In vitro stability of a β-glucanase preparation from Trichoderma longibrachiatum and its effect in a barley based diet fed to broiler chicks

A feeding experiment and a series of in vitro incubations in conditions simulating those of the gastrointestinal tract were carried out to evaluate the efficacy of a liquid, crude β-glucanase preparation from Trichoderma longibrachiatum for use as feed supplement in poultry barley based diets. Addition of the β-glucanase preparation at a level of 0.129 g kg−1 to a barley based mash diet significantly (P < 0.05) improved feed consumption, weight gain and feed:gain ratio. Viscosity of the small intestinal content was reduced significantly (P < 0.05) when β-glucanase was added. For in vitro evaluation the β-glucanase preparation was incubated at low, neutral and high pH, with or without proteolytic enzymes (pepsin and pancreatin). Before the β-glucanase determination pH was restored to 5. At pH 2 in glycine-HCl buffer, β-glucanase retained 20% of original activity at 15 min, and was almost inactivated at 45 min. At pH 3.2 β-glucanase was essentially stable, its relative activity decreasing to 90% only at 90 min. Similar results were obtained with added pepsin (4000 U ml−1), suggesting that the β-glucanase preparation was resistant to proteolysis by pepsin. When β-glucanase preparation was incubated at pH 8.5 (0.1 M NaHCO3HCl buffer) β-glucanase activity decreased progressively, with only 30% of activity remaining at 90 min. Incubation at pH 7 (0.1 M phosphate buffer) did not affect the activity of β-glucanase; however, when pancreatin (2 mg ml−1 pancreatin 8 USP) was added β-glucanase activity was reduced to 50% in 15 min, and at pH 8.5 was almost completely inactivated. To determine thermal stability, β-glucanase was incubated at various temperatures at pH 5 (0.1 M sodium acetate buffer) for 10 min. At 70°C activity was reduced to 65%, at 80°C to 20%, and at 100°C it was almost totally inactivated. These results suggest that supplementary enzymes survive the potential hazards of the gastrointestinal tract in sufficient quantity to improve performance in broiler chicks fed barley based diets.