In this study, we aimed to investigate the acid tolerance response (ATR) and the formation pattern of crossprotection in acid-adapted and non-adapted strains during the production of fermented sausage. Listeria innocua was selected as a surrogate for L. monocytogenes. It was induced in an acidic environment (pH 5.4) for 18 hours, yielding an acid-adapted strain. The survival counts of acid-adapted and non-adapted L. innocua during sausage fermentation and the changes in acid, heat and osmotic resistance were determined. The results indicated that the counts of the acid-adapted and non-adapted strains decreased by 1.33 (lg(CFU/g)) and 1.06 (lg(CFU/g)), respectively, at the end of sausage production, the decrease in the former being significantly smaller than that in the latter (P < 0.05). Moreover, the D values of the acid-adapted strain under acidic, thermal and hypertonic conditions during the fermentation process were significantly higher than those of the non-adapted strain (P < 0.05). This suggests that the acid stress in raw meat could significantly enhance the survival of L. innocua during the production of fermented sausage and significantly improve its acid, heat and osmotic resistance. The acid, heat and osmotic resistance of the non-adapted strain significantly increased during the production of fermented sausage (P < 0.05), indicating that ATR occurred in L. innocua during the sausage production process, triggering cross-protection against heat and osmosis. Although both acid-adapted and non-adapted L. innocua were significantly inhibited during sausage production, there were still a large number of residues at the end of the production process (the number of colonies declined < 5 (lg(CFU/g)) during the production process), and the acid, heat and osmotic resistance significantly increased during the production process. These results suggest that the potential risk of ATR in pathogenic bacteria should be fully considered in the improvement of the fermentation process.

A total of seven lactic acid bacteria strains with bioprotective potential were isolated and characterized from vacuum-packaged chilled beef. By morphological observation, physiological and biochemical identification and 16S rDNA sequencing, they were determined as Lactobacillus sakei. All isolates grew well at 25‒35 ℃, and RS-16 and RS-25 grew better and had a stronger acid-producing ability. Antibiotic resistance and virulence genes were detected in RS-33 and RS-41 but not any of the other strains. The results of agar diffusion test showed that the seven isolates had antagonistic effect on all indicator strains, and the antagonistic effect of strains RS-16 and RS-25 on Salmonella typhimurium was better than that of the other strains (P < 0.05). Organic acids secreted by the isolated strains were found to have antibacterial activity.

With the increasing consumer demand for chilled meat, food safety issues related to chilled meat such as the prevalence and change of pathogenic bacteria during the processing, storage and consumption of chilled meat and their effects on public health have aroused great public concern. Quantitative microbial risk assessment (QMRA) is the core of chill meat safety risk analysis, which provides a theoretical basis for hazard analysis, determination of the critical control points and formulation of food safety goals and regulations. Since the promulgation of the Food Safety Law and the establishment of the Food Safety Risk Assessment Center in China, significant progress has been made in quantitative microbial risk assessment. In this paper, recent research on the quantitative risk assessment of common food-borne pathogens in livestock and poultry meat products is summarized, and recent progress in the application of process risk model, modular process risk model and omics technology in QMRA is reviewed. The current status of the application of quantitative microbial risk assessment in food safety management is summarized to provide reference for the development and application of quantitative microbial risk assessment in chilled meat.

Some serotypes of Escherichia coli (E. coli) such as E. coli O157:H7 can cause serious diseases in humans. Pathogenic E. coli is widespread in primary agricultural products and encounter various environmental stresses during food processing. After a period of adaptation to a weakly acidic environment, it develops an inducible acid tolerance response, which enhances its ability to survive in a strongly acidic environment and may also enhance its resistance to heat, cold, osmotic pressure and antibiotics, posing a great threat to food safety. This article provides an overview of recent progress in research on the inducible acid tolerance response, two-component regulatory system, pH homeostatic system, cell membrane fluidity regulation, macromolecular protection and cross-protection of E. coli, which may provide theoretical guidance for deep understanding of the stress response of E. coli during food processing and for the development of measures for its prevention and control in the future.

To inhibit the development of adaptive acid tolerance response (ATR) and concurrent multiple stress resistance in Salmonella induced by the residual acid environment from carcass decontamination by organic acid spraying, the inhibitory effect of the addition of oregano essential oil and calcium chloride at different subinhibitory concentrations during acid adaptation on the ATR of Salmonella was investigated by determining the survival ability of Salmonella in acidic, thermal, hyperosmotic and oxidative environments before and after adaptation, and the possible mechanism was explored by determining the relative expression of stress resistance genes before and after treatments. The results indicated that the residual acid (pH 5.4) generated during carcass processing might induce ATR and heat-resistant cross-protection in Salmonella, suggesting a potential food safety risk. After 2 h treatment with hydrochloric acid at pH 3, the loss of the adapted strain in the 1/2 MIC oregano essential oil and 10 mmol/L CaCl₂ treatment group increased by 1.32 (lg(CFU/mL)) compared with the control group, and oregano essential oil combined with CaCl₂ had a synergistic inhibitory effect on ATR. The addition of oregano essential oil and calcium chloride during acid adaptation down-regulated the expression of the phoP and rpoS genes, which in turn intervened in the two-component system and global transcription factors, thereby suppressing ATR development. Sub-inhibitory concentrations of oregano essential oil inhibited the formation of the acid and heat resistance of acid-adapted Salmonella, but increased the resistance to hyperosmosis, whereas CaCl₂ at a concentration of 10 mmol/L combined with sub-inhibitory concentrations of oregano essential oil reduced the osmotic resistance. The results of the current study help to understand the effects of essential oil and CaCl₂ on the acid adaptation process of Salmonella and provide a theoretical basis for risk control for the use of organic acids in the beef industry.