Enhanced bound antioxidant capacity of oat bran treated with green tea infusion modulates antioxidant release and short chain fatty acid formation during colonic fermentation

Bound antioxidants play a significant role in human health due to their slow and continuous release throughout the colon. Oat bran (OB) is a key source of bound antioxidants; however, its antioxidant capacity is limited. This capacity could be enhanced through treatment with green tea infusion (GTI) under optimum conditions, resulting in GTI treated OB. This study investigated the release of antioxidants from GTI treated OB during both <i>in vitro</i> digestion and colonic fermentation using <i>in vitro</i> batch and SHIME model systems. Antioxidant capacity was determined in both soluble and insoluble fractions using the QUENCHER approach. The released antioxidant capacity during <i>in vitro</i> batch fermentation was associated with catechin metabolites. The effects on gut microbiota metabolites, specifically short chain fatty acids (SCFA), were examined. Additionally, the interaction between OB and green tea extract (GTE), referred to as OB + GTE, during co-digestion and fermentation was tested. Compared to GTE alone and OB + GTE, GTI treated OB showed superior antioxidant activity (2-6-fold higher) in both insoluble and soluble fractions during short- and long-term exposure. The antioxidant release during fermentation of GTI treated OB was strongly correlated with the concentration of pyrogallol (<i>r</i> = 0.693) and 3,4-dihydroxyphenylacetic acid (<i>r</i> = 0.625). Half of its antioxidant capacity remained in the insoluble fraction. Both GTI treated OB and OB + GTE stimulated SCFA production, with concentrations of 25.25 ± 2.53 mM and 30.62 ± 5.03 mM in the distal colon, respectively. These findings suggest that the enhanced bound antioxidant capacity of OB has beneficial health effects on colon health by increasing antioxidant capacity and stimulating SCFA production.