Physicochemical characteristics, hydroxycinnamic acids (ferulic acid, P-coumaric acid) and their ratio, and in situ biodegradability: comparison of genotypic differences among six barley varieties.
Barley contains hydroxycinnamic acids, mainly ferulic acid (FA; 3-methoxy-4-hydroxycinnamic acid) and p-coumaric acid (PCA; 4-hydroxycinnamic acid). Ferulic acid is produced via the phenylpropanoid biosynthetic pathway and 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 cell wall polysaccharides. p-Coumaric acid is also covalently linked to polysaccharides (minor) and lignin (major), but does not form the inhibitory cross-linkages as FA does and is considered to represent cell wall lignification. The objectives in this study were to (1) determine genotypic differences in physicochemical characteristics in terms of (a) two major low molecular weight hydroxycinnamic acid profiles (FA, PCA, PCA-to-FA ratio, which are associated with digestion and lignification), (b) particle size distributions (mean, median), (c) hull content, and (d) digestion-resistant fiber fractions and (2) determine genotypic differences in in situ solubilization kinetics of FA and PCA. The barley varieties grown during three consecutive years (2003, 2004, and 2005) included AC Metcalfe, CDC Dolly, McLeod, CDC Helgason, CDC Trey, and CDC Cowboy. These barleys were grown at the Kernen Crop Research Farm (KCRF, University of Saskatchewan) and managed using standard agronomic production practices. Results showed that there were significant differences in hull content (P < 0.05) among the barley varieties, with Mcleod having the highest (11% DM) and CDC Dolly and CDC Helgason the lowest hull content (9% DM). Ferulic acid ranged from 555 to 663 microg/g of DM (P < 0.05). p-Coumaric acid ranged (P < 0.05) from 283 to 345 microg/g of DM. PCA-to-FA ratios ranged (P < 0.05) from 0.49 to 0.56. Mean particle size ranged (P < 0.05) from 3.06 to 3.66 mm, and median particle size ranged (P < 0.05) from 2.71 to 3.04 mm. In situ DM degradability ranged from 44 to 49%. In situ solubilized FA fractions ranged (P < 0.05) from 60 to 72% and of PCA ranged (P < 0.05) from 71 to 81%. In conclusion, CDC Dolly was best and McLeod barley was poorest as feed barley in terms of hull and FA contents. There were significant genotypic differences in FA, PCA and their ratio, hull content, particle size distribution, and in situ solubilization of FA and PCA among the barley varieties.