The total antioxidant capacity, total phenolics content and starch hydrolase inhibitory activity of fruit juices following pepsin (gastric) and pancreatin (duodenal) digestion

Abstract

The objective of the study was to evaluate the stability of the antioxidant activity, total phenolics content and starch hydrolase inhibitory activities of 22 commercially available fruit juices using an in vitro digestion model. These are important parameters as far as consumers are concerned due to their associated therapeutic properties. The Oxygen Radical Absorbance Capacity (ORAC) assay, Ferric Reducing Antioxidant Power (FRAP) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays as well as the inhibition of α-amylase and α-glucosidase were carried out. All 22 fruit juices were a significant source of polyphenols with values varying between 235 and 389 μg gallic acid equivalents per mL. Twelve out of the 22 juices showed a statistically significant increase (P < 0.05) in polyphenol content following the duodenal phase of digestion. ORAC values correlated better with the total phenolics content (R 2 = 0.975) as compared with FRAP (R 2 = 0.893), DPPH (R 2 = 0.821) and ABTS (R 2 = 0.752). IC50 values of the α-amylase inhibitory activity kept increasing following both digestion phases, indicating the reduced ability of the juices to inhibit this enzyme. However, the IC50 values of the α-glucosidase inhibitory activity kept decreasing, indicating a better efficacy to inhibit this enzyme. Overall, all fruit juices were observed to be a significant source of antioxidants with starch hydrolase inhibitory properties.