Assessment of fibrolytic activities of 18 commercial enzyme products and their abilities to degrade the cell wall fraction of corn stalks in in vitro enzymatic and ruminal batch cultures

Fibrolytic activity distributions of 18 enzyme products, mostly obtained in China, were examined in terms of protein concentration and fibrolytic activities on model substrates. The hydrolytic capacities were determined by an in vitro ruminal degradation assessment and the enzymatic release of reducing sugars or ferulic acid from neutral detergent fibre fractions of corn stalks (NDFcs). Most enzyme products were characterized by xylanase, carboxymethyl cellulase (CMCase) and β-glucanase (EG), which had the potential to improve in vitro dry matter disappearance of NDFcs after a 16-h enzymatic pre-treatment followed by a 24-h ruminal degradation using a batch culture method (P<0.05). Quadratic effects of xylanase, CMCase, EG and ferulic acid esterase (FAE) occurred on the release of reducing sugars or ferulic acid from NDFcs (P<0.05). The effective fibrolytic activity combinations required to reach the highest release of reducing sugars were 418-1385U xylanase, 111-567U CMCase, 347-376U EG and 2.0U FAE per g NDFcs substrate. The addition of an enzyme product with a dominant FAE activity did not alter the total volatile fatty acid production at a low dose level of 1.0mg/g or 4140U/g substrate of corn stalks after a 48-h in vitro batch culture. However, a lower ratio of non-glucogenic to glucogenic acids occurred in the fermentation of corn stalks with inclusion of the FAE dominated enzyme product (P<0.05). These results suggest that all enzyme products in China were characterized or blended with enzyme extracts with xylanase, CMCase and EG. The rational combination of enzyme products necessary to reach a specific FAE activity with a specific fibrous forage, together with xylanase, CMCase and EG activities, should be considered in the design of a compound enzyme product for enhancing the cell wall degradation of fibrous crop residues, based on scientific understanding of the mode of enzymatic actions in the rumen.