Interesterification triacylglycerol, reaction

The fatty acid or alcohol groups present in an ester can be exchanged in a number of ways by reaction with an excess of other fatty acids (acidolysis), alcohols (alcoholysis), or other esters (interesterification). Generally, the starting point will be a triacylglycerol, and these reactions provide routes by which the composition and properties of oils and fats can be modified. 

Modification of the Properties of Fats and Oiis Transesterification reactions (interesterification and acidolysis) of triacylglycerols have been an important tool in fats and oils processing for the modification of their physical and rheological properties by changing the composition and distribution of their fatty acids. 

Lipases (triacylglycerol hydrolases, EC 3.1.1.3) are enzymes that catalyze reactions such as hydrolysis, interesterification, esterification, alcoholysis, acidolysis, and aminolysis [1]. There is an increasing interest in the development of lipase applications to oleochemical transformations to obtain esters of long-chain fatty acids, as monoalkyl esters of fatty acids [2]. Utilization of lipase as a catalyst for the production of biodiesel, defined as a mixture of monoalkyl esters, is a clean technology due to its nontoxic and environmental fnendly nature, requiring mild operating conditions compared with chemical method [3]. 

Fig. 3.1. Argentation thin-layer chromatography plate of a L-P-P/P-L-P regioiso-meric mixture obtained by interesterification (left lane) total milk fat triacylglycerols (TAG middle lane) and CLA-P-P obtained from the reaction of 1,2-dipalmitin with CLA (right lane). P, palmitic acid L, linoleic acid. CLA-containing TAG were found between bands two and three and in band six. (Published with permission from Ref. 28 and redrawn from original.)...

In equation (12.3), TGI (triacylglycerol) and FAl (fatty acid) are converted to TG2 and FA2 by interesterification via a reversible reaction of equal rates. In equation (12.4), hydrolysis of TGI to DGl (diacylgly-cerol) and FA3 is reversible with synthesis at different reaction rates. From a combination of the two reactions, the formation rates of the reactants TGI, FAl, TG2, FA2, DGl and FA3 can be obtained as follows ... 

Acidolysis is a reaction of triacylglycerols with carboxyhc acid, which leads, under acid catalysis, to the exchange of acyl residues. The reaction is in dynamic equilibrium and if the equihbrium is not shifted by removing reaction components, the product contains all components, including the starting reactants (Figure 3.79). Of all the interesterification reactions, acidolysis currently has the least practical significance. 

The reaction of triacylglycerols with alcohol is called alcoholysis. It can be catalysed by acids (sulfuric acid or 4-toluenesulfonic acid), and then an interesterification reaction, which is a parallel reaction to esterification of free fatty acids occurring in the fat. Alcoholysis is kinetically similar to esterification. The base catalysed reaction employs methoxides, hydroxides and carbonates of alkali metals. The most commonly used catalysts are sodium methoxide, sodium hydroxide or potassium hydroxide. Industrially produced alcoholysis products are methyl, ethyl or propyl esters (Figure 3.82) of fatty acids. Analogous to hydrolysis, mixing of fat (oil) with alcohol gives a two-phase system... 

Modified triacylglycerols can occur in different polymorphic forms, and these influence the melting properties of the fat, the softening point, the solids content, etc. Analysis of such properties is commonly performed using differential scanning calorimetry (DSC). DSC has been used to determine the physical properties of sTAG formed from interesterification products of triolein and tristearin (Seriburi and Akoh, 1998) and from acidolysis reactions between stearic acid and coconut oil (Rao et al., 2001). 

Stmctured triacylglycerols (see Chapter 6) of the type CGC (where C represents caprylic acid, and G represents GLA) have been prepared in a two-step process. In the first stage the triacylglycerol GGG is prepared from glycerol, GLA, and Candida antarctica lipase. This is then subjected to acidolysis with caprylic acid or interesterification with ethyl caprylate in the presence of Rhizopus delemar lipase. A typical reaction product contains 53% caprylic acid and 47% GLA with CCG (58%) and CGG (29%) as the major triacylglycerols (Kawashima etal., 2001). This particular work was carried out only on a laboratory scale but there are many reports of this type of enzymatic process being carried out on a kilogram scale. At present such compounds are probably too expensive to be incorporated into functional foods and are more likely to be used in pharmaceutical preparations. 

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