ASSESSMENT OF SHELF LIFE AND QUALITY ASPECT OF MARKET SALTED AND LABORATORY PREPARED SALTED HILSA ( Tenualosa ilisha )

Microbs This study was conducted to compare different qualities of laboratory prepared salted hilsa and salted hilsa from different markets of Bangladesh. There were five treatment namely T1 = Fresh hilsa, T2=Laboratory prepared salted hilsa, T3 = Salted hilsa from Boro Bazar, Rajshahi, T4 = Salted hilsa from Mechoya bazar, Mymensingh, and T5= Salted hilsa from Kewatkhali, Mymensingh.All samples were evaluated by studying proximate composition, TVBN value, salt concentration and total microbial load. Moisture, crude protein, crude lipid and ash content of fresh hilsa were 60.98%, 19.92%, 17.51% and 1.18% respectively while moisture, crude protein, crude lipid and ash content of laboratory salted hilsa were 42.92%,25.55%,21.23% and 10.21% respectively. Moisture was significantly higher in fresh hilsa than salted hilsa and the crude protein, crude lipid and ash were significantly higher in salted hilsa than fresh hilsa due to dehydration of salted hilsa. TVB-N content of fresh, laboratory prepared, Rajshahi market, Mechoya bazar and Kewatkhali market sated hilsa were 2.26, 3.74, 4.65, 5.04 and 5.29 mg/100g respectively which showed the best quality product was laboratory prepared salted hilsa. Similarly, salt content of fresh, laboratory prepared, Rajshahi market, Mechoya bazar and Kewatkhali market sated hilsa were 10.26, 15.61, 23.65, 25.04, and 28.31 % respectively which resulted excess salt content of market samples. The total Bacterial Load (CFU/g) of fresh, laboratory prepared, Rajshahi market, Mechoya bazar and Kewatkhali market sated hilsa were 1.75×10, 2.37×10, 1.83×10, 3.26×10, and 2.55×105, respectively.


INTRODUCTION
Bangladesh is an agro based country enriched with enormous fisheries resources.Fish is very important food stuff in developing countries due to its high protein content and nutritional value.Fish provides more than 50% of the animal protein for the populations of 34 countries (Bhuiyan, 1987).Among the fishes hilsa is rich in protein, fat, vitamins and minerals.It is considered as the national fish due to its popularity, economic importance and historically securing the largest share of landing with approximately 354.8 metric tons annually combined from island and marine capture (Department of fisheries, FRSS Report, 2015).Hilsa, the national fish of Bangladesh has been playing a very important role in our economy.In fishes, proximate composition means the composition of the fish flesh.Fish flesh contains four basic ingredients in varying proportions major nutrients such as water (70-80%), protein (18-20%), fat (5%) and minerals (5%) and minor nutrients such as vitamin, carbohydrate.It has high nutritional value in terms of fats and proteins that are not commonly available in other foods.Food quality of market salted hilsa varies with salting procedure and other factors.Fish quality is all those attributes which fish eater or buyer consciously or unconsciously consider or expect to be present in fish in terms of nutritional benefit, dietary satisfaction and that it does not contain any harmful bacteria or pathogen and that it is caught from unpolluted water (Mansur, 2012).
In our country the catch of hilsa is available more or less round the year, but the catch is very high during the monsoon (i.e.June to October) with peak harvest in September (FRI, 1991).During this period a large quantity of hilsa fishes are caught which amounts about 90% of total catch.The main landing centres of hilsa fish are located at Chandpur, Cox's Bazar, Chittagong, Barisal and Khulana.Large amount of hilsa spoils each year due to inadequate preservation facilities.Fish preservation has been practiced in Bangladesh for a long time; the simplest methods employed are drying, salting, freezing and semi-fermentation.Drying is not suitable for hilsa, because hilsa contains high amount of fat, which causes more oxidation and rancidity.Fatty fishes are less suitable for long term freezing, because most of pelagic fatty species contain large proportion of dark muscle which leads to muscle protein deterioration more quickly than lean fishes during freezing and frozen storage.Some of the hilsa are frozen.A few are smoked but, although available before, are not found in the market now (Nowsad, 2007).High lipid content makes the hilsa very susceptible to oxidative rancidity, along with rapid autolytic and bacteriological decomposition (Nowsad, 2010).So, adequate handling and immediate icing for the fish are required.Salting is the oldest and effective method of fish preservation which provides the following advantages.Salting is a simple and low cost fish preservation technique; It does not require any equipment or machinery; it can be done anywhere; Salt is easily available and salting can be done throughout the year, especially during monsoon when other low-cost preservation like sun-drying is not possible; It keeps the fish edible for a long time compared to other preservation methods.The following objectives were set for in this study; to know the nutritional value of laboratory prepared hilsa and market salted hilsa, to know the microbial load of laboratory prepared hilsa and market salted hilsa, to compare the nutritional and microbial composition of laboratory prepared hilsa and market salted hilsa, to determine the salt content and shelf life of laboratory prepared and market salted hilsa.

MATERIALS AND METHODS
The study was conducted during January 2018 to June 2018 and was carried out in the Laboratory of Processing and Microbiology, Fisheries Microbiology Lab., Fish Processing and Quality Control Lab., Fish Harvesting Lab and Post-Graduate Lab., Department of Fisheries Technology,Bangladesh Agricultural University.

Collection of Sample
The hilsa fish was collected from Kamal Ronjit Market, Mymensingh and the salted hilsa was collected from Kewatkhali bazar, Mymensingh, Mechoya Bazar, Mymensingh, Boro Bazar, Rajshahi, respectively.

Preparation of salted hilsa
The raw fishes were eviscerated, cleaned, washed, weighed and cut the fish into chunk and finally prepared for salting.The raw fishes were enrolled by dry salt (fish: salt = 4: 1), stacked in straw mat and stored for a salting or curing period, at room temperature.Then the extracted water of the fishes due to salt action was removed from the mat.Thus the fishes were always allowed to remain in dry condition for the production of dry salt cured fish.

Bio-chemical analysis
AOAC (1980) method was followed for bio-chemical analysis of the T. ilishahomogeneity of the samples was done by using a blender.
Moisture was determined by placing an accurately weighed known amount of ground sample in a preweighted porcelain crucible in an electric oven at 105 0 C for 24 hours until constant weight was obtained.The loss of moisture was calculated as percent moisture.

Determination of Salt Content
In this determination, 1.0g fish sample was taken from ground fish sample in a conical flask and was mixed with 10 ml distilled water, was stirring and mixed for half an hour so that all the salt in the muscle becomes soluble in water.Then the solution was filtered with filter paper and an aliquot of 0.2 ml from the solution (filtered) was taken in another conical flask to which 10 ml of distilled water was added followed by an addition of 2 drops of 5% Potassium Chromate and mixed properly.Titration was done with 0.

Microbial analysis
Total bacterial count of fresh and salted hilsa samples was done by Standard Plate Count (SPC) method.Standard plate count expressed as Colony Forming Units per gram (CFU/g) of the samples were determined by using consecutive decimal dilution technique using spread plates.Only plates having 30 to 300 colonies were considered for counting in order to get acceptable values.No. of bacteria per gram of the fish sample (CFU/g) was calculated by using the following formula:

RESULTS AND DISCUSSIONS
Moisture, crude protein, crude lipid and ash content of raw hilsa were 60.98%, 19.92%.17.51% and 1.18% respectively (Figure 1).Kaisar, 2014 found that the moisture, crude protein , crude lipid and ash content of raw hilsa was 56.816%, 18.709%,18.932%and 1.266% which are more or less similar with the present study.The moisture, crude protein, crude lipid and ash content of raw hilsa was 65.735, 18.55%, 14.44% and 0.81 (Dewan, 2010) which are also similar with the current research work.Moisture, crude protein, crude lipid and ash content of laboratory salted hilsa were 42.92%, 25.55%, 21.23% and 10.21%, respectively (Figure: 2-7).Moisture, crude protein, crude lipid and ash content of Salted Hilsa, collected from Boro Bazar, Rajshahi were 45.38%, 22.56%, 17.73% and 14.23% respectively.Moisture, crude protein, crude lipid and ash content of Salted Hilsa, collected from Mechoya Bazar, Mymensingh were 45.73%,21.91%,17.39%and 14.91% respectively (Figure: 2-7).Moisture, crude protein, crude lipid and ash content of Salted Hilsa, collected from Kewatkhali Bazar, Mymensingh were 47.82%,21.35%,16.24%and 15.32% respectively (Figure: 2-7).Chakraborty et al. (1997) reported that moisture content of dry salted, wet salted and sundried salted fish showed significant decreases from an initial 71.80% to 37.06%, 44.90% and 25.95% respectively.Shamim et al. (2011) studied the proximate composition of different portion of hilsa collected from two regions of the Bay of Bengal and found the highest protein content (21.89%) in ventral where lowest (20.50%) in caudal region.In this study, we found highest protein content (23.62 ± 0.28%) in dorsal region of fresh sample and lowest (20.79 ± 0.17%) in dorsal region of salted fish.Kaisar, 2014 showed that the moisture, crude protein, crude lipid and ash content of salted hilsa collected from Chadpur was 47.236%, 24.232%, 17.264% and 15.795% which are more or less similar with the present study.Results showed a premium quality of salted hilsa found laboratory prepared product.It can be concluded a best quality of salted produced found from laboratory due to use of best quality ingredient and appropriate method.TVB-N value of fresh, laboratory prepared and salted Hilsa Qualitative analysis of fresh and salted Hilsa of different samples collected from local fish market of Mymensingh and Rajshahihas been done on the basis of TVBN value and the results are presented in Table 1.TVBN value of fresh hilsa was 10.26mg/100g.on the other hand, TVBN value of laboratory prepared, Rajshahi Market, Mechoya bazar and Kewatkhali market sated hilsa were 15.61,23.65,25.04and28.31 mg/100g, respectively.Kaisar, 2014 was found that the TVB-N value of raw and salted hilsa collected from Chadpur was 0.886 and 2.847 mg/100g which are more or less similar with the current study.Connell (1995) the upper limit of TVB-N is 30 mg/100g for fin fish dried products acceptability.However, the findings of this study shows that's the TVB-N content obtained from our dry fishes are very close with the previous studies.
The result of fresh and salted hilsa is shown in following table.Salt content of fresh hilsa was 1.52%.Similarly salt content of laboratory prepared, Rajshahi market, Mechoya bazar and Kewatkhali market sated hilsa were 2.95%, 5.57%, 6.07%, and 6.98% respectively.Levanidor (1958) reported that during salting of herring, the loss of soluble substances in the brine was only 0.5% of the initial weight of the fish.Mansur et al. (1998) found that the initial protein content of ordinary salt and pure salt processed hilsa were 16.42% and 16.23% respectively and the final protein Content were 26.58% and 26.87% respectively on 16th day of observation.
About 3-5g prepared sample was taken in pre-weighed porcelain crucible and was placed in muffle furnace at 550 0 c for 6 hours.Then the crucibles were cooled in desiccators.The average in percentage of each sample of the remaining materials was taken as ash.Ash content (%) = Crude protein content was determined by AOAC (1980) methods.Total nitrogen was calculated by using the following formulaprotein: Nitrogen% x 6.25Prepared fish sample was weighed and taken in a paper thimble and placed it insidethesoxhlet apparatus to determine the crude lipid content of the prepared sample.Lipid content was calculated by using following formula-TVB-N content of the sample can be calculated by the following formula-TVB-N (mg/ 100 g sample) = 05 N AgNO3 solutions up to the end point which was indicated by the brick-red color.Salt content of the samples was determined by the following formula: S1 × V1 = S2 × V2 Where, V1= Volume of sample V2= Volume of titrant S1= Strength of sample (NaCl) S2= Strength of titrant (AgNO3) % of NaCl = S1 × 58.5 (molecular wt. of NaCl)

Table 1 .
Proximate composition of fresh and salted Hilsa