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

Importance of the Topic

The iodine value and fatty acid composition in crude palm oil are key quality parameters directly affecting its market value, nutritional profile, and suitability for food and non-food applications. Traditional methods such as gas chromatography require chemical reagents, time-consuming sample preparation, and higher operational costs. Rapid, reagent-free techniques like near-infrared spectroscopy (NIRS) improve throughput and cost efficiency in quality control workflows.

Study Objectives and Overview

This study aimed to develop and validate NIR spectroscopy models for the rapid determination of iodine value (IV) and relative contents of palmitic (16:0), oleic (18:1), and linoleic (18:2) acids in crude palm oil using the Metrohm NIRS DS2500 Liquid Analyzer. Twenty crude palm oil samples covering a range of IVs were analyzed to build robust calibration models and assess their performance against reference gas chromatography (GC) methods.

Methodology

Samples were equilibrated at 60°C to ensure complete liquefaction and measured in transmission mode across the 400–2500 nm range using 8 mm disposable vials. Calibration and cross-validation were performed with the Vision Air complete software package. Reference values for fatty acid composition were obtained by GC following methyl esterification. Iodine values were calculated from combined oleic and palmitic acid concentrations.

Instrumentation

• Metrohm NIRS DS2500 Liquid Analyzer (400–2500 nm, heated sample holder up to 80°C)
• 8 mm disposable measurement vials
• Vision Air complete software
• Gas chromatograph for reference measurements

Main Results and Discussion

High correlation was achieved between NIRS predictions and GC reference 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 models demonstrated precision and accuracy suitable for routine quality control, with minimal sample handling and rapid measurement times under one minute.

Benefits and Practical Applications

• Eliminates need for chemical reagents and extensive sample preparation
• Delivers results in less than one minute, enabling high-throughput screening
• Reduces operational costs and workload in quality control laboratories
• Provides reliable data for product specification, regulatory compliance, and process monitoring

Future Trends and Potential Applications

Advancements in NIRS instrumentation and chemometric algorithms are expected to further improve sensitivity and broaden the range of analyzable compounds in vegetable oils. Integration with automation platforms and process analytics technology can enable real-time quality monitoring in production, supporting Industry 4.0 initiatives. Expanded spectral databases and machine learning approaches may also enhance model robustness across diverse sample matrices and processing conditions.

Conclusion

The Metrohm NIRS DS2500 Liquid Analyzer offers a rapid, accurate, and reagent-free alternative to conventional GC analysis for determining iodine value and fatty acid profiles in crude palm oil. The validated models deliver high correlation and low error metrics, making NIR spectroscopy a valuable tool for routine quality control in both laboratory and production settings.

References

• Metrohm Application Note AN-NIR-115: Determination of iodine value and fatty acid profile in palm oil by NIRS
• GC methods for fatty acid methyl ester analysis