Quality attributes and drying rate of Silver Cyprinid (Rastrineobola Argentea) during different processing methods

Abstract

The proper handling and processing of the highly perishable silver cyprinid (Rastrineobola argentea) could contribute towards alleviation of food insecurity by directly acting as a food resource and through employment for income generation among vulnerable groups. Despite the many processing techniques used, the quality and value of silver cyprinid still remains low. This research was therefore carried out to establish how effective the methods used by the artisanal processors are in producing high quality silver cyprinid fished from Lake Victoria in Uganda. This was done by comparing the effect of the current artisanal processing methods on the quality attributes and the drying rate of silver cyprinid in four major landing sites (Kiyindi, Kasekulo, Katosi, and Ssenyondo) along the shores of Lake Victoria in Uganda. The quality attributes measured were proximate composition (moisture, fat, ash and protein content), lipid oxidation (FFA, PV, and TBARS), microbial counts (yeasts and molds, total plate count and total coliforms), and microbial spoilage (TMA). The drying rate was calculated and drying rate curves drawn. It was observed that drying on nets placed on the ground (most prevalent at 41.7%) and on raised racks were the two main strategies for human grade silver cyprinid. Salting was carried out mainly on silver cyprinid for export. On average salting was done at concentrations of 4g of salt per 100g of wet fish and 10g of salt per 100g of wet fish. Raised rack drying led to lower microbial counts and spoilage and a less extent of lipid oxidation than the net on ground drying. Fish from all the sites was highly nutritious as evidenced by the high protein (ranging from 62.8 ± 4.4 to 73.3 ± 10.2 % dry basis) and fat content (ranging from 11.5 ± 2.9 to 13.3 ± 1.9 % dry basis). The average moisture content, PV, FFA, total plate count, total coliforms and yeasts and molds were higher for all the sites than the standard values. The overall quality of fish by the end of processing in Kiyindi was higher than in all the other sites. The rate of drying of salted fish (6.18 ± 0.1 g water/g db, hour) was lower, under the same conditions than the rate of drying of the unsalted fish (7.93 ± 0.1 g water/g db, hour). Salt reduced the microbial load, TMA and FFA and increased the PV and TBARS of the silver cyprinid. Offshore salted samples had coliforms below detectable limits while those salted onshore and the unsalted sample had detectable coliforms. A reduction in drying rate was observed with increase in salt concentration. Salting at a concentration of four grams of salt per 100g of wet fish offshore and drying on raised racks was found to be the most effective method currently being used since it resulted in reduced microbial load while not entirely compromising on the extent of lipid peroxidation.