Overview
ISO 6092:1980 is an internationally recognized standard published by the International Organization for Standardization (ISO) that specifies the routine method for determining the titratable acidity in all types of dried milk. This method is essential in the dairy industry for quality control and product consistency, focusing on assessing the acidity which impacts flavor, shelf life, and safety of dried milk products.
The standard outlines a procedure based on the reconstitution of dried milk with water followed by titration using sodium hydroxide, with phenolphthalein as the indicator and cobalt(II) sulphate as a reference color solution. The measurement expresses acidity in terms of millilitres of sodium hydroxide needed to neutralize 10 grams of solids-not-fat.
Key Topics
- Scope & Application: Applies to all types of dried milk, including instant and non-instant varieties. It is a routine chemical analysis method used worldwide.
- Principle: Dried milk is reconstituted with water, and the titratable acidity is measured by volumetric titration using 0.1 mol/L sodium hydroxide solution and phenolphthalein as the indicator.
- Reagents:
- Sodium hydroxide solution (0.1 mol/L, accurately standardized)
- Phenolphthalein solution as the pH indicator
- Cobalt(II) sulphate heptahydrate solution for color reference
- Apparatus Required: Analytical balance, burette (with 0.1 ml graduations), pipettes, measuring cylinders, and conical flasks with ground glass stoppers.
- Procedure Highlights:
- Accurate weighing of sample portion based on solids-not-fat content
- Preparation of reconstituted milk with precise water volume
- Titration until faint pink endpoint persists for about 5 seconds
- Use of reference color solution to standardize end-point detection
- Calculation: Titratable acidity is calculated by multiplying the volume of sodium hydroxide used by a factor of 2, which corresponds to 10 grams of solids-not-fat in dried milk.
- Repeatability & Accuracy: The method ensures consistent results with defined repeatability limits and includes a step to compare results against a reference method (ISO 6091).
Applications
- Quality Control: Monitors acidity in dried milk products to ensure they meet industry and regulatory standards, affecting taste and microbial stability.
- Product Development: Assists food scientists in formulating dried milk with desired properties by tracking changes in acidity during processing.
- Regulatory Compliance: Used by dairy producers to comply with international food safety and quality standards.
- Food Safety: Facilitates early detection of spoilage or contamination by measuring acidity that affects shelf life in powdered dairy products.
- Analytical Laboratories: Provides a standardized routine method for dairy chemists in laboratories worldwide for consistent acidity measurement in dried milk.
Related Standards
- ISO 6091: Dried milk - Determination of titratable acidity (Reference method) – a more detailed and possibly time-consuming method used for verification and calibration.
- ISO/R 707: Sampling milk and milk products – important for obtaining representative samples prior to acidity determination.
- ISO/R 1736: Dried milk - Determination of fat content – used to calculate solids-not-fat content required for sample preparation.
- IDF Standard No. 26: Moisture content determination of dried milk – supports calculation of solids-not-fat content essential for titration accuracy.
By adhering to ISO 6092:1980, dairy manufacturers and laboratories ensure accurate, reliable, and reproducible measurements of titratable acidity in dried milk, supporting high product standards and consumer safety globally.
