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

Abstract

Phenolics have been identified and quantified in nine varieties of barley and 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 (+)-gallocatechin. The most abundant compounds were the dimers procyanidin B3 and prodelphinidin B3. The main trimeric procyanidin was procyanidin C2. After malting, the phenolic content decreased for all varieties. Catechin monomers were the most affected. Beside polyphenols, barley and malt extracts contained other antioxidants: carotenoids (lutein and zeaxanthin) and tocopherols (α, δ and γ). The antioxidant activity was measured using three methods: capacity to react with DPPH. (ARP), inhibition of lipoxygenase activity (LoxI) and inhibition of cooxidation of β-carotene in a linoleate model system (AOP). The inhibition of cooxidation of β-carotene in a linoleate 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 the 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 compound, although flavan-3-ols were good inhibitors of lipoxygenase activity. © 1999 Society of Chemical Industry