Protective effects of exopolysaccharide of a medicinal fungus on probiotic bacteria during cold storage and simulated gastrointestinal conditions.

The efficacy of probiotic health products depends on the capability of the constituent probiotic bacteria to survive through long period of cold storage and the gastrointestinal tract. This study was to evaluate the protective effects of a high-molecular weight (MW) exopolysaccharide (EPS) from a medicinal fungus Cs-HK1 on three different bifidobacteria. The EPS had a total dietary fiber content about 70% (w/w), which was close to its total carbohydrate content. It was resistant to artificial gastric acid (pH 2) with no more than 4% (w/w) hydrolysis in 6 h. EPS at 5 g/L significantly increased the survival rate of the probiotic bacteria during cold storage (4 °C) and in simulated gastric acid, reducing the death rate of different bacterial strains by 50% to 70%. The protective effect of EPS was weaker when the concentration was decreased to 3 g/L or when the MW of EPS was reduced by partial degradation with power ultrasound. EPS also showed significantly protective effect on the all bacterial strains in bile juice. The results have demonstrated the potential value of Cs-HK1 EPS as a novel prebiotic fiber for the formulation of synbiotic products with probiotic bacteria.