Saccharomyces boulardii (S. boulardii) has been used as a probiotic for the prevention or treatment of various human gastrointestinal diseases for many years. Thus, S. boulardii has a wide range of application prospects in medicine and food industry. The experiments were investigated with effecting of carbon sources (galactose, sucrose, fructose, maltose, lactose, glucose, and soluble starch), nitrogen sources (tryptone, casein, yeast extract, peptone, soy peptone, beef extract and malted milk; ammonium sulfate, urea, diammonium hydrogen citrate, triammonium citrate, ammonium nitrate, ammonium chloride and potassium nitrate), prebiotics (xylo-oligosaccharide, isomaltooligosaccharide, fructo-oligosaccharide, galacto-oligosaccharide, stachyose, raffinose and inulin) on the number of viable cells and dry cell weight of S. boulardii. The optimum concentration of 5 % glucose or sucrose, 2 % peptone or yeast extract, 0.4 % urea, 0.2 % fructo-oligosaccharide and 0.6 % galacto-oligosaccharide for S. boulardii grew better in medium.

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Cell-envelope proteinases (CEPs) can hydrolyze casein into functional peptides, which is beneficial to the health of the host. The single factor experiment screened out that the optimal conditions for CEP production by Lactobacillus plantarum LP69 were 37°C, 20h, initial pH of 7, and optimal inoculation amount of 5%. The best conditions for this experiment were obtained by orthogonal experiment: time 22h, temperature 39°C, initial pH value of 6, and inoculation amount of 5%. Under this culture condition, the target protease activity of Lactobacillus plantarum LP69 reached 22.31±0.82U/mL, the protein content was 19.07±0.36mg/mL, and the specific activity was 1.17±0.06U/mg. The specific activity significantly increased by 15.8% compared with the control (p<0.05).

Background. The chemical synthesis of antioxidants has exposed more and more of their disadvantages. Therefore, the development of safe, healthy and efficient natural antioxidants has become a research hotspot. At present, antioxidant peptides are gradually becoming more popular due to their strong antioxidant activity and high safety. Materials and methods. The aim of this experiment was to obtain the optimum fermentation conditions for producing antioxidant peptides from Lactobacillus casei L61. The effects of various factors (fermentation temperature, fermentation time, concentration of regenerated milk and inoculum) on the production of antioxidant peptides by Lactobacillus casei L61 were studied using a single factor test. Four methods (DPPH radical scavenging activity, the ability to chelate iron, hydroxyl radical scavenging rate, total reduction force) were used to determine antioxidant activity in vitro. The optimum fermentation conditions were determined by orthogonal experiment. Results. The results showed that the optimal fermentation conditions for the production of antioxidant peptides by L61 were 11% reconstituted milk, 5% inoculated milk, fermentation at 41℃ and 16 hours of fermentation time. Under these conditions, the results of the orthogonal test showed that the DPPH radical scavenging rate of the whey sample was 59.97 ±0.87%, which was higher than those of the other 9 groups, and significantly higher than that of the control group (41.97 ±1.37%). Conclusion. The concentration of reconstituted milk and the amount of inoculated milk had a significant effect on the production of antioxidant peptides by Lactobacillus casei L61. It provides a reference for the optimization of the fermentation nutritional composition of antioxidant peptides produced by Lactobacillus casei L61.