Abstract:In order to explore the decay-causing abilities of beef-derived Pseudomonas strains with varying protease activities and lipase activities towards chilled beef, seven Pseudomonas strains with greatly different enzyme-producing abilities were screened based on enzymatic activities. The isolated strains included three strains of Pseudomonas fluorescens (PP3413、PP754、PL1415), one strain of P. putida (P011), one strain of P. poae (PL347), one strain of P. salomonii (PP1438), and one strain of Pseudomonas libanensis (PL1459). Then, the stains were used to re-contaminate the surface of sterile chilled fresh beef. At the end of storage (8 d), the number of Pseudomonas and TVB-N values for the samples inoculated with Pseudomonas fluorescens (PP3413, PP754 and PL1415) were relatively high (8.97~9.65 log CFU/g, and 20.35~25.02 mg/100 g, respectively). However, the number of Pseudomonas and TVB-N values of the beef samples inoculated with PL347 (which had the highest lipase activity) were 6.25 log CFU/g and 13.95 mg/100 g, respectively, which were significantly lower than those of other treatment groups (p<0.05). In addition, the TVB-N values of the samples contaminated by the strains with stronger protease-producing abilities, PP754 (25.02 mg/100 g) and PP3413 (22.06 mg/100 g) were higher than those of the strains with stronger lipase-producing abilities, PL1459 (21.80 mg/100 g) and PL1415 (20.35 mg/100 g). In summary, P. fluorescens had relatively high enzymes-producing ability and decay-causing ability, with the strains with stronger protease-producing abilities likely having higher decay-causing abilities towards beef than those with stronger lipase-producing abilities. However, the specific relationship between the decay-causing ability of Pseudomonas towards chilled fresh beef and its enzyme-producing ability needs to be further confirmed.
