Optical Characteristics of the Black Seed Oil: Fluorescence and Adulteration Detection

Understanding the optical characteristics, especially the fluorescence properties of vegetable oils, particularly black seed oil (BSO), is an essential prerequisite for the development of the future applications in both medicinal and nutritional fields. In this way, it is essential to identify the roles played by the components such as unsaturated fatty acids, carotenoids, flavonoids, vitamin E, and chlorophylls in the BSO fluorescence spectra. In the current landscape, challenges arise from the adulteration of BSO with impurities such as sunflower oil (SO), complicating efforts to obtain pure BSO. Here, dependence of the BSO fluorescence on excitation wavelength has been examined using UV- visible diode lasers (λ = 355, 405, 440, 532 and 660 nm) as excitation sources. Though conjugated unsaturated fatty acids, flavonoids and chlorophylls are mainly contributed to the fluorescence due to UV excitation, wavelengths in the visible range specifically excite carotenoids, vitamin E, and chlorophylls. By utilizing the laser-induced fluorescence (LIF) technique, we explored the effects of inner filters and setup geometry to gain deeper insights into the BSO fluorescence dynamics. Differential spectral analysis (DSA) revealed that adulteration of BSO with SO alters its fluorescence features. As a result, a novel approach is proposed for adulteration detection, based on the simultaneous excitation of BSO and SO by a 405 nm laser, benefit to indirect excitation of the carotenoids of BSO by fluorescence emission of SO within the spectral range of 400-500 nm, which results in the enhancement of BSO fluorescence in the region of 500-600 nm.