Iodine value, FFA, refractive index, and fatty acid composition in edible oils

Significance of the Topic

Edible oils are fundamental to human nutrition and the quality assessment of these oils is crucial for food safety, regulatory compliance and consumer trust. Parameters such as iodine value, free fatty acids, refractive index and fatty acid profile provide insight into oil stability, purity and nutritional content. Traditional analytical methods often demand extensive sample preparation and use harmful chemicals, prompting a shift toward rapid, solvent-free strategies. Near-infrared spectroscopy (NIRS) offers a high-throughput, eco-friendly alternative with minimal operational costs.

Objectives and Overview

This study aimed to establish a rapid, multiparameter NIRS method for simultaneous quantification of eight quality metrics in edible oils within one minute. Targeted parameters include iodine value, free fatty acids, refractive index and the relative amounts of palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2) and alpha-linolenic (C18:3) acids. Calibration models were developed using Vis-NIR spectra from 397 samples spanning sunflower, rapeseed, sesame and soybean oils. The predictive performance was validated against established reference methods.

Methodology and Used Instrumentation

A Metrohm NIRS DS2500 Liquid Analyzer operating in transmission mode at 40 °C collected spectra across 400–2500 nm. Samples were measured directly in disposable 8 mm glass vials without preparation. Model development and validation utilized Vision Air Complete software. Reference data were obtained via gas chromatography (iodine value, fatty acid composition), titration (free fatty acids) and a refractometer (refractive index).

• DS2500 Liquid Analyzer
• 8 mm disposable vials
• Vision Air Complete software

Main Results and Discussion

All eight parameters showed strong agreement with reference methods (R² > 0.94). The iodine value model achieved R² = 0.999 and SEC = 0.29 g/100 g. Free fatty acids prediction reached R² = 0.983 (SEC = 0.08 g/100 g). Refractive index yielded R² = 0.996. Fatty acid content models delivered R² values from 0.967 (stearic acid) to 0.999 (oleic and linoleic acids) with low calibration and cross-validation errors, confirming robustness.

Benefits and Practical Use of the Method

NIRS enables simultaneous evaluation of multiple oil quality attributes in under one minute without solvents or sample preparation. Analysis time is reduced by up to 95% for certain parameters, leading to significant cost savings. The non-destructive approach enhances laboratory throughput and can be integrated directly into production lines for real-time monitoring. Users benefit from simplified workflows, improved safety and immediate results.

Future Trends and Possibilities

Implementation of rugged, automated NIRS instruments will support on-site and in-line process analytics. Advances in chemometrics and machine learning will improve model transferability across diverse oil matrices. Connectivity with digital quality-management platforms and cloud services will enable remote monitoring and predictive maintenance. Similar NIRS strategies could be extended to biodiesel, cosmetics and pharmaceutical lipids.

Conclusion

The Metrohm NIRS DS2500 Liquid Analyzer provides rapid, accurate and reproducible multiparameter analysis of edible oils, matching traditional techniques while eliminating the need for solvents and extensive sample preparation. High correlation with reference methods underscores its suitability for routine quality control in both industrial and research laboratories. Adoption of this NIRS solution promotes sustainable practices, lowers costs and enhances productivity.

References

• Metrohm Application Note AN-NIR-111