Screening of phytase-producing molds and partial characterization of phytase for feed application

Optimization of fermentation conditions using 3 percent corn meal was done by batch process. The effect of varying initial concentrations of glucose was studied. The medium with 1.5-2.0 percent (w/v) glucose gave the highest enzyme activity. Glucose concentrations higher than 2 percent favored biomass production more than phytase production. There was no significant increase in the activity of phytase as the concentration of sodium nitrate was increased from 0.5 percent to 2 percent. However, the medium with 0.5 percent sodium nitrate was considered optimum because it had the highest specific enzyme productivity. Aeration had a beneficial effect on phytase production up to a certain point when enzyme production was not suppressed in favor of biomass production. Initial pH values of the medium higher than pH 7 tended to retard the growth of the inoculum and consequently gave low phytase yield. Initial pH value of 6.0 was found optimum for phytase formation. Monitoring of fermentation revealed that growth reached its peak after four days and declined thereafter. Phytase formation began on the seventh day, even after the mold had stopped growing. This may suggest release of intracellularly confined phytase. The pH of the medium decreased from pH 5 tp pH 3 at the end of fermentation. The crude phytase enzyme produced was active at 30-60 deg C and its activity was optimum at 55 deg C. The enzyme was stable at 45 deg C for three hours but lost its activity considerably after preincubation at a temperature higher than 60 deg C. It was active at pH 2.5-5.5 with pH optimum at 5.0-5.5. It was stable at pH 2.5-5.5 for 30 minutes at 45 deg C. The crude phytase can be stored at refrigeration or freezing temperature for 33 days without significant loss in its activity. Evaluation of the effect of the crude phytase on the nutritional value of the feeds through digestion trial on broilers showed an increase in the digestibility of phosphorus and calcium by 30 percent. These characteristics of the crude phytase indicate its applicability in reducing phosphorus excretion, in formulating environmentally friendly diets, and in reducing mineral phosphorus supplements by releasing phytin-bound minerals in the feeds prior to or during digestion in the gastro-intestinal tract of monogastric animals