Preliminary Study on Acyl Incorporation and Migration in the Production of 1,3-diacylglycerol by Immobilized Lipozyme RM IM-catalyzed Esterification

Abstract

The acyl migration in the production of 1,3-diacylglycerol (1,3-DAG) by immobilized lipozyme RM IM-catalyzed esterification reaction in a solvent-free system was investigated, particularly including the acyl migration of 1,3-DAG to 1,2-diacylglycerol (1,2-DAG), which affected by some of the system's parameters (substrate molar ratio, enzyme load and reaction temperature). The results showed that all parameters had strong positive influences on acyl migration. With the increasing substrate molar ratio of oleic acid to glycerol from 1:1 to 3:1, the acyl migration showed a decreasing-increasing pattern. However, the degree of acyl migration increased gradually concomitant with the increasing of enzyme load (2 _ 10 wt% of substrates) and reaction temperature (45 _ 75℃). The conditions for the highest yields of 1,3-DAG and the relatively low levels of acyl migration were optimized as follows: temperature 65℃, oleic acid/glycerol molar ratio 2:1, enzyme load 6%, reaction time 2 h, 0.01 MPa vacuum, 200 rpm stirring speed.Keywords: 1,3-diacylglycerol, esterification, lipozyme RM IM, acyl migration IntroductionDiacylglycerol (DAG), has two configurations, namely, 1,3-DAG and 1,2(2,3)-DAG, which are known to be used as additives or carriers in the food, medicine, cosmetic industry, and so on (Fureby et al., 1997;Kaewthong et al., 2005). It is reported that 1,3-DAG oil has beneficial effects on suppressing the accumulation of body fat and preventing the increase of bodyweight (Meng et al., 2004; Reyes et al., 2008;Lo et al., 2008; Yanai et al., 2008;Morita et al., 2009). However, because of the minor content of 1,3-DAG in the natural form, the synthesis of 1,3-DAG becomes more significant. So, more and more attentions have been paid to 1,3-DAG production in recent years.In the preparation of 1,3-DAG, several chemoenzymatic and biotechnological methods are available (Guanti et al., 2004; Villeneuve et al., 2000). It seems that high yield of 1,3-DAG cannot be obtained by direct chemical methods because this methods lack positional selectivity. The enzymatic synthesis of 1,3-DAG has been considered more effective due to its milder and simpler reaction conditions, higher selectivity, greener process and safe products. In general, the preparation of 1,3-DAG enzymatically by direct esterification, glycerolysis, interesterification, partial hydrolysis, or the combination of partial hydrolysis and esterification (Blasi et al., 2007;Cheong et al., 2007; Weber et al., 2004; Yang et al., 2004;Liu et al., 2011; Palla et al., 2012). Comparing with other methods, Z. Meng et al. 176 when the direct esterification used, the fatty acid and glycerol can fast synthesis 1,3-DAG, especially, when the reactions are carried out in a solvent-free system. Lipozyme RM IM is well known as one of the lipases with a strict 1,3-positional specificity, which was used to catalyze esterification of glycerol with oleic acids for 1,3-DAG production in the solvent-free system. Acyl migration should occur during the 1,3-DAG production process, which was n...

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