Selective lipase-catalyzed hydrolysis for removal of diglyceride in palm oil

Abstract

Palm-based transformer oil is an environmentally friendly and renewable alternative to mineral-based oil for use as an insulating oil. However, the crystallization of palm oil at low temperatures can cause operational issues in transformers. In this research, low diglyceride palm oil is first proposed as a promising base stock for palm-based insulating oil to overcome this issue. The research focuses on the removal of diglycerides (DG) from palm oil by selective enzymatic hydrolysis under a solvent-free system. The results indicate that the lipase GS-250G specifically catalyzes only DG molecules without hydrolyzing TG molecules, despite TG molecules being more prone to hydrolysis than DG molecules due to their higher concentration in palm oil. This unique behavior is probably attributed to steric hindrance by bulky amino acids surrounding the catalytic pocket of lipase GS-250G. Under optimum conditions (30 °C, atmospheric pressure, water content of 16 wt%, agitation speed of 850 rpm, lipase loading of 0.005 wt%, and 4 h of reaction time), the lipase GS-250G reduced the DG content in palm oil from 7 % to 0.5 % with a degree of DG hydrolysis of 95 %. After purification, the final product was composed of 99 % triglyceride (TG). The cold stability test suggested that the nucleation and crystallization rate during the crystal formation of palm oil were reduced by decreasing the DG content. The finding suggests that the proposed procedure in this work is a rapid and environmentally sustainable method for DG removal, which can solve the major problem of palm oil. This discovery opens new opportunities for palm oil to be used as a raw material only for insulating oil but also for various palm based products.