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Complex cell walls of barley hulls contain phenolic constituents — hydroxycinnamic acids, mainly ferulic acid (3-methoxy-4-hydroxy-cinnamic acid, FA) and para-coumaric acid (4-hydroxycinnamic acid, PCA). Ferulic acid is produced via the phenylpropanoid biosynthetic pathway and is covalently cross-linked to polysaccharides by ester bonds and to components of lignin mainly by ether bonds. Various studies have consistently indicated that FA is among the factors most inhibitory to the biodegradability of plant cell wall polysaccharides. PCA is also covalently linked to polysaccharides (minor) and lignin (major), but PCA does not form the inhibitory cross-linkages as FA does. It is considered to represent plant cell wall lignification. The objective of this study was to determine the genotypic variation and magnitude of difference in the concentration of the hydroxycinnamic acids in terms of FA and PCA as well as their ratios in barley hull and seeds in sixteen varieties of barley collected during three years. These data will be correlated to barley nutrient availability in future study. The barley varieties included CDC Cowboy, Valier, TR251, Newdale, RCSL97, KXN/TLN-147 (AU), WABAR2160 (AU), Harrington, CDC Copeland, CDC Kendall, AC Metcalfe, CDC Dolly, McLeod, CDC Bold, CDC Helgason and CDC Trey. The focus of this study was on ferulic acid because of its inhibitory effect on rumen degradation and digestion which are highly related to nutrient availability in animals. The results showed significant differences (P < 0.01) a mong the barley varieties in ferulic acid and p-coumaric acid and their ratio. Whole barley seed contained higher (P<0.05) ferulic acid concentration than p-coumaric acid, ranging from 509 to 679 μg/g DM for ferulic acid and 131 to 345 μg/g DM for p-coumaric acid. The ratios of ferulic acid to p-coumaric acid ranged from 1.8 to 3.9. The ferulic acid concentration in hull was higher (P < 0.05) than that in whole seed, ranging from 2,320 to 4,206 μg/g DM. Percentage of ferulic acid content in hull and dehulled seed ranged from 38 to 70% and 30 to 62%, respectively. Growth year affect affected the hydroxycinnamic acid profiles in barley seed and hull. In conclusion, there were large differences in the ferulic acid and para-coumaric acid among the barley varieties indicating genotypic variation. Harrington contained highest and Valier contained lowest FA in whole seed. Barley TR251 contained lowest % of FA content in the hull and highest % of FA content in the dehulled seed. Future study is needed to understand the relationship between the hydroxycinnamic acid profile in barley seeds and hull and nutrient utilization and availability of barley in animals.

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