Overview
EN ISO 11213:1995 - "Modified starch - Determination of acetyl content - Enzymatic method" describes a validated laboratory procedure for quantifying acetyl content in modified starch (both granular and cold‑water soluble). The method measures total and free acetate; bound acetyl is obtained by subtraction. It is suitable for acetyl contents up to 2% (m/m) and uses enzymatic conversion to generate NADH, measured spectrophotometrically at 340 nm.
Key topics and technical requirements
- Scope: Applies to modified starch and starch derivatives (granular or cold‑water soluble).
- Principle: Hydrolyse acetyl groups with dilute HCl to release acetate; convert acetate to acetyl‑CoA using adenosine‑5'‑triphosphate (ATP) and coenzyme A (CoA) in the presence of acetyl‑CoA synthetase (ACS). Subsequent enzyme reactions (malate dehydrogenase, citrate synthase) produce NADH; increase in absorbance at 340 nm is proportional to acetate concentration.
- Free vs. total acetyl: Free acetate is determined from an aqueous extract/filtrate of dispersed starch. Total acetyl requires acidic hydrolysis and solubilization prior to enzymatic assay. Bound acetyl = total − free.
- Analytical conditions: Typical temperature control (20–25 °C), cuvette path length 10 mm, molar absorption coefficient of NADH at 340 nm (6.30 L·mmol−1·cm−1).
- Sample prep: Sieve (800 µm), grind if necessary, homogenize; correct results for moisture.
- Reagents and apparatus: Analytical‑grade reagents, MDH/CS and ACS enzyme preparations, ATP/CoA/NAD reagent mix, spectrophotometer at 340 nm, boiling water bath for hydrolysis.
- Performance/precision: Method precision established by interlaboratory study; repeatability and reproducibility criteria are specified (repeatability: within 5% of higher result; reproducibility: within 8% of higher result). Refer to Annex B for statistical details.
Applications and users
- Quality control in starch manufacturing and food ingredient production
- Product specification testing for acetylated starches used in food, feed, paper, and pharmaceutical formulations
- R&D and process validation where acetylation level affects functionality (e.g., thickening, stability, film properties)
- Regulatory and certification laboratories validating conformity to product standards
Related standards
- ISO 3696 - Water for analytical laboratory use
- ISO 1666 - Starch - Determination of moisture content
- ISO 5725 - Precision of measurement methods and results
Keywords: EN ISO 11213:1995, modified starch, acetyl content, enzymatic method, acetyl measurement, acetyl‑CoA synthetase, NADH 340 nm, bound acetyl, free acetate.