Extraction of bound phenolics from shiitake mushrooms (Lentinus edodes) by combined acid and base hydrolysis procedures and analysis of phenolic profiles and antioxidant capacities

Shiitake mushrooms contain free phenolics (FPs) and bound phenolics (BPs). BPs embedded in mushrooms are generally neglected and underestimated. Methods of hydrolysis with acid, base and their combination in different sequences were developed to release BPs. The contents, compositions and antioxidant capacities of FPs and BPs were investigated. Results found that BPs yielded with combining base and acid hydrolysis received the highest value (25.67 mg gallic acid equivalents (GAE)/100 g dry weight (DW)), which was higher than FPs (20.62 mg GAE/100 g DW). LC-ESI-QqQ-MS/MS analysis demonstrated that gallic acid, protocatechuic acid, caffeic acid, and ferulic acid presented in all BPs fractions, whereas hesperidin, luteolin, quercetin, and cinnamic acid were affected by hydrolysis methods and procedures. BPs fractions with higher phenolic content showed strong antioxidant capacities. These results demonstrate the importance of BPs and can be applied to enhance the amount and bioavailability of BPs from shiitake mushrooms and other foods.