Total phenolics, capsaicinoids, antioxidant activity, and α-glucosidase inhibitory activity of three varieties of pepper seeds

Abstract

ABSTRACT Chopped pepper, a traditionally fermented condiment product in China, is widely consumed because of its good flavor. However, large amounts of by-product, namely, chopped pepper seeds (CPS) are produced annually during the manufacture of chopped pepper product, and this material is generally classified as solid waste, which causes waste of resource. In this work, the total phenolics (TPC) and capsaicinoids content, antioxidant property, and α-glucosidase inhibitory activity (GIA) of three varieties CPS (i.e., WPS, LPS, and BRPS) were assessed. The effects of solvents with different polarities, including 80% methanol, 80% acetone, and 80% ethanol, in extracting the bioactive compounds were also investigated. The results indicated that the studied CPS were rich in total phenolics and capsaicinoids with contents of 3,934–6,208 μg GAE/g dw and 1,052–3,692 μg/g dw, respectively. Three capsaicinoid compounds, namely, capsaicin, dihydrocapsaicin, and nordihydrocapsaicin, in the CPS were identified and quantified by HPLC. All CPS samples exhibited potent antioxidant property and GIA. Moreover, the different extraction solvents exhibited considerable influence on TPC, capsaicinoid content, antioxidant capacity, and GIA. Regardless of different polarities extraction solvents, BRPS had the highest level of phenolics, capsaicin, dihydrocapsaicin and nordihydrocapsaicin and exhibited the strongest antioxidant activity and GIA among the three varieties CPS studied. In practical applications, the use of 80% ethanol is recommended for the extraction of bioactive compounds from BRPS, because it is environment friendly. Positive correlations between phenolics, capsaicinoids, antioxidant activity, and GIA were observed by PCA and linear correlation analysis. Thus, CPS, especially BRPS, is abundant and can be a cheap source of natural antioxidants and anti-diabetic compounds, making it an interesting ingredient in the potential future development of nutraceuticals or functional food products and bringing great advantages for food and pharmaceutical industries, consumers, and producers. Abbreviations CPS: chopped pepper seeds; WPS: wild pepper seeds; LPS: linear pepper seeds; BRPS: bright red pepper seeds; TPC: total phenolics content; HPLC: high-performance liquid chromatography; ABTS: 2, 2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt; FRAP: ferric reducing antioxidant power; DPPH: 2,2-diphenyl-1-picrylhydrazyl; vitamin C: ascorbic acid; RP: reducing power; GIA: α-glucosidase inhibitory activity; PCA: principal component analysis.