Selected biochemical and microbial changes in Penaeus shrimp inoculated with Planococcus citreus were examined to determine the potential of this organism to contribute to spoilage of shrimp. Biochemical and microbial studies were conducted following storage of Penaeus shrimp at 5 C for 0, 4, 8, 12 and 16 days. Three samples, a control (raw shrimp), an irradiated (600 Krad) control and an irradiated (600 Krad) sample inoculated with P. citreus, were analyzed for changes in aerobic plate count, pH, total volatile nitrogen/amino acid nitrogen (TVN/AA-N) ratio, trimethyl amine-nitrogen (TMN) and total extractable protein (TEP). P. citreus counts increased in the inoculated shrimp from 3.0 × 103 bacteria/gram at 0 day to 1.5 × 108 bacteria/gram at the 16th day. By the 16th day of storage, the pH of the inoculated shrimp was significantly higher than the pH of the other samples. P. citreus inoculated onto irradiated shrimp was able to produce a TVN/AA-N ratio of 1.3 by the 10th day of storage, about the same time as that developed by the natural flora on raw shrimp. The increase in TMN content of the control (raw shrimp) and the inoculated sample were not significantly different. P. citreus was also able to bring about a significant decrease in the percent TEP of shrimp during storage. These changes indicate the capabilities of P. citreus in lowering the overall quality of Penaeus shrimp.

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