BIOCHEMICAL CHANGES IN SHRIMP INOCULATED WITH PSEUDOMONAS, BACILLUS AND A CORYNEFORM BACTERIUM1,2

Abstract

White shrimp (Penaeus setiferus) washed with ethanol and sterile water were inoculated with a fluorescent Pseudomonas, non-fluorescent Pseudomonas, Bacillus, and a coryneform bacterium. Washing reduced the microbial load but growth occurred on control samples during refrigerated storage. Samples inoculated with Pseudomonas became putrid 2–3 days sooner than their controls. Addition of coryneform bacteria delayed spoilage. Shrimp inoculated with Bacillus spoiled at the same time as the non-inoculated controls. Inoculation of shrimp with Pseudomonas species (a) retarded development of melanosis; (b) produced volatile nitrogen in the atmosphere surrounding shrimp but only after spoilage had taken place; (c) caused higher levels of water-soluble protein, non-protein nitrogen, and total volatile nitrogen than in their corresponding controls; and (d) reached higher pH levels sooner than the controls. No significant changes occurred in volatile reducing substances. Sterile shrimp juices exhibited more extensive melanosis than juices inoculated with Pseudomonas. No marked changes in amounts of soluble protein or non-protein nitrogen were noted upon storage of inoculated juices. Juices inoculated with Pseudomonas had higher levels of total volatile nitrogen after storage than comparable controls. Proteolysis by the fluorescent Pseudomonas was indicated by major changes in elution profiles on Sephadex G-100. Compared with sterile controls, levels of free amino acids decreased in juices inoculated with Pseudomonas or Bacillus and stored at 5 C.