A comparative study on the polyphenolic content, antibacterial activity and antioxidant capacity of different solvent extracts of Brassica oleracea vegetables

Brassica vegetables are rich in polyphenols, flavonoids and glucosinolates. Investigation was undertaken to optimise the best solvents among 60% ethanol, acetone and methanol for the extraction of polyphenols from Brassica vegetables. Furthermore, different properties such as antibacterial activity and antioxidant capacity were also investigated. Results showed that a 60% methanolic extract showed the highest total phenolic content which was 23.6, 20.4 and 18.7mggallic acid equivalents(GAE)g ^-1 extract for broccoli, Brussels sprouts and white cabbage, respectively. The hydroxybenzoic acid content of various solvent extracts ranged from 5.86 to 8.91GAEg ^-1 extract for broccoli, 2.70 to 5.44GAEg ^-1 extract for Brussels sprouts and 3.69 to 4.86GAEg ^-1 extract for white cabbage, while the hydroxycinnamic acid content ranged from 0.78 to 1.26chlorogenic acid equivalents (CAE)g ^-1 extract for broccoli, 1.41 to 3.45CAEg ^-1 extract for Brussels sprouts and 0.49 to 1.14CAEg ^-1 extract for white cabbage. A concentration-dependent antioxidative capacity was confirmed for different reactive oxygen species, and moderate antibacterial activity was observed against a number of Gram-negative and Gram-positive food spoilage and food pathogenic bacteria. Solvents significantly affected polyphenolic content and its different properties, and the methanol was found to be the best solvent for the extraction of polyphenols from studied Brassica vegetables.