Determination of phytase activity in feed by a colorimetric enzymatic method: collaborative interlaboratory study

Area of Science:

• Animal Nutrition
• Enzyme Assays
• Analytical Chemistry

Background:

• Microbial phytase is crucial for improving phosphorus utilization in animal feed.
• Accurate determination of phytase activity is essential for feed quality control and efficacy.
• Existing methods require validation for reliable and consistent results.

Purpose of the Study:

• To validate a colorimetric assay for determining microbial phytase activity in feed.
• To assess the performance of the assay through collaborative laboratory studies.
• To establish method performance characteristics according to AOAC guidelines.

Main Methods:

• Two collaborative studies (fyt9404 and fyt9410) involving multiple laboratories.
• Analysis of feed samples with known phytase activity levels (200-400 U/kg) in duplicate.
• Statistical analysis of repeatability relative standard deviation (RSDr) and reproducibility relative standard deviation (RSDR) following AOAC guidelines.

Main Results:

• Repeatability (RSDr) ranged from 2.5% to 8.6%, and reproducibility (RSDR) ranged from 14.0% to 27.6% across studies.
• Exclusion of invalid data from specific laboratories improved RSDr values in one study.
• No outliers were identified in study fyt9404, indicating consistent performance.

Conclusions:

• The validated colorimetric assay is suitable for determining microbial phytase activity in feed.
• The assay provides acceptable repeatability and reproducibility for routine analysis.
• The collaborative study confirmed the reliability of the method for feed industry applications.