Chemical, Spectrocopical and Chemiometric Analyses of Vegetable Oils Submitted to Thermal Stress

Yao Tsung Lee¹, Donyau Chiang², Mao Kuo Wei³ and Sanboh Lee¹*

• ¹Department of Materials Science and Engineering, National Tsing Hua University, Taiwan
• ²Taiwan Instrument Research Institute, National Applied Research Laboratories, Taiwan
• ³Department of Materials Science and Engineering, National Dong Hwa University, Taiwan

Received:June 10, 2021;   Published:June 22, 2021

*Corresponding author:Sanboh Lee, Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan

DOI: 10.32474/SJFN.2021.04.000179

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Abstract

In this work, chemical transformations and kinetic behavior of raw soybean oil and olive oil samples were evaluated by traditional and spectroscopic methods after continuous thermal stress. Initially, a multivariate classificatory study (PLS-DA) was carried out, using data from mid-infrared spectroscopy to differentiate 44 commercial oils samples (olive, canola, sunflower, corn and soybean). In this step, 19 important spectral regions were selected for sample’s classification. Two figures of merit were calculated (sensitivity and specificity) with this model presenting values above 83.3% of sensitivity for all classes and above 71.4% for 4 classes in specificity. In the next stage, soybean oil and olive oil samples were subjected to thermal stress for 15 h (5 h / day) at 200 °C. The results obtained by tradition methods as total acidity index demonstrated that soybean oil has a greater variation when compared to olive oil, and that after 4 and 11 hours of heating, soybean oil and olive oil, respectively, were outside the Brazilian Health Surveillance Agency standards. For the peroxide index, it was possible to determine that both oils suffered oxidation and the results demonstrated also that soybean oil suffered a greater degradation in relation to olive oil. Finally, a PCA, using mid-infrared data from the kinetic studies of soybean and olive oils thermal degradation, were carried out and proved that molecular changes occurred basically in 8 spectral regions, resulting from the formation of sub products resulting from the thermal oxidation of the fatty acids presented in the samples.

Keywords:Vegetable oils; mid infrared; thermal stress; PLS-DA; PCA