Conversion of condensed tannin from chokeberry to cyanidin: Evaluation of antioxidant activity and gut microbiota regulation

•Condensed tannins from chokeberry were converted into cyanidin by hot acid-alcohol treatment.•The optimum treatment conditions were determined by response surface methodology.•Hot acid-alcohol treatment could effectively improve the antioxidant activity of chokeberry.•Hot acid-alcohol treatment could change the negative effect of chokeberry on intestinal flora diversity into a positive effect.