Triacylglycerols interesterification

Ferrari, R., Esteves, W. and Mukherjee, K. (1997) Alteration of steryl ester content and positional distribution of fatty acids in triacylglycerols by chemical and enzymatic interesterification of plant oils. J. Am. Oil Chem. Soc., 74(2), 93—96. 

Rousseau, D., Hill, A.R., Marangoni, A.G. 1996a. Restructuring butterfat through blending and chemical interesterification. 1. Melting behavior and triacylglycerol modifications. J. Am. Oil Chem. Soc. 73, 963-972. 

Interesterification involves an exchange of acyl groups within and between triacylglycerol molecules. This re-distribution of the fatty acids results in modification of the physical properties and nutritional properties of the fat (Frede, 1991). The traditional process of interesterification involves the use of chemicals. 

Chemical interesterification randomizes the fatty acid distribution in the triacylglycerol. The extent of modification of the fat depends on the composition of the starting fat and whether a single or a blend of fats is used and the conditions of the chemical interesterification process (Mickle et al., 1963 Huyghebaert et al., 1986 Rousseau and Marangoni, 2002). 

Early work showed that interesterification of milk fat resulted in an increase in the melting point of milk fat and the concentration of high melting triacylglycerols (de Man, 1961). The effect on the melting point of milk fat was greater in the case of directed interesterification compared to random interesterification. The use of solvents in the interesterification process also enhances its effects on the melting point of the modified milk fat (Weihe, 1961). 

A reduced level of low molecular weight monounsaturated triacylglycerols (C36 and C38) and increased levels of trisaturated triacylglycerols (C44-C50) was obtained on undirected chemical interesterification of milk fat with sodium methoxide (0.5%) as catalyst, resulting in a wider temperature range for crystallization compared to native milk fat (Parviainen et al., 1986). 

Figure 8.8. Effect of chemical interesterification on the relative proportion (w/w) of milk fat triacylglycerols as a function of carbon number (CN). TAG = triacylglycerol. Noninteresterified milk fat (O-O), interesterified milk fat-15 min ( - ), 30 min ( - ), 60 min ( - ), 90 min (A-A), and 120 min (A-A)- (Reproduced with permission from Rousseau et al., 1996a).

When interesterification of milk fat was carried out at 100°C with 0.2% sodium, there was an increase in middle-melting point triacylglycerols but only small effects on the melting properties of milk fat (Timms and Parekh, 1980). These authors concluded that although the interesterified milk fat was more compatible with cocoa butter than unmodified milk fat, the effects were not sufficient to warrant the use of interesterification (Timms and Parekh, 1980). 

A comparison of physical mixtures of milk fat-corn oil and of blends that were interesterified (0.5% sodium methoxide, 65-70°C under reduced pressure) showed that interesterification increased the softening point of the blends (Rodrigues and Gioielli, 2003). There were only small changes in the total disaturated-monounsaturated and monounsaturated-diunsaturated triacylglycerols but there were marked differences in the symmetrical and asymmetrical contents of the triacylglycerols... 

Solvent-free enzymatic interesterification of milk fat alone or with other fats or fatty acids provides the most acceptable route for modification of the triacylglycerol structures in milk fat and further research and development in this field is expected to provide physical and physiological benefits. From a nutritional perspective, it is of interest to examine the effects of randomized milk fat on serum cholesterol. Christophe et al. (1978) reported that substitution of native milk fat with chemically-randomized interester-ified milk fat reduced cholesterol levels in man. However, others found that there was no effect on serum cholesterol levels in man as a result of substitution of ezymatically randomized milk fat (De Greyt and Huyghebaert, 1995). Further studies are required to determine if interesterilied milk fat provides a nutritional benefit. 

Another promising area for adaptation of enzyme bioreactor technology is that of lipid modification. Several examples are a) the interesterification of triacylglycerols to change their composition b) limited lipolysis for production of flavors and c) conversion of cholesterol to forms that are not absorbed. The potential stabilization of enzymes to the presence of organic solvents would provide a definite advantage to enzyme bioreactor technology for the modification of lipid molecules. 

Lipase. Interesterification of triacylglycerols in the presence of a regiospecific lipase or a nonspecific lipase and free fatty acids can be used to modify the physical or nutritional characteristics of fats. Lipases from Aspergillus sp. (47,48) and Rhizopus... 

The lipase-catalyzed interesterification process can be used for the production of triacylglycerols with specific physical properties, and it also opens up possibilities for making so-called structured lipids. An example is a triacylglycerol that carries an essen-... 

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. 

Natural oils and fractionated oils usually have their acyl chains organized in a nonrandom manner, but they become randomized after interesterification with a chemical catalyst. There is no change in fatty acid composition, only in triacylglycerol composition, but this leads to a modification of the physical properties. More selective interesterification can be achieved with enzymic catalysts (Section 8.5). 

Figure 3. Formation of triacylglycerols during interesterification [Adapted from (2)].

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]. 

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