Varietal influences on antihyperglycemia properties of freshly harvested apples using in vitro assay models

The well-known health benefits of apples have been attributed in part to the presence of polyphenols and related antioxidant capacity. The consumption of apples could provide health benefits by reducing the risk for chronic diseases such as metabolic syndrome disease, including type 2 diabetes. Thus, the objective of this study was to investigate the phenolic-linked antihyperglycemia bioactive factors in aqueous and 12% ethanol extracts of peel and pulp from 10 different freshly harvested apple varieties commonly consumed in the United States. The extracts were analyzed for total soluble phenolics, 2,2-diphenyl-1-picrylhydrazyl-linked antioxidant activity, and their associated in vitro α-glucosidase and α-amylase inhibitory activities. In general, peel extracts had higher total soluble phenolic content and related antioxidant capacity than pulp extracts. Quercetin derivatives, protocatechuic acid, chlorogenic acid, and p-coumaric acid were detected, and the amount varied significantly between aqueous and ethanolic extracts. Honeycrisp and Red Delicious varieties had the highest total phenolic contents and a significant correlation with antioxidant capacity (r = 0.91). In addition, high α-amylase and α-glucosidase inhibitory activities in aqueous pulp extracts were found. However, the peel extracts had the highest α-glucosidase inhibitory activity along with low α-amylase inhibitory activity. No correlation between α-amylase inhibitory activity and total phenolic content was observed. However, positive correlations between α-glucosidase inhibitory activity and total phenolics in aqueous (r = 0.50) and ethanolic (r = 0.70) extracts were observed. This study provides the biochemical rationale for animal and clinical studies to determine the suitable varieties with optimum bioactive factors with antihyperglycemia potential.