Overview
ISO 5518:2007 specifies a precise spectrophotometric method for determining the benzoic acid content in fruits, vegetables, and derived products. Benzoic acid is commonly used as a preservative, making its quantification crucial for food safety, quality control, and regulatory compliance. This international standard provides laboratories with a reliable procedure to extract, purify, and measure benzoic acid concentration accurately. However, the method excludes samples containing p-chlorobenzoic acid or cinnamic acid due to their interference with the determination process.
Key Topics
- Scope and Limitations:
- Applicable to fruits, vegetables, juices, jams, and other derived food products.
- Not suitable if p-chlorobenzoic acid or cinnamic acid is present because of overlapping absorption spectra and chemical transformations during oxidation.
- Method Principle:
- The sample is homogenized, acidified, and benzoic acid is extracted using diethyl ether.
- Alkaline re-extraction and purification by oxidation with acidified potassium dichromate remove interfering substances.
- Purified benzoic acid is then quantified by UV spectrophotometry, measuring absorbance at key wavelengths (267.5 nm, 272 nm, 276.5 nm).
- Sample Preparation:
- Liquid, pulpy, thick, and solid products have tailored preparation steps, ensuring representative sampling and accurate analysis.
- Neutralization with sodium hydrogen carbonate prevents benzoic acid loss by volatilization during processing.
- Reagents and Equipment:
- Use analytical grade reagents such as tartaric acid, sodium hydroxide, potassium dichromate, and diethyl ether.
- Essential apparatus includes volumetric flasks, separating funnels, spectrophotometer (UV range), water bath, and analytical balance.
- Calibration and Calculation:
- Establishes a calibration curve using standard benzoic acid solutions to correlate absorbance with concentration.
- Results expressed in milligrams per liter (mg/L) or milligrams per kilogram (mg/kg) depending on sampling method.
- Performance and Repeatability:
- Method offers repeatability with absolute differences not exceeding 10 mg/L or mg/kg in 95% of cases, ensuring reliable routine use.
Applications
- Food Quality Control:
- Accurate detection of benzoic acid levels in fresh and processed fruits and vegetables to ensure compliance with food safety limits.
- Regulatory Compliance:
- Enables producers and regulatory agencies to verify preservative concentrations per national and international food legislation.
- Research and Development:
- Supports studies on preservative efficacy, food shelf life, and formulation improvements in fruit and vegetable products.
- Food Industry Laboratories:
- Ideal for routine testing of juices, jams, sauces, and frozen products for benzoic acid content to maintain product integrity and consumer safety.
Related Standards
- ISO 2951 - Fruit and vegetable products - Determination of sorbic acid content - Spectrophotometric method
- ISO 6636 - Fruit and vegetable products - Determination of sulphur dioxide content
- ISO 7507 - Fruit and vegetable products - Determination of ascorbic acid content
- Codex Alimentarius - General standards for food additives, including maximum levels for benzoic acid in foods
By following ISO 5518:2007, laboratories ensure the accurate and consistent quantification of benzoic acid, supporting food safety, quality assurance, and regulatory adherence in the international food supply chain.
Open preview (PDF)Fruits, vegetables and derived products — Determination of benzoic acid content — Spectrophotometric method
