Soluble Antioxidant Compounds Regenerate the Antioxidants Bound to Insoluble Parts of Foods

This study aimed to investigate the regeneration potential of antioxidant capacity of an insoluble food matrix. Investigations were performed in vitro with several food matrices rich in dietary fiber (DF) and bound antioxidants. After removal of the soluble fraction, the antioxidant capacity (AC) of the insoluble fraction was measured by the QUENCHER procedure using ABTS(•+) or DPPH(•) radicals. After measurement, the insoluble residue was washed out to remove the excess of radicals and treated with pure antioxidant solution or antioxidant-rich beverage to regenerate depleted antioxidants on the fiber. Results revealed that the antioxidant capacity of compounds chemically bound to the insoluble moiety could be reconstituted in the presence of other hydrogen-donating substances in the liquid phase. Regeneration efficiency was found to range between 21.5 and 154.3% depending on the type of insoluble food matrix and regeneration agent. Among the food matrices studied, cereal products were found to have slightly higher regeneration efficiency, whereas antioxidant-rich beverages were more effective than pure antioxidants as regeneration agents. Taking wheat bran as reference insoluble material, the regeneration abilities of beverages were in the following order: green tea > espresso coffee > black tea > instant coffee > orange juice > red wine. These results highlighted the possible physiological relevance of antioxidants bound to the insoluble food material in the gastrointestinal tract. During the digestion process they could react with the free radicals and at the same time they can be regenerated by other soluble antioxidant compounds present in the meal.