Abstract of PhD Thesis

A study of selected enzymes for animal feed application

Angela Boyce (2006) - University of Limerick

The use of microbial-derived enzymes in animal feed is well established and has increased dramatically in the last decade.  While initial screening studies in this area focused on identifying microorganisms capable of producing large quantities of the enzyme of interest, emphasis has now shifted to identifying enzymes with physicochemical properties better suited to in-feed application.  This study focuses on the enzymes phytase and β-glucanase.  Phytase is added to animal feed mainly to improve phytate-phosphorus bioavailability and reduce phosphate pollution, while incorporation of endo-β-glucanase in poultry diets reduces the anti-nutritive effects of 1,3-1,4-β-glucan, a non-starch polysaccharide of the endosperm cell wall of cereals.

The relevant physicochemical properties of a number of commercial phytase and β-glucanase products were assessed in order to determine their suitability for use in animal feed.  Important parameters examined included enzyme thermal stability, the effect of temperature and pH on activity and in vitro stability under simulated upper monogastric digestive tract conditions.  It was evident that the products assessed were not ideally suited for in-feed application on the basis of their physicochemical properties.

Several microorganisms were screened for ability to produce phytase and endo-β-glucanase with the ultimate objective of identifying enzymes with physiochemical properties more suitable for use in animal feed.  Based on initial application-relevant assessment of the crude enzymes produced, a phytase produced by Mucor hiemalis Wehmer and an endo-1,3(4)-β-glucanase from Rhizomucor miehei (DSM 1330) were purified to apparent homogeneity and characterised in detail.  The endo-1,3(4)-β-glucanase was found to be of potential commercial interest as a feed additive, mainly by virtue of its thermal stability and stability under simulated avian upper digestive tract conditions, which exceeded that of the commercial products assessed.

A diafiltration-based assay method, suitable for determination of phytase activity when present in animal feed at normal industrial inclusion levels, was developed.  This sensitive and technically straightforward method overcomes the difficulties traditionally associated with in-feed phytase quantification, which is necessary for regulatory, quality control and research purposes.  Two assay methods, used to assess β-glucanases for animal feed application, were evaluated in terms of their suitability for this purpose.