Interesterification random chemical

The oxidative stability of the product or margarine basestock obtained from SBO and methyl stearate by chemical interesterification with regioselectivity was evaluated and compared with that of the basestock from which FAs were randomized by H. Konishi et al. (144). 

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). 

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). 

Chemical interesterification would lead to randomization of all of the acyl chains, and the products would have different melting behavior from that required by a cocoa butter equivalent (188). 

Two basic types of chemical interesterification are practiced random and directed. Both involve the use of transition metals, such as sodium, or more commonly derivatives, such as sodium methoxide, as a catalyst. The differences between these two interesterification reactions are summarized in Table 22. 

Chemical interesterification results in a complete randomization of acyl groups in the TAGs. Interesterification, alone or in combination with other processes, extends... 

Two basic types of chemical interesterification processes involving the use of metal catalysts are employed random and directed. 

Again, the use of lipase catalyst for interesterification of edible fats and oils has advantages over the classical chemical catalysts. One of the most attractive features is the unique specificities possible with their use. Nonspecific lipases provide reactions like the random chemical catalyzed interesterification. Specific lipases make it possible to produce fats and oils with a customized triglyceride structure. The enzymatic process can be selective with the use of a positional specificity lipase. These processes are usually much slower and more sensitive to the reaction conditions to provide a better control over the reaction results. Also, the lipases can operate under milder reaction conditions, temperature and pressure, that minimize the formation of side products. 

Interesterification is performed either by chemical or enzyme catalysis and involves at least two oils that have different fatty acid compositions. In chemical interesterification, alkali metals (sodium, potassium) and alkali-metal alcoholates (e.g., methylate, ethylate) are used as catalysts. Sodium methylate is the most widely used catalyst. The dried and deacidified oil is stirred at 80 to 100°C in the presence of alcoholate (0.1-0.3% of fat weight) and when the reaction is completed the catalyst is destroyed, by addition of water, and subsequently removed. The interesterified fat is recovered and then bleached and deodorized. Chemical interesterification progresses randomly with no regioselectivity (positional specificity) on the carbons of the glycerol moiety of the TAG (Gunstone, 1994). 

Much research has been carried out on the chemical interesterification of milkfat. Milkfat, like most fats, does not have a random distribution. Butyric and caproic acids, for example, are predominantly located at the sn-3 position, whereas palmitic acid is mostly at sn-l and sn-2 positions (Kuksis et al., 1973). Interesterification of milkfat can be a powerful means of modifying its functional properties. 

An alternative method is interesterification where the fatty acids are rearranged. This can be done chemically, which gives a random distribution, or by using enzymes. The advantage of enzymes is that they are very specific in their action. It is quite possible using a lipase to remove... 

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. 

In the interesterification of fats, 1,3-positional specific lipases catalyze reactions in which only the fatty acids in the a-positions of the triglycerides take part, whereas positional nonspecific lipases are able to catalyze reactions in which the fatty acids from both the a- and / -positions take part. In transesterification between two types of fat, the positional non-specific lipase is therefore able to randomize the fatty acids, resulting in the same fatty acid composition in the triglycerides as obtained in the commercially important chemical randomization process. In ester synthesis, positional non-specific lipases catalyze the reaction with both primary and secondary alcohols whereas positional specific lipases are more or less specific for primary alcohols. 

Another type of reaction that can be catalyzed by an enzyme in the presence of a supercritical fluid, that has commercial potential, is the interesterification of vegetable oils to produce a randomized product having quite different physical and chemical properties than the starting materials. Jackson et al. [52] have interesterified a variety of starting materials by dissolving them in SC-CO2 and transporting them over immobilixed beds of... 

Lipase-catalysed interesterification has found many applications in production of edible and specialty lipids due to mild reaction conditions, high catalytic efficiency, the inherent selectivity of natural catalysts and production of much purer products as compared to chemical methods (Sonnet, 1988). Lipases (hydrolases) are used for hydrolysis and ester synthesis. They are classified as non-specific or random, positional specific or 1,3-specific and acyl group- or structure-specific, depending on their activity towards fatty acids... 

A schematic representation of enzyme catalysed interesterification processes and products is shown in Figure 12.6. These processes generally involve hydrolysis and re-synthesis. Under restricted water conditions, interesterification is found to be predominant (Matsuo et aL, 1980, 1981 Coleman and Macrae, 1980). Chemically catalysed interesterification processes lead to randomization of the acyl groups along the glycerol chain. Using lipases with regio-specificity, the acyl transfers are restricted to the fatty acids located at the precise positions specific to the enzyme. 

Two types of interesterification are presently in use chemical and enzymatic. Enzymatic modifications rely on the use of random or regiospecific (1,3-or 2-specific) and fatty acid-specific lipases as catalysts, whereas for chemical modifications metal alkali catalysts are usually employed. 

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