Mechanism of the interaction between insoluble wheat bran and polyphenols leading to increased antioxidant capacity

This study aimed to provide an in-depth investigation of the interaction between insoluble wheat bran and polyphenols. Treatment with tannic acid, but not gallic acid, increased the bound antioxidant capacity of insoluble wheat bran depending on its aqueous concentration (p < 0.05). Among the beverages tested (white and red wines, black and green tea infusions), treatment with green tea infusion caused the highest increase in the total antioxidant capacity. Temperature, time, air and pH were found to significantly affect the reaction between insoluble wheat bran and polyphenols. The bound antioxidant capacity of insoluble bran increased to above 100 mmol TE.kg(-1) after treatment with green tea infusion at optimum conditions (50 degrees C, pH 9.0, no airflow). Concentration of free amino groups available in wheat bran significantly decreased (59.5%) after the treatment The results suggested that polyphenols are oxidized to quinones under alkaline conditions further bound to free amino groups available on the surface of wheat bran. (C) 2014 Elsevier Ltd. All rights reserved.