Hydrolysis of Plant Mannans by Rumen Protozoal Enzvmes

Abstract

Mannans or heteromannans (gluco-or galactoglucomannans) are commonly considered to be present in plants only in wood or associated with seeds. The present authors (Gaillard and Bailey 1968) have, however, recently isolated from the leaves and stems of red clover (Trifolium pratense) a polysaccharide fraction giving on hydrolysis galactose, glucose, mannose, and xylose (approximate ratios 1: 4·0: 2·0: 1·3), and which may, therefore, contain a mannan or heteromannan. This polysaccharide is designated "clover mannan" in the present work. Although apparently absent from grasses, such mannans may be common as minor constituents of pasture legume leaves and stems; for example, 1-2% of polymer mannose was reported present in lucerne (Hirst, MacKenzie, and Wylam 1959). Ivory nut (Phytelephas macrocarpa) mannan has been reported to be digested by ruminants (Beals and Lindsey 1916) and these pasture-plant mannans are probably also digested, presumably after hydrolysis by mannanases secreted by the rumen microflora. The only study of the action of rumen microorganisms on plant mannans appears to be that of Williams and Doetsch (1960), who isolated from the rumens of cows fed guaran (soluble galactomannan) several bacteria which could grow on this poly-saccharide and which secreted extracellular mannanase.