ISO 8069:2005 PDF

Overview

ISO 8069:2005 (IDF 69:2005) - "Dried milk - Determination of content of lactic acid and lactates" specifies an enzymatic spectrophotometric method for measuring lactic acid and lactates in all types of dried milk (milk powder). The method quantifies lactic content and expresses results as mg lactic acid per 100 g non‑fat solids, supporting consistency in dairy quality control and analytical reporting.

Key topics and technical requirements

• Scope: Applies to all types of dried milk; provides a complete laboratory procedure from sample preparation to calculation and reporting.
• Analytical principle: Simultaneous enzymatic oxidation of L‑ and D‑lactate by L‑LDH and D‑LDH (with NAD cofactor) to produce NADH, followed by conversion of pyruvate via glutamate pyruvate transaminase (GPT). NADH formation is measured spectrophotometrically at 340 nm and is proportional to lactic acid/lactates content.
• Reagents and enzyme preparations: Includes requirements for reagent purity and storage (e.g., NAD, potassium hexacyanoferrate(II), zinc sulfate, NaOH, buffer solutions) and specifications for enzyme suspensions (activity limits, storage at 0–5 °C, handling on ice).
• Apparatus: Standard laboratory equipment plus a spectrophotometer at 340 nm and specified volumetric glassware and pipettes.
• Sample handling and preparation: Test‑portion dissolution, fat/protein precipitation (potassium hexacyanoferrate(II), zinc sulfate, NaOH), filtration or centrifugation, blank controls.
• Validation and quality control: Procedures to check reagent activity and recovery (using lithium L‑ and D‑lactate standards), and sections on precision (interlaboratory, repeatability, reproducibility).
• Ancillary requirements: Calculation/reporting rules and a normative annex on Good Laboratory Practice (GLP) for enzymatic analyses.

Applications and practical value

• Quality control of milk powder and dried dairy ingredients for manufacturing, export, and specification compliance.
• Monitoring fermentation-related acidity or storage‑related changes in lactic content that affect flavor, shelf life and reconstitution behavior.
• Regulatory and conformance testing in commercial dairy laboratories and national control institutes.
• Research and method development in dairy science where accurate measurement of both L‑ and D‑lactates is required.

Who should use this standard

• Dairy industry QC laboratories, milk powder manufacturers, analytical service labs, food safety/regulatory agencies, and research laboratories working on dairy product composition and stability.

Related standards

• Sampling guidance referenced in the document: ISO 707 | IDF 50 (sampling of milk powder).

Keywords: ISO 8069:2005, dried milk, lactic acid, lactates, enzymatic method, spectrophotometric, milk powder analysis, dairy quality control, IDF 69.