Overview
ISO 4134:2021 - Meat and meat products - Determination of L-(+)-glutamic acid content - Reference method - defines laboratory reference procedures for measuring free L-(+)-glutamic acid (glutamate) in meat and meat products (including livestock and poultry). The standard specifies two validated assay routes: the spectrophotometer method and the light absorption microplate reader method. Both rely on enzymatic conversion of L-(+)-glutamic acid (glutamate dehydrogenase and NAD) and a colorimetric formazan end‑point measured at 490 nm.
Key topics and requirements
- Scope and applicability: Free L-(+)-glutamic acid in fresh and processed meat and poultry products.
- Principle: Extraction of free glutamic acid with perchloric acid, pH adjustment (to alkaline), enzymatic reduction of NAD by glutamate dehydrogenase, NADH-driven reduction of iodonitrotetrazolium chloride via diaphorase to form a formazan dye measured at 490 nm.
- Two validated methods:
- Spectrophotometer method (detailed reagents, apparatus, extraction and measurement steps).
- Light absorption microplate reader method (higher throughput option using microplates).
- Reagents and conditions: Includes dilute perchloric acid extraction (c = 1.0 mol/L), triethanolamine phosphate buffer (pH 8.6), KOH solutions for neutralization, and defined enzyme/NAD mixtures.
- Analytical performance: Includes instructions for calibration (standard curves and linear regression), calculation of L-(+)-glutamic acid concentration, and documented precision metrics - repeatability, reproducibility, interlaboratory test results and detection limit.
- Sampling & sample prep: Sampling is not prescriptive but recommends representative sampling (see CAC/GL 50-2004), homogenization, temperature control and storage instructions to avoid composition changes.
- Reporting and safety: Specifies minimum reporting content for test reports and includes an informative annex on safety practices when handling strong acids and reagents.
Applications
- Quality control in meat processing (flavour profiling, glutamate content monitoring).
- Regulatory and compliance testing where free glutamate must be quantified.
- Food research and product development investigating umami contributors or ingredient effects.
- High-throughput laboratories can adopt the microplate reader method for increased sample throughput while maintaining reference-method traceability.
Who should use this standard
- Food testing laboratories, meat processors, regulatory agencies, contract testing providers, and researchers requiring a validated reference method for quantifying free L-(+)-glutamic acid in meat and poultry products.
Related standards
Normative references cited include ISO 648, ISO 1042, ISO 1442 (moisture reference), ISO 3696 (water for analytical use) and ISO 8655‑2 (piston pipettes). These support laboratory equipment, sampling and quality controls referenced in ISO 4134:2021.
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