Abstract: Pseudomonas spp., Acinetobacter spp. and Brochothrix thermosphacta isolated from chilled raw tuna (Thunnus obesus) at the end of shelf life were explored for their spoilage potential. Bacterial counts and growth kinetic parameters, sensory quality, total volatile basic nitrogen (TVB-N) and biogenic amine contents and the yield factor of metabolic products, YTVB-N/CFU, were assayed on sterile T. obesus inoculated separately with each of the three isolates during chilled storage. It was found that the modified Gompertz, Baranyi-Roberts, and Logisitic models could describe the dynamic growth of Pseudomonas spp., Acinetobacter spp. and Brochothrix thermosphacta at cold temperature. The Lag phase of the 3 bacterial strains were 10.85, 83.93 and 79.11 h, respectively, and the relative maximum growth rates were 0.045 7, 0.182 9 and 0.111 1 h-1, respectively. The shelf life of inoculated tuna was 96, 108 and 105 h, respectively. The TVB-N contents of sterile T. obesus inoculated with Pseudomonas spp., Acinetobacter spp. and B. thermosphacta were 27.32, 22.80 and 24.85 mg/100 g, respectively. The changes in biogenic amines contents of T. obesus during chilled storage revealed that the capability of Pseudomonas spp. to produce biogenic amines was stronger than that of Acinetobacter spp. and B. thermosphacta. The biogenic amine index of tuna inoculated with Pseudomonas spp. was 155.84 after 96 h storage, which was higher than the threshold value of 100. This study also showed that YTVB-N/CFU values for the 3 strains were 7.36 × 10-8, 1.85 × 10-8 and 5.07 × 10-8 mg TVB-N/CFU, respectively, indicating that Pseudomonas spp. played the most important role in spoilage of chilled raw T. obesus, followed by B. thermosphacta and Acinetobacter spp..

Key words: tuna, dominant spoilage bacterial, growth curve, biogenic amine, total volatile basic nitrogen, spoilage potential