Abstract:The survival of Lactobacillus casei in its fermented lychee juice was investigated in an artificial gastric juice and artificial intestinal juice model. At the same time, the antimicrobial activities of the fermented juice against six common foodborne pathogens (Salmonella, Shigella sonnei, Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus and Enterobacter sakazakii) were examined using the agar diffusion method, considering the effects of acids and enzymes. The results showed that in the simulated gastrointestinal digestion model, the viable counts of Lactobacillus casei were 260, 8.63×107, 9.57×107 and 1.15×108 CFU/mL, respectively, after a 4-h incubation in an artificial gastric juice at pH 1.5, 2.0, 3.0 or 4.0, while above 107 CFU/mL after a 12-h digestion in the artificial intestinal juice. In terms of antimicrobial activity, the fermentation broths subjected to different treatments such as deacidification, hydrogen peroxide removal and enzymatic hydrolysis exhibited significant inhibitory effects on five common foodborne pathogenic bacteria including Salmonella enteritidis, except for Enterobacter sakazakii. Exopolysaccharide, H2O2 and protein peptides were the main antimicrobial substances against five common pathogenic bacteria. These results will lay a theoretical foundation for in vitro experiments on whether Lactobacillus casei fermented lychee juice could offer beneficial effects in the gastrointestinal tract and provides a scientific basis for local food industrial development and application.
