¹H-NMR analysis, antioxidant activity, and α-amylase and α-glucosidase inhibitory potential of ten common Thai edible flowers

Abstract

BACKGROUND: Edible flowers have been used in cooking as foods as well as medicine alternatives. The objectives were to identify a major class of organic compounds in edible flowers by applying proton nuclear magnetic resonance (1H-NMR) metabolite fingerprinting and to evaluate bioactivity including antioxidant and α-amylase and α-glucosidase inhibitory activities. RESULTS: A total of 32 metabolites including five organic acids, eight sugars, 11 amino acids and eight phenolic compounds were identified by using 1H-NMR at 600 MHz. The aromatic proton of phenolic compounds was observed at the low-field region ranged between δ 5.5 ppm and 10.0 ppm. Total phenolic content (TPC) of the extracts of edible flowers ranged from 6.0 mg GAE g−1 dry weight (DW) to 47.97 mg GAE g−1 DW. Antioxidant activity varied from 140.5 mmol L−1 TE g−1 DW to 985.2 mmol L−1 TE g−1 DW. The extracts from edible flowers showed dose-dependent inhibition against enzyme. The extract of African marigold (Tagetes erecta L.) had the highest half maximal inhibitory concentration (IC50) against α-amylase at 0.13 mg mL−1 while the extract of flower of Sesban agasta (Sesbania grandiflora Desv.) had the lowest IC50 against α-amylase at 0.63 mg mL−1. Moderate correlation was found between IC50 values against α-glucosidase and antioxidant activity values (R2 = 0.66) (P < 0.05). CONCLUSION: 1H-NMR application provided metabolomic fingerprinting of edible flowers and the in vitro inhibitory potential activity against key enzymes related to diabetes indicated that specific edible flowers have a potential use for dietary management during the early stages of hyperglycaemia. © 2021 Society of Chemical Industry.