Role of Planococcus citreus in the spoilage of Penaeus shrimp

Abstract

An extensive survey of marine products revealed that only products containing shrimp contained P. citreus P. citreus isolates accounted for 13–24% of the microbial flora of Penaeus shrimp during extended ice storage. After 10 days of shrimp ice storage, Plano-coccus and Pseudomonas were the predominant microorganisms present in Penaeus shrimp. All isolates recovered exhibited good growth over a range of pH 7–10, 5–35 °C and 5–120 g NaCl/1. Proteolysis studies revealed that P. citreus isolates were able to hydrolyze gelatin, cottonseed, soy and more important to the fisheries microbiologists, shrimp protein. P. citreus grew well at ice and refrigerated temperatures (5 °C) and all isolates tested produced an active extracellular enzyme system capable of degrading shrimp protein at this temperature. P. citreus counts increased in the inoculated shrimp stored at 5 °C from 3.0 x 103 bacteria/gram to 1.5 × 108 bacteria /gram at the 16th day. The potential of P. citreus as a “spoiler” of raw shrimp was shown by the rapid increase in total volatile nitrogen/amino acid nitrogen (TVN/AA-N) ratio, pH and trimethyl-amine nitrogen (TMN) content as well as the reduction in percent total extractable protein (TEP) of the inoculated samples. The extracellular proteolytic enzyme of P. citreus was active at refrigeration or iced temperatures; however, maximum activity was exhibited at 35 °C and pH 8. The importance of the extracellular protease enzyme for shrimp quality is discussed.