Insights into kinetic, isotherm, and thermodynamic of ultrasound mode- and amplitude-dependent carotenoid and chlorophyll degradation or/and adsorption

Abstract

Experimental data were analyzed to investigate the underlying adsorption or degradation mechanism of carotenoids and chlorophylls over the bleaching of sunflower oil through different amplitudes of horn and bath ultrasound (ultrasound-assisted bleaching; UAB), temperature, time, and bleaching clay. Quantifying the color removal efficiency in both batch and continuous systems, along with the corresponding process time and energy consumption, is paramount for evaluating the energy-related performance of the treatment method. The adsorption of pigments onto activated bentonite was notably rapid and effective when ultrasound was employed. In both bleaching processes, the adsorption kinetics of carotenoids and chlorophyll exhibited a pseudo-second-order behavior. At the same time, a pseudo-first-order equation provided a better fit for the control conditions. Moreover, intra-particle diffusion contributed to the adsorption mechanism, although it was not the only rate-limiting step in the adsorption of pigments on the clay. It is hypothesized that carotenoid and chlorophyll adsorption occur through physisorption in control conditions, while chemical reactions play a role in pigment removal under sonication. The Freundlich isotherm yielded precise estimates of the adsorption equilibrium data for carotenoid and chlorophyll during ultrasonic bleaching, suggesting a multilayer adsorption mechanism under ultrasound exposure. The thermodynamic study found that pigment adsorption was feasible, spontaneous, and endothermic. According to the results, horn and bath ultrasound, especially at higher voltages, can remarkably remove carotenoid and chlorophyll from sunflower oil compared to the traditional bleaching process.