Microbiological Quality and Shelf-Life Extension of Oysters (Crassostrea Gasar) Subjected to Hurdle Approach Involving Sodium Metabisulphite, Calcium Hypochlorite and Storage Temperature

This study set out to develop an efficient treatment for the quality control of oysters (Crassostrea gasar) using calcium hypochlorite [Ca(OCl)2] and sodium metabisulphite (Na2S2O5) during a challenge test under ambient and refrigerated storage. Artificially inoculated oyster samples were treated in groups consisting of various treatments as follows: 10 ppm Ca(OCl)2 and 100 ppm Na2S2O5 combined treatment; 10 ppm Ca(OCl)2 sole treatment and sterile deionized water treatment (control). The treated samples were then stored under refrigerated (4°C) and ambient (28±2°C) conditions for 96 h. Samples were subjected to analysis at intervals to determine their microbiological (total heterotrophic bacterial counts, coliform counts, and Salmonella counts), chemical (trimethylamine, pH), and sensorial (visual appearance, odour, and texture) attributes. The Ca(OCl)2 and Na2S2O5 combined treatment significantly inhibited (p<0.05) the increase in the magnitude of the different microbial groups, trimethylamine (TMA) content, and pH when compared with the Ca(OCl)2 sole treatment and control groups. Heterotrophic bacterial counts in oysters treated with both chemicals were 7.23 log10CFU/g and 5.66 log10CFU/g at the end of storage for samples kept at ambient and refrigerated conditions respectively. Organoleptic evaluation conducted by a team of panelists showed that oysters subjected to the combined treatment followed by refrigerated storage showed higher quality scores than the control and other treatments during the study and hence, maintained the fresh¬ness and overall acceptability of the seafood. Combined treatment using Ca(OCl)2 and Na2S2O5 prevented robust microbial proliferation, sustained the quality of freshly harvested oysters, and extended their shelf life by 4 days during refrigerated storage.