HPLC-FRAP methodology and biological activities of different stem bark extracts of Cajanus cajan (L.) Millsp

Cajanus cajan. (L.) Millsp. (C. cajan) (Family: Fabaceae) also known as pigeon pea, is a famous food and cover/forage crop bearing a high amount of key amino acids (methionine, lysine and tryptophan). This study investigated into the total phenolic (TPC), flavonoid content (TFC), antioxidant ]2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2 -azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity, total antioxidant capacity (TAC) (phosphomolybdenum) and metal chelating] activities and enzyme [alpha-amylase, alpha-glucosidase, tyrosinase, acetyl-(AChE), butyry1-(BChE) cholinesterase] inhibitory effects of four extracts (methanol, hexane, ethyl acetate, aqueous) prepared from C. cajan stem bark. Direct identification of antioxidants was also conducted using the high performance liquid chromatography-ferric reducing antioxidant power (HPLC-FRAP) system. The highest TPC and TFC were recorded with the methanolic (23.22 +/- 0.17 mg GAE/g) and ethyl acetate extracts (19.43 +/- 0.24 mg RE/g), respectively. The methanolic extract exhibited important antioxidant activity with DPPH (38.41 +/- 0.05 mg Trolox equivalent (TE)/g), ABTS (70.49 +/- 3.62 mg TE/g), CUPRAC (81.86 +/- 2.40 mg TE/g), FRAP (42.96 +/- 0.59 mg TE/g) and metal chelating (17.00 +/- 1.26 mg ethylenediaminetetraacetic acid equivalent/g). p-coumaric and caffeic acid were the predominant antioxidants in the samples. Results from enzymatic assays showed the potential abilities of hexane extract in inhibiting the AChE, BChE, alpha-amylase and alpha-glucosidase enzymes. From the results obtained in this study, it can be concluded that C. cajan can be considered as a promising source of antioxidants and key enzyme inhibitors that can be exploited for future bioproduct development. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the antioxidant and enzyme inhibitory effects of extracts from Cajanus cajan stem bark. The methanolic extract showed significant antioxidant activity, while the hexane extract exhibited potential abilities in inhibiting key enzymes. Cajanus cajan could be a promising source of antioxidants and enzyme inhibitors for future bioproduct development.