A New Rapid and Quantitative Assay to Determine the Phytase Activity of Feed

The fortification of animal feed with enzymes in order to optimize feed utilization has become a standard for the meat production industry. A method for measuring levels of active enzymes that can be carried out quickly would ensure that feed has been supplemented with the appropriate amount of enzyme. Phytase is the most widely used feed enzyme and is routinely quantified with an activity assay in a limited number of specialized laboratories. As an alternative, we report here the development of a rapid and easy method to perform a quantitative assay for the phytase from Citrobacter braakii. The method is suitable for use at local sites with a minimum lab setup and will reduce delays and potential interferences due to improper sample storage and shipment. The new assay is based on a lateral flow immunoassay that utilizes magnetic immune-chromatographic test (MICT) technology to quantify the phytase content of a feed extract. After extraction of the phytase from the feed, the sample is simply diluted and added to a reaction tube containing a specific anti-phytase antibody coupled to superparamagnetic particles. The mixture is then applied on an assay cassette, where the formed particle-antibody-phytase complexes are captured by immobilized antibodies on a nitro-cellulose strip housed in a cassette. The cassette is placed in the MICT reader that measures the magnetic signal of the captured particles. Using the calibration information stored in the cassette barcode, the signal is converted to a phytase concentration, given as phytase activity (FYT) per kilogram of feed. The accuracy and robustness of the assay compared to the ISO phytase activity assay were demonstrated through a large validation study including real feed samples from different compositions and origins. The MICT assay is the first quantitative assay for feed enzymes that is fast, reliable, and simple to use outside of a specialized reference laboratory and that is suitable for use in place of the current ISO assay.