Quality Control of Palm Oil

Importance of the Topic

This study addresses the rapid and accurate determination of the iodine value in refined, bleached, and deodorized palm oil, a critical parameter for assessing unsaturation level and oxidative stability. Conventional wet chemical titration methods are laborious, costly, and generate chemical waste; thus, implementing a fast, reagent-free spectroscopic alternative is highly valuable in quality control workflows.

Objectives and Study Overview

The main goals of this investigation were:

• To develop and validate Vis-NIR calibration models for iodine value in palm oil using Metrohm analyzers.
• To compare analytical performance between the new DS2500 Liquid Analyzer and the established XDS RapidLiquid Analyzer.
• To demonstrate a streamlined workflow requiring minimal sample preparation and rapid results.

Methodology and Instrumentation

Palm oil samples were measured in transmission mode over 400–2500 nm with controlled temperature (60 °C) using disposable 8 mm vials. Viscous samples were liquefied by a vial heater to ensure reproducible spectra. Data acquisition and model development were performed in Vision Air Complete software, and calibration quality was assessed by cross-validation against reference titration values.

Used Instrumentation

• DS2500 Liquid Analyzer: Robust Vis-NIR analyzer (400–2500 nm) with built-in temperature control up to 80 °C and support for disposable vials.
• XDS RapidLiquid Analyzer: Rapid Vis-NIR analysis system with tempered compartment for quartz cuvettes or glass vials.
• NIRS XDS Vial Heater: Module for heating vials up to 200 °C to reduce sample viscosity.
• Disposable 8 mm Glass Vials: Transmission vials for single-use measurements.
• Vision Air Complete Software: Platform for instrument control, data management, method development, and routine analysis.

Main Results and Discussion

Calibration models for iodine value exhibited excellent linear correlation with reference titration values (R2 = 0.998) for both instruments. The DS2500 achieved a standard error of calibration and cross-validation of 0.49 g I2/100 g, while the XDS RLA showed 0.55 g/100 g and 0.54 g/100 g, respectively. These figures confirm high precision and demonstrate a marginal accuracy improvement with the DS2500.

Benefits and Practical Applications

• Elimination of chemical reagents and waste, promoting greener laboratory practices.
• Rapid analysis (<1 minute per sample) enabling high throughput in QC and production settings.
• Minimal training required due to intuitive software and automated temperature control.

Future Trends and Applications

• Extension of Vis-NIR models to additional oil quality parameters such as free fatty acids, moisture, DOBI, and carotene content.
• Integration with sample automation systems and robotics for online monitoring.
• Application of advanced machine learning algorithms to enhance calibration robustness and transferability.

Conclusion

The Metrohm DS2500 Liquid Analyzer provides a fast, accurate, and cost-effective Vis-NIR method for determining iodine value in palm oil, outperforming the XDS RLA in precision while eliminating reagents and reducing analysis time. Adoption of this technique can streamline quality control across laboratory and production environments.

References

• Metrohm AG, Application Note AN-NIR-044: Quality Control of Palm Oil – Environmentally friendly determination of FFA content, iodine value, moisture, DOBI, and carotene content.