In vitro characteristics of lactic acid bacteria probiotics performance and antioxidant effect of fermented soymilk

Lactic acid bacteria (LAB) are generally used for soymilk fermentation to improve its nutritional and health-related qualities. Twenty-five LAB strains isolated from soybeans and fermented dairy products (FDP) were screened for probiotic candidates. To obtain bacteria with probiotic properties and effective antioxidant activities for soymilk fermentation, their performance at pH (2.5–3.0) and bile salt (0.3–0.5 mg/100 mL) were evaluated, and two strains ( Lactobacillus plantarum NCU001563 and Streptococcus thermophilus NCU074001) were selected. Further, the obtained strains showed excellent gastrointestinal fluid resistance ability, cell adhesion susceptibility, β-glucosidase activity, and were sensitive to the various antibiotics. LAB both strains and fermented soymilk supernatant (FSMS) displayed a strong inhibitory effect on pathogenic strains. Nevertheless, when treated with catalase and proteases at pH 6.2, FSMS demonstrated a significant decrease of antibacterial activity. Finally, the antioxidant results indicated fermented soymilk (FSM) has stronger antioxidant activity than non-fermented soymilk (NFSM) by evaluating 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals scavenging activity, 2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) radical scavenging activity, and ferric reducing antioxidant power (FRAP ) . The results indicated that both LAB strains have excellent potential as probiotics and can have good application for soymilk fermentation products.