Leaf Infusion of Ribes magellanicum Poir.: A Traditional Beverage from Southern Patagonia with Strong Inhibitory Effects on α-Glucosidase

Infusions of the leaves of Ribes magellanicum (Grossulariaceae) are used as a digestive in southernmost South America. This work aimed to assess the composition and activity of infusions and MeOH:H2O 7:3 extracts of R. magellanicum leaves on enzymes related to metabolic syndrome (α-glucosidase, α-amylase, and pancreatic lipase), as well as their antioxidant capacity. Samples from a longitudinal gradient from central southern Chile to the islands in the Beagle Channel were investigated. Lyophilized infusions and extracts were used for all determinations, including inhibition of the selected enzymes, total phenolic (TP), total flavonoid (TF), total procyanidins (TPC), and antioxidant capacity (DPPH, FRAP, TEAC, and ORAC). The composition of the samples was assessed by HPLC-DAD. Some 99 compounds were tentatively identified by HPLC-MSn. The main phenolics were quantified using calibration curves with reference compounds. Relevant differences exist in the ratio of constituents in infusions compared to hydroalcoholic extracts. The samples were inactive towards α-amylase and pancreatic lipase at 100 and 50 µg/mL, respectively. Assay-guided isolation of α-glucosidase inhibitors led to fractions with high activity (IC50: 0.02–0.05 µg/mL). The strong inhibition of α-glucosidase and antioxidant capacity of the infusion and extracts of R. magellanicum leaves support its traditional use in southern Patagonia.