In vitro screening of phenolic compounds, potential inhibition against α-amylase and α-glucosidase of culinary herbs in Thailand

Herbs that are commonly used in Thai dishes were selected for evaluation in order to determine their phenolic compounds, antioxidant activity, and in vitro potential inhibition against alpha-amylase and alpha-glucosidase. The total phenolic content ranged from 2.89 to 75.26 mg GAE/g dw. The three aqueous herb extracts with the highest total phenolic content were yellow-berried nightshade (Solanum xanthocarpum), holy basil (Ocimum sanctum) and acacia (Acacia pennata). The antioxidant activity was expressed as percent inhibition of DPPH, ranging from a high of 85% in bitter gourd (Monordica charantia) to a low of 0% in garlic (Allium sativum) and shallot (Allium cepa). A high correlation (r = 0.70, p < 0.05) was observed between total phenolic content and antioxidant activity for the herb extracts in the Solanaceae family while, an insignificant high and negatively correlation (r = -1.00, p > 0.05) for the herb extracts in the Cucurbitaceae and Umbelliferae families was observed. All of the herbs had caffeic content, varying from 0.00 to 23.93 mg/g dw. Peppermint (Mentha canalenisa), galangal (Languas galangal) and holy basil (O. sanctum) had a significant p-coumaric acid content. The first and second obtained principal component represented 60% of the total variation. The potential inhibition against alpha-amylase for the herbs extracts ranged from 0% to 58%, while the highest percentage was observed in the acacia (A. pennata) extract. The potential inhibition against alpha-glucosidase varied from 7% to 100%. A high correlation (r = 0.68, p < 0.05) was observed between alpha-amylase inhibition and caffeic acid content for aqueous extracts in the Alliaceae, Cucurbitaceae, and Leguminosae families, while a high correlation (r = 0.49, p < 0.05) was observed between alpha-glucosidase inhibition and total phenolic content for the aqueous extracts of all herbs. Therefore, specific culinary herbs showed to have a potential use for dietary management during the early stages of hyperglycaemia. (C) 2011 Elsevier Ltd. All rights reserved.