ISO 6492:1999

Overview

ISO 6492:1999 specifies a laboratory method for determining fat content in animal feeding stuffs (excluding oilseeds and oilseed residues). The standard describes sample classification, required reagents and apparatus, step-by-step extraction procedures, and calculation and reporting rules. It distinguishes two sample categories-Category A (no hydrolysis) and Category B (requires acid hydrolysis)-and provides precision data (repeatability and reproducibility) from interlaboratory tests.

Key topics and technical requirements

• Scope and categories
  • Applicable to most animal feeding stuffs except oilseeds and oilseed residues.
  • Category B: straight animal-origin feeds (including milk), certain vegetable feeds that require hydrolysis (gluten, yeast, soya, potato proteins, heat‑treated feeds), and compound feeds where ≥20% of fat originates from these products.
  • Category A: feeding stuffs not in Category B.
• Principle
  • Extraction of fat with light petroleum (boiling range 40–60 °C) or equivalent (technical hexane), with a hydrolysis step (HCl 3 mol/L) for Category B.
  • Preliminary light‑petroleum extraction recommended for samples with high fat content (≥200 g/kg).
• Apparatus & reagents
  • Soxhlet‑type extractor (≈100 ml syphoning volume), extraction thimbles, drying oven (103 °C), vacuum oven (80 °C, <13.3 kPa), anhydrous sodium sulfate, acetone, filtration aid (diatomaceous earth).
• Procedure highlights
  • Preliminary extraction: ~2 h (Soxhlet) and concentration of extract.
  • Hydrolysis (Category B): reflux with HCl for 1 h, filtration, drying, then Soxhlet extraction (main extraction).
  • Main extraction (typical): 6 h Soxhlet extraction with control of siphoning/reflux rate.
  • Solvent removal, drying and accurate weighing of residues to calculate fat content (g/kg).
• Precision
  • Repeatability (r) and reproducibility (R) limits provided. Example: Category A r = 2.5 g/kg, R = 7.7 g/kg; Category B r = 5.0 g/kg, R = 12.0 g/kg.

Applications and users

• Who uses it
  • Analytical and quality control laboratories in animal feed manufacturing.
  • Regulatory agencies performing feed composition testing.
  • Research institutions studying feed nutrition and composition.
• Practical uses
  • Routine determination of fat content for labeling, nutritional formulation, QC and compliance.
  • Comparative testing across batches and suppliers.
  • Supporting feed formulation and energy-content calculations.

Related standards

• ISO 6498 - Preparation of test samples (feed).
• ISO 6497 - Sampling of animal feeding stuffs.
• ISO 659, ISO 734‑1, ISO 736 - Methods for oil/oilseed residue oil determination (when ISO 6492 is not applicable).

Keywords: ISO 6492, animal feeding stuffs, fat content determination, Soxhlet extraction, hydrolysis, light petroleum extraction, feed analysis, laboratory method.