Palm oil is currently the most widely produced and consumed vegetable oil in the world. It has many uses as a raw material for both food and non-food industries (e.g., personal care and cosmetic products). The marketability of crude palm oil (CPO) is determined by many quality indicators such as iodine value (IV) and fatty acid composition.

This Application Note demonstrates how near-infrared (NIR) spectroscopy is an ideal alternative to traditional analysis techniques like gas chromatography. NIRS can provide results in less than one minute without requiring any sample preparation or chemical reagents, increasing the productivity and reducing costs.

20 samples of crude palm oil (CPO) with varying iodine values (IV) were kept in a water bath at 60 °C for at least 30 minutes to liquify them. These samples were then measured at 60 °C on a Metrohm NIRS DS2500 Liquid Analyzer (Figure 1) in transmission mode over the full wavelength range (400–2500 nm) using 8 mm disposable vials. Data acquisition and prediction model development was performed with the Vision Air complete software package from Metrohm.

The reference method of gas chromatography (GC) was used after the methyl esterification of the fatty acids. The concentration of the fatty acids was derived from corresponding peak area. The iodine values were calculated from the combined concentrations of oleic acid and palmitic acid.

The measured Vis-NIR spectra (Figure 2) were used to create a prediction model for quantification of iodine value (IV), linoleic acid (18:2), oleic acid (18:1), and palmitic acid (16:0) in CPO. The quality of the prediction models was evaluated using correlation diagrams which display a high correlation between the Vis-NIR prediction and the GC results. The respective figures of merit (FOM) display the expected precision and confirm the feasibility during routine analysis (Figures 3–6)

This Application Note displays the benefits of using the Metrohm NIRS DS2500 Liquid Analyzer for routine quality control analysis of crude palm oil. Compared to conventional methods, the determination with Vis-NIR spectroscopy does not need any sample preparation. Consequently, this leads to a reduction of workload (Table 2) and operating costs.

Internal reference: AW NIR CH-0066-042023