Performance and quality assessment of salt curing of Taki (Channa punctatus), Shol (Channa striatus) and Tengra (Mystus tengra)

Abstract

Salting of fish is widely used as one of the most important low-cost traditional method for fish-preservation and considered as a concentrated source of nutrients to all categories of people throughout the world including Bangladesh. Salt-cured fishes are highly appreciated because of their characteristic taste, texture and storage stability. So, attempts have been made in the present study to preserve three freshwater fishspecies of Bangladesh viz., large size fish Shol (Channa striatus, Bloch; 1801), medium size fish Taki (Channa punctatus, Bloch; 1793) and small size fish Tengra (Mystus tengra, Hamilton- Buchanan; 1822) with five different types of salt-curing method viz., Dry salting (DS), Pickle curing (PC), Brine salting (BS), Sun-dried salting (SDS) and Turmeric treated sun-dried salting (SDS+T). Studies were conducted on their sensory (characteristics & scores), proximate (moisture, protein, fat, ash) chemical (salt, TVB-N, FFA, pH) and bacteriological (SPC & HBC count) quality assessment during storage period both at room (26-320C) and refrigeration (40C) temperature using standard methods of analyses. Important mineral composition e.g. Ca, Mg, Fe, Cu Zn, and Mn were also determined in fresh fish and freshly processed salted fish-products. The present study showed that, the content of moisture, protein, fat, ash, TVB-N (Total Volatile base-Nitrogen), FFA (Free Fatty Acid), pH and SPC (Standard Plate Count) of freshly collected shol fish was 77.03±0.12%, 19.52±0.07%, 1.93±0.07%, 1.44±0.11%, 4.41±0.01 mg/100g, 0.6±0.06%, 6.9±0.06, and 2×105 cfu/g; taki fish was 78.65±0.07%, 16.89±0.10%, 2.50±0.06%, 1.36±0.11%, 3.43±0.02 mg/100g, 0.5±0.10%, 7.0±0.06 and 1.1×105 cfu/g and tengra fish was 74.27±0.07%, 16.96±0.07%, 6.04±0.06%, 2.67±0.08%, 4.27±0.02 mg/100g, 0.9±0.21%, 7.0±0.10 and 5×105 cfu/g respectively. Fresh shol, taki and tengra fish had Ca 11.2, 16.35 and 22.025; Mg 10.125, 9.425 and 11.4; Fe 1.475, 1.275 and 2.25; Cu 0.7, 0.65 and 0.55; Zn 0.25, 0.425 and 1.275; Mn 0.1, 0.05 and 0.125 mg/100g of fish respectively. ‘Salt ripening’ of five different types of salted shol, taki and tengra was obtained by assessing changes in salt penetration rate and its effect on moisture content, fluid loss pattern in fish muscles and percent weight loss of fishes during ripening period. After salt-ripening moisture (%) content, pH value, SPC (cfu/g) and HBC (cfu/g) load decreased whereas protein (%) (except BS tengra), fat (%), ash (%), salt (%) and FFA (%) value increased in salted fish samples when compared to the fresh fish samples. Salt (NaCl) content in freshly prepared salted products ranged between 13.77% & 17.10%. Preferability study was also done with the taste testing of ‘Fish-curry’ prepared from 5 different types of freshly processed salted Shol, Taki and Tengra fish-products so that these kinds of new products could find good market. Taste testing study showed the greater acceptability of turmeric treated sun-dried salted (SDS+T) shol, taki and tengra fish over the others. It was also observed that salted fish products are a good source of minerals. Mineral elements detected were in the decreasing order of Ca>Mg>Fe>Zn>Mn>Cu in fresh processed five types of shol, taki and tengra fish-products respectively. xxvii During storage period, protein, fat, ash, salt and sensory score were found to be decreased whereas moisture, TVB-N, FFA, pH, SPC and HBC value increased both room and refrigeration temperature, but the increase in room temperature was more prominent than the products stored in refrigeration temperature. However, there was a general decline in sensory characteristics and scores on flavor, color and texture of salted fish-products during storage (a total period of 36 months) and the acceptability score <4.5 (in 1-9 point hedonic score on quality) was considered as rejected or spoiled for all salted fish samples. There was also found direct relation between moisture & chemical composition (TVB-N, FFA, pH) and moisture & bacterial count (SPC, HBC) whereas inverse relation was revealed between sensory score & TVB-N, FFA, pH value during entire storage period. Visually there was found no fungal attack in all of 5 types of salted shol, taki and tengra fish products during the storage period. The overall quality of all salted fish-products were excellent in fresh process condition and five types of salted products stored at refrigeration temperature were found in better condition as determined by sensory, biochemical and bacteriological analysis. From the overall performance, it has been proved that these three fishes were highly acceptable in salted condition and turmeric treated sun-dried salting (SDS+T) method was found as the best. On the basis of quality-standard and shelf-life performance, the five salting methods can be arranged as follows: Turmeric treated sun dried salting (SDS+T)>Sun-dried salting (SDS)>Dry salting (DS)>Pickle curing (PC)>Brine salting (BS). Among the three species, five categories of salted tengra fish-samples showed better performance in respects of shelf life study. The highest shelf life was found to be 36 months in SDS+T tengra at refrigeration storage whereas lowest was found in 75 days in BS taki at room temperature. Thus the present study provides information about the suitability of different salting methods of three commercially important fishes to produce a very stable and safe product with long storage life. By assessing the nutritional quality as well as the feasibility of the method, it can be recommended to incorporate the turmeric treated sun-dried salting (SDS+T) method in commercial scale which further may contribute in national economy of Bangladesh.