Effects of freezing period and meat juice model type on the survival, hydrophobicity, and acid resistance of Listeria monocytogenes and Salmonella Typhimurium.

BACKGROUND

The survival of food-borne pathogenic bacteria in food processing environments and increasing their resistance to antimicrobials is one of the most crucial challenges in food safety. The present study aimed to investigate the effects of freezing period (0-60 days) and meat juice model (beef, mutton, and goat juices) on the survival, hydrophobicity, and acid resistance of Listeria monocytogenes and Salmonella Typhimurium.

METHODS

The survival of L. monocytogenes and S. Typhimurium in different meat juice models during the freezing period (0, 1, 2, 3, 4, 7, 14, 21, 30, and 60 days) was determined by colony counting method. The cell surface hydrophobicity of the bacteria was measured by bacterial adhesion to hydrocarbon assay. Changes in the bacterial resistance to acetic acid and lactic acid were evaluated by determining minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC).

RESULTS

The survival of both bacteria was significantly higher in mutton juice than in other juices (p < 0.05). The survival rate of L. monocytogenes in freezing conditions was higher than that of S. Typhimurium. The amount of hydrophobicity was increased during the freezing period, and the highest increase was observed in the mutton juice. The increase in hydrophobicity of S. Typhimurium was higher than L. monocytogenes. The acid resistance of both bacteria, especially L. monocytogenes, was increased with increasing freezing time.

CONCLUSION

Freezing stress and meat juice model type could change the survival, hydrophobicity, and acid resistance of L. monocytogenes and S. Typhimurium. The mutton juice model showed the highest protective effect on both bacteria during the freezing period. Meanwhile, the bacteria inoculated in the mutton juice model exhibited significantly higher hydrophobicity than those in other meat juices. The acid resistance of L. monocytogenes was significantly increased, especially in the mutton juice model, at the end of the freezing period.