Various approaches have been used to study the relationship between prebiotics and probiotics. The utilization of different carbohydrates by probiotics depends on the biochemical properties of the enzymes and substrates required by the microbial strain. However, few studies have systematically analyzed the ability of probiotics to utilize different prebiotics. Here, we investigated the effects of prebiotics from different manufacturers on the proliferation of 13 strains of the Lactobacillus group and the genus Bifidobacterium co-cultured in vitro. Inulin, fructose-oligosaccharide (FOS), and galactose-oligosaccharide (GOS) had broad growth-promoting effects. FOS significantly promoted the proliferation of B. longum. When strains from Lactobacillus group and Bifidobacterium were co-cultured, FOS caused each strain to proliferate cooperatively. GOS was effectively used by L. rhamnosus and L. reuteri for energy and growth promotion. L. casei and L. paracasei fully metabolized inulin; these strains performed better than other strains from Lactobacillus group and Bifidobacterium. Media containing a mixture of oligosaccharides had stronger effects on the growth of B. animalis subsp. lactis, L. acidophilus, and L. rhamnosus than media containing single oligosaccharides. Thus, different oligosaccharides had different effects on the growth of probiotics, providing a scientific basis for the use of synbiotics in health and related fields.

Direct vat-set starter cultures are the key ingredient for the production of fermented dairy products. The characteristics of the strains used for fermentation determine the fermentation time, texture and flavor of the fermented milk products. In this study, a large-scale analysis of the acid production rate, texture, carbon source utilization characteristics of Streptococcus thermophilus strains was conducted. All 100 S. thermophilus strains were divided into six groups according to the acid production rate and into two groups according to the consistency texture. A universal medium, basing on the carbon sources metabolic properties were optimized (0.5% lactose and 3.5% glucose), to culture all of the tested strains. Among them 40 strains were used to test pH-controlled conditions using this universal culture medium. After 5–7 h of fermentation, the optical density (OD) values of all fermented products exceeded 10, suggesting the potential for high-density cultivation of S. thermophilus. Although the OD could be further increased by adding more glucose, this may have hindered subsequent lyophilization because of high residual lactic acid in the fermented product. Next, the application of Streptococcus thermophilus strains in fermented milk was studied. Monocultures and co-cultures of strains were evaluated and compared. The results revealed the existence of symbiotic or competitive relationships between different S. thermophilus strains. Based on the findings, the mixing ratio of three symbiotic S. thermophilus strains was optimized. A co-culture of these three strains yielded fermented milk with high viscosity, low post-acidification, good sensory properties and processability.

Introduction: Type 2 diabetes mellitus (T2DM) is a metabolic disease that has led to a significant global public health burden.Methods: In this work, we investigated the effects of Lacticaseibacillus rhamnosus Hao9 on T2DM in mice with high-fat diet- and streptozotocin (STZ)-induced diabetes (diabetic mice) and explored the underlying mechanisms.Results: We found that 10⁹ colony forming units (CFUs) of Hao9 per day significantly reduced fasting blood glucose and insulin levels (p < 0.001) in diabetic mice. Moreover, Hao9 enhanced liver antioxidant capacity and significantly decreased glucose-6-phosphatase and phosphoenolpyruvate carboxykinase expression in the livers of diabetic mice (p < 0.001). Hao9 also reduced the serum concentrations of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNFα), interleukin-1β (IL1β), and IL6 (p < 0.05) and improved intestinal barrier function in diabetic mice. The composition of the gut microbiome was modulated by Hao9, with an increased abundance of Roseburia, Eubacterium, and Lacticaseibacillus, and decreased abundance of Escherichia/Shigella. Notably, Lacticaseibacillus was detected at both weeks 5 and 12 post-treatment, suggesting sustained colonization of the gut by Hao9.Discussion: The supplementation of Hao9 improved gut microbiota, glucose metabolism, and insulin levels significantly in T2DM mice. That means Hao9 contributes to improving T2DM symptoms with its potential beneficial effects. Therefore, Hao9 is a promising dietary supplement for the treatment of T2DM.

Aim: A comprehensive safety assessment of potential probiotic strains was essential for their application in the food industry. This article systematically evaluated the probiotic characteristics, whole-genome sequence analysis and safety of Lacticaseibacillus paracasei LC86 and Lacticaseibacillus casei LC89.Methods: Firstly, the two strains of lactic acid bacteria selected were identified. Secondly, whole-genome sequencing was performed on LC86 and LC89, and their antibiotic resistance, pathogenicity, and virulence genes were analyzed. We tested various properties of the two strains, included tolerance, cell adhesion, hemolytic activity, catalase activity, gelatin hydrolysis, arginine hydrolysis ability, bile salt hydrolysis capacity, mucin degradation, bioamine, D-/L-lactic acid production and antibiotic susceptibility, to confirm the safety of LC86 and LC89 both in vitro and in vivo. Additionally, we studied the acute toxicity of LC86 and LC89 in mice through a 14-day oral gavage experiment.Results: The two strains selected were identified as Lacticaseibacillus paracasei and Lacticaseibacillus casei. The genomes of both LC86 and LC89 were devoid of virulence, antibiotic resistance and pathogenicity genes. LC86 and LC89 exhibited good tolerance to temperature, artificial gastric fluid and artificial intestinal fluid; they were non-hemolytic, their catalase activity, gelatin hydrolysis, arginine hydrolysis and bile salt hydrolysis were all negative. They exhibited the capability to break down proteins and demonstrated sensitivity to a range of antibiotics. The oral LD₅₀ for both LC86 and LC89 in mice was >2 × 10¹⁰ CFU/kg.Conclusion: The experimental results above demonstrated the probiotic characteristics and safety of LC86 and LC89, indicating their potential as candidates for probiotics for human and animal applications.