Characteristics of Postbiotics Lacticaseibacillus paracasei Lab5 and Its Application in the Preservation of Refrigerated Duhei Pork

In this study, the screening of lactic acid bacteria with significant inhibitory effect on Listeria monocytogenes. It was determined that the inhibitory substances existed in cell-free fermentation supernatant (CFS), cell pellet or bacterial lysate. The thermal stability, pH stability, and protease sensitivity of the inhibitory substances were investigated. The growth curve and the minimum inhibitory concentration (MIC) of the selected strain were also determined. Finally, the preliminary application was in the cold storage and preservation of Duhei pork. The preservation effect was evaluated by sensory evaluation, pH, meat colour, viable cell counts, total volatile basic-nitrogen (TVB-N) and thiobarbituric acid-reactive substances (TBARS). The experimental results showed that a strain of Lacticaseibacillus paracasei Lab5 from pickle juice showed notable inhibition of Listeria monocytogenes, with an inhibition zone diameter of 38.28±1.97 mm, the inhibitory substances were present in the CFS, which was treated at 60~121 ℃ for 25 min, and its inhibition zone diameter of inhibition against Listeria monocytogenes and Escherichia coli still reached more than 32.07±2.1 mm and 11.53±0.44 mm. No significant difference in bacteriostatic activity in the pH 3.0~8.0 (P>0.05). Proteinase K treatment had the greatest effect on the inhibitory activity, as it reduced the diameter of the circle of inhibition of Listeria monocytogenes by 7.69 mm; It was shown that Lacticaseibacillus paracasei Lab5 CFS had good thermal、pH stability and was less sensitive to six proteases (chymotrypsin, trypsin, enterokinase, proteinase K, papain, pepsin). In the preservation application of refrigerated Duhei pork, it was found that at 9 d of refrigeration, Lacticaseibacillus paracasei Lab5 postbiotics treatment groups (2MIC and 4MIC groups) had significantly reduced the viable cell counts of the meat by 99.7% compared to the control, decreased the pH by 0.33, and reducing TBARS reactants by 0.66 mg/kg, and 0.91 mg/kg in meat (P