An Efficient Binary Solvent Mixture for Monoacylglycerol Synthesis by Enzymatic Glycerolysis

Abstract

The present study was aimed at selecting an efficient binary solvent mixture for monoacylglycerol (MAG) synthesis by enzymatic glycerolysis of soybean oil. Solvent combinations of tert-butanol/isopropanol (v/v) at different ratios were studied. Of the investigated cases, tert-butanol:isopropanol at ratio 80:20 was the most suitable organic medium. The optimum conditions for MAG synthesis under the selected mixture were: water 10 wt% based on glycerol, Lipozyme TL IM 15 wt% based on oil and glycerol, weight ratio of solvent to oil 4:1, and molar ratio of glycerol to oil 3.5:1. Under these conditions with a 4-h reaction, the yield of MAG was 72.0% where the triacylglycerol (TAG) content was reduced to only 1.0% (based on acylglycerols). Fatty acid ester (FAE) formation from the solvents was very low in the final product (1.3% based on reaction mixture). The selected binary solvent mixture has good physical properties with low melting point (-26.5°C), which can avoid the risk of crystallization in practical operations.

Glycerolysis of sardine oil catalyzed by a water dependent lipase in different tert-alcohols as reaction medium

“…Therefore, it is important to determine the optimal water content in the reaction medium since it affects lipase activity and therefore the reaction rate and yield product. On the other hand, when the water content is too high it does not enhance the MAG yield resulting in an increase in by-product formation, such as FFA (Zhong et al, 2009). Therefore water control is important to ensure enzyme activity as well as to minimize hydrolytic side reactions.…”

“…Therefore an optimal amount of water to be added to the reaction medium taking into account the MAG yield and the FFA formation at the different mole ratios glycerol:oil does exist. In addition, mass transfer limitations of the lipophilic substrate, the sardine oil, from the reaction medium to the vicinity of the enzyme can become important at high water content since, as described in the literature (Cheirsilp et al, 2007;Zhong et al, 2009), an excess of water can surround the particles instead of forming a thin mono-hydration layer for catalytically-active conformation. Zhong et al (2009) found that the highest yield of MAG was obtained when 10 wt% of water was added to the glycerolysis system of soybean oil with Thermomyces lanuginosus lipase and TB/Isopropanol (80:20) as solvent system.…”

“…According to the equilibrium law, an increase in the glycerol content will shift the equilibrium towards MAG production. In the literature, it has been also described that glycerol can act as an effective stabilizer against thermal and solvent de-activation (Zhong et al, 2009). However, in the case of water-dependent lipases, the glycerol content can also directly affect the lipase activity due to its influence on the polarity of the reaction medium.…”

“…This result agrees with some previous studies on glycerolysis of different types of oils. Zhong et al (2009) selected 3.5:1 as optimum glycerol:soybean oil mole ratio, in their study on the glycerolysis reaction in a mixture of TB/Isopropanol (80:20) as reaction medium. Pawongrat et al (2007) used MTBE as solvent and showed that the optimum mole ratio of glycerol to tuna oil for MAG production was 3:1.…”

“…The commercial 1,3-specific lipase Lipozyme RM IM (from Rhizomucor miehei) immobilized on a macroporous anion-exchange resin has been used as biocatalyst. In addition to its specificity, Lipozyme RM IM is cheaper than the non-specific Novozym 435 commonly used in enzymatic glycerolysis (Zhong et al, 2009). The effect of water content in the reaction medium has been analyzed since it affects the lipase activity and therefore the reaction rate and MAG yield.…”