Antioxidant Capacity and Anti-diabetic Activity of Wild Berry Stem Infusions

Abstract

The potential health benefits of green tea sand herbal teas have led to an increased demand of specialty tea products in the food market. Aims: To determine the proximate composition, phytochemical compositions and hypoglycemic potentials of the methanol and hot water extracts of the stems of wild berries from Eastern Canada. Study Design: Extraction of the air-dried stems of wild berries with both methanol and hot water, and testing the various extracts for the proximate composition, phytochemical composition and hypoglycemic potentials in comparison to green tea and rose-hip fruit. Place and Duration of Study: The stems of wild blueberry, raspberry and blackberry along with rose-hip fruits were collected from the wild habitats of Windsor area of Nova Scotia, Canada in the year 2013; while the commercial green tea was purchased from a local store (Bulk Barn, Truro, Nova Scotia). Methodology: Phenolic composition and characterization was done using spectrophotometric analyses and UPLC-ESI-MS. Carotenoid and caffeine content were measured using HPLC-PDA. The antioxidant capacities were evaluated using ferric reducing ability of plasma (FRAP), 2,2-diphenyl-1-picrylhydrazyl(DPPH)and oxygen radical absorbance capacity (ORAC) assays. The anti-diabetic properties were investigated by α-amylase, α-glucosidase and advanced glycation products (AGEs) inhibition assays in vitro. Results: The extracts consisted of phenolic acids, carotenoids, dihydrochalcones and flavonoids. The highest total phenolic content was observed in the stem extracts of blueberry (3019 and 4267 mg catech in equivalents (CE)/L for methanol and hot water extraction, respectively). The total antioxidant capacity was also the highest in blueberry stem, followed by blackberry stem. The blackberry stem and raspberry stem exhibited the greatest inhibition of α-amylase and α-glucosidase activities (IC50=20-68 and 10-28 mg/L, respectively). Raspberry stem extract exhibited the highest anti-AGE activity with IC50 of 1.0-3.1 mg/L. Conclusion: The present findings demonstrate a potential use of wild berry stems as a value-added ingredients in herbal tea blends.