Evaluation of molecular spectroscopy for predicting oxidative degradation of biodiesel and vegetable oil: Correlation analysis between acid value and UV-Vis absorbance and fluorescence

The present study evaluated the applicability of UV Vis absorption and fluorescence spectroscopy for monitoring oxidation level of oil extracted from white sesame seeds (Sesamum indium L.) and its respective biodiesel degraded at 110 degrees C for various times. Correlations between spectroscopic data and acid value of the samples demonstrated that both optical techniques could be used to monitor the oxidative degradation. Additionally, a quantitative model to predict the acid value of oil and biodiesel using the UV-Vis absorption data was proposed. The prediction model was tested using a cross-validation (leave-one-out) analysis and demonstrated, for the first time, that the acid value of both biodiesel and vegetable oil can be predicted by applying the same protocol for UV-Vis spectra analysis. An average error of about 3 and 8% was achieved for the predicted acid value of the oil and biodiesel samples with respect to the measured acid values, respectively. Therefore, UV-Vis absorption technique could be applied to quantitatively monitor the oxidative degradation of vegetable oil and biodiesel in a rapid and practical way.