Cereal Chem 60:255 - 259. | VIEW
Sorghum Phenolic Acids, Their High Performance Liquid Chromatography Separation and Their Relation to Fungal Resistance.
D. H. Hahn, J. M. Faubion, and L. W. Rooney. Copyright 1983 by the American Association of Cereal Chemists, Inc.
A high performance liquid chromatographic (HPLC) method was developed for the separation and identification of substituted benzoic and cinnamic acids (phenolic acids) of Sorghum bicolor (L.) Moench. Eight phenolic acids were identified in sorghum extracts. In order of decreasing polarity they were: gallic, protocatechuic, p-hydroxybenzoic, vanillic, caffeic, p-coumaric, ferulic, and cinnamic acids. In addition to these eight compounds, 12 other peaks were separated from the grain extracts, but these have not been identified. Protocatechuic, p-hydroxybenzoic, caffeic, p-coumaric, and ferulic acids were found in the free form in all seven sorghum varieties with means of 8.9, 5.9, 6.4, 37.6, and 34.7 micrograms/g, respectively. Protocatechuic, p-hydroxybenzoic, caffeic, p-coumaric, and ferulic acids were also found in the bound form in all seven sorghum varieties with means of 82.0, 18.3, 30.8, 82.1, and 163.2 micrograms/g, respectively. Gallic acid was found only in the bound form with a mean of 23.6 micrograms/g. Vanillic acid was found in six varieties in the free form with a mean of 31.8 micrograms/g and in four varieties in the bound form with a mean of 38.4 micrograms/g. Cinnamic acid was found in four varieties in the free form with a mean 6.7 micrograms/g. Cinnamic acid was found in the bound form in only one variety at a concentration of 19.7 micrograms/g. Free phenolic acids were extracted from ground sorghum by shaking in methanol. The crude extracts were cleaned up before chromatography by passage through C18 Sep-Pak cartridges (Waters Associates). Bound phenolic acids were released from the residue of the free phenolic acid extraction by hydrolysis in 2N HCl. The phenolic acids were removed from the hydrolysate by an ethyl acetate partition. Mean recoveries for the extraction of free and bound phenolic acids were 94.4 and 72.1%, respectively. Sorghum grain resistant to fungal attack contained both a greater variety and larger amounts of the identified phenolic acids and unknown compounds than did susceptible varieties. Resistant sorghums also had a greater pecentage of their total, identified phenolic acids in the free form. However, resistance to fungal attack could not be attributed solely to phenolic acid content or profile. Tannin content and physical characteristics of the grain also contribute to fungal resistance.