Antioxidant composition and activity of barley (Hordeum vulgare) and malt extracts and of isolated phenolic compounds

Phenolics have been identified and quantified in nine varieties of barley a nd their corresponding malts as flavan-3-ols, flavonols, phenolic acids and apolar esters. Flavan-3-ols are monomers, (+)-catechin and (-)-epicatechin , and polymers constituted mainly by units of (+)-catechin and (+)-gallocat echin. The most abundant compounds were the dimers procyanidin B3 and prode lphinidin B3. The main trimeric procyanidin was procyanidin C2. After malti ng, the phenolic content decreased for all varieties. Catechin monomers wer e the most affected. Beside polyphenols, barley and malt extracts contained other antioxidants: carotenoids (lutein and zeaxanthin) and tocopherols (a lpha, delta and gamma). The antioxidant activity was measured using three m ethods: capacity to react with DPPH. (ARP), inhibition of lipoxygenase acti vity (LoxI) and inhibition of cooxidation of beta-carotene in a linoleate m odel system (AOP). The inhibition of cooxidation of p-carotene in a linolea te model system did not allow varieties to be discriminated. They all have high antioxidative properties. Using this assay, tocopherols were the best antioxidants. The ARP (antiradical power) was correlated positively with th e amount of total flavan-3-ols (r = 0.89) and increased with the degree of polymerisation. The LoxI assay allowed discrimination of the nine varieties of barley and their corresponding malts but was not correlated with any co mpound, although flavan-3-ols were good inhibitors of lipoxygenase activity . (C) 1999 Society of Chemical Industry.