UHPLC-QToF-MS characterization of bioactive metabolites from Quercus robur L. grown in South Africa for antioxidant and antidiabetic properties

Abstract

The leaves and stem bark extracts of Quercus robur L. grown in South Africa have been investigated for their bioactive metabolites using UHPLC-QToF-MS. The UHPLC-QToF-MS profiling of the various extracts revealed the presence of twenty-seven compounds. These compounds were majorly grouped into flavonoids, phenolic acid and triterpenoids such as alnusiin, (+)-catechin, cis-3,4-leucopelargonidin, (-)-gallocatechin, ellagic acids, gallic acid, luteoforol, kaempferol-3-o-(6-o-cis-coumaryl)glucoside, myricitrin, neohesperidin, neriifolin, pheophorbide a, pheophytin a, procyanidin B5, pedunculagin, quercetin 3-O-[beta-D-xylosyl-(1- > 2)-beta-D-glucoside and quercitrin. The aqueous bark extract had the highest total phenol content (TPC) (320 mg GAE/g DW) and total flavonoids content (TFC) (505 mg QE/g DW), whereas the 80% aqueous acetone leaves extract had the highest proanthocyanidins levels (Pro) (433 CE/g DW). The 80% aqueous acetone extract had the best 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging capability with an IC50 value of 8.16 µg/mL. The 80% aqueous ethanol extract had the highest 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) scavenging ability with an IC50 value of 7.73 µg/mL. The aqueous leaves extract had the best ferric reducing antioxidant power assay (FRAP) ability with values of 558 µg/mL GAE. The most significant inhibitory effects on digestive enzyme activity were obtained with the 80% aqueous methanol bark and aqueous bark extracts at the concentration of 7.81 µg/mL, yielding inhibition values of 62 and 97% on α-amylase and α-glucosidase, respectively higher than the positive control used (acarbose). These findings calls attention to the phytochemical content, antioxidant and inherent antidiabetic activity of Q. robur L. grown in South Africa and therefore potentiate its potential application in the food and pharmaceutical industries, with a focus in the prevention of diabetes.