ISO 6493:2000

Overview

ISO 6493:2000 specifies a laboratory polarimetric method for determination of starch content in animal feeding stuffs and raw materials for feed. The method measures the optical rotation of acid‑treated, solubilized starch and corrects for optical activity from ethanol‑soluble substances. It provides a standardized analytical procedure, required reagents and apparatus, calculation formulae and precision data to ensure reproducible starch content analysis for feed quality control.

Key topics and requirements

• Scope and limitations
  • Applicable to most animal feeding stuffs and raw materials; not suitable for materials containing other optically active substances insoluble in 40% ethanol (e.g., potato pulp, beet products, soya, lupine, inulin‑rich materials).
  • Not applicable for starches with amylose > 40% (e.g., some high‑amylose maize starches).
  • Heat/moisture treatments of samples can reduce measurable starch; caution is noted.
• Analytical principle
  • Acid decomposition and partial hydrolysis of a measured test portion, gelatinization by heating, clarification (Carrez reagents), measurement of optical rotation at 589.3 nm using a polarimeter (200 mm tube).
  • Correction for the optical rotation of ethanol‑soluble substances (separate extraction).
  • Calculation uses measured rotations and published specific optical rotations for different starch types (rice, potato, maize, wheat, etc.).
• Reagents and apparatus
  • Requires specified reagents (40% ethanol, HCl at defined concentrations, Carrez clarification solutions, saccharose standard) and equipment (analytical balance, pH‑meter, boiling water bath, polarimeter/saccharimeter).
• Quality and precision
  • The standard includes instructions on sample preparation (reference to ISO 6498), acid‑consumption compensation, calculation, and reporting.
  • Precision data from interlaboratory tests (repeatability and reproducibility limits) are provided for typical feed matrices.

Applications and users

• Who uses ISO 6493: feed testing laboratories, animal feed manufacturers, grain processors, regulatory agencies, and research institutes concerned with feed composition and nutritional labeling.
• Practical applications
  • Routine quality control of starch content in compound feeds, cereals and raw feed materials.
  • Verification of feed formulation and energy content estimates.
  • Regulatory compliance testing and interlaboratory method harmonization.

Related standards

• ISO 3310‑1 - test sieve requirements (sample grinding/sieving)
• ISO 3696 - water for laboratory use
• ISO 6498 - preparation of test samples for animal feeding stuffs
• ISO 6497 - recommended sampling methods (referenced)

Keywords: ISO 6493, starch determination, polarimetric method, animal feeding stuffs, feed testing, polarimeter, starch content analysis, feed quality control.