Overview
ISO 21415-2:2015 specifies a laboratory mechanical method for determining wet gluten content and the gluten index in wheat flours (Triticum aestivum L. and Triticum durum Desf.). The standard applies directly to flours and to ground whole wheat when the particle-size distribution meets the normative requirement (Table B.1). The method isolates wet gluten by forming a paste with a sodium chloride solution, washing out starch and soluble components, then centrifuging and weighing the gluten. The gluten index is defined as the percentage of wet gluten remaining on a sieve after centrifugation.
Key topics and technical requirements
- Scope: Wet gluten and gluten index by mechanical extraction (automatic units).
- Sample size: Typical test uses 10 g sample (weighed to 0.01 g).
- Reagents: Sodium chloride solution (20 g/L) and Lugol’s iodine/potassium iodide for starch detection.
- Apparatus: Automatic gluten separation unit (e.g., Glutomatic-type), peristaltic pump, mixing/washing chamber, sieves (polyester 88 µm and polyamide 840 µm), centrifuge, balance (0.01 g).
- Centrifuge specifications: Device capable of ~6 000 rpm producing ~2 000 g (used for gluten index determination).
- Procedure highlights:
- Paste formation by controlled addition of NaCl solution (manufacturer suggestion ~4.8 ml, adjustable 4.2–5.2 ml).
- Continuous washing until starch-free (checked with iodine).
- Centrifugation and weighing of wet gluten; gluten index = % retained on sieve.
- Precision and reporting: The standard includes interlaboratory precision, repeatability and reproducibility information and requires reporting of the extraction technique since mechanical and manual methods (ISO 21415‑1) can give non-equivalent results.
- Granulometry requirement: Ground wheat must meet Table B.1 particle-size specifications for valid application.
Applications and users
- Quality control in flour mills and grain processors: Routine measurement of wet gluten and gluten strength for product specification and blending decisions.
- Bakeries and food manufacturers: Ingredient characterization to predict dough handling, baking performance and end-product quality.
- Analytical laboratories and feed testing labs: Official testing, research and method validation using standardized mechanical extraction.
- Breeding and agronomy research: Comparative evaluation of wheat lots (Triticum aestivum and durum) for protein functionality.
Keywords: ISO 21415-2:2015, wet gluten, gluten index, wheat flour testing, mechanical gluten determination, Glutomatic, sodium chloride solution, Lugol’s solution, gluten testing standard.
Related standards
Open preview (PDF)Wheat and wheat flour — Gluten content — Part 2: Determination of wet gluten and gluten index by mechanical means