Analysis of edible oils and fats

Importance of the Topic

Edible oils and fats play a central role in food production, pharmaceuticals and personal care. Maintaining their purity and stability is essential for consumer safety, nutritional value and product shelf life. Analytical methods that quantify key quality parameters help manufacturers, laboratories and regulatory agencies monitor raw materials, processing and finished products.

Objectives and Overview

This bulletin reviews seven critical analytical determinations used in routine quality control of edible oils and fats. It highlights practical adaptations of international standards for:

• Water content
• Oxidation stability
• Iodine value
• Peroxide value
• Saponification value
• Acid number and free fatty acids
• Hydroxyl value
• Nickel traces

The aim is to propose efficient workflows, reduce analysis time, avoid harmful solvents and integrate automation where feasible.

Applied Instrumentation

Key instruments cited in these methods include:

• Karl Fischer titrators (coulometric and volumetric)
• Rancimat oxidative stability tester
• Automated titrators with DET mode and DIS-Cover sample handling
• Potentiometric cells and solvent-resistant electrodes
• Voltammetric analyzers with mercury drop and multi-mode electrodes

Methodology and Instrumentation

Water content is measured by Karl Fischer titration: coulometric mode for low-moisture oils (<0.1 %) and volumetric mode for butter and margarines. Oxidation stability uses the Rancimat accelerated test at controlled temperature and airflow to record induction times. Iodine value determination is adapted from EN ISO 3961, using glacial acetic acid, magnesium acetate catalyst and potentiometric end-point detection in under 10 min. Peroxide value follows EN ISO 27107 principles with a 1-decanol/acetic acid solvent and iodine liberation titrated titrimetrically. Saponification number employs ethanolic KOH reflux and potentiometric back-titration to reveal the average fatty acid chain length. Acid number and free fatty acid content are assessed by direct titration of the extracted oil in an ethanol/ether mixture using KOH. Hydroxyl value is determined according to ASTM E1899: reaction of hydroxyl groups with toluene-4-sulfonyl isocyanate in acetonitrile, followed by titration with tetrabutylammonium hydroxide. Nickel residues from hydrogenation catalysts are quantified by differential pulse polarography after acid digestion, complexation with dimethylglyoxime and pH adjustment.

Main Results and Discussion

Method adaptations significantly reduce cycle times and eliminate chlorinated or pyridine-based solvents. Water determinations achieve drift levels below 10 µg/min. Rancimat tests accurately distinguish oxidation induction times between 0.5–15 h for various oils at 120 °C. The modified iodine value method shortens reaction time from 1–2 h to 5 min while maintaining compliance with multiple standards. Automated peroxide and acid value titrations deliver repeatable results within specified limits. Hydroxyl value analysis proceeds in under 12 min, compared to 40 min in ISO methods. Polarographic nickel trace analysis attains detection of 0.3 mg/kg Ni in margarine.

Benefits and Practical Applications

These streamlined protocols offer:

• Faster throughput and higher laboratory productivity
• Improved safety by omitting toxic solvents
• Enhanced reproducibility through automation and standardized reagents
• Compliance with multiple international norms (EN ISO, ASTM, AOAC, AOCS, USP, Ph. Eur.)
• Versatility across liquid oils, solid fats, spreads and cosmetic formulations

Future Trends and Potential Applications

Advancements in inline process monitoring and chemometric data analysis will further accelerate quality control. Novel solvent-free titrations, micro-fluidic reactors for accelerated oxidative tests and miniaturized voltammetric sensors may enable real-time, at-line screening. Integration with LIMS and cloud-based reporting will support regulatory compliance and supply-chain transparency.

Conclusion

The seven analytical parameters summarized here form a robust framework for edible oil and fat quality assessment. By implementing optimized methods, laboratories can achieve faster, safer and more reliable results while fully aligning with global standards.

References

• EN ISO 8534: Animal and vegetable fats and oils – Karl Fischer water content
• EN ISO 3961: Determination of iodine value
• EN ISO 6886: Oxidation stability (Rancimat)
• EN ISO 27107 / 3960: Peroxide value
• EN ISO 3657: Saponification value
• EN ISO 660: Acid value and free fatty acids
• ASTM E1899: Hydroxyl value by TSI reaction
• AOCS Cd 12b-92: Rancimat oxidative stability
• AOCS Cd 1d-92: Iodine value cyclohexane-acetic acid