Absorption and fluorescence profiles of biodiesel blends from Acrocomia aculeata kernel and pulp oils: Optical responses of α-tocopherol and β-carotene under thermal degradation

The search for new, more sustainable, and ecologically safe sources of energy has encouraged studies involving the production of biofuels from non-petroleum origin. Among the options for new energy sources, biodiesel is an important substitute for polluting fuels, with several cleaner and greener oils being suggested, especially new plant resources. This field evolved significantly in the last decades, and new raw materials for biodiesel production are welcome for new advances. In this vein, a potential source for biodiesel production is explored here, that is, two distinct biodiesels produced from different parts of the Acrocomia aculeata fruits-pulp and kernel. Results showed that biodiesel from pulp had an induction period of 12.77 h, similar to 3x higher than biodiesel from kernel, 3.96 h; iodine values in biodiesel pulp were similar to 7.5x higher than the kernel, 82 and 11 g I-2/100 g, respectively. These results are due to the profile of different antioxidants in these biodiesels and unsaturations in the fatty acids carbon chains. The degradation behavior of these biodiesels was monitored by the acid value via the traditional titration method, attesting the blend oxidation until 48 h of thermal degradation. In parallel, UV-Vis absorbances and fluorescence compared pure biodiesels and its blends with beta-carotene and alpha-tocopherol standards. The wavelength at 445 nm was efficient in monitoring the degradation of blends rich in beta-carotene-B25, B50, B75, B100. Primary and secondary compounds produced in the oxidative process were monitored at 230 and 270 nm, respectively, showing the pulp biodiesel antioxidant effect on the kernel one. Additionally, from the fluorescence contour map, it was possible to analyze regions of excitation/emission capable of monitoring the degradation process of the blends, found 415 nm, similar to expected for kernel and pulp oils described in the literature. Thus, the study provides information about changes in the optical profiles of biodiesel naturally rich in tocopherol and carotenoid antioxidants, encouraging the development of analytical methods based on absorption and fluorescence spectroscopies for this important resource of vegetable oils.