Overview
ISO 5519:2008 specifies a validated laboratory method for extracting and measuring sorbic acid content in fruits, vegetables and derived products. The standard defines a steam‑entrainment extraction procedure followed by two optional analytical techniques: Technique A - ultraviolet (UV) spectrophotometry (256 nm) and Technique B - colourimetric/photocolorimetric determination (532 nm) using Schmidt’s reaction. ISO 5519 covers sample preparation, reagents, apparatus, procedure, calculation, repeatability and test reporting.
Key topics and technical requirements
- Extraction principle: quantitative entrainment of volatile sorbic acid by steam distillation after homogenization of the representative test sample.
- Sample types and test portions: liquid, thick (jams, marmalades) and solid products - typical test portion ~10 ml or 10 g depending on matrix.
- Steam‑distillation apparatus: detailed fractionating column and condenser specifications; performance checks required (e.g., recovery of acetic acid ~99.5% and limited lactic acid carry‑over).
- Technique A (UV spectrophotometry):
- Measurement at 256 nm.
- Uses a copper catalyst to oxidize interfering sulfur dioxide.
- Guidance for removing essential oil interferences by alkaline evaporation/reconstitution.
- Technique B (Schmidt’s reaction / colorimetry):
- Based on oxidation (chromic/sulfuric acid) and reaction with thiobarbituric acid to produce a pink chromogen measured at 532 nm.
- Requires removal of ethanol and essential oils by evaporation of an aliquot when necessary.
- Reagents and stability: lists analytical reagents (tartaric acid, sorbic acid standards, chromic/sulfuric solution, thiobarbituric acid, etc.) and notes on reagent preparation/use.
- Quality control: calibration curve procedures, blank tests, duplicate determinations and repeatability information are specified.
Applications and users
ISO 5519 is aimed at laboratories and quality teams involved in:
- Food safety and preservative analysis (sorbic acid is a common preservative/fungistat).
- Juice, jam, sauce and vegetable product testing for regulatory compliance and labeling.
- Contract analytical labs, plant QC laboratories and research institutes performing routine or confirmatory determinations of sorbic acid.
The standard helps ensure reproducible, comparable results across laboratories and supports compliance with food additive regulations.
Related standards
- Prepared by ISO/TC 34 (Food products), SC 3 (Fruit and vegetable products).
- Use alongside other ISO methods for food additive and preservative analysis and general laboratory quality management standards.
Keywords: ISO 5519, sorbic acid determination, steam distillation, spectrophotometry 256 nm, colorimetry 532 nm, fruits and vegetables, food analysis, preservative testing.