In this study, a Lactobacillus strain was isolated from the feces of healthy 3-month-old infants in Guangzhou, identified and named as Bifidobacterium longum B2-01 by molecular biology, and its probiotic properties, such as in vitro antioxidant activity and hepatoprotective activity, and high-density culture were investigated. The results showed that B2-01 had a strong ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl, superoxide anion, and 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radicals and to resist lipid peroxidation. At the highest concentration of 10% (V/V) in the fermentation supernatant of DMEM medium, strain B2-01 increased the survival rates of L02 cells against hydrogen peroxide damage and alcohol damage to 89.10% and 91.38%, respectively, while significantly reducing the transaminase activity in hepatocytes. The optimal conditions for high-density culture were determined as follows: yeast extract concentration 3.45%, glucose concentration 2.48%, lactose concentration 2.79%, bacteriological peptone concentration 3%, and oligogalactose concentration 2.5%. Under these conditions, the maximum viable bacterial count of 4.20 × 10⁹ CFU/mL was observed in the fermentation broth, which was 6.45 times as high as that before optimization (7.71 × 10⁸ CFU/mL).

Studies have shown that probiotic has good antidiabetic and antioxidant activities and great inhibitory effects on human cancer cell lines. This paper took α-glucosidase and α-amylase inhibition rate, superoxide anion radical scavenging rate, ferrous ion chelating rate and reducing activity as indexes, and compared the antidiabetic and antioxidant capacities in vitro between Enterococcus faecalis EF-ZA1107-06 and Lactobacillus rhamnosus GG (LGG). The effects of EF-ZA1107-06 on cellular oxidative stress were investigated by measuring the enzyme activities of glutathione peroxidase (GSH-Px), total superoxide dismutase (T-SOD) and catalase (CAT) in Caco-2 cell lines. The anticancer activity and mechanism were also preliminarily explored using HepG2 and MDA-MB-231 cell lines. The results show that the supernatant of EF-ZA1107-06 has the highest scavenging rate of superoxide anion free radical from 40.78% to 59.61% and strongest ferrous ion chelating ability from 39.28% to 56.59%, while the lysate of EF-ZA1107-06 has the highest reducing activity, equivalent to 1.072 mmol/L equivalent cysteine, which is remarkably higher than that of LGG lysate (P < 0.05). The inhibition of α-amylase and α-glucosidase activity confirms the antidiabetic activity of EF-ZA1107-06. Meanwhile, EF-ZA1107-06 can reduce oxidative damage caused by H₂O₂ to Caco-2 cells to a certain extent and inhibit the S phase and G2 phase of HepG2 cells, but only the S phase of MDA-MB-231 cells. The induction of the early apoptosis of HepG2 cells and MDA-MB-231 cells confirms the anticancer activity of EF-ZA1107-06.

Enterococcus was isolated from 1-month-old baby feces in Guangzhou and the strain was identified as Enterococcus faecalis by molecular biology and was named Enterococcus faecalis EF-ZA1107-06. The strain was evaluated for its safety and some probiotic potential properties. The results show that the strains does not produce nitroreductase and has no hemolytic activity. It is highly sensitive to many kinds of antibiotics, does not contain plasmids, and has no acute toxicity to the mice. EF-ZA1107-06 was proved as an edible safe strain. High tolerance was observed by EF-ZA1107-06 strain for simulated gastrointestinal condition. After continuous exposure to simulated saliva for 10 min, simulated gastric juice for 2 h, and simulated intestinal juice for 3 h, the survivability was still above 65%, which was comparable to that of Lactobacillus rhamnosus GG (LGG). EF-ZA1107-06 can inhibit the growth of Escherichia coli, Salmonella, Pseudomonas aeruginosa, Candida albicans, Listeria monocytogenes, Staphylococcus aureus. The inhibitory effect of its supernatant on Escherichia coli is significantly stronger than that of LGG. The supernatant, lysate and suspension of the EF-ZA1107-06 strain all have certain DPPH free radical scavenging capacity and hydroxyl radical scavenging ability. DPPH free radical scavenging rate of 2×10⁸ CFU/mL EF-ZA1107-06 suspension is (93.16±0.17)%. The hydroxyl radical scavenging rate of the suspension is (90.48±1.12)%. The cholesterol removal rate of 2×10⁸ CFU/mL EF-ZA1107-06 fermentation broth is (44.29±0.30)%. The EF-ZA1107-06 strain has high cholesterol scavenging ability.

In order to increase the number of organisms per unit volume of fermentation broth and provide a basis for the development and application of Lactobacillus rhamnosus ZB1107-01 (LR-ZB1107-01) obtained in the early stage of the study, which is well tolerated by simulated gastrointestinal tract, this paper initially performs medium optimization and probiotic properties investigation of the strain. First, the growth curve of strain LR-ZB1107-01 in MRS medium was measured to clarify its growth pattern in liquid medium. Next, the number of viable bacteria in the fermentation broth of strain LR-ZB1107-01 was used as the detection index, and different kinds of nitrogen sources, carbon sources and growth factors were examined unilaterally to determine the optimal medium components, and response surface tests were conducted to optimize the medium ratios and select the best medium. Finally, the in vitro safety of the nitro reductase activity and amino decarboxylase activity was evaluated. The results show that the viable bacteria count concentration can reach 8.56×10⁸ CFU/mL, if three nutrients and contents that significantly affected the viable bacteria count are changed as follows: the addition of D-isoascorbic acid at 0.02%, magnesium sulfate at 0.12% and peptone at 3%, based on the glucose content of MRS medium at 2% and combined with the optimized culture conditions. The viable bacteria count is about 10.7 times higher than that in MRS medium. The in vitro safety evaluation results indicate that LR-ZB1107-01 is negative for both nitroreductase and amino acid decarboxylase, suggesting that the strain has a certain safety profile. This achievement has a certain guiding effect on the industrial production of probiotic strains and the subsequent development of products.