ISO 25136:2026

• Abstract:

  This document specifies a spectrophotometric method for the determination of the hydroxypropyl group content of modified starches.

• Status: Published
• Publication Date: 16-Aug-2026
• ICS: 67.180.20 - Starch and derived products
• Technical Committee: ISO/TC 93 - Starch (including derivatives and by-products)
• Drafting Committee: ISO/TC 93/WG 9 - Modified starches
• Current Stage: 6060 - International Standard published
• Start Date: 17-Aug-2026
• Due Date: 19-Jun-2027
• Completion Date: 17-Aug-2026

Overview

ISO 25136:2026 specifies a standardized spectrophotometric method for determining hydroxypropyl content in modified starches. Developed by the International Organization for Standardization (ISO), this standard provides guidance on accurate, repeatable, and internationally recognized analytical procedures, supporting quality control and product specification in the starch industry. Determining hydroxypropyl content is vital for verifying the modification degree of starches used in a wide range of food, pharmaceutical, and industrial applications.

Key Topics

• Hydroxypropyl Content Determination
  The standard outlines a precise methodology for quantifying the hydroxypropyl groups in modified starch samples. The measured hydroxypropyl content is expressed as a percentage of the sample’s mass.

• Spectrophotometric Method
  Using a spectrophotometer, the hydroxypropyl groups are detected after chemical reaction and color development, with absorbance measured at 590 nm. This approach ensures reliable and sensitive detection.

• Reagents and Equipment
  The standard details the necessary laboratory-grade reagents such as concentrated sulfuric acid, sodium bisulfite, ninhydrin, and 1,2-propanediol, as well as the required analytical apparatus (e.g., pipettes conforming to ISO 648, spectrophotometer, balance).

• Sample Preparation and Procedure
  Guidance is provided for sample homogenization, extraction, and the stepwise analytical protocol to ensure consistent and reproducible results.

• Precision and Quality Assurance
  The standard discusses the method’s repeatability and reproducibility, validated through interlaboratory testing, and specifies procedures for blank tests and quality control documentation.

Applications

Implementing ISO 25136:2026 offers significant practical value across several industries:

• Food Industry
  Used in quality control laboratories of food manufacturers to ensure compliance with regulatory requirements concerning food additives and modified starch content.
• Pharmaceuticals
  Valuable for verifying starch derivatives used in drug formulation, ensuring the consistency of excipients.
• Industrial Starches
  Applied in non-food sectors-such as paper, textiles, and adhesives-where the functional properties of modified starch depend on the degree of substitution.

By standardizing hydroxypropyl content determination, manufacturers and laboratories can:

• Ensure Product Consistency
  By adhering to a harmonized testing protocol, stakeholders can achieve reliable batch-to-batch quality.
• Facilitate Trade and Compliance
  Documented analytical accuracy supports product certification, regulatory approval, and international trade.
• Optimize Process Control
  Accurate measurement allows precise adjustments during starch modification processes.

Related Standards

Adherence to ISO 25136:2026 is supported by reference to several related standards and guidelines:

• ISO 3696: Water for analytical laboratory use – specification and test methods
• ISO 648: Laboratory glassware – single-volume pipettes
• ISO 1666: Starch – determination of moisture content – oven-drying method
• CAC/GL 50-2004: General Guidelines on Sampling
• ISO 5725-1 & ISO 5725-2: Accuracy (trueness and precision) of measurement methods and results

These references ensure robust, internationally aligned laboratory practices in both sample handling and measurement accuracy.

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By following ISO 25136:2026, organizations benefit from a reliable, evidence-based method for hydroxypropyl starch analysis, advancing quality assurance, regulatory compliance, and global market access. For laboratories and manufacturers, this standard is essential for the efficient and credible assessment of modified starch products.

International
Standard
ISO 25136
First edition
Modified starch — Determination
2026-08
of hydroxypropyl content —
Spectrophotometric method
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 Spectrophotometric method for hydroxypropyl content .1
5 Reagents . 1
6 Apparatus . 2
7 Sampling . 3
8 Preparation of test sample . 3
9 Procedure . 3
9.1 Preparation of the calibration graph .3
9.2 Test portion .3
9.3 Preparation of the test solution .3
9.4 Determination .4
9.5 Blank test .4
9.6 Moisture content .4
9.7 Number of determinations .4
10 Calculation and expression of results . 5
11 Precision . 5
11.1 Interlaboratory test . .5
11.2 Repeatability .5
11.3 Reproducibility .5
11.4 Repeatability and Reproducibility .5
12 Test report . 6
Annex A (informative) Precision of the method.7
Bibliography .8

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 93, Starch (including derivatives and by-
products).
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
International Standard ISO 25136:2026(en)
Modified starch — Determination of hydroxypropyl content
— Spectrophotometric method
1 Scope
This document specifies a spectrophotometric method for the determination of the hydroxypropyl group
content of modified starches.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1666, Starch — Determination of moisture content — Oven-drying method
3 Terms and definitions
The following terms and definitions apply to this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
hydroxypropyl content
mass of hydroxypropyl groups divided by the mass of the test portion of hydroxypropylated starch, which
represents the proportion or concentration of hydroxypropyl groups within the starch sample
Note 1 to entry: It is expressed as a fraction or percentage of the total mass of the sample.
4 Principle
4.1 Spectrophotometric method for hydroxypropyl content
In concentrated sulfuric acid, the hydroxypropyl group in modified starches is oxidized to produce propylene
glycol, which is subsequently dehydrated to yield propionaldehyde and propenol. In this acidic medium,
propionaldehyde and propenol react with ninhydrin to form purple-colored complex. The hydroxypropyl
conte
...