Soxhlet extraction cycle-dependent diversity in phenolic profile and antioxidant potency of red cabbage (Brassica oleracea var. capitata F. rubra)

Abstract

Introduction: The Brassicaceae vegetables are a rich source of secondary metabolites that exhibit several health benefits and protection against numerous degenerative diseases.

Objectives: The current study was performed to investigate the effect of Soxhlet extraction cycles on the phenolic profile of red cabbage (Brassica oleracea var. capitata F. rubra) and its biological activities.

Materials and Methods: The red cabbage sample was harvested from the research fields of Ayub Agricultural Research Institute Faisalabad, Pakistan. The ethanol extracts were prepared using 1-, 2-, 4-, and 8-cycles Soxhlet extraction technique. The antioxidant potential of red cabbage extracts was estimated by evaluation of total phenolic contents (TPC), total flavonoid contents (TFC), DPPH radical scavenging capacity and reducing power. The identification and quantification of polyphenols were carried out by RP-HPLC. The antibacterial activity of red cabbage extracts was determined against Escherichia coli and Staphylococcus aureus and the antiproliferative activity was carried out by MTT mitochondrial viability assay against the human A549 cancer cell line.

Results: Gallic acid, p-hydroxyl benzoic acid, chlorogenic acid, and p-coumaric acid were the major phenolic acids, whereas catechin and quercetin were the major flavonoids detected in the red cabbage extracts. The extraction cycles were found to have significant (p ≤ 0.05) effects on the phenolic profile of the red cabbage extracts.  TPC of extracts ranged from 5.22-11.72 mg/g dry matter, measured as gallic acid equivalent, while the TFC ranged from 1.64-5.19 mg/g dry matter; measured as catechin equivalent. The 4-cycles extract of red cabbage exhibited the maximum TPC, TFC, and DPPH free-radical scavenging and reducing activity.

Conclusion: The study concluded that the Soxhlet extraction cycles could exert a considerable effect on the yield and polyphenol composition of red cabbage extracts as well as their antioxidant potential. Antibacterial and antiproliferative activities were observed by all the extracts of red cabbage.