Phenolic Compounds of Barley Grain and Their Implication in Food Product Discoloration

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Abstract
Barley grains contain significant amounts of phenolic compounds that may play a major role in the discoloration of food products. Phenolic acid and proanthocyanidin (PA) composition of 11 barley genotypes were determined, using high-performance liquid chromatography and liquid chromatography−mass spectrometry, and their significance on food discoloration was evaluated. Abraded grains contained 146−410 μg/g of phenolic acids (caffeic, p-coumaric, and ferulic) in hulled barley and 182−282 μg/g in hulless barley. Hulled PA-containing and PA-free genotypes had comparable phenolic acid contents. Catechin and six major barley PAs, including dimeric prodelphinidin B3 and procyandin B3, and four trimers were quantified. PAs were quantified as catechin equivalents (CE). The catechin content was higher in hulless (48−71 μg/g) than in hulled (32−37 μg/g) genotypes. The total PA content of abraded barley grains ranged from 169 to 395 μg CE/g in PA-containing hulled and hulless genotypes. Major PAs were prodelphinidin B3 (39−109 μg CE/g) and procyanidin B3 (40−99 μg CE/g). The contents of trimeric PAs including procyanidin C2 ranged from 53 to 151 μg CE/g. Discoloration of barley flour dough correlated with the catechin content of abraded grains (r = −0.932, P < 0.001), but not with the content of individual phenolic acids and PAs. Discoloration of barley flour dough was, however, intensified when total PA extracts and catechin or dimeric PA fractions were added into PA-free barley flour. The brightness of dough also decreased when the total PA extract or trimeric PA fraction was added into heat-treated PA-free barley flour. Despite its low concentration, catechin appears to exert the largest influence on the discoloration of barley flour dough among phenolic compounds. Keywords: Phenolic acids; proanthocyanidins; catechin; barley; discoloration