Apple peels as an edible source of phenolic bioactive compounds with antidiabetic and antiglycation properties

Apples (Malus domestica Borkh.) are one of the most consumed fruits around the world with a high production of peels as wastes and by-products. In this work, peels from different commercial and local apple samples are explored as a source of phenolic bioactive compounds that could be directly related to the prevention of type 2 diabetes. Six different cultivars from local and commercial apple samples were processed to obtain the phenolic compounds by ultrasonication of the peels using methanol as the solvent. The phenolic content was explored using the Folin-Ciocalteu assay and the quantification of 37 individual phenolic compounds was carried out by high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS/MS). Cellular viability was determined by performing the MTT assay in Caco-2 cell cultures exposed to the phenolic extracts. Subsequently, the capacity to inhibit α-glucosidase, α-amylase and pancreatic lipase enzymes, as well as antiglycation and antioxidant activities, was evaluated. These apple peel samples were considered a source of phenolic compounds with hyperoside, delphinidin 3,5-diglucoside, chlorogenic acid, phlorizin, epicatechin and procyanidin B2 as the main constituents. All samples neutralized the production of advanced glycation end-products and exhibited antiradical activities in a dose-dependent manner; four samples (Amarilla de Octubre, Manzana Helada, Verde Doncella and Pinova) inhibited α-glucosidase but only the sample known as "Amarilla de Octubre" was successful in inhibiting pancreatic α-amylase. Cytotoxicity was discarded in Caco-2 cell cultures at physiological concentrations considering these extracts as a source of phenolic compounds with antidiabetic, antiglycation and antioxidant properties.