Lacticaseibacillus rhamnosus is a generalist that can adapt to different ecological niches, serving as a valuable source of probiotics. The genome of L. rhamnosus X253 contains one chromosome and no plasmids, with a size of 2.99 Mb. Both single-copy orthologous gene-based phylogenetic analysis and average nucleotide identity indicated that dairy-derived L. rhamnosus X253 was most closely related to the human-intestine-derived strain L. rhamnosus LOCK908, rather than other dairy strains. The adaptation of L. rhamnosus X253 and the human-intestine-derived strain L. rhamnosus GG to different ecological niches was explained by structural variation analysis and COG annotation. Hemolytic assays, API ZYM assays, and antimicrobial susceptibility tests were performed to validate risk-related sequences such as virulence factors, toxin-encoding genes, and antibiotic-resistance genes in the genomes of L. rhamnosus X253 and GG. The results showed that L. rhamnosus GG was able to use L-fucose, had a higher tolerance to bile salt, and adhered better to CaCo-2 cells. In contrast, L. rhamnosus X253 was capable of utilizing D-lactose, withstood larger quantities of hydrogen peroxide, and possessed excellent antioxidant properties. This study confirmed the safety and probiotic properties of L. rhamnosus X253 via complete genome and phenotype analysis, suggesting its potential as a probiotic.

Gray sufu, a traditional fermented food derived from soybeans, undergoes a complex fermentation process. This study aimed to investigate the dynamics of the microbial community during sufu fermentation and its relationship with key quality characteristics. Through systematic sampling of sufu at different phases of fermentation, 143 bacterial genera and 84 fungal genera involved in the process were identified. Among these, Chishuiella, Enterococcus, Lactococcus, and Weissella emerged as the predominant bacterial communities. After seven days of ripening fermentation, Trichosporon supplanted Diutina as the predominant fungus, accounting for more than 84% of all fungi. Using redundancy analysis, significant correlations between microbiota and physicochemical properties were uncovered. Chishuiella and Empedobacter displayed positive relationships with pH, soluble protein, and amino nitrogen content. In addition, five biogenic amines were detected, and it was determined that tyramine accounted for more than 75% of the total biogenic amines in the final gray sufu products. Spearman correlation analysis revealed significant positive relationships between Lactococcus, Enterococcus, Tetragenococcus, Halanaerobium, and Trichosporon and the five biogenic amines examined. These findings shed light on the complex interactions between microorganisms and biogenic amines during the fermentation of gray sufu, thereby facilitating the development of microbial regulation strategies for better quality control.

Bacillus cereus is a food-borne pathogen that can produce cereulide in the growth period, which causes food poisoning symptoms. Due to its resistance to heat, extreme pH, and proteolytic enzymes, cereulide poses a serious threat to food safety. Temperature, pH, and a_w can influence cereulide production, but there is still a lack of research with multi-environmental impacts. In this study, the effects of temperature (15~45 °C), pH (5~8), and a_w (0.945~0.996) on the emetic reference strain B. cereus F4810/72 growth, cereulide production, relevant ces genes (cesA, cesB, cesP), and transcription regulators genes (codY and abrB) expression at transcription level were studied. B. cereus survived for 4~53 h or grew to 6.85~8.15 log₁₀ CFU/mL in environmental combinations. Cereulide accumulation was higher in mid-temperature, acidic, or high a_w environments. Increased temperature resulted in a lower cereulide concentration at pH 8 or aw of 0.970. The lowest cereulide concentration was found at pH 6.5 with an increased a_w from 0.970 to 0.996. Water activity had a strong effect on transcriptional regulator genes as well as the cesB gene, and temperature was the main effect factor of cesP gene expression. Moreover, environmental factors also impact cereulide synthesis at transcriptional levels thereby altering the cereulide concentrations. The interaction of environmental factors may result in the survival of B. cereus without growth for a period. Gene expression is affected by environmental factors, and temperature and pH may be the main factors influencing the correlation between B. cereus growth and cereulide formation. This study contributed to an initial understanding of the intrinsic link between the impact of environmental factors and cereulide formation and provided valuable information for clarifying the mechanism of cereulide synthesis in combined environmental conditions.

Probiotics are universally recognized for their health benefits, despite the fact that their effects depend on the strain. Identification and enumeration of probiotic strains are required prior to evaluating their effectiveness. Lacticaseibacillus rhamnosus X253 is a potential probiotic strain with antioxidant capacity. Comparative genomics and single nucleotide polymorphisms (SNPs) were used to identify a strain-specific locus within the holA gene for strain X253 that was distinct in 30 different L. rhamnosus strains. Using quantitative PCR, the primers and probe designed for the locus were able to distinguish L. rhamnosus X253 from the other 20 probiotic strains. The chosen locus remained stable over 19 generations. The sensitivity of the assay was 0.2 pg genomic DNA of L. rhamnosus X253, or 10³ cfu/mL bacteria of this strain. In terms of repeatability and reproducibility, relative standard deviations (RSD) were less than 1% and 3%, respectively. Additionally, this assay achieved accurate enumerations of L. rhamnosus X253 in spiked milk and complex powder samples. The strain-specific assay could be used for quality control and compliance assessment of dairy products.

Milk lipids are fundamental to the nutritional quality, functional properties, and processing behavior of dairy products. In this study, we employed an untargeted lipidomics approach based on ultra-high-performance liquid chromatography coupled with ultra-high-performance liquid chromatography–high-resolution mass spectrometry (UHPLC-HRMS) to systematically characterize the lipid profiles of ten milk types from eight animal species, including camel, mare, donkey, goat, buffalo, yak, Jersey, and Holstein. A total of 640 lipid species were identified, spanning triglycerides (TGs), phospholipids (PLs), sphingolipids (SPs), ceramides (Cer), wax esters (WEs), and other subclasses. A statistical analysis revealed significant differences in lipid types and abundances among the milk samples. Camel milk exhibited the highest lipid diversity, with notable enrichment in phospholipids and sphingolipids, conferring superior emulsifying properties and stability. Mare milk was rich in polyunsaturated fatty acids (PUFAs), such as linoleic acid and alpha-linolenic acid, making it ideal for developing health-focused dairy products. Despite having the lowest total lipid content, donkey milk was enriched in cholesterol esters and PUFA, suitable for low-fat functional dairy products. Goat milk featured a balanced lipid composition with higher levels of medium-chain fatty acids (MCFAs), promoting digestibility. Buffalo milk was characterized by high TG and wax ester (WE) levels, offering high energy density and suitability for rich dairy products. Yak milk contained higher levels of ceramides (Cer) and saturated fatty acids, reflecting adaptations to high-altitude environments. Jersey milk and Holstein milk displayed similar lipid profiles, with stable compositions suitable for versatile dairy product development. Principal component analysis (PCA), hierarchical clustering, and volcano plot analyses further confirmed species-specific lipidomic signatures and revealed several potential lipid biomarkers, such as LPC (O-16:0) in Hongyuan yak milk, suggesting applications in geographical indication (GI) traceability. This study offers a comprehensive lipidomic landscape across diverse milk sources, providing molecular insights to guide the development of tailored, functional, and regionally branded dairy products.