A series of experiments was conducted to determine the effect of pH on β-glucanase activity and to monitor the effect of passage through the stomach on the ability of enzymes to degrade β-glucans. In exp. 1, β-glucanase activity was determined in 10 commercially available enzyme products at 5 pH levels (2.5, 3.5, 4.5, 5.5 and 6.5) using a discontinuous assay. Little activity was evident at pH 2.5, and activity was only slightly increased at pH 3.5. The highest activity occurred at pH 4.5 and 5.5. Enzyme activity declined quickly at pH 6.5. Experiment 2 evaluated the capability of β-glucanase to recover activity after incubation at suboptimal pH levels. Five enzyme preparations were incubated at three pH levels (2.5, 3.5 and 4.5) for 15, 30, 60 or 120-min. The pH level was then increased to pH 5.5, which was the optimum pH for activity determined in exp. 1. All enzyme products were relatively stable at pH 4.5 and 5.5. Enzyme products treated at pH 3.5 started to lose activity and all enzyme products exhibited a deterioration effect when incubated at pH 2.5. However, all enzymes recovered some activity upon return to pH 5.5. Experiment 3 was designed to evaluate the amount of β-glucanase activity leaving the stomach of the pig. Six barrows cannulated with a simple T-cannulae located at the start of the duodenum were used in a 6 × 6 Latin square design experiment. The diets consisted of a control and five diets supplemented with the same enzymes used in exp. 2. The level of β-glucanase activity in the digesta from pigs fed any of the diets decreased over time as pH decreased. However, across all products, 52 and 26% of initial activity could still be detected 60 and 240 min after feeding. Experiment 4 was conducted to evaluate the effectiveness of the five enzyme sources in improving the performance of pigs fed hulless barley-based diets. Supplementation of hog growing-finishing rations with any of the enzyme products failed to significantly (P > 0.05) improve daily gain, feed intake or feed efficiency. The digestibility coefficients for dry matter, crude protein and energy showed a general trend towards improved digestibility with enzyme supplementation (P > 0.05) with Biofeed producing a significant increase. The overall results of these experiments indicate that although the low pH found in the stomach of the pig is detrimental to enzyme activity, some enzyme activity is retained in the small intestine of the pig. Therefore, the low gastric pH of the pig and its effects on enzyme activity cannot completely explain the lack of response of pigs to β-glucanase. Key words: β-glucanase, pH, pig, enzyme
Zn2+ depletion blocks endosome fusion
