Phenolic extraction from apple peel by cellulases from Thermobifida fusca

With the optimization of the pretreatment conditions for the crude Thermobifida fusca cellulase activity and phenolic release from apple peel, we focused on the activity of individual purified cellulase related to the antioxidant activity. The overall phenolic release was significantly increased in a synergistic manner with combined pretreatment, not with individual pretreatment such as boiling, acid, and pectinase treatment. Approximately 60 mg of reducing sugar equivalent were produced per g of apple peel by treatment with T. fusca crude extract, and up to 3 times more reducing sugars were released when the apple peel was boiled and then treated with acid and pectinase. There was good correlation between the release of phenolics and reducing sugar by cellulase treatment and also between the amount of total phenolics and antioxidant capacity by each enzyme treatment (r² > 0.95). Among the tested enzymes purified from T. fusca cell extract, cellulase activity on apple peel was the highest with cellulase 6A (Cel 6A; 43% digestion), and the highest antioxidant capacity was obtained by incubation with Cel 6B (16 mg vitamin C equiv/g). Synergism in the activity was found from the combined treatment with Cel 6A and 6B in both cellulase activity and antioxidant capacity after 20 h of incubation. Cel 9A (progressive endocellulase) exhibited greater cellulase activity and antioxidant capacity than Cel 9A cd which lacks in cellulose-binding module, indicating that the cellulose-binding domain might play important roles in cellulolysis of apple peel. This study could provide some insights into the action mechanism of various cellulases on the digestion of cellulose-containing byproducts and expand the opportunity for cellulase utilization in the extraction of functional ingredients from the plant-derived byproducts.