Bleaching of crude marula oil using activated bentonite and activated marula shells: A comparative analysis

Abstract

Refining of edible and cosmetic oil consists of various steps which include bleaching process. Bleaching is an important step as it removes colour pigments resulting in improvement of taste of oil and appearance. In this work, activated bentonite and activated marula shells were used to refine crude marula oil. Fresh bentonite was activated using H2SO4 whilst marula shells were activated using both H2SO4 and KOH. Vacuum bleaching of crude marula oil was performed using both the activated bentonite and activated marula shells. Fresh, activated, spent bentonites and marula shells were analysed using X-ray Diffraction (XRD), Fourier transform infrared (FTIR), X-ray Florescence (XRF), Thermal gravimetric analysis (TGA) for phase identification, elemental composition of crystalline material, functional groups present and thermal decomposition of the materials. Analysis of β-carotene and chlorophyll was done using UV-visible spectrophotometer on bleached and crude marula oils. Acid values (AV) and free fatty acids (FFA) values in the oil were calculated using standard procedures. The effects of acid activation parameters were investigated namely, acid concentration and activation time. Acid and alkali activation improved the adsorption properties of fresh bentonite and fresh marula to remove colour pigments. Increase in acid concentration and activation time resulted in increase in bleaching capacity of adsorbent. Optimum acid concentrations for activation were 2 N and 15 N for bentonite and marula shells respectively and optimum activation times were 7 and 1.5 h for bentonite and marula shells respectively. The study indicated that activated bentonite and activated marula shells are effective and were successful in improving the appearance of crude marula oil to the required quality standards. Marula shells are a by-product waste in cosmetic oil processing and its use assists in waste utilization in-line with circular economy principles.