With the increasing demand for health, probiotic lactic acid bacteria are finding increasingly wide application in the fields of food and medicine. Spray drying, as a commonly used method to prepare a lactic acid bacterial powder, has the advantages of high efficiency and sustainability, but it exposes lactic acid bacteria to adverse factors such as high temperature, dehydration, and oxidation. Studies have shown that using stress treatment and exogenous addition of trehalose can improve the spray drying resistance of lactic acid bacteria, but there were currently only a few studies. Stress treatment can trigger the protective mechanism of lactic acid bacteria, enhancing their tolerance. Trehalose, as a natural protective agent, can stabilize the cell membrane structure, preserve protein integrity, and thus improve the resistance of lactic acid bacteria. More importantly, stress treatment can increase intracellular trehalose accumulation in lactic acid bacteria, and can also introduce exogenous trehalose into the cells, thereby improving the spray-drying resistance of lactic acid bacteria. This finding lays a theoretical foundation for the preparation of a highly active lactic acid bacterial powder.

To explore the in vitro mechanism of action of lactic acid bacteria (LAB) in reducing uric acid, this study focused on 16 LAB strains isolated from traditional fermented milk in Hulunbuir, Inner Mongolia, China. Through comprehensive evaluation of purine metabolite (xanthine, hypoxanthine, adenine, and guanine) degradation and time-dependent xanthine oxidase (XO) inhibition by viable/dead bacterial suspensions (intracellular/extracellular components), six strains with superior XO-inhibitory were screened. Suspensions of both live and dead cells, intracellular components, and extracellular secretions from these six strains all exhibited strong inhibitory effects on XO. Among these strains (whether live or dead), the extracellular secretions of Lactiplantibacillus plantarum HN2-3, Lactobacillus helveticus M1-1, Lactobacillus rhamnosus N1-4, and L. plantarum N2-4 exhibited significantly stronger inhibitory effects on XO compared to their intracellular extracts (P < 0.05). Meanwhile, in Streptococcus thermophilus ST0, there was no significant difference in inhibition activity between intracellular and extracellular components of both live and dead cells (P > 0.05). Finally, the extracellular secretions from live L. helveticus M1-2 cells and their intracellular components exhibited comparable levels of XO inhibition (P > 0.05). These results indicated some variability in the inhibition of XO. Furthermore, regardless of the viability of all the six strains, their suspensions, extracellular secretions, and intracellular components exhibited varying degrees of scavenging activity against hydroxyl radical, superoxide anion radical, and 1,1-diphenyl-2-picrylhydrazyl radical. In particular, the XO inhibition activity of live strains showed a positive correlation with the antioxidant activity of these bacteria. These findings provide important scientific evidence for the development of novel functional foods and medicines based on LAB.

More and more evidence shows that lactic acid bacteria play an important role in improving calcium absorption and promoting bone health. However, there is a lack of systematic research on the mechanism by which lactic acid bacteria promote calcium absorption. In this article, the calcium absorption mechanism, the effect of lactic acid bacteria on calcium absorption and its mechanism are reviewed. Lactic acid bacteria promote calcium absorption mainly by 1) increasing intestinal absorption of vitamin D, thereby affecting the transcellular pathway of calcium absorption; 2) secreting phytase to increase the intestinal concentration of free calcium ions; 3) metabolizing prebiotics to produce short-chain fatty acids, thus reducing intestinal pH, increasing the surface area of microvilli, and affecting the signaling pathway of mineral absorption; 4) transforming lactose into lactic acid and short-chain fatty acids to increase the body’s absorption of calcium; 5) producing bioactive substances, increasing the content of soluble calcium in the intestinal tract and improving the bioavailability of calcium; and 6) directly or indirectly regulating bone metabolism and affecting bone homeostasis through the gut-bone axis. Lactic acid bacteria play an important role in promoting calcium absorption and maintaining bone metabolic balance, suggesting the potential of supplementation of lactic acid bacteria as a novel method to promote calcium absorption and prevent osteoporosis. This review lays the theoretical foundation for developing more efficient and targeted calcium supplements based on lactic acid bacteria.

In this study, the effects of heat shock-repair combined with addition of trehalose in lyoprotectant on the freeze-drying resistance and room temperature storage stability of Lactiplantibacillus plantarum LIP-1 were investigated. The results showed that the freeze-drying survival rate of the combined treatment group with heat shock-repair and 4 g/100 mL trehalose addition was 81.65%, which was significantly higher than those of the control group without heat shock-repair treatment (59.92%) and the heat shock-repair treatment group (70.23%) (P < 0.05). The damage degree of cell wall and cell membrane in the combined treatment group was significantly reduced compared with that in the control group. The addition of trehalose maintained a high proportion of unsaturated fatty acids in the cell membrane, reduced cell membrane damage, and significantly enhanced the freeze-drying resistance of the strain while improving its room temperature storage stability. After eight weeks of storage, the survival rate of the combined treatment group was 51.66%, which was significantly higher than those of the control (12.09%) and heat shock-repair (43.79%) groups (P < 0.05), and the intracellular fluorescence intensity was 1969.23 ± 37.22, which was significantly lower than those in the control (3475.21 ± 106.56) and heat shock-repair (2843.95 ± 52.12) groups (P < 0.05). To sum up, the combined treatment could improve the freeze-drying resistance and room temperature storage stability of the strain.

Adenine acts as a growth promoter to promote the growth of the lactic acid bacteria (LAB), but the effect on the viability of freeze-dried strains has rarely been studied. In this study, adding 0.01 g/L of adenine to medium increased the growth and freeze-dried viability of Lactiplantibacillus plantarum LIP-1. Further research has found that L. plantarum LIP-1 synthesized large amounts of adenosine triphosphate (ATP) by metabolizing adenine. Elevated intracellular ATP content caused feedback inhibition on the conversion pathway of pyruvate to lactic acid, while promoting the conversion of pyruvate to acetyl coenzyme A (acetyl-CoA). After a large accumulation of acetyl-CoA in the cells, there was sufficient substrate for the synthesis of cell membrane fatty acids. Elevated intracellular ATP content also activated the acyl-CoA thioesterase activity to catalyse the conversion of saturated fatty acids to unsaturated fatty acids, thereby improving the integrity of the cell membrane and reducing damage to the cell membrane during the freeze-drying process. Additionally, a reduction in the amount of pyruvate converted into lactate prevented the decrease in intracellular pH (pH_in), which alleviated the degree of acid stress on the strain, resulting in less DNA damage and improved DNA stability. It is concluded that L. plantarum LIP-1 reduced the degree of cell membrane and DNA damage by metabolizing adenine and improved the freeze-dried viability of the strain.

Amino acids are often used as probiotic growth factors. Their addition to the growth medium is found to effectively enhance the resistance of the strain to adverse environments. In this research, we found that adding 0.05 g/L L-cysteine to culture medium improved the freeze-drying survival rate of the strain. We investigated the internal mechanism behind this phenomenon and found that the addition of L-cysteine can reduce DNA damage to bacterial cells during the freeze-drying process. In comparison to the control group without L-cysteine, the treatment group with the addition of 0.05 g/L of L-cysteine exhibited an up-regulation of the metC gene, leading to the metabolism of L-cysteine into pyruvate and NH₃, which raised the intracellular pH, reduced DNA damage, and consequently enhanced the resistance of Lactiplantibacillus plantarum LIP-1 to freeze-drying.