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Staphylococcus aureus is a common pathogen found in cheese whose Staphylococcal enterotoxins (SE) are the main pathogenic factors that cause food poisoning. The objective of this study was to construct two models to evaluate the safety of Kazak cheese products in terms of composition, changes in S. aureus inoculation amount, Aw, fermentation temperature during processing, and growth of S. aureus in the fermentation stage. A total of 66 experiments comprised of five levels of inoculation amount (2.7–4 log CFU/g), five levels of Aw (0.878–0.961), and six levels of fermentation temperature (32–44 °C) were performed to confirm the growth of S. aureus and the presence of SE limit conditions. Two artificial neural networks (ANN) successfully described the relationship between the assayed conditions and the growth kinetic parameters (maximum growth rates and lag times) of the strain. The good fitting accuracy (R2 values were 0.918 and 0.976, respectively) showed that the ANN was appropriate. Experimental results showed fermentation temperature had the greatest influence on the maximum growth rate and lag time, followed by the Aw and inoculation amount. Furthermore, a probability model was built to predict the production of SE by logistic regression and neural network under the assayed conditions, which proved to be concordant in 80.8–83.8% of the cases with the observed probabilities. The maximum total number of colonies predicted by the growth model in all combinations detected with SE exceeded 5 log CFU/g. Within the range of variables, the minimum Aw for predicting SE production was 0.938, and the minimum inoculation amount for predicting SE production was 3.22 log CFU/g. Additionally, as competition between S. aureus and lactic acid bacteria (LAB) occurs in the fermentation stage, higher fermentation temperatures are conducive to the growth of LAB, which can reduce the risk of S. aureus producing SE. This study can help manufacturers to make decisions on the most appropriate production parameters for Kazak cheese products and to prevent S. aureus growth and SE production. • The growth of S. aureus during fermentation processing was developed. • Probability model of SE production were developed during cheese maturation. • Temperature, Aw, and inoculum size are key factors for controlling SE-production. • SE production boundaries were described by logistic regression and neural network. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of NSLAB on Kazakh cheese ripening was studied. • Cheeses made using P. acidilactici , S. epidermidis , and L. rhamnosus were prepared. • NSLAB cheeses had different protein contents, free fatty acid contents, and pH. • NSLAB cheeses had different flavor compounds and odor profiles (volatile components). • NSLAB can be used as an adjunct starter to make Kazakh cheese. Xinjiang is a multiethnic region of China. Traditionally, most ethnic minorities are known to produce and consume cheese. Nomadic people have been reported to use lactic acid bacteria (LAB) for decades to produce fermented dairy products as part of a balanced diet. Non-starter LAB (NSLAB) contribute to different degrees of ripening, depending on the cheese variety. In the present study, we screened three types of NSLAB with good proteolysis and autolytic abilities from traditional Kazakh cheese: Pediococcus acidilactici R3-5, Staphylococcus epidermidis R4-2, and Lactobacillus rhamnosus R9-6. A control (no NSLAB) was also included, resulting in four distinct types of cheese samples. We used gas chromatography-mass spectrometry and the electronic nose system to identify volatile compounds and analyze the effect of NSLAB on cheese flavor at the ripening stage. The physicochemical indicators changed significantly during the ripening of Kazakh cheese. Compared with the control, the protein content, free fatty acid content, pH, flavor compounds, and odor profiles of the test cheeses were significantly different. The major chemical differences among cheeses were the synthesis of some key volatile components (ethyl caprylate, ethyl caprate, myristyl carbonate, capric acid, caprylic acid, nonanal, and benzyl alcohol). NSLAB can be used as an adjunct starter to make Kazakh cheese and the use of NSLAB affected the cheese flavor quality positively. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus (S. aureus) is a common pathogen found in dairy products whose enterotoxins are the main pathogenic factors that cause food poisoning. In this study, a total of 399 samples of retail Kazak cheese collected from 4 regions in Xinjiang (China) were qualitatively and quantitatively analyzed for the presence of bacteria. Among them, 56 (14%, 95% CI: 10.6–17.4%) samples were found to be positive for S. aureus , and their distribution and degree of contamination vary from region to region, with 19.4% (31/160) in Altay, 10.7% (23/215) in Yining and 22.2% (2/9) in Tacheng, and corresponding geometric mean level of 5.8, 4 and 3 most probable number/gram, respectively. In addition, 62 strains of S. aureus were isolated from the positive samples. The most frequently detected gene in the 3 regions was staphylococcal enterotoxin gene c (sec) (29%), followed by sea (25.6%), see (9.8%), sed (8%), seb (3.2%). Finally, the analysis of 13 resistance genes and the minimum inhibitory concentration (MIC) of 12 antibiotics in 62 strains of S. aureus identified 13 methicillin-resistant S. aureus strains (21%). The S. aureus isolates showed most resistance to penicillin (69.3%), followed by erythromycin (27.4%) and clindamycin (24.2%). There were 17 (27.4%) strains of S. aureus with multiple drug resistance, and one strain was even resistant to 10 antibiotics. A high frequency of bla Z (45.2%) and mec A (16.1%) resistance genes was found among the S. aureus isolates. Among the penicillin-resistant strains, 60.5% (26/43) had the bl aZ gene. The findings of this study suggest that S. aureus has spread across different regions of Xinjiang. The presence of S. aureus strains in Kazak cheese during the selling period poses a potential threat to public health and underscores the need for the continuous monitoring of these cheeses. • The comprehensive study on Staphylococcus aureus isolated from retail artisanal Kazak cheese in Xinjiang, China. • High prevalence of S. aureus in Kazak cheese. • S. aureus strains exhibited multiple drugs and carried various enterotoxin and antimicrobial resistance genes. • S. aureus strains are opportunistic pathogens, which are potential safety hazards for consumers. • S. aureus may spread among different regions in Xinjiang. [ABSTRACT FROM AUTHOR]