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Antioxidant Capacity and Stability of Phenolic Compounds in Aronia Kefir during in vitro Digestion

Aronia (Aronia melanocarpa) is an underutilized berry that is rich in bioactive compounds, such as anthocyanins and phenolic acids. Phenolic compounds are strong antioxidants that may provide health benefits for chronic diseases, such as type 2 diabetes. Kefir is a fermented dairy beverage which contains several species of live micro‐organisms and may help to maintain gut health. The live microbes in kefir create a dynamic environment with an acidic pH which could protect the anthocyanins in aronia from degradation. In this study, aronia juice was incorporated into a fermented kefir product. Aronia kefir was subjected to an in vitro digestion process to evaluate the antioxidant capacity, stability of bioactive components and the potential effects on carbohydrate‐hydrolyzing enzymes. Mouth, stomach, and small intestinal environments were simulated using corresponding digestive juices (containing enzymes) where pH, time and temperature were controlled. An aliquot was removed from each step for analysis. UPLC‐DAD was used to quantify anthocyanins and phenolic acids in each fraction. The antioxidant capacity was measured using 2, 2‐diphenyl‐1‐picrylhydrazyl (DPPH) free radical scavenging assay. The inhibitory effects of digested aronia kefir on carbohydrate‐hydrolyzing enzymes were assessed by measuring the IC20 values against α‐amylase and IC50 values against α‐glucosidase. The control sample was processed under the same conditions with the absence of digestive enzymes. The results of this study showed that mouth digestion did not alter the quantity of phenolic compounds or the antioxidant capacity of aronia kefir. After gastric digestion, the amount of phenolic compounds was elevated compared to the mouth digesta, which led to an improvement in the antioxidant capacity. Intestinal digestion resulted in a slight increase in cyanidin‐3‐galactoside and a decrease in neo‐chlorogenic acid. The amount of chlorogenic acid was enhanced significantly compared to gastric digesta. Antioxidant capacity of intestinal digesta was also improved. After digestion, aronia kefir exhibited strong inhibitory activity toward α‐glucosidase and moderate inhibition to α‐amylase. This result indicates that digested aronia kefir has the potential to decrease or slow the absorption of carbohydrates, thus helping to maintain blood glucose levels. This study demonstrates that accessible anthocyanins and phenolic acids in aronia kefir were stable during digestion and exhibited high antioxidant capacity. Hence, incorporating aronia kefir into a healthy diet is potentially beneficial to diabetic patients to help decrease oxidative stress and to better control their blood glucose level.