Quantitative Measurement of Fiber Fractions of Cool- and Warm-Season Grass Herbage Using Cell-Wall-Degrading Enzymes

Quantitative in vitro methods using commercial cellulase (CEL), pectinase (PECT), and hemicellulase (HCEL) preparations were developed to simplify prediction of digestibility of cool- and warm-season forage grasses. Samples of orchardgrass (Dactylis glomerata L. var. Pennlate), tall fescue (Festuca arundinacea Schreb. var. KY 31) (cool-season grasses), big bluestem (Andropogon gerardi Vitman var. NY 1145), and switchgrass (Panicum virgatum L. var. KY 1625) (warm-season grasses) were taken at advancing stages of maturity. Isolated cell-wall material (CWM) was prepared by repetitively extracting lyophilized, ground tissue with aqueous and organic solvents. Relative solubilities of CWM digested individually with CEL, HCEL, or PECT were 100:30:40, respectively. When enzyme preparations were used sequentially, the influence of CEL, HCEL, and PECT on CWM solubility depended on the order in which the enzyme preparations occurred in the sequence. The fraction of CWM solubilized with CEL was similar to that obtained when CWM was digested with CEL, HCEL, and PECT simultaneously. Solubilities of cell-wall material in unfractionated tissues digested with CEL were comparable to those of corresponding CWM digested with CEL; thus, the laborious steps required for isolation of cell-wall material can be avoided. Keywords: Cool-season grass; warm-season grass; orchardgrass; Dactylis glomerata L.; tall fescue; Festuca arundinacea Schreb.; big bluestem; Andropogon gerardi Vitman; switchgrass; Panicum virgatum L.; fiber; digestibility; cell-wall-degrading enzymes; cellulase; pectinase; hemicellulase