The optimization of peptides - producing conditions for antioxidant peptides in goat milk by Lactobacillus casei L61.

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. 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%). CONCLUSIONS: 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.

Antioxidant Peptides from Goat Milk Fermented by Lactobacillus casei L61: Preparation, Optimization, and Stability Evaluation in Simulated Gastrointestinal Fluid.

Antioxidant peptides are currently the focus of many studies, since they eliminate free radicals in the human body without harmful effects. In the present study, Lactobacillus casei L61 was used as a starter culture to ferment goat milk because of its high capacity to produce antioxidant peptides. An optimal nutrients formula (casein, casein peptone, glucose, soybean peptone, inulin, calcium lactate, and cysteine) was investigated by Plackett⁻Burman (P⁻B) and Box⁻Behnken (B⁻B) designs for response surface methodology (RSM). Antioxidant peptides were successively isolated and purified from the fermented goat milk. Furthermore, the stability of the antioxidant peptides was evaluated in a simulated gastrointestinal tract at 37 °C. The results showed that calcium lactate, glucose, and casein peptone significantly affected the antioxidant activity of goat milk. The optimal additive amounts were 0.99% (w/v) calcium lactate, 0.21% (w/v) glucose, and 0.29% (w/v) casein peptone. The hydroxyl free radical scavenging rate increased significantly (p < 0.001) from 56.50 ± 0.57% to 88.01 ± 0.69%; the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate increased up to 63.48 ± 1.22% under the optimal conditions (n = 3). Our research provides a fitted mathematical model for antioxidant peptides production. Besides, these antioxidant peptides had great stability during simulated gastrointestinal digestion.