Preparation of the Wood Ear Mushroom Auricularia auricula-judae (Agaricomycetes) Polysaccharides by Neutral Protease and Their Antioxidant Stress Capacity

Response surface methodology with a Box-Behnken design was used to investigate the effects of a neutral protease on Auricularia auricula-judae polysaccharide (AAP) extraction yield. Four ethanol concentrations (30%, 50%, 70%, and 90%) were used to grade AAPs. Optimal fractions with a high polysaccharide recovery rate and a strong free radical scavenging rate were obtained, and their antioxidant stress effect was studied using Caenorhabditis elegans as the model organism. The results showed that among the factors affecting AAP yield (temperature, liquid-to-A. auricula-judae powder, enzyme usage, time, pH, etc.), temperature, ratio of liquid-to-A. auricula-judae powder, and time had the most obvious effects. AAP yield reached 13.91% ± 0.95% at a temperature of 7°C, liquid-to-material ratio of 75 mL/g, and extraction time of 70 min. High AAP recovery rates and strong free radical scavenging rates of 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt and 1,1-dibenzoyl-2-trinitrophenylhydrazine were obtained by 30% ethanol (AAPs1). Results from the anti-hydrogen peroxide and methyl viologen stress experiment showed that AAPsl could significantly prolong the life of worms under oxidative stress compared to the negative control group (P < 0.05).