Enzymatic synthesis of mono-diacylglycerides using off-grade crude palm kernel oil and waste glycerol from biodiesel production

Abstract

Enzymatic transesterification of mono-diacylglycerides (MDGs) is a promising solution to overcome the limitations of chemical transesterification such as low product selectivity, high-temperature reactions, and toxic residue. In this work, we synthesized MDGs by enzymatic transesterification using off-grade crude palm kernel oil (CPKO) and glycerol obtained from waste of biodiesel production as substrates, which was never reported previously. The waste glycerol was purified by acidification and neutralization processes. This study aimed to observe the influence of three important factors: concentration of Candida antarctica at 0.05–0.50 % (w/w), concentration of substrate at 1:1–1:10 (molar), and reaction temperature at 30–75 °C on the yield of MDGs. The reaction was performed in 300 mL of n-hexane for 8 h at a stirring speed of 400 rpm. The substrate conversion to MDGs was determined based on the reduction of free fatty acid (FFA) which was also confirmed by the gas chromatography. The study found that the concentration of Candida antarctica significantly affected substrate conversion compared to other factors. The optimum yield of MDGs was 69.84 %, which was achieved at a Candida antarctica concentration of 0.20 % (w/w). It contains 36.61 % of monoglycerides (MGs) and 33.23 % of diglycerides (DGs). The characteristics of optimum MDGs were similar to commercial products and agreed with Food and Agriculture Organization. Optimum MDGs were classified as oil-in-water emulsifiers with a hydrophilic-lipophilic balance (HLB) of 3.2. Application of 1.0 % (v/v) MDGs as emulsifiers can maintain emulsion stability for 30 days of storage, with a creaming index of 33.30 % and droplet size of ±326.09 μm.