
We have tried to know the background of salt curing of hilsa in Bangladesh and as a result we come to know that hilsa fish is mainly cured through dry salting process. Salt fermentation and wet salting are also practiced in some areas. Among the fresh water and marine harvest of the country fresh hilsa fish is the most relished in term of taste, texture and flavor.
 
Due to the problems associated with transportation, preservation, storage and marketing, the consumers do not always get the fresh fish. On the other hand, the price abruptly falls down or a large quantity of the catch undergoes spoilage due to limited scope for long term preservation during glut period.
 
hilsa is a dark flesh high lipid species. Sun drying is not an appropriate preservation method for the species because of atmospheric oxidation or rancidity problems. Long term chilling is not useful due to rapid spoilage of dark muscles. Considering the constitutional nature of the species and usefulness and acceptability of different fish preservation methods and above all, socio- economic structure and food habit of the local consumer, salting seems to be the best suited method for the preservation of hilsa fish.
 
Although both dry and wet salting are done for hilsa, the extent and magnititude of dry salting are higher than wet-salting. But while working in the salt curing of hilsa fish, roe and sorpunti fish in the fish technology laboratory IFST, BCSIR, Dhaka, we have applied seven different curing methods
 
Fine salt causes a rapid removal of water from the surface and makes it hard and this prevents further penetration of salt to the inside. Fine grain salts readily dissolves in water and is good for wet salting (Clucas and Ward, 1996).
 
Hilsa fish and roe were salt cured by adopting the methods which have been mentioned in the chapter 3. Roe was salted by brine solution. Sorpunti fish were salt cured by following methods also mentioned in chapter 3.
 
Hilsa fish were also treated with salt, sugar and preservative. Out of the seven methods adopted and applied during the salt curing process, salt cured product treated with salt, sugar and preservative is newly adopted in our country for the first time in laboratory scale and the product quality is best in comparison with the other salt cured products.
 
The raw materials used in this method is easily available in market, it takes no longer time than the other methods and the storage stability and the quality is better than the  other salt cured products. Considering all the factors mentioned above, we have decided the technological procedure of salt, sugar and preservative treatment as the best one in comparison with the other salt curing methods studied during the present investigation.
 
Out of the other salt curing methods such as preparatory, mixed, pickle, dry, brine it is observed that the technological procedure in case of preparatory salt curing methods may be arranged in order of availability of the raw materials, procedure of the method, time required for completion of the method and finally with the quality of the finished product as follows:
 
Preparatory> Mixed > Pickle > Dry > Brine
 
Performance of any processing and preservation method indicates the availability of the raw materials with minimum cost from the local source. It also indicates the time required for getting the finished fish product at the completion of the processing and preservation method as well as the product quality in fresh processed condition. 
 

 
Fig.6 (a). Line diagram showing the weight change during the period of
     different methods salt curing of hilsa fish in the laboratory 
 
The results of changing weight of the experimentally salt cured hilsa fish products while four different kinds of salt curing methods had been applied in the laboratory have been represented in Fig.6 (a). indicating the performance of different salt curing methods. It is evident from the results represented by line diagram in Fig. 6 (a). that the different salt curing methods have consumed different period of time to produce the finished salt cured hilsa fish product in the laboratory. The mixed salt cured Hilsa fish products have been found to produce the finished product at the end of 12 days of processing method whereas the brine salt cured hilsa fish product have been found to take 22 days of processing period to produce the finished product. The pickle cured hilsa fish product have been found to consume 20 days of processing period. That is performance of the mixed salt curing method is better than the other two methods namely pickle and brine curing methods whereas pickle curing method is better than the brine salt curing method.

 
Fig. 6 (b). Line diagram showing the weight change during the period of different
                  method of salt curing of sorpunti fish. 
 

 
Fig. 6 (c). Line diagram showing the weight change during the period of mixed
                 and pickle salting of hilsa fish and brine salting of roe (with sugar
                 and preservative)
 
It is to be mentioned here that the period required for attaining more or less constant weight of the processed fish sample during application of different salt curing methods have been considered to be the time for producing the finished processed product.
 
Though the dry salt cured hilsa fish product have been found to consume 12 days period for producing the finished product yet its product quality as per sensory test have been found to be in between pickle and brine cured fish. That is the performance of the mixed salt curing method of hilsa fish have been found to be better than that of the brine salt curing methods. 
. 
According to the level of performance, the four finished salt cured product of hilsa fish may be arranged as follows
Mixed > Pickle > Dry > Brine
 
In case of sorpunti fish, the salted product follows the similar trend with time in respect of processing methods which have been represented in Fig.6 (b). But here the preparatory salted product have been found to be the best product among the all products according to its performance.
 
Results of weight change towards attaining more or less constant weight thereby indicating the performance of the salt cured hilsa fish and roe treated simultaneously with  sugar and preservative have been represented in Fig. 6 (c).
 
Results represented by line diagram of Fig. 6(c). have shown that the mixed salt cured hilsa fish have consumed 16 days and pickle cured fish samples treated with sugar and preservative have consumed 20 days of processing period to produce the finished product. Whereas the brine salt cured roe also treated with sugar and preservative have been found to consume 16 days of processing period.
 
 
4.3.    QUALITY ASSESSMENT AND STORAGE STABILTY
 
4.3.1. STUDIES ON THE RECONSTITION PROPERTIES OF SALT CURED FISH
 
4.3.1.1. Background: Curing of fatty species of fish specially hilsa fish in Bangladesh on commercial basis have been found to contribute in the field of employment earnings both local and foreign currency and nutritional and economic development. But some problems associated with the production of commercially salt cured hilsa fish do not allow the fish product to be of standard quality. To asses the level of quality standard of the commercially salt cured hilsa fish with that of the experimentally salt cured hilsa fish, there are so many procedures through which we can ascertain the level of quality standard. Reconstitution properties of any dry food materials are used as an index of quality standard including cured hilsa fish (both commercial and experimental grade).
      
Reconstitution is a process where in a processed fish food is allowed to remain in water for a certain period and simultaneously it is allowed to absorb water with a view to reconstitute to its original form before processing and preservation. And for this reason, reconstitution properties of any processed fish food are used to monitor of its ability to go to its original form by absorbing water from the solution. In practice, the processed fish food sample which absorb maximum percent of water in the same period of reconstitution are considered to be the best processed fish product and get the high score of acceptability by the panel of judge during sensory assessment by putting overall acceptability score.
 
4.3.1.2. Expected Outcome:
 
●Study on the nature and trend of reconstitution properties of the experimentally salt cured hilsa and sorpunti fish with that of the commercially salt cured hilsa fish would be able to indicate the quality standard of the cured fish products in respect of the salt curing method applied and species of fish used.
● Would be able to indicate the best method of salt curing process.
● Would be able to indicate the nature of degrading quality of the commercially salt cured hilsa fish.
● Will also reflect the best suitable fish species of fish (hilsa and sorpunti) studied in the present thesis work.
● To suggest and recommend inlight of he expected outcome of the present work so that the fish processors, fish consumers as well as the academic professionals might be benefited.
 
 
4.3.1. 3. Objectives: An understanding of the difference in quality between various dried products comes from the consideration of reconstitution properties. The work for investigating the reconstitution properties of the salt cured fish products like hilsa and sorpunti both from experimental origin and from commercial origin have been undertaken with the following objectives.
● To arrange the salt cured fish products according to the level and standard of quality.
● To asses the quality of the cured fish products by using reconstitution properties as an quality index.
● To have an clear idea about the unsatisfactory processing conditions or prolonged storage which may give a product that will require periods more and will be difference in tenderness and juiciness from the control.
 
4.3.1.4. Experimental: In order to ascertain the nature and extent of reconstitution properties of the salt cured hilsa fish, sorpunti fish and of salt cured roe an experiment have been designed and carried out in the fish technology laboratory by taking the above mentioned processed fish products as research material. Together with water, two other solution of Na₂CO₃ and Ca(OH)₂ ranging from 1-20% have been taken in order to obtain the optimum level of concentration of the two chemicals where maximum percent of water level is absorbed. From the observed water level uptake by the processed fish products while kept in different concentrations of the two chemicals maximum level of water have been found to be absorbed at 5% level of both of the chemicals. From this sort of observation, we have decided to carry out the experiment on reconstitution properties of the experimental processed fish product simultaneously in three conditions, one in plain water and the other two in 5% Na₂CO₃ solution and in 5 % Ca(OH)₂ solution. Five of the processed salt cured best product of the experimental fishes and commercially salted product have been taken as research materials for the present study (roe, mixed, pickle cured product treated with salt, sugar and preservative, mixed salted hilsa and preparatory salted sorpunti).
 
4.3.1. 5. Result and Discussion:
 
Reconstitution properties of the experimentally salt cured hilsa fish, roe and sorpunti fish and that of the commercially salt cured hilsa fish have been studied with a view to find out the standard of quality of the fish products and to pinpoint at the unsatisfactory processing methods and improper storage of the commercially salt cured fish. In the present quality study we have observed the nature and extent of weight gain, content of percent protein and moisture at its highest level of weight gain/ water uptake.  During the process of reconstitution we have also assessed its quality by sensory method, Overall acceptability score (O.A.S) were given to the experimentally salt cured samples as well as to the commercially salt cured hilsa fish. Highest level of score were given to a sample which uptakes maximum level of water content thereby gaining its maximum weight within the same period of reconstitution process.
 
Principle of sensory score that had been adopted in the experiment of reconstitution properties was that the cured fish product which gained highest weight through uptake of water were given the highest sensory score thereby indicating its quality standard.
 
Results on the study of reconstitution properties of roe, mixed, pickle salted hilsa treated with salt, sugar and preservative and mixed salted hilsa, preparatory salted sorpunti and commercially salted hilsa have been represented in Table no 13 (a), 13 (b), 13 (c), 13 (d), 13 (e) and in 13 (f) respectively.
 
In respect of the O.A.S value against the different salt cured fish samples of the present study indicates that all of the experimentally salt cured fish products are better in quality than that of the commercially salt cured hilsa fish. But there are differences in quality among the experimentally salt cured fish samples. In order of quality standard assessed by reconstitution properties we may arrange all of the cured fish products as follows:
BSSP (roe) > MSSP > PSSP > MSH/ PSS > CSH.
 
Table 13 (a). Showing reconstitution properties of experimentally salted roe as
                      indicated by the change in weight as well as by sensory score
          (S.S) value (salt+ sugar+ preservative) at different period of
          reconstitution in the  laboratory
 

 
Salt cured roe treated with salt, sugar and preservative while reconstituted in only water, in 5 % sodium carbonate, 5 % Ca(OH)₂, solution have been found to gain their weight from an initial weight of 10 g to 15.1 g, 22.2 g and 23.6 g at the end of 30 hours reconstitution period and this weight gain remain more or less constant in all the solution up to 48 hours and this product have been marked as the best quality product among the 5 experimentally salt cured fish product together with the commercially salt cured hilsa fish product.
 

 
Fig. 7 (a) Bar diagram showing the nature and extent of reconstitution properties of
                  the experimentally salted roe treated with salt, sugar and preservative
 
Variation in weight gain in case of salt cured roe treated with salt, sugar, and preservative is evident from the results represented in Table 13 (a).
 
Reconstitution properties of the experimentally salted roe treated with salt, sugar and preservative have been represented in Fig.7 (a) showing the nature and extent of reconstitution properties while reconstitution was carried out in the laboratory. The nature and extent of reconstitution have been indicated by the change in weight as well as by the sensory score value during the study period of reconstitution properties.
 
At the end of 30 hours of reconstitution the same weight of experimentally mixed salted fish sample have been found to gain their weight upto 15.1 g , 18.1 g and 20.2 g in water, in 5% Na₂CO₃ and in 5 % Ca(OH)₂ respectively which was represented in Table 13 (b). and in Fig. 7 (b). This variation in weight gain may be due to the variation in pH of the concern reconstituting solution. According to Wang et al. (1954) the highest level of rehydration occur in Ca-salts whose pH is 7.0 and this findings is in good agreement with the results of the present experiment of reconstitution properties.
 
Table 13 (b).  Showing reconstitution properties of experimentally mixed salted hilsa
                        as indicated by the change in weight as well as by sensory score value
                        (salt+ sugar+ preservative) at different period of reconstitution in the
                        Laboratory
 
 

 
 

 
Fig. 7 (b). Bar diagram showing the nature and extent of reconstitution properties of
                 the experimentally mixed salted hilsa fish treated with sugar and
                 preservative
 
 
Table 13 (c). Showing reconstitution properties of experimentally pickle salted hilsa
                       as indicated by the change in weight as well as by sensory score value
                       (salt+ sugar+ preservative) at different period of reconstitution in the
                       laboratory
 

 
 

 
Fig. 7 (c) Bar diagram showing the nature and extent of reconstitution properties of
                the experimentally pickle salted hilsa fish treated with sugar and
                preservative
 
It is evident from the results represented in Table 13 (c) and in Fig. 7 (c) at the end of 30 hours of reconstitution the same weight of experimental sample have been found to gain their weight, up to 15.1 g , 23.5 g and 26.7 g in water 5 % Na₂CO₃ and in 5 % Ca(OH)₂ respectively. Reconstitution properties of the experimentally pickle salted hilsa treated with sugar and preservative in respect of weight gain at different time interval have been represented in Table 13 (c) and in Fig. 7 (c).
 
Table 13 (d) Showing reconstitution properties of experimentally mixed salted hilsa
                      as indicated by the change in weight as well as by sensory score value at
                      different period of reconstitution in the laboratory
 

 
At the end of 30 hours of reconstitution the same weight of experimentally mixed salted hilsa fish sample have been found to gain their weight, up to 15.2 g , 17.2 g and 19.1 g in water 5 % Na₂CO₃ and in 5 % Ca(OH)₂ respectively in Table 13 (d) and in Fig. 7 (d).

 
 
Fig. 7 (d). Bar diagram showing the nature and extent of reconstitution properties of
                 the experimentally mixed salted hilsa fish
 
Table 13(e). Showing reconstitution properties of experimentally preparatory salted
                     sorpunti as indicated by the change in weight as well as by sensory score
                     value at different period of reconstitution in the laboratory
 

 
 

 
Fig. 7 (e) Bar diagram showing the nature and extent of reconstitution properties of
                the experimentally preparatory salted sorpunti fish
 
At the end of 30 hours of reconstitution the same weight of experimentally preparatory salted sorpunti fish sample have been found to gain their weight, up to 14.5 g , 18.5 g and 19.6 g in water 5 % Na₂CO₃ and in 5 % Ca(OH)₂ respectively and was represented in Table 13 (e) and in Fig.7 (e).
 
Table 13 (f) Showing reconstitution properties of commercially salted hilsa fish as
                     indicated by the change in weight as well as by sensory score value at
                     different period of reconstitution in the laboratory 
 

 

 
Fig. 7 (f) Bar diagram showing the nature and extent of reconstitution properties of
                the experimentally preparatory salted sorpunti fish
 
 
At the end of 30 hours of reconstitution the same weight of commercial sample have been found to gain their weight, upto 13.1 g , 14.1 g and 15.1 g in water 5% Na₂CO₃ and in 5 % Ca(OH)₂ respectively and was represented in Table 13 (f) and in Fig. 7 (f). This variation in weight gain may be due to the variation in pH of the concern reconstituting solution.
 
Reconstitution is a process where the salt cured fish products are kept in different solution such as water and in solutions of other chemicals adsorp water and were allowed to gain weight at more or less constant level. During the present study different salt cured fish products including the experimentally and commercially salt cured fish products were kept in water and in 5 % solution of Na₂CO₃  and Ca(OH)₂  until the reconstitution process is completed.We have determined the % moisture and % protein content of samples. It was done to find out the level of moisture and protein content during reconstitution and thereby correlates its standard of quality. The results of this experiment indicating in the level of % moisture and % protein content of different salt cured fish products at the end point of reconstitution have been represented in Table 14.    
 
The product which have been found to contain highest level of protein content among the other salt cured fish sample at the end point of reconstitution have been considered to be the best one. And the salt cured fish sample which have been found to contain lowest level of protein content have been considered to be the inferior quality.
 
Table 14 Showing variation in moisture and protein content at the end point of
                reconstitution of the different salt cured products while reconstituting in the
                laboratory
 

 
No significant relationship have been found between moisture and protein content while the samples are kept in different solutions during reconstitution process.
From the overall findings of the study and the reconstitution properties of the aforementioned salt cured fish product we may conclude that the quality standards of the experimentally salt cured products have been found to have a clear variation due to the following reasons

 
The inferior quality of the commercially salt cured hilsa fish in comparison with the controlled salt cured sample might be due to the following reasons

 
4.3.2 SORPTION PROPERTIES
 
4.3.2.1. Background for working with sorption properties of salt cured fish product: Cured fish product whether it is obtained with or without salt treatment through the use of solar energy by direct or indirect means is a very popular type of fish product in Bangladesh. The amount of foreign exchange earnings indicates the extent of interest by the foreign countries for consumption of the salt cured hilsa fish product outside the country. It also indicates about the feasibility of the extended market abroad which in turn opens the possibility of producing more cured hilsa fish product and thus the possibility of more employment and more earnings in this specific sector of fish processing in Bangladesh. Storage stability of cured fish product is a matter of great concern to the fish processing personnel as well as to the marketing personnels during storage, distribution and marketing. The stability of such salt cured fish products is closely related to equilibrium moisture content or “active water” rather than to total moisture content during storage under different relative humidity condition, (Rockland, 1969).
 
A dry foodstuffs will adsorp or desorp moisture from its surrounding depending on the ambient relative humidity (Frazier, 1958).
 
An understanding of moisture sorption characteristics of a particular foodstuff is, therefore necessary in order to ascertain to what extent the material can be dried at a particular drying condition (FAO, 1976)
 
How much moisture the dried product will adsorb during storage at a given set of condition and what should be the optimum storage conditions to give the product maximum storage stability it is needed to observe the sorption of that cured fish product during storage.  
 
About 15% of the world fish catch is preserved by curing, i. e. salting, drying or smoking or a combination of these treatments. Fish curing is of particular importance in southeast asia where it accounts for almost 30 % of the total fish harvest. However, a considerable proportion of cured fish produced in that region does not reach the consumer because of ‘spoilage’ during processing and distribution or is of poor quality when it reaches to the consumer. Mould formation is an important cause of spoilage of cured fish (FAO, 1981). In fact the visible growth of moulds in the cured fish product is caused by poor storage and distribution at high humidity condition which makes the fish product unacceptable to the consumer as well as to the panel of judges of sensory assessment. 
 
4.3.2.2. Expected Outcome  
● Findings of the present study may be helpful for indicating suitable RH condition for extending storage stability.
● RH range which influences rapid deterioration of the cured fish sample during storage may be identified.
● Study on the adsorption and desorption behaviour of the cured fish samples may be helpful for formulating proper storage condition for extending storage stability.
       
4.3.2.3. Objectives: Any dried food material such as dried fish, salt cured fish, smoked fish while stored for future transportation and marketing without proper packaging, sanitation etc. in a country like Bangladesh, the surrounding temperature and relative humidity condition plays a very vital role for its rapid deterioration or extending its storage stability.
 
If the surrounding relative humidity (RH) become higher than the moisture level of the dried fish product it will adsorb moisture from its sorrounding air until it attains equilibrium moisture content.
 
On the other hand if the RH become lower than the moisture content of the dried product, it releases moisture to the surrounding until it attains equilibrium moisture content.
 
The adsorption or desorption of moisture of the cured fish products to attain equilibrium moisture of the product, it acts in favour of rapid deterioration or restoration of storage stability.Keeping  in mind the view point of the influence of RH and temperature on the storage stability of the cured fish product we have planned and designed to study the sorption properties of cured fish products with the following objectives
● To find out suitable storage stability condition in respect of RH and temperature.
● To identify the RH and temperature which influences a rapid deterioration of the cured fish product.
● To give proper recommendation and guideline for proper storage for prolonging the storage stability in respect of RH and temperature.
 
4.3.2. 4. Experimental: The air in a sealed container in which saturated solution of various salts is kept, together with some of the solids, remains at a constant humidity. If wet objects were inserted, the surplus moisture goes into solution and more solid dissolves until the same constant humidity is restored. Likewise, if dry objects are inserted more solid is precipitated and constant humidity is restored. Useful salts with their percentage humidities at normal room temperature which were used in the present study are lead nitrate (RH- 98), ammonium sulphate (RH – 86), sodium nitrate (RH- 66), calcium chloride (RH- 35), sodium hydrogen sulphate (RH- 52), phosphoric acid ( RH – 9).The influence of RH on the change of adsorption/desorption may be classified based on the effect of change into three groups
 
1) RH       0-15     desorption  change is minimum
2) RH  15- 55   the maximum stability of the product due to minimum change in desorption
3) RH        55 and above, water adsorption is rapid and deterioration is also rapid.
 
 
4.3.2. 5. Results and discussion : During study of adsorption/desorption properties of  the experimentally mixed salted hilsa fish, preparatory salted sorpunti and commercially salted hilsa fish samples in the desiccator having different RH (9%-98%) conditions moisture content of the samples were determined at different time interval until the moisture content become more or less constant. Fig.8 (a) shows the gain/loss of water in vapour phase, adsorption/desorption processes of experimentally mixed salted hilsa fish occurred at different RH (9%-98%) as a function of time at room temperature for a sample initially containing 10 g of water/100 g of solid. It is clear from the results represented in Fig.8 (a) that adsorption took place at very high rates at high RH over 81% and above. And the system attained equilibrium position in about 150 hours. The rates of adsorption were comparatively slower at lower RH (66%) and the system in this cases attained equilibrium within 50 hours. Similar phenomena were also observed in desorption process at RH (9%-35%). No adsorption/desorption took place in the sample kept at RH 52%. Because the initial moisture content in the samples were equilibrium with this RH. The initial rapid rates of adsorption at higher RH conditions were probably due to random surface water sorption. The final slower rates were due to slower rates of diffusion and migration rate of water through the materials (Rockland, 1969).The shorter time required for obtaining equilibrium position in the adsorption/desorption processes in the lower RH are due to shorter differences between the initial and final water activities. The amount of water adsorbed or desorbed by each process was found to have increased with increasing differences between the initial sample water activity and the final adsorption/desorption water activity.
 
The results of adsorption/desorption of moisture in case of experimentally preparatory salted sorpunti fish have been represented in Fig. 8 (b) and the same results in case of commercially salted hilsa fish product have been represented in Fig. 8 (c).
 
The rate of adsorption/desorption of moisture of the salt cured fish products have been found to differ from each other. The rate of adsorption at higher RH above 80 that is 85-98% of the CSH have been found to be higher in comparison with the other two salt cured fish samples (MSH and PSS).

 

 
Fig. 8 (a). Line diagram showing the rate of adsorption/desorption of moisture in
                 experimentally MSH fish samples while sorption properties were studied at
                 different RH
 
MSH- Mixed Salted Hilsa
RH- Relative Humidity
 

 
Fig. 8 (b). Line diagram showing the rate of adsorption/desorption of moisture in
                  experimentally PSS fish samples while sorption properties were studied at
                  different RH
 
PSS- Preparatory Salted Sorpunti
RH- Relative Humidity

 
 
Fig. 8 (c). Line diagram showing the rate of adsorption/desorption of moisture in
                 experimentally CSH fish samples while sorption properties were studied at
                 different RH
 
CSH- Commercialy Salted Hilsa
RH- Relative Humidity
 
At RH 85% the MSH, PSS, CSH products have been found to attain moisture level at 42, 45, 60% respectively. At RH 98% the MSH, PSS, CSH have been found to attain moisture level at 54, 60, 75% respectively which were represented in Fig. 8(a), 8(b) and 8 (c). The findings of the rate of adsorption/desorption rates of the three salt cured products clearly indicates variation due to species variation and variation in salt curing processes. The rate of adsorption of CSH is higher in comparison with other two products.
 
The product quality of the (MSH, CSH, PSS) products were assessed by determination of Total Volatile Nitrogen (TVN) after storage of the samples at different RH for a period of 18 days. The results of TVN value have been represented against different RH ranging from 9-98% in Fig. 9.
 

 
                      Fig. 9. Showing variation in TVN value of MSH, PSS and CSH at
                                 different RH condition during the study of sorption
                                  properties in the laboratory                     
Indications
TVN- Total Volatile Nitrogen
MSH- Mixed Salted Hilsa
PSS- Preparatory Salted Sorpunti
CSH- Commercially Salted Hilsa
 
It is evident from the results represented in Fig. 9 that the TVN values did not change  significantly in the samples stored below 66% RH. However the TVN values rose sharply in the region over 80% RH indicating a rapid spoilage of the samples at these conditions, visual fungal infestations were observed in the samples at this high RH condition and makes unacceptable of the cured fish sample.
 
A lack of available moisture at the surface had probably been an important preservative factor in region below 66% RH and a plentitude of available surface water had favoured the spoilage actions in the region over 80% RH (Frazier, 1958). Several other workers (Block, 1953), (Shewan, 1956), (Scott, 1957) have also demonstrated that microbiological proliferation occurs at high water activities, generally in the region over 75% RH because free water has dominant influence in this region. In a tropical country like Bangladesh the average ambient RH remains in the region over 85% for about 5 months (June – October) in a year. Under such humid condition special measures should be taken to protect the dehydrated/cured fish product against moisture adsorption and subsequent microbial spoilage.
 
The TVN value of salt cured fish samples have been found to cross 200 mg N/100 g fish sample while the samples become unacceptable by visual fungal infestations. In our present study similar level of TVN content have been observed when the samples have been found to be infested by visual fungal growth.
 

 
                           Fig. 10. Moisture sorption isotherm of different types of
                                        salted fish products
Indications
MSH- Mixed Salted Hilsa
PSS- Preparatory Salted Sorpunti
CSH- Commercially Salted Hilsa
 
Moisture sorption isotherms of different kinds of salt cured fish products (MSH, PSS, CSH) have been represented in the Fig. 10. The curves are all similar in nature but have different moisture levels at the same RH.
 
Experimentally MSH have been found to adsorb minimum amount of moisture throughout the entire RH (9-98). The difference between other curves may be due to variation in the intrinsic characteristics (Frazier, 1958) between different species of fish. A moisture sorption isotherm of heterogeneous biological material represents the integrated hygroscopic properties of numerous constituents which vary among the products in respects to both quality and quantity (Rockland, 1969).
 
The moisture sorption isotherm that has been represented in Fig. 10. can be divided into 3 local isotherm such as (i) initial steep region ranging from 0-15% RH (ii) middle flattened region ranging from 15%- 55% RH and (iii) final steep region over 55% RH. The slope of the curve in the region (iii) is about 1.0.This means that an increase of 1% RH can increase the moisture content of the product by 1%. The slope is only about 0.2in the region (ii) and 0.3 in the region (i). This means that the effect of the changes in the ambient RH on the EMC of the product is minimum in the region (ii) of the isotherm thus indicating a maximum stability of the product in the range of 15% to 55% RH.        
 
Based on the findings of the present study on sorption properties of salt cured fish products such as mixed hilsa and preparatory salted sorpunti, commercially salted hilsa while sorption process were applied by keeping the fish samples in a closed chamber like desiccator with constant RH with the application of saturated solution of different salts, we have observed that RH have a great influence on the storage stability/unstability of the cured fish products. We may recommend to store the cured fish product in RH condition (15-52%) during the period of high humidity (June-October) which is favourable for prolonging storage stability and restoring the keeping quality for a long time which will be beneficial in terms of meeting the demand for nutrition, economic gain etc.
 
It will also be helpful to decrease the loss of the fish product due to deterioration.
 
Careful storing of the salt cured products in the RH region below 52 might prolong the storage stability and thereby restore the standard of product quality.
 
4.4. STORAGE STABILITY:
 
Storage stability of any cured fish product is very important because it is our clear observation based on experiment that the cured product which remain more or less stable during the storage period retain its standard of quality for longer period than that of the product which is not storage stable. Actually the storage stability of cured fish product is disturbed by the environmental RH conditions of the stored room. In other words we can say that even when we stored the best quality cured product in a high humid condition (above 80% RH) the fish product will be disturbed by taking more and more moisture content and will cross the limit of moisture level favoring the growth of moulds, fungus etc. and will be deteriorated and will loose its consumer acceptability. On the other hand if we stored a comparatively inferior quality fish product having RH in the region 9-52, the product will loose water to the surrounding and will be more and more stable and thereby it will be acceptable by the consumer even after a long storage period.
 
Experimentally salt cured sorpunti fish products were kept in polythene, plastic pot and refrigerator and their storage stability were observed from the month of Feb- May’ 06.   
 
The salt cured sorpunti fish with the application of different salt curing methods were kept in polythene bag and in plastic pot at room temperature and the same number of samples were kept in the lower chamber of the refrigerator to observe the effect of RH and temperature on the storage stability of the products. The fish samples kept in polythene bag and plastic pot at room temperature were stored in the month of February 2006 and their quality and weight change were observed upto the month of May, 2006. The change in weight of the experimentally salted sorpunti fish samples were observed due to the change in RH and ambient temperature. Irrespective of the salt cured products by different salt curing methods the weight of the fish samples have been found to decrease upto 60 days due to low RH condition (RH- 18)          

 
Fig. 11 (a). Showing changes in weight of the preparatory salte sorpunti fish product during different periods of  the storage stability study
                                        

 
Fig. 11 (b). Showing changes in weight of the mixed salted sorpunti  fish product during different periods of the storage stability study

               Fig. 11 (c). Showing changes in weight of the pickle salted sorpunti 
                                 fish product during different periods of the storage stability
                                 study

 
                Fig. 11 (d). Showing changes in weight of the dry salted sorpunti 
                                   fish product during different periods of the storage stability
                                   study

 
             Fig. 11 (e). Showing changes in weight of the brine salted sorpunti 
                               fish product during different periods of the storage stability
                               study
 
After that starting from the month of April range of RH and temperature have been found to increase which were reflected by the increasing weight of the fish samples by adsorption of moisture from the surrounding atmosphere and visual fungal infestation were observed. 
 
On the other hand while storing the salt cured sorpunti fish samples in the lower chamber in the refrigerator, very negligible change in weight have been observed during the storage period and no fungal infestation were observed and color, texture, taste everything remain more or less similar throughout the storage period. In other words, storage stability of the cured fish samples have been found to be more effective and stable without loosing its quality.
 
Based on the findings of sorption properties of the experimentally salt cured hilsa fish, sorpunti fish and commercially salt cured hilsa fish products while keeping the fish samples in different RH conditions ranging from 9-98 %, we have kept five different types of salt cured sorputi fish in polythene, plastic pot at room temperature to observe the influence of relative humidity of the environment on the stored fish samples to verify the findings of the sorption properties studies,  We have also kept these salt cured product of sorpunti fish simultaneously in the lower temperature of refrigerator which maintains lower RH and lower temperature condition. The fish were stored during the month of February’ 2006 – May’ 2006 and their change in weight and physical appearance were observed and recorded at different time interval.
 
The results of change in weight of the experimentally preparatory salted sorpunti fish while stored in polythene and plastic pot at room temperature and in refrigerator at different periods of storage stability study had been represented in Fig. 11 (a). It is evident from the results represented in Fig 11(a). that the salt cured fish samples kept in polythene and in plastic pot at room temperature undergoes a decreasing weight upto 40 and 60 days and then gained weight upto 60 and 70 days and then become more or less stable in weight. The probable cause in the trend of weight change of the preparatory salted sorpunti fish is that the fish sample during the period of low RH losses its moisture to the surrounding air and thereby it decreases its weight and during the period of High RH it gained moisture from the surrounding air as a result it gained its weight which after certain period become more or less stable. Whereas the experimentally salt cured sorpunti fish while stored in the lower chamber of the refrigerator have been found to show very insignificant change in weight as have been predicted in the results shown in Fig. 11 (a)
 
The preparatory salt cured sorpunti fish product kept in polythene and plastic pot, at room temperature have been found to deteriorated by fungal infestation at the end of 100 and 90 days of storage period. On the other hand same fish sample kept in the lower chamber of the refrigerator having lower RH did not show any deterioration during the same length of storage period.
 
The mixed salted sorpunti fish products have been kept in polythene and plastic pot spoiled within 80 and 90 days and the pickle cured products have been spoiled within 70 and 80 days. Likewise dry salt cured sorpunti fish products have been spoiled within 60 and 70 days which were represented in Fig. 11(b), 11(c), 11 (d). Similarly the brine cured sorpunti fish products have been spoiled within a short time in polythene and plastic pot respectively. Inspite of moisture content of the brine cured product when it was kept in low humid condition in the lower chamber of the it did not show any spoilage change and become storage stable and the results were represented in Fig. 11 (e).     
 
The overall findings of the five category of experimentally salt cured sorpunti fish product while observing the influence of ambient RH on the quality change of the fish product by storing the processed fish samples in polythene, in plastic pot and in the refrigerator become more or less similar change in respect of moisture gain/loss with the variation in RH condition and also indicated by the deterioration of the samples at ambient RH. But no deterioration is observed in the fish samples kept in refrigerator.
 
 
SUMMARY AND CONCLUSION
 
Fish is one of the most perishable food item among all other food items around the world. With a view to minimize the spoilage loss of fresh fish during post harvest, handling, storage and marketing different kinds of processing and preservation methods have been developed. In our country hilsa fish are salted by using dry and wet salting methods which actually do not fulfill the standard quality starting from the initial point to the end point of the product. Those methods of processing and preservation of fish can be divided into two broad spectrum/ classes. One class include very old and traditional methods of processing and preservation method and other one includes modern and updated processing and preservation method for fish.
 
Old and traditional methods include drying, salting, smoking etc. Modern methods include icing, freezing, cold storage, canning, freeze drying, fermentation etc.
 
We cannot give up the use of old and traditional methods of fish processing and preservation and for this reason we are trying to update this methods to adjust with modern civilization. Salting is a suitable processing and preservation technique for country’s greatest harvest of fatty fish like hilsa fish. With a view to improve the product quality and to extend the shelf life of the product we have applied the process of dry salting, pickle salting, brine salting, and mixed salting methods for producing improved salt cured hilsa fish in the laboratory.
Methods applied for the salting of another fatty species of fish product of Bangladesh like sorpunti fish were preparatory salting, dry salting, pickle salting, brine salting, and mixed salting. A modern and newly approached salt curing method for preservation and processing of hilsa fish by using salt, sugar and preservative had been practiced in the laboratory scale in course of the present study. All of the approaches are updated than the commercial salting method for producing. Hilsa fish product and the method with salt, sugar and preservative is very much innovative and  updated.
During our present research study on “Investigation on different salt curing methods in the quality and storage stability of salt cured hilsa” we have designed and planned and worked on technological aspect and  performance of various methods of salt curing of hilsa and sorpunti fish. We have also gone through detail analytical work for biochemical composition including few essential minerals in fresh and processed condition.
 
Correlations among the nutrients have been computed and recorded and interpreted separately. Their quality as well as storage stability and quality of all the experimentally salt cured fish products have been investigated and were compared with that of the commercially salt cured hilsa fish in the laboratory. 
 
Moisture, protein, fat and ash content of the freshly collected hilsa fish had been found to contain 58.1± 6.4 to 60.5±5.1, 21.8±2.3 to 23.2±2.3, 17.7±2.4 to 19.4±2.1 and 2.1±0.3 to 2.4±0.6 (%) respectively. P, Ca content of the freshly accepted hilsa fish have been found to contain 0.30±0.2 to 0.45±0.2, 193.91±3.7 to 196.23±3.4, 55.67±5.5 to 54.85±5.7 mg/100g of fish sample. Commercially salted fish had been found to contain moisture, protein, fat, ash and salt content varies from 45.2 to 47.6, 25.4 to 27.2, 5.9 to 6.6, 9.7 to 10.1 and 10.9 to 12.0 % respectively. And Fe, P, Ca have been found to contain 0.5 to 0.9, 191 to 196, 105.9 to 108.8 mg/100g of fish sample. Moisture, protein, fat, ash and salt content of the experimentally mixed salt cured hilsa fish varies from 38.1to 41.2,  34.1 to 35.5, 6.3 to 7.2, 7.9 to 8.5 and 10.9 to 12.2 % respectively. And Fe, P, Ca content of the product have been found to contain 0.7 to 1.2, 191.5 to 196.9, 110.45 to 116.45 mg/100g of fish sample.
 
In case of pickle salted product moisture, protein, fat, ash and salt content varies from 42.1to 43.7, 31.1 to 32.9, 5.2 to 6.0, 8.3 to 8.9 and 10.9 to 11.2 % respectively. And Fe, P, Ca content of the same product have been found to contain 0.6 to 0.9, 190.5 to 193.5, 106.9 to 109.8 mg/100g of fish sample. The moisture, protein, fat, ash and salt content of the dry salted product varies from 35.2 to 37.4, 35.4 to 37.1, 5.6 to 7.2, 9.6 to 10.2 and 9.2 to 11.0 % respectively. And Fe, P, Ca content of the experimentally dry salt cured hilsa fish have been found to contain 1.1 to 1.5, 112.4 to 116.8, 191.5 to 195.8 mg/100g of fish sample.
 
The moisture, protein, fat, ash and salt content of the brine salted product varies from 46.1 to 48.2, 25.9 to 28.0, 4.1 to 5.2, 8.7 to 10.1 and 9.1 to 10.5 % respectively. And Fe, P, Ca content of the experimentally brine salt cured hilsa fish have been found to contain 0.5 to 0.8, 190.5 to 195.9, 104.1 to 107.3 mg/100g of fish sample.
 
Sorpunti fish in fresh raw condition contained moisture, protein, fat, moisture and ash ranging from 35.5-37.9 %, 27.5-29.2 %,10.5-12.1%, 10.1-11.2 % respectively.  Fe, P, Ca content of the fresh Sorpunti fish have been found to contain 0.3 to 0.5, 120.1 to 123.9, 220.2 to 224.8 mg/100g of fish sample.
 
Preparatory salted product contained moisture, protein, fat, ash and salt content ranging from 35.5 to 37.9, 27.5 to 29.2, 10.5 to 12.1, 10.1 to 11.3, 10.5 to 12.5 % respectively. Fe, P, Ca content of the product contain 1.8 to 2.5, 120.1 to 123.9, 333.1 to 440.2 mg/100g of fish sample.
 
The mixed salted sorpunti fish contained moisture, protein, fat, ash and salt content ranging from 37.5 to 40.5, 25.3to 28.0, 8.9 to 11.0, 10.6 to 11.4, 10.9 to 13.0 % respectively. Fe, P, Ca content of the same product contain 1.6 to 2.3, 121.5 to 125.8, 426.5 to 430.2 mg/100g of fish sample.
 
Biochemical composition of pickle salted sorpunti fish product contained moisture, protein, fat, ash and salt content ranging from 41.5 to 43.7, 23.5 to 25.5, 8.9 to 10.5, 9.1 to 10.4, 10.1 to 12.0 % respectively. Fe, P, Ca content of the product contain 1.6 to 2.1, 120.2 to 123.8, 415.2 to 418.5 mg/100g of fish sample.
 
Biochemical composition of dry salted sorpunti fish contained moisture, protein, fat, ash and salt content ranging from 30.0 to 33.1, 33.2 to 35.0, 9.6 to 11.0, 11.5 to 12.1, 10.1 to 11.5 % respectively. Fe, P, Ca content of the same product contain 1.8 to 2.6, 120.3 to 123.8, 442.8 to 445.2 mg/100g of fish sample.
 
Brine salted sorpunti fish contained moisture, protein, fat, ash and salt content ranging from 45.0 to 47.8, 21.5 to 23.0, 9.9 to 11.5, 9.5 to 10.2, 10.5 to 12.5 % respectively. Fe, P, Ca content of the same product contain 1.2 to 1.9, 120.3 to 125.1, 402.1 to 405.2 mg/100g of fish sample
 
Roe in fresh acceptable condition contained moisture, protein, fat, ash and ranging from 60.0 to 62.1, 29.0 to 30.5, 7.8 to 8.8, 2.1to 2.7 % respectively. Fe, P, Ca content of the same product contained 6.5 to 6.9, 490.1 to 494.4, 37.1 to 40.7 mg/100g of fish sample.
 
The salted roe contained moisture, protein, fat, ash and salt content ranging from 35.3 to 36.3, 33.5 to 35.1, 11.4 to 13.3, 6.5 to 7.7, 9.9 to 11.4 % respectively. Fe, P, Ca content of the product contain 19.2.4 to 20.3, 480.5 to 493.8, 74.2 to 81.4 mg/100g of fish sample.
 
Moisture, protein, fat and ash content of the mixed salted hilsa fish product treated with salt, sugar and preservative have been found to contain 35.3 to 37.3 %, 31.9 to 33.7 %, 10.7 to 12.1, 10.7 to 12.1 and 6.4 to 7.5 % respectively and salt and (%) sugar varied from 6.2 to 7.9 and 2.1 to 3.1 %. In case of pickle cured hilsa fish product treated with salt, sugar and preservative, salt and (%) sugar varied from 6.1 to 8.0 and 2.3 to 3.1% and moisture, protein, fat and ash content of the same product have been found to contain 36.1 to 38.3 %, 30.0 to 31.7 %, 10.7 to 12.3, 6.1 to 7.5 % respectively. Moisture, protein, fat, ash, salt and sugar content of the roe treated with sugar and preservative contained 35.3 to 36.3, 33.5 to 35.1, 11.4 to 13.3, 6.5 to 7.7, 6.1 to 7.2 and 2.0 to 2.9 % respectively.  
 
Performance of any processing and preservation method indicates the availability of the raw materials with minimum cost from the local source. It also indicates the time required for getting the finished fish product at the completion of the processing and preservation method as well as the product quality in fresh processed condition. 
 
According to the level of performance, the four finished salt cured hilsa fish product may be arranged as follows
 
Mixed > Pickle > Dry > Brine
 
According to the level of performance, the five finished salt cured sorpunti fish product  may be arranged as follows
 
Preparatory> Mixed > Pickle > Dry > Brine
 
Reconstitution is a process where in a processed fish food is allowed to remain in water for a certain period and simultaneously it is allowed to absorb water with a view to reconstitute to its original form before processing and preservation. And for this reason, reconstitution properties of any processed fish food are used to monitor of its ability to go to its original form by absorbing water from the solution. In practice, the processed fish food sample which absorb maximum percent of water in the same period of reconstitution are considered to be the best processed fish product and get the high score of acceptability by the panel of judge during sensory assessment by putting overall acceptability score.
 
The product which have been found to contain highest level of protein content among the other salt cured fish sample at the end point of reconstitution have been considered to be the best one. And the salt cured fish sample which have been found to contain lowest level of protein content have been considered to be of the inferior quality.
 
In respect of the O.A.S value against the different salt cured fish samples of the present study indicates that all of the experimentally salt cured fish products are better in quality than that of the commercially salt cured hilsa fish. But there are differences in quality among the experimentally salt cured fish samples. In order of quality standard we may arrange all of the cured fish products as follows:
 
BSSP (roe) > MSSP > PSSP > MSH/ PSS >CSH.
Storage stability of cured fish product is a matter of great concern to the fish processing personnel as well as to the marketing personnels during storage, distribution and marketing. The stability of such salt cured fish products is closely related to equilibrium moisture content or “active water” rather than to total moisture content during storage under different relative humidity condition.
 
The rate of adsorption/desorption of moisture of the products have been found to differ from each other. The rate of adsorption at higher RH above 80 that is at 85-98% RH the CSH have been found to be higher in comparison with the other two salt cured fish samples (MSH and PSS).
 
The product quality of the (MSH, CSH, PSS) products were assessed by determination of Total Volatile Nitrogen (TVN) after storage of the samples at different RH for a period of 18 days. The results of TVN have been represented against different RH ranging from 9-98%.
 
It is evident that the TVN values did not change significantly in the samples stored below 66% RH. However the TVN values rose sharply in the region over 80% RH indicating a rapid spoilage of the samples at these conditions, visual fungal infestations were observed in the samples at this high RH condition.
 
We have observed that RH have a great influence on the storage stability/unstability of the fish products. We may recommend to store the cured fish product in RH condition (15-52%) during the period of high humidity (June-October) which is favourable for prolonging storage stability and restoring the keeping quality for a long time which will be beneficial in terms of meeting the demand for nutrition, economic gain etc.
 
The overall findings of the five category of experimentally salt cured sorpunti fish while observing influence of ambient RH on the fish quality by storing the processed fish samples in polythene, in plastic pot and in the refrigerator become more or less similar with the findings of moisture gain/loss with the variation in RH condition and also indicated by the deterioration of the samples at ambient RH. But no deterioration is observed in the fish samples kept in refrigerator.
 
PRACTICAL CONCLUSION 
● Irrespective of differences in technological aspect among all of the experimentally salt curing methods, experimentally salt cured hilsa fish product  have been found to be better in quality than that of the commercially salt cured hilsa fish.
● Performance study indicates that mixed salt cured hilsa fish product is better in quality than the other salt cured products like pickle, dry and brine.
 
Mixed > Pickle > Dry > Brine
 
● Fish processors may use preparatory salt curing process for producing best quality salt cured sorpunti fish having more storage stability. Other methods of salt curing follows the following pattern in order of quality.
 
   Preparatory > Mixed > Pickle > Dry > Brine
 
● Salt, sugar and preservative treated hilsa fish product are better in quality than all other experimentally salt cured fish product.
● Roe treated with sugar and preservative have been found to be better in quality than the roe cured with salt only.
● Experimentally salt cured fish products have been found not to contain sands, dirty materials etc. and do not develop any off taste, color and odor whereas commercially salt cured hilsa fish product have been found to contain higher level of acid insoluble ash indicating the presence of sand and dirty material in it. It is also inferior in its appearance, taste, odor etc. and is not so storage stable in comparison with the experimental one.
● All of the experimentally salt cured fish product are better in quality and storage stable.
● In view of the present study we may recommend to follow the mixed salt curing process in case of hilsa fish for its improved quality.
● In case of sorpunti fish, preparatory salt curing method may be followed for its improved quality and stability.
● Salt, Sugar and preservative treated hilsa fish product is the most satisfactory cured fish product having quality as well as taste.
● To overcome the problem which were associated with the commercially salted fish in our country we may recommend the experimental salt curing methods for salt curing of fatty fish species of fish like hilsa, sorpunti etc.
● It is therefore recommended  to apply these experimentally used techniques in our country by fish processing personels.
 
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