Effects of storage temperature and preservative treatment on shelf life of the pond-raised freshwater fish, silver perch (Bidyanus bidyanus).

Sensory and microbiological characteristics of pond-raised freshwater silver perch (Bidyanus bidyanus) fish, during cold storage over a period of 25 days were evaluated. Whole fish (averaging 400 g each) were stored in cold storage rooms at either 0 to 2 degrees C, 5 degrees C, or 5 degrees C + potassium sorbate as a preservative. The organoleptic and hypoxanthine test results show that the treatment of potassium sorbate can slow the process of spoilage by about 5 days. Yet, the most important factor affecting the shelf life of these fish is the storage temperature. Keeping the fish at 0 to 2 degrees C can prolong the storage prior to spoilage by 10 days compared with those kept at 5 degrees C. These results obtained through organoleptic tests are corroborated by both the chemical (hypoxanthine and total volatile basic nitrogen) and to some extent by the physical (cosmos) tests. The initial total bacteriological counts were 5 x 10(2) CFU/cm2 for fish surface and <10(2) CFU/g for fish flesh, and these counts rose continuously, reaching about 106 CFU/g (0 to 2 degrees C) and 10(7) CFU/g (5 degrees C) in flesh and 10(7) to 10(8) CFU/cm2 on the surface by the end of the storage period. The addition of potassium sorbate led to a smaller increase in bacterial numbers, especially during the first 15 days. Bacterial composition fluctuated during storage. The initial load on the fish surface was predominantly mesophilic and gram positive and consisted mostly (80%) of Micrococci, Bacillus, and Corynebacterium. During the next 10 days, these bacteria were practically replaced by gram-negative flora comprised mostly of Pseudomonas fluorescens that rapidly increased with storage time and accounted for 95% after 15 days.