AGRICULTURAL MATERIALS Determination of Phytase Activity in Feed: Interlaboratory Study GISELE GIZZI European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium PETER THYREGOD FEFANA Asbl (European Union Feed Additives and Premixtures Association Manufacturers), Ave Louise 120, Box 13, B-1050 Brussels, Belgium; Novozymes A/S, Krogshoejvej 36, DK-2880 Bagsvaerd, Denmark CHRISTOPH VON HOLST 1 European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium GERARD BERTIN FEFANA Asbl, Ave Louise 120, Box 13, B-1050 Brussels, Belgium; Alltech EU Regulatory Dept, 14 Place Marie-Jeanne Bassot, 92300 Levallois-Perret, France KURT VOGEL FEFANA Asbl, Ave Louise 120, Box 13, B-1050 Brussels, Belgium; DSM Nutritional Products Ltd, PO Box 3255, 4002 Basel, Switzerland MAI FAURSCHOU-ISAKSEN FEFANAAsbl, Ave Louise 120, Box 13, B-1050 Brussels, Belgium; Danisco A/S, Enzyme R&D, Edwin Rahrs Vej 38 DK-8220 Brabrand, Denmark ROLAND BETZ FEFANA Asbl, Ave Louise 120, Box 13, B-1050 Brussels, Belgium; BASF Aktiengesellschaft, GKA/O- E210, 67056 Ludwigshafen, Germany RICHARD MURPHY FEFANA Asbl, Ave Louise 120, Box 13, B-1050 Brussels, Belgium; Alltech Bioscience Centre, Sarney, Summerhill Rd, Dunboyne, County Meath, Ireland BETINA BRANDT ANDERSEN FEFANA Asbl, Ave Louise 120, Box 13, B-1050 Brussels, Belgium; Novozymes A/S, Krogshoejvej 36, DK-2880 Bagsvaerd, Denmark An interlaboratory study was conducted to determine the performance characteristics of a new method for the determination of phytase activity in feed samples. The method is based on the principle that inorganic phosphate is released from the substrate phytate under defined assay conditions and has been validated for its suitability to measure the enzyme activity of various phytase products. Two different experimental designs of the study were applied, allowing for the estimation of the precision of the method under repeatability, intermediate precision and reproducibility conditions, respectively. The relative standard deviation for repeatability (RSD r ) ranged from 2.2 to 10.6% and the RSD for reproducibility (RSD R ) ranged from 5.4 to 15%. The suitability of the validated method for the intended purpose was demonstrated. The obtained performance profile of the method validated in this study was comparable to that of similar methods that were exclusively validated for one phytase product. P hytases are widely used as feed additives for monogastric animals. These enzymes can release inorganic phosphate from phytate (myo-inisitol hexakisphosphate), the major storage form of phosphorus in many plants (1). Monogastric animals lack an active phytase and therefore cannot use the phosphorus from phytic acid. Feed supplementation with phytase increases the availability of phophorus from phytate in the feed and thereby reduces the environmental pollution due to excess phosphate excretion. In addition, phytase also increases the feed value, because phytate can act as an antinutrient factor in animal feed by chelating minerals such as calcium. For analytical reasons, the phytase content in feed is determined via the phytase activity and expressed as units (U)/kg feed. The analytical method is based on the principle that phytases release inorganic phosphate from the GIZZI ET AL.:JOURNAL OF AOAC INTERNATIONAL VOL. 91, NO. 2, 2008 259 Received October 8, 2007. Accepted by EB December 11, 2007. 1 Author to whom correspondence should be addressed; e-mail: christoph.von-holst@ec.europa.eu Downloaded from https://academic.oup.com/jaoac/article/91/2/259/5656042 by guest on 17 August 2023