Overview
ISO 5567:1982 specifies a laboratory method for the determination of volatile organic sulphur compounds in dehydrated garlic. The procedure isolates sulphur volatiles by maceration in an aqueous medium, collects them by distillation into an alkaline receiver, and quantifies the sulphur species by argentimetric titration (silver precipitation followed by titration with ammonium thiocyanate). The standard includes a recommended distillation apparatus drawing and prescribes reagents, equipment and reporting requirements.
Key topics and technical requirements
- Scope: Determination of volatile organic sulphur compounds in dehydrated garlic; results expressed as allyl sulphide equivalent.
- Sample preparation: Homogenize and reduce sample particle size; typical test portion ≈ 10 g (weighing to 0.01 g).
- Maceration and extraction: Macerate sample in ~100 ml water at controlled temperature, typically in a thermostatted bath (37 ± 1 °C) for 2 hours; ethanol and a few drops of vaseline oil are added to reduce foaming and aid distillation.
- Distillation apparatus: Glass-jointed 250 ml round-bottom flask, Liebig condenser and 250 ml conical receiving flask; avoid contact with copper or rubber (use glass joints).
- Collection & chemical treatment: Distill until ≈ 60 ml distillate collected into ammonium hydroxide solution; neutralize to pH 7 ± 0.1 with nitric acid before further processing.
- Argentimetric determination: Add silver nitrate to precipitate sulphur species, reflux, filter and wash precipitate; dissolve/acidify as required and titrate with standardized ammonium thiocyanate using ferric-ammonium alum indicator to a persistent pink end point.
- Reagents & apparatus tolerances: Analytical-grade reagents (AgNO3 0.1 mol/L, NH4OH 10%, NH4SCN 0.1 mol/L, etc.); thermostatted bath, precision burette (±0.05 ml) and fritted-glass filtration (porosity 4–16 µm).
- Quality control: Two determinations on the same prepared sample; repeatability requirement - difference between paired results must not exceed 5% of the mean.
Applications and users
- Food laboratories performing compositional or quality testing of dried garlic and garlic powders.
- Spice manufacturers and ingredient suppliers monitoring flavour-active sulphur volatiles and meeting product specifications.
- Food safety and regulatory bodies requiring standardised analytical methods for trade, specification compliance and labeling.
- R&D groups studying garlic processing effects on volatile sulphur profiles.
This method is practical when a quantitative, reproducible measurement of total volatile organic sulphur (reported as allyl sulphide equivalents) is required for quality control, specification or comparative studies.
Related standards (if applicable)
- Laboratories should consider complementary methods for volatile profiling (e.g., GC-based methods) when identification of individual sulphur compounds is needed. Where formal traceability is required, align ISO 5567 testing with laboratory accreditation and relevant ISO/IEC 17025 practices.
