Comparative studies on the in vitro properties of phytases from various microbial origins

The physical and chemical properties of six crude phytase preparations were compared. Four of these enzymes (Aspergillus A, Aspergillus R, Peniophora and Aspergillus T) were produced at commercial scale for the use as feed ad ditives while the other two (E. coli and Bacillus) were produced at laborat ory scale. The encoding genes of the enzymes were from different microbial origins (4 of fungal origin and 2 of bacterial origin, i.e., E. coli and Ba cillus phytases). One of the fungal phytases (Aspergillus R) was expressed in transgenic rape. The enzymes were studied for their pH behaviour, temper ature optimum and stability and resistance to protease inactivation. The ph ytases were found to exhibit different properties depending on source of th e phytase gene and the production organism. The pH profiles of the enzymes showed that the fungal phytases had their pH optima ranging from 4.5 to 5.5 . The bacterial E. coli phytase had also its pH optimum in the acidic range at pH 4.5 while the pH optimum for the Bacillus enzyme was identified at p H 7.0. Temperature optima were at 50 and 60 degreesC for the fungal and bac terial phytases, respectively. The Bacillus phytase was more thermostable i n aqueous solutions than all other enzymes. In pelleting experiments perfor med at 60, 70 and 80 degreesC in the conditioner, Aspergillus A, Peniophora (measurement at pH 5.5) and E. coli phytases were more heat stable compare d to other enzymes (Bacillus enzyme was not included). At a temperature of 70 degreesC in the conditioner, these enzymes maintained a residual activit y of approximately 70% after pelleting compared to approximately 30% determ ined for the other enzymes. Incubation of enzyme preparations with porcine proteases revealed that only E. coli phytase was insensitive against pepsin and pancreatin. Incubation of the enzymes in digesta supernatants from var ious segments of the digestive tract of hens revealed that digesta from sto mach inactivated the enzymes most efficiently except E. coil phytase which had a residual activity of 93% after 60 min incubation at 40 degreesC. It c an be concluded that phytases of various microbial origins behave different ly with respect to their in vitro properties which could be of importance f or future developments of phytase preparations. Especially bacterial phytas es contain properties like high temperature stability (Bacillus phytase) an d high proteolytic stability (E. coli phytase) which make them favourable f or future applications as feed additives.