Inactivation is a crucial step in the production of postbiotics, with thermal inactivation being the prevailing method employed. Nevertheless, the impact of thermal treatment on bioactivity and chemical composition remains unexplored. The objective of this study was to assess the influence of heating temperature on the antioxidant, anti-inflammatory properties and the chemical composition of ET-22 and BL-99 postbiotics. The findings revealed that subjecting ET-22 and BL-99 to thermal treatment ranging from 70 °C to 121 °C for a duration of 10 min effectively deactivated them, leading to the disruption of cellular structure and release of intracellular contents. The antioxidant and anti-inflammatory activity of ET-22 and BL-99 postbiotics remained unaffected by mild heating temperatures (below 100 °C). However, excessive heating at 121 °C diminished the antioxidant activity of the postbiotic. To further investigate the impact of thermal treatments on chemical composition, non-targeted metabolomics was conducted to analyze the cell-free supernatants derived from ET-22 and BL-99. The results revealed that compared to mild inactivation at temperatures below 100 °C, the excessive temperature of 121 °C significantly altered the chemical profile of the postbiotic. Several bioactive components with antioxidant and anti-inflammatory properties, including zomepirac, flumethasone, 6-hydroxyhexanoic acid, and phenyllactic acid, exhibited a significant reduction in their levels following exposure to a temperature of 121 °C. This decline in their abundance may be associated with a corresponding decrease in their antioxidant and anti-inflammatory activities. The cumulative evidence gathered strongly indicates that heating temperatures exert a discernible influence on the properties of postbiotics, whereby excessive heating leads to the degradation of heat-sensitive active constituents and subsequent diminishment of their biological efficacy.

Globally, dental caries is one of the most common non-communicable diseases for patients of all ages; Streptococcus mutans (S. mutans) is its principal pathogen. Lactobacillus paracasei (L. paracasei) shows excellent anti-pathogens and immune-regulation functions in the host. The aim of this study is to evaluate the effects of L. paracasei ET-22 on the formation of S. mutans biofilms. The living bacteria, heat-killed bacteria, and secretions of L. paracasei ET-22 were prepared using the same number of bacteria. In vitro, they were added into artificial-saliva medium, and used to coculture with the S. mutans. Results showed that the living bacteria and secretions of L. paracasei ET-22 inhibited biofilm-growth, the synthesis of water-soluble polysaccharide and water-insoluble polysaccharide, and virulence-gene-expression levels related to the formation of S. mutans biofilms. Surprisingly, the heat-killed L. paracasei ET-22, which is a postbiotic, also showed a similar regulation function. Non-targeted metabonomics technology was used to identify multiple potential active-substances in the postbiotics of L. paracasei ET-22 that inhibit the formation of S. mutans biofilms, including phenyllactic acid, zidovudine monophosphate, and citrulline. In conclusion, live bacteria and its postbiotics of L. paracasei ET-22 all have inhibitory effects on the formation of S. mutans biofilm. The postbiotics of L. paracasei ET-22 may be a promising biological anticariogenic-agent.

Dental caries is a common and multifactorial biofilm disease that is associated with dietary habits and microbiota. Among the various pathogens inducing caries, S. mutans is the most extensively studied. Promoting oral health with probiotics has gained considerable attention. Lactobacillus paracasei (L. paracasei) strains were reported to modulate the gut microbiota and enhance host resistance to disease. Our previous research has found that L. paracasei ET-22 (ET-22) could inhibit S. mutans biofilms in vitro. However, the preventive effect in vivo and functional mechanism of ET-22 on dental caries were unclear. In this study, the preventive effects of ET-22 on dental caries in mice were checked. Meanwhile, the functional mechanism of ET-22 was further investigated. Results showed that the supplementation of ET-22 in drinking water significantly improved the caries scoring of mice. The microbiota of dental plaques revealed that the live and heat-killed ET-22 similarly regulated the microbial structure in plaque biofilms. Functional prediction of PICRUSt showed that the addition of live and heat-killed ET-22 may inhibit biofilm formation. By the in vitro trials, the live and heat-killed ET-22 indeed inhibited the construction of S. mutans biofilms and EPS productions of biofilms. This evidence suggests that ET-22 can restrain dental caries by regulating the microbiota of dental plaques and inhibiting biofilm formation, which may be partly mediated by the body components of ET-22.

Lactobacillus-enriched yogurt is in increasingly high demand due to its health benefits, but the product stability requires an understanding of the microbial dynamics during fermentation and storage. This study investigated the interactions between probiotic pairs (L. paracasei L9 and L. acidophilus LAC) and starter culture (HYY) through fermentation kinetics, microbial viability, organic acid profiles, and metabolomics. The results demonstrated that L. paracasei L9 significantly increased the titratable acidity from 25.20 ± 7.01 °T to 36.56 ± 3.47 °T at 3 h and reduced the fermentation time by 0.5 h, whereas L. acidophilus LAC showed minimal effects. L. paracasei L9 achieved higher viability (8.4 lg CFU/g) via the high-affinity lactose transport and Leloir pathway, whereas the L. acidophilus LAC growth remained limited (6.9 lg CFU/g). The metabolomic investigation revealed the L9 + HYY upregulated glycerophospholipid metabolism and pantothenate/CoA biosynthesis to support rapid biomass accumulation. In contrast, LAC + HYY modulated the arginine and branched-chain amino acid metabolism for acid tolerance. During 21 days of storage, there were no significant differences in final TA values and lactic acid content among the probiotic supplementation groups. L9 + HYY remained stable (>9.0 lg CFU/g) by upregulating the aromatic amino acid biosynthesis and suppressing the purine/sulfur metabolism, whereas L. acidophilus LAC decreased to 6.02 lg CFU/g. These findings demonstrate the dual role of L. paracasei L9 in accelerating the fermentation and maintaining the microbial stability through metabolic reprogramming, which guides the development of improved probiotic yogurts.

In the pathogenesis of dental caries, Streptococcus mutans (S. mutans) plays a central role. S. mutans can produce extracellular polysaccharides, which can help the bacteria form biofilms on the tooth surface, create a stable living environment, and hinder the removal of bacteria by natural defense substances in the oral cavity such as saliva. Meanwhile, the oral microbiota and dietary habits exert long-term influences on its development. This study, employing the BALB/c mouse model, explored the effects of L. paracasei L9 on dental caries. In the experiment, mice underwent the S. mutans inoculation and were subsequently treated with L. paracasei L9 or S. salivarius K12 for 28 consecutive days. The results showed that L. paracasei L9 significantly ameliorated early enamel caries, and both L. paracasei L9 and S. salivarius K12 cooperatively downregulated the expressions of critical cariogenic factors, effectively suppressing the initial adhesion of S. mutans and the formation of dental plaques. L. paracasei L9 reshaped the oral microbiota of caries-affected mice, selectively reducing pathogens abundances and augmenting abundances of probiotics such as Lactobacillaceae and Streptococcus salivarius. This study offers a strategic approach for the management of dental caries, highlighting the potential of these probiotics in the field of oral health.

The addition of Bifidobacterium animalis subsp. lactis and prebiotics to fermented milk can enhance its flavor and sensory properties; however, research on the effects of their combined supplementation on flavor profiles remains limited. This study investigated the impact of simultaneously adding B. lactis IU100 and resistant starch type III (RS3) to fermented milk on flavor and texture. The results showed that co-supplementation shortened the fermentation time by 1 h. It also increased hardness by 28.8%, springiness by 1.14 mm, and water holding capacity by 12.45%, accompanied by the formation of a more continuous and dense gel network. Headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC-MS) combined with odor activity value analysis indicated the enrichment of 115 key aromatic compounds, among which ethyl caprylate, ethyl n-butyrate, 1-octanol, and 2,3-heptanedione were identified as representative flavor compounds associated with fruity and creamy notes. KEGG pathway analysis revealed that 24 differential metabolites were predominantly enriched in purine metabolism and amino acid-related pathways. Within these pathways, coordinated enzymatic reactions convert α-keto acids and fatty acid metabolites into key flavor esters and catalyze the formation of volatile alcohols from amino acids and aromatic fatty acid precursors. Overall, this combined strategy effectively optimized fermentation efficiency, texture, and flavor through the targeted reprogramming of microbial metabolic flux.