CHARACTERIZATION OF LIGNIN-CARBOHYDRATE COMPLEXES OF ITALIAN RYEGRASS AND ALFALFA

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Abstract
Lignin-carbohydrate complexes (LCC) were isolated from Italian ryegrass (Lolium multiflorum Lam.) and alfalfa (Medicago sativa L.) stems and their chemical and physical properties, and enzymatic degradation examined. The LCCs, soluble in water, were composed of guaiacyl-syringyl lignin and hemicellulosic carbohydrate mostly consisting of xylose, glucose and arabinose. Enzymatic hydrolysis of the LCCs produced water-insoluble materials which were markedly rich in lignin. In both plant species, the carbohydrate of the insoluble material had a high proportion of arabinose. The insoluble material of Italian ryegrass contained two to three times more xylose and arabinose than that of alfalfa. The Italian ryegrass LCC released significant amounts of p-coumaric and ferulic acids by alkaline and acid hydrolysis, but the alfalfa LCC did not, indicating a more complex structure of the cell wall matrix of Italian ryegrass. The ferulic acid in ryegrass lignin may be responsible for restricting enzymatic degradation of hemicellulose in ryegrass more than occurs in legumes.Key words: Lignin-carbohydrate complex, enzymatic hydrolysis, hemicellulose, ferulic acid, Italian ryegrass, alfalfa

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