Determination of iodine value and fatty acid profile in palm oil by NIRS

Importance of the Topic

Crude palm oil is one of the world’s most produced and consumed vegetable oils, serving both food and non-food industries. Key quality parameters such as iodine value and fatty acid profile determine market value, functionality and stability. Traditional analyses require time-consuming sample preparation and chemical reagents. Near-infrared spectroscopy (NIRS) presents a rapid, non-destructive alternative for routine quality control.

Objectives and Study Overview

This application note evaluates the performance of a Metrohm NIRS DS2500 Liquid Analyzer for simultaneous prediction of iodine value and relative contents of palmitic, oleic and linoleic acids in crude palm oil. A set of 20 samples with varying iodine values served to develop calibration models and to compare NIRS predictions against gas chromatography (GC) as the reference method.

Methodology and Instrumentation

Samples of crude palm oil were equilibrated at 60 °C in a water bath for 30 minutes to ensure complete liquefaction. Spectra were recorded in transmission mode over 400–2500 nm using 8 mm disposable vials on the NIRS DS2500 Liquid Analyzer. Data handling and model building employed the Vision Air software. Reference values were obtained by GC after methyl esterification of fatty acids. Iodine values were calculated from combined concentrations of oleic and palmitic acids measured by GC.

Main Results and Discussion

Calibration models demonstrated excellent agreement with reference GC data:

• Iodine value: R2 = 0.994, SEC = 0.10%, SECV = 0.11%
• Palmitic acid (16:0): R2 = 0.9836, SEC = 0.15%, SECV = 0.15%
• Oleic acid (18:1): R2 = 0.9851, SEC = 0.11%, SECV = 0.12%
• Linoleic acid (18:2): R2 = 0.9916, SEC = 0.03%, SECV = 0.04%

The high coefficients of determination and low cross-validation errors confirm the robustness of NIRS models for routine analysis. Spectral features in the Vis-NIR region correlate strongly with specific functional groups of fatty acids, enabling accurate quantification without separation steps.

Benefits and Practical Applications

• Rapid analysis: results in under one minute per sample
• No chemical reagents or extensive sample preparation required
• Reduced operational costs and waste generation
• Enhanced laboratory productivity and potential for in-line process monitoring

Future Trends and Applications

Integration of NIRS with automated sampling robots and flow-through cells can further boost throughput in industrial environments. Advances in machine learning algorithms promise to refine calibration models, extend applicability to blended oils, and detect minor components. Portable NIR devices may enable field-based quality checks along the supply chain.

Conclusion

Near-infrared spectroscopy using the Metrohm DS2500 Liquid Analyzer offers a rapid, reliable and reagent-free approach for determining iodine value and fatty acid composition in crude palm oil. The method yields performance comparable to gas chromatography, while significantly reducing analysis time and cost. Its robustness and ease of operation make it well suited for routine quality control in both laboratory and production settings.