2.1. Collection of the fishes and location of the experiment: The fresh fish (Taki and Shoal) had been collected from the river Meghan 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, starts in the month of January, 2012. The whole experimental period covered 18 months of duration started from January, 2012 to July, 2013.
2.2. Preparation of fish: The fishes were carefully washed with cooled tap water. Head, scales, fins, gills and viscera were removed and again washed with tap water to remove blood, slime and unnecessary flesh. Due to the presence of hard shield like bony elements, bones of head are discarded as waste.
2.3. Fresh Sample: A few fresh fish-samples of Taki and Shoal fish species was taken to the laboratory for quality analysis. 6 or 7 slice was taken randomly which represented the parts from whole body of the fish. Then the slices were chopped with skin and finally ground with an electric blender to make a homogenous sample before being sampled for analysis.
2.4. Brine salting (BS) method: Being a safe, antimicrobial and incidental food additive, toxic for some microorganisms, depressor of water activity (aw ) of the food, sodium chloride has been used as a seasoning and flavor enhancer as well as a preservative or curing agent. During this experiment A 30% salt solution is prepared (30 gm salts 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 (260C-300C) for the production of brine-salted fish. The fish in brine were kept immersed by putting a glass weight. During brine-salting process moisture content decreased and salt content increased considerably during the first 6 to 7 days which is called ripening period.
2.5. Storage of the product: At the end of the ripening period, brine-salted product of two fishes was packaging with plastic bag maintaining aseptic condition as far as possible and was stored at refrigeration temperature (40C). The preservation period of product is linked to the amount of salt added; therefore a straight proportion is present between the amount of salt used and the preservation period.
2.6. Sampling Regime and Procedures: Evaluation of quality changes in brine salted Taki and Shoal fishes were carried out 3 month interval for refrigeration temperature (40C), until the fish become spoil or inedible condition. The experiment was done for second time at regular intervals during salting period. There are some parameters which determine the quality of salted fish during storage condition, such asfreshness test by sensory scores, TVB-N value, pH, FFA etc. Freshness test of the fishes indicate the quality test in term of odor, color and appearance in different species. TVB-N value, pH, FFA of fishes is important indicator to determine the quality of fish.
2.7. Estimation of sensory score: Determination of the quality of Brine salted taki and shoal fish was made by trained panel of six judges in BCSIR, IFST Lab. following 9-point hedonic scales. Comparison was carried out in terms of sensory characteristics, such as color, flavor, texture and general appearance. The panel was requested to rate each sensory feature of the end products. The average score of 5 was considered to be the borderline of acceptability (9. Like extremely; 8. Like very much; 7. Like moderately; 6. Like slightly; < 5. Bad.)
2.9. Estimation of pH: A 1 g sample of the fish flesh was homogenized in 10 ml of distilled water and the mixture was filtered. The pH of the filtrate was measured using a pH meter (Mettler Toledo 320-s, Shanghi, China). 2.10. FFA (Free fatty acid) estimation: Oil sample used throughout the work was prepared by extracting the brine salted taki and shoal fish by Folch reagent (chloroform and methanol in the ratio of 2:1 v/v).The brine-salted fish was first cut into small pieces and then ground. The ground material was then mixed with folch reagent in a large wide mouthed stopper glass bottle for 24 hours at room temperature after 15 minutes stirring with glass rod. Extraction was facilitated by occasional shaking. The mixture was filtered through a Buchner funnel and the filtrate was evaporated in batches under heater or oven at 600 C. Seven gram of well-mixed oil was taken into 250 ml flask and 50ml ethanol was added, previously neutralized by adding 2 ml phenolphthalein solution. Titration was done by 0.25 N sodium hydroxide (NaOH) with vigorous shaking until permanent final faint pink color appeared and persisted for at least one minute. The value was reported as a percentage (%) of free fatty acid expressed as oleic acid. Milli liter of 0.25 N NaOH required for titration corresponds to the percentage of free fatty acid. Data were analyzed by using SPSS for windows-20 statistical programme with five percent level of significance.