Factors Affecting The Optimization Of Lipasecatalysed Palm-Based Esters Synthesis

The lipase synthesis of esters using palm oil fractions and long chain alcohol as substrates was carried out. Various lipases were tested for their suitability for the reaction. Among the enzymes tested, Lipozyme IM exhibited the highest percentage yield of palm oil ester (more than 75%) compared with the other lipases. Two methods, classical method (one-variable at-a-time) and response surface methodology (RSM),w ere employed for optimization of the reaction. By the classical method, five parameters such as reaction time, temperature, amount of enzyme, molar ratio of substrates and various organic solvents of the reaction system were investigated The optimum yield was achieved at the reaction temperature of 40 - 500C for palm oil (PO) and 400C for palm kernel oil (PKO) alcoholysis, a reaction time of 5 - 7 h for PO and 7 - 10 h for PKO, 0.15 g of enzyme for both PO and PKO alcoholysis, molar ratio at 3: 1 (alcohol: PO or PKO), and the best solvent for the reactions was hexane. Percentage yields of esters obtained at these optimum reaction conditions were 83, 80 and 81% for refined, bleached and deodorized (RBD) palm oil, RBD palm stearin (PS) and RBD palm olein (PL), respectively and 87, 90 and 86% for RBD palm kernel oil, RBD palm kernel stearin (PKS) and RBD palm kernel olein (PKL) , respectively. The classical method of optimization involves varying one parameter at a time and keeping the other parameters constant. However, this method is inefficient as it fails to understand relationships between the variables (reaction time, temperature, molar ratio and amount of enzyme) and the response (percentage yield). RSM is an effective statistical technique for the investigation of complex processes. RSM comprising of a five-level, four-factor central composite rotatable design (CCRD) was used to evaluate the interactive effects of synthesis reaction time (2.5 - 10 h of PO, 5 - 15 h of PKO), temperature (30 - 700C of PO, 30 - 500C of PKO), amount of enzyme (0.1 - 0.2 g of PO or PKO) and substrates molar ratio (1: 1 - 5: 1 alcohol to PO or PKO) on the percentage yield of esters and to obtain the optimum conditions for enzyme-catalyzed alcoholysis of palm-based ester. The optimum conditions derived by RSM of PO and PKO were: reaction time at 7.38 and 10 h, temperature of 53.9% and 44.20C, amount of enzyme of 0.149 and 0.157g, and substrates molar ratio 3.41: 1 and 3.78: 1 (alcohol: PO or PKO), respectively. The actual experimental yield of PO and PKO were 84.6% and 90.8% under these optimum conditions, which compared well with the maximum predicted value of 85.4% and 91.8% for PO and PKO, respectively. The composition of esters synthesized from PO at optimum reaction condition are 0.8% of oleyl laurate, 3.8% of oleyl myristate, 35.5% of oleyl palmitate, 4.5% of oleyl stearate, 33.3% oleyl oleate and 6.2% of oleyl linoleate. Meanwhile, The composition of esters synthesized from PKO are 0.7% of oleyl caproate, 5.7% of oleyl caprylate, 3.7% of oleyl caprate, 36.7% of laurate, 13.10% of oleyl myristate, 8.8% of oleyl palmitate, 2.5% oleyl stearate, 14.1% of oleyl oleate and 2.4% of oleyl linoleate. These optimum conditions were also used in alcoholysis of PS, PL, PKS and PKL, which gave the average percentage yield of more than 80%.

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