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Palm oil is currently the most widely produced and consumed vegetable oil globally and is used as a raw material in many industries. Crude palm oil (CPO) is used in various edible products, including cooking oil, margarine, and processed foods. CPO can be refined to remove impurities and improve color, flavor, and odor. Several steps are involved (e.g., degumming, neutralization, bleaching, deodorization) to produce refined bleached deodorized palm oil (RBDPO). RBDPO is used for frying purposes and is also found in foods like instant noodles and ice cream.

If the palm oil composition is found to be out of specification during production, the process stops, and the oil is recycled. Determination of key quality parameters like iodine value and the fatty acid profile of palm oil can be determined easily in just a few seconds without sample preparation using near-infrared spectroscopy (NIRS).

OMNIS NIR Analyzer and a sample filled in a disposable vial.
Figure 1. OMNIS NIR Analyzer and a sample filled in a disposable vial.

In this application, 20 samples of crude palm oil (CPO) and 30 samples of refined, bleached, deodorized palm oil (RBDPO) were kept in a water bath at 60 °C for at least 30 minutes to liquify them. All samples were measured with an OMNIS NIR Analyzer Liquid in transmission mode at 60 °C using 8 mm disposable vials. Data acquisition and prediction model development were performed with OMNIS software.

Gas chromatography (GC) was used as a reference method after the methyl esterification of the fatty acids. The concentration of the fatty acids was derived from the corresponding peak area. Determination of iodine value in palm oil was possible by a calculation from the combined concentrations of oleic acid (18:1) and linoleic acid (18:2) according to the obtained fatty acid composition of palm oil.

Another set of CPO samples (681) was used to determine the water content. These samples were treated in the same manner as described above and measured using NIR spectroscopy. Karl Fischer (KF) titration was used as a standard method in this case.

Table 1. Hardware and software equipment overview.
Equipment Metrohm number
OMNIS NIR Analyzer Liquid 2.1070.0010
Holder OMNIS NIR, vial, 8mm 6.07401.070
Disposable vial, 8mm, transmission 6.7402.240
OMNIS Stand-Alone license 6.06003.010
Quant Development software license 6.06008.002

The measured NIR spectra of CPO (Figure 2) and of RBDPO (Figure 3) were used to create prediction models for the quantification of iodine value (IV), linoleic acid (18:2), oleic acid (18:1), and palmitic acid (16:0) for the two different palm oils. A quantification model was created for water content present in palm oil using another set of CPO samples.

The quality of the prediction models was evaluated using correlation diagrams (Figures 4–12) which display a high correlation between the NIR predictions and the results given by primary methods (i.e., GC and KF titration). The respective figures of merit (FOM) display the expected precision and confirm the feasibility during routine analysis.

Figure 2. Overlay of NIR spectra from CPO samples analyzed on an OMNIS NIR Analyzer Liquid at 60 °C.
Figure 3. Overlaid NIR spectra of RBDPO samples analyzed on an OMNIS NIR Analyzer Liquid at 60 °C.
Figure 4. Correlation diagram and the respective figures of merit for the prediction of iodine value in RBDPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC(mg/100g) SECV(mg/100g) R²CV
IV 0.31 0.34 0.999
Figure 5. Correlation diagram and the respective figures of merit for the prediction of palmitic acid (16:0) in RBDPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC (%) SECV (%) R²CV
16:0 0.53 0.63 0.996
Figure 6. Correlation diagram and the respective figures of merit for the prediction of oleic acid (18:1) in RBDPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC (%) SECV (%) R²CV
18:1 0.75 0.98 0.985
Figure 7. Correlation diagram and the respective figures of merit for the prediction of linoleic acid (18:2) in RBDPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC (%) SECV (%) R²CV
18:2 0.14 0.21 0.994
Figure 8. Correlation diagram and the respective figures of merit for the prediction of iodine value in CPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC(mg/100g) SECV(mg/100g) R²CV
IV 0.11 0.14 0.984
Figure 9. Correlation diagram and the respective figures of merit for the prediction of palmitic acid (16:0) in CPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC(%) SECV(%) R²CV
16:0 0.11 0.14 0.984
Figure 10. Correlation diagram and the respective figures of merit for the prediction of oleic acid (18:1) in CPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC(%) SECV(%) R²CV
18:1 0.12 0.14 0.969
Figure 11. Correlation diagram and the respective figures of merit for the prediction of linoleic acid (18:2) in CPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using GC.
Parameter SEC(%) SECV(%) R²CV
18:2 0.02 0.03 0.984
Figure 12. Correlation diagram and the respective figures of merit for the prediction of water content in CPO using an OMNIS NIR Analyzer Liquid. The reference values were evaluated using KF titration.
Parameter SEC(%) SECV(%) R²CV
Water 0.044 0.044 0.714

This Application Note displays the benefit of using the OMNIS NIR Analyzer Liquid for routine analysis in laboratories that measure various palm oil quality parameters. Compared to other conventional methods like Karl Fischer titration and GC, determinations with NIR spectroscopy do not require any sample preparation or chemical reagents. This ultimately leads to a reduction in workload (Table 2) and costs.

Table 2. Time to result overview for the parameters of iodine value, fatty acid composition, and water content in palm oil by standard methods.

Parameter Method Time to result
lodine value, Fatty acid composition Gas chromatography ∼30 min sample preparation (Methyl esterification + sample preparation) + ∼20 min GC
Water content KF titration ∼10 min per sample
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Internal reference: AW NIR CH-0066-042023