Soluble and insoluble-bound phenolic bioactive compounds of Tortola bean leaf and their antioxidant properties in chemical-based assays and Caco-2 cells

Tortola bean leaves are an agricultural by-product from Tortola beans, which is widely consumed in Chile. Free, esterified, etherified, and insoluble-bound phenolics of Tortola bean leaves were evaluated for total phenolic content (TPC), antioxidant properties, and phenolic profile using UPLC-MS/MS for the first time, thus all results presented are novel considering previous literature. The soluble phenolics (free + esterified + etherified) presented higher TPC values (4667.03 mu g gallic acid equivalent/g dry weight), reducing power (1474.26 mmol Trolox equivalent/100 g dry weight) and antioxidant activity towards peroxyl radicals (245.24 mmol Trolox equivalent/100 g dry weight). The free phenolics fraction showed the highest TPC and equal or higher antioxidant properties in chemical assays. Furthermore, it showed the highest phenolics content as evaluated by UPLC-MS/MS, regardless of the fraction (free, esterified, etherified, or insoluble-bound). Quercetin and rutin derivatives were the most abundant compounds (323.12-421.31 mu g/g dry weight), mainly in the fraction containing free phenolics (50%). Free phenolic enriched in quercetin and their derivatives exhibited similar antioxidant protection to those of commercial quercetin in Caco-2 cells subjected to an oxidative challenge induced by exogenous hydrogen peroxide. Tortola bean leaves thus merit further consideration from academia and industry to develop nutraceuticals and/or functional foods.