Adsorption of protein on activated carbon used in the filtration of mucilage derived from Pereskia aculeata Miller

Abstract

Mucilage is derived from Pereskia aculeata Miller via precursors obtained by an extraction process. However, this process produces dark liquor whose coloring is not desirable in the final food additives. Therefore, a fixed-bed filtration system with activated carbon was used for pigment elimination and clarification of the final product. Color parameters and protein contents were evaluated by comparing the extract and the filtrate. At the same time, an experimental study was conducted that monitored changes in pH and in the adsorption kinetics of proteins on the activated carbon using reactor tanks at various temperatures and residence times. When using a filtration column, the results showed an increase in parameters L*, b* and Hue angle, thereby indicating that the filtrate was closer to the yellow color when compared with the liquor feed. The results obtained using reactor tanks showed that the protein contents and the pH were dependent on the contact time of the substrate with the activated carbon and on the temperature. The experimental time necessary to reach equilibrium was of 15.15 h for treatments at 30 °C, 19.70 h at 45 °C, and 26.06 h at 60 °C. In these equilibrium conditions, the experimental adsorbed quantities of protein (qe) were 223.03 mg/g, 232.02 mg/g and 332.02 mg/g respectively. The pH value increased linearly as a function of temperature and residence time in the reactor. Reaction-based kinetic models were expressed by the pseudo-first order, pseudo-second order, Weber–Morris and Elovich models. Specifically, sorption kinetics follows the pseudo-second order mechanism for protein adsorption. Scanning electron microscopy analyses proved that the non-diffusive is the sorption mechanism of protein on activated carbon surface.