Polyphenolic Antioxidant Mobilization in Apple Pomace by Different Methods of Solid-State Fermentation and Evaluation of Its Antioxidant Activity

An investigation was carried out to understand the changes and mobilization of polyphenolics and the improvement in their antioxidant properties in apple pomace by solid-state fermentation using Generally Recognized as Safe grade fungus, Phanerochaete chrysosporium, by different fermentation techniques, such as flask, tray, and fermentor. β-glucosidase, ligninolytic enzymes activity, and polyphenolic-linked antioxidant activity of apple pomace during solid-state fermentation was studied. During the course of solid-state fermentation, there was an increase in the extractable polyphenolic content (15.53 to 29.28 mg of gallic acid equivalents per gram of dry weight (DW)) on the 7th day followed by a decline in the polyphenol content. Antioxidant activity was measured by 1,1-diphenyl-2-picrylhydrazyl radical inhibition system, and the increase in activity (∼35%) was directly proportional to polyphenolic content over the course of solid-state fermentation. After an initial lag phase with little activity, the β-glucosidase activity increased by 6-, 7-, and 6-fold in flask (18.12 U/g DW samples), fermentor (44.52 U/g of DW sample), and tray fermentation (46.66 U/g DW sample) methods, respectively. Both polyphenolics and antioxidant capacity correlated with the increase in the β-glucosidase activity and showed that the enzyme played an important role in the release of polyphenolic aglycones from apple pomace and therefore increased the antioxidant capacity. In addition, ligninolytic enzymes showed a direct correlation with the mobilization and polymerization of polyphenolic content during the solid-state fermentation.