Determination of iodine value in frying oils with NIR spectroscopy

Significance of the Topic

The iodine value is a key indicator of the degree of unsaturation in vegetable oils and reflects their oxidative stability. Accurate and rapid determination of iodine value is essential for quality control in the edible oil industry, where blends of soybean and palm oil are used to balance nutritional properties, taste, and shelf life.

Objectives and Overview of the Study

This application note describes the development of a near-infrared spectroscopy (NIRS) method to quantify iodine value in soybean-palm oil blends. The goal was to establish a rapid, reagent-free alternative to conventional titration or gas chromatography, enabling real-time monitoring of blend composition in food laboratories.

Methodology and Instrumentation

A total of 21 oil blends covering iodine values from 60 to 130 g per 100 g were prepared. Samples were preheated to 60 °C using a vial heater to ensure liquidity. Spectra were collected in transmission mode in 8 mm disposable vials with a DS2500 Liquid Analyzer over the range 400–2500 nm. Data acquisition and model development were performed with Vision Air Complete software.

Instrumentation

• DS2500 Liquid Analyzer
• NIRS XDS Vial Heater
• 8 mm vial holder
• Vision Air 2.0 Complete software

Main Results and Discussion

Calibration models exhibited excellent linearity with R2 = 0.999. The standard error of calibration was 0.20 g/100 g and the standard error of cross-validation was 0.22 g/100 g, demonstrating high predictive accuracy. Correlation diagrams confirmed near-perfect agreement between NIR predictions and reference titration values. Spectral features in the Vis-NIR region reliably correlate with unsaturation levels.

Benefits and Practical Applications of the Method

• Measurement time below one minute per sample compared to 1–2 hours by titration
• No chemical reagents or waste generation
• Minimal sample preparation and operator training
• Reduced laboratory workload and running costs

Future Trends and Potential Applications

Advances may include extension of NIRS models to other oil types and multicomponent blends, integration of in-line process analyzers in production lines, and coupling with automation for high-throughput screening. Development of portable NIR instruments and AI-driven calibration transfer will further expand field applications in quality control and supply chain management.

Conclusion

The Metrohm DS2500 Liquid Analyzer combined with NIRS provides a rapid, robust, and environmentally friendly method for determining iodine value in frying oil blends. Its high accuracy, low operating costs, and ease of use make it a superior alternative to classical titration methods for routine quality control in food laboratories.