Stability and stabilization of potential feed additive enzymes in rumen fluid

Four commercial preparations of fibrolytic enzymes, from Irpex lacteus, Tri choderma viride, Aspergillus niger, and a mixture designed to be similar to the I. lacteus extract, were incubated in vitro with digesta taken from th e rumen of sheep receiving a grass hay/concentrate diet, and the survival o f major enzyme activities was measured. Some activities, including the beta -1,4-endoglucanase and xylanase from the extract derived from Aspergillus n iger, were stable for at least 6 h in rumen fluid. The same activities in t he other extracts also retained substantial activity for several hours. bet a-Glucosidase and beta-xylosidase activities were much more labile, most be ing almost completely destroyed after 1 h, and sodium dodecyl sulfate-polya crylamide gel electrophoresis indicated that most proteins in the extracts were digested extensively after up to 7 h of incubation. Adding bovine seru m albumin (0.5 g/l) to the incubation increased the half-life of Trichoderm a viride beta-glucosidase activity from less than 0.5 h to 3 h. Proteins ex tracted from plant materials, particularly the soybean 7S globulin fraction , also conferred protection from proteolytic breakdown, but none was as eff ective as bovine serum albumin. It was concluded that the stability of most fibrolytic enzymes in rumen fluid is not likely to be a limiting factor in the use of enzymes as feed additives for ruminants; but if the enzymes are not stable, means can be found for their stabilization. (C) 2000 Elsevier Science Inc. All rights reserved.