Overview
ISO 3593:1981 specifies a standardized method for the determination of ash content in starch. This method involves the incineration of a starch test portion at a high temperature (900 °C) until all carbon is completely oxidized. It evaluates both natural mineral substances present in native starches and added mineral substances in modified starches, applicable to ash contents up to 2%. The standard excludes hydrolysis products, oxidized starches, and starches containing more than 0.2% chloride; for those, ISO 5809 is recommended.
This International Standard was developed by ISO Technical Committee ISO/TC 93 for starch and related products. It ensures reliable, repeatable, and internationally recognized results for the mineral residue remaining after starch combustion, supporting quality control and product characterization efforts in the starch industry.
Key Topics
- Scope and Applicability
- Applies to native and modified starches with ash ≤ 2%.
- Does not apply to hydrolysis products, oxidized starch, or high-chloride starches (>0.2%).
- Uses incineration at 900 ± 25 °C until carbon residue disappears.
- Apparatus Required
- Platinum or heat-resistant ashing dishes (approx. 40 ml capacity).
- Electric furnace with temperature control and ventilation.
- Desiccator with efficient desiccant to cool samples post-incineration.
- Analytical balance (precision to 0.0001 g).
- Standard laboratory utensils such as hot plates or burners.
- Test Procedure
- Clean and pre-heat the ashing dish to a constant weight.
- Weigh accurately 2 to 10 grams of starch sample (typically 5-10 g depending on starch type).
- Pre-incinerate the sample to carbonize it without loss by projection of material.
- Incinerate fully at 900 °C until residue is free of carbon (about 1 hour).
- Cool in desiccator and weigh to determine ash weight.
- Calculations and Reporting
- Ash content expressed as percentage by mass on both as-received and dry basis.
- Requires at least two replicate tests, reporting the average.
- Repeatability criteria defined: differences between duplicates must be ≤ 0.02% ash absolute for ≤ 1% ash content or ≤ 2% of mean for >1% ash.
- Complete test report includes sample identification, conditions, and method details.
Applications
ISO 3593:1981 is critical for industries and laboratories involved in:
- Quality control of native and modified starch products.
- Verification of mineral residue limits in starch-based food, pharmaceutical excipients, and industrial starches.
- Compliance with regulatory and customer requirements where ash content affects product usability or purity.
- Supporting research and development by providing accurate measurement of mineral content in starch derivatives.
- Process monitoring in starch production to identify and control added mineral substances or impurities.
The standard’s precision and repeatability enable consistent evaluation across global supply chains, helping stakeholders maintain quality and safety standards in starch-related products.
Related Standards
- ISO 5809 – Starch including derivatives and by-products – alternative ash determination method for products with chloride content over 0.2%.
- ISO 1666 – Starch – Determination of moisture content using oven drying, essential for converting ash results to dry basis.
- Other ISO standards from Technical Committee ISO/TC 93 related to starch derivative testing and characterization.
Understanding and applying ISO 3593:1981 supports conformity with international best practices for ash determination in starch, ensuring reliable data for product quality, regulatory compliance, and manufacturing efficiency.
