Overview
ISO 13904:2016 - "Animal feeding stuffs - Determination of tryptophan content" specifies a validated laboratory method for measuring total and free tryptophan in animal feeds (complete feeds, complementary feeds, raw materials, ingredients, concentrates) and for determining free tryptophan in commercial pure substances and premixtures containing >2% tryptophan. The standard describes sample preparation, alkaline hydrolysis for total Trp, mild-acid extraction for free Trp, and quantification by reversed-phase HPLC with fluorescence detection. It does not distinguish between D- and L-tryptophan.
Key topics and technical requirements
- Scope and applicability: Feeding stuffs, raw materials, concentrates, and high‑purity products/premixtures (>2% Trp).
- Sample preparation: Grinding to specified particle sizes (e.g., 0.5 mm for feeds; 0.25 mm for pure products); drying or defatting when required.
- Total tryptophan: Alkaline hydrolysis with saturated barium hydroxide, heated at 110 °C for 20 h, followed by addition of an internal standard.
- Free tryptophan: Extracted under mild acidic conditions (HCl) with an internal standard (α‑methyltryptophan). For high‑purity products the internal standard may be added after extraction.
- Chromatography and detection: Reversed‑phase C18 HPLC column (example 125 × 4 mm, 3 µm) with fluorescence detection. Mobile phase formulations and stability checks are specified; an alternative phosphate/methanol mobile phase is noted in Annex B.
- Standards and controls: Use of high‑purity tryptophan and control substances (≥99%); calibration and control checks (recovery 99–101% for control solution).
- Quality parameters: Procedures for calculation, repeatability, reproducibility and interlaboratory precision are provided.
Applications and practical value
- Feed quality control: Ensures accurate specification of tryptophan content for nutritional labeling and formulation.
- Ingredient certification: Verifies tryptophan levels in raw materials and premixtures for suppliers and integrators.
- Regulatory compliance: Supports laboratories performing official analyses for trade and safety.
- Research and formulation: Useful in nutrition research, feed formulation optimization, and amino‑acid balance studies.
Who uses ISO 13904: feed testing laboratories, feed manufacturers, ingredient suppliers, quality assurance teams, and regulatory/academic laboratories performing amino‑acid analysis.
Related standards
- Developed by ISO/TC 34/SC 10 (animal feeding stuffs). For broader context, consult other ISO methods on amino‑acid analysis and animal feeding stuffs produced by the same technical committee.
Keywords: ISO 13904:2016, tryptophan determination, animal feeding stuffs, HPLC fluorescence, total and free tryptophan, alkaline hydrolysis, feed analysis, quality control.
