Development of Probiotic-Fermented Black Mulberry (Morus nigra L.) Juice and Its Antioxidant Activity in C2C12 Cells

Black mulberry (Morus nigra L.) is considered a medicinal and food-homologous plant in China. An obstacle to its widespread use is that its annual season and shelf life are extremely short. In this paper, fermented black mulberry juice (FBMJ) was prepared with various probiotic strains, and response surface methodology was used to determine the optimum production conditions for achieving the maximum active substance content in the resulting product. The fermentation process increased levels of biological enzymes and total phenols in the resulting juice. When the ratios of the Lactobacillus inocula to the total inoculum were 27.96% for L. paracasei, 15.37% for L. casei, 16.64% for L. plantarum, and 5.12% for L. delbrueckii, the B. animalis subsp. lactis content reached 15.83%, the L. fermentum content reached 19.08%, and the superoxide dismutase (SOD) activity reached 310 U/g. To study the antioxidant characteristics of the juice, C2C12 cells were treated with H2O2 to induce oxidative stress and the cytoprotective activity of FBMJ was subsequently evaluated. After treatment with FBMJ for 24 h, cell viability was found to be protected under H2O2 exposure, while SOD and glutathione peroxidase (GSH-Px) levels were increased. The reactive oxygen species level and malondialdehyde content were also decreased. These results provide molecular evidence for the antioxidant effect of FBMJ and demonstrate that lactic acid bacteria fermentation has a positive effect on black mulberry juice (BMJ).