Effect of selected washing treatments and drying Temperatures on biochemical and microbiological Quality of dagaa (rastrineobola argentea)

Abstract

Dagaa (Rastrineobola argentea) is one of the most important fish foods for the lowincome households in the Nyanza Province, Kenya. However, the off-flavour and offodour that results from the traditional sun-drying process of sun-dried dagaa is a major disincentive to the use of the fish for human consumption, hence leading to utilization in animal feed. Chemical analyses for pH, Thiobarbituric reactive substances (TBARS), Total volatile bases-nitrogen (TVBN) and aerobic bacterial counts were carried out on dagaa sampled from various process steps within the open field sun-drying and market conditions. Dagaa was also oven-dried at 30oC, 40oC and 50oC after washing with selected solutions namely salted (3% sodium chloride), chlorinated solutions (100ppm) and potable tap water (control). Results indicated that TBARS values increased significantly (p<0.05) from 1.39 mgMA/kg in fresh fish to 10.55 mgMA/kg in the market samples. The TVBN values increased significantly (p<0.05) from 9.42 mgMA/kg in fresh fish to 29.51 mg/ 100g in the market samples. The pH values declined significantly (p<0.05) from pH 6.72 in the fresh fish to pH 5.88 in the market samples .Lipid oxidation (TBARS) was significantly (p<0.05) higher in dagaa subjected to salted-wash treatments when compared to the chlorinated and control-wash treatments. The rate of lipid oxidation was significantly (p<0.05) higher at elevated temperatures of 50oC relative to 30oC and 40oC conditions. The TVBN levels observed in the salted and chlorinated-wash treatments showed significantly (p<0.05) lower TVBN values when compared with the control-wash treatments. However, the values of TVBN obtained at 30oC were significantly (p<0.05) higher when compared with the 40oC and 50oC drying temperature conditions. The salted-wash treatments resulted in lower pH values relative to the chlorinated and control-wash treatments on drying at 30oC and 40oC. In this study, the most appropriate treatment that showed the least TVBN and moderate TBARS values was drying the dagaa at 50oC after washing with chlorinated solution.