Interesterification randomization

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). 

There are two types of interesterification random, which is carried out in the fully molten state, and directed, which is carried out with the fat partially solidified. The two types produce different results but the former is far more common and interesterification may be assumed to refer to the random type (randomisation), unless otherwise stated. The usual catalyst employed is sodium methoxide at about 0.1%. 

RandomiZation/Interesterification. Transesterification occurs when a carboxyUc acid (acidolysis) or alcohol (alcoholysis) reacts with an ester to produce a different ester (20). Ester—ester interchange is also a form of transesterification. If completely unsaturated triglyceride oil (UUU) reacts with a totally saturated fat (SSS) in the presence of an active catalyst such as sodium, potassium, or sodium alkoxide, triglycerides of intermediate composition may be formed. 

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... 

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). 

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). 

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. 

Interesterification (INES) is the exchange of acyl radicals between an ester and an acid (aci-dolysis), an ester and an alcohol (alcoholysis), or an ester and an ester (transesterification), and can be random, directed, or enzymatic. The process has been called intraesterification if an exchange of positions occurs within the same molecule, and randomization if exchange occurs between molecules.44,48 The principles can be used to position fatty acids on mole-... 

From Bookish, M., Fats and Oils Handbook, AOCS Press, Champaign, IL, 1998, with permission. bFrom Sonntag, N. V, Fat Splitting, Esterification, and Interesterification, in Bailey s Industrial Oil and Fat Products, 4th ed Vol. 2., D. Swem, Ed., pp. 97-173, John Wiley Sons, New York, 1982. With permission. cn = native r = randomized. 

The main objective in interesterification is to produce solids free from trans fatty acids for later use in compounded fat products. The final fat, or a series of base stocks, can be made for future blending. Randomization can improve the functionality of a fat, as shown... 

The temperature optimum for interesterification is 85°C or higher, and the half-life in continuous acidolysis of spy bean oil with lauric acid at 60°C is above 2500 h. The non-specificity makes the catalyst useful in random interesterification of different fats. The catalyst has some saturated fatty acid specificity. Two lipase components (A and B) were purified. Lipase A is important for interesterification, and Lipase B is important in ester synthesis. 

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. 

Interesterification may be either random or directed. In random interesterification the acyl groups are randomly distributed as demonstrated by the following example where equal proportions of tristearin (S—S—S) and triolein (O—O—O) are allowed to interesterify. 

In directed interesterification, the course of the reaction is shifted away from production of a population of acylglycerols with a fully random fatty acid distribution. This is achieved by a modification of reaction conditions to selectively remove from reaction some of the produced acylglycerol species as they are formed. Most... 

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). 

The crystal structures of margarines based on sunflower or canola oil (rape-seed) along with hydrogenated oil are stabilized in the p form by interesterification leading to randomization of the glycerol esters. 

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). 

Interesterification. The least known and practiced processing technique available to the fats and oUs processor for modification of the physical properties of an oil is interesterification, often referred to as rearrangement. The ability to modify the melting point and functional crystallization characteristics without changing the fatty acid composition makes interesterification a process with a number of unique possibilities. The benefits of the random interesterification processes are summarized in Table 21 (133). 

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. 

Some companies are producing low-trans- or zero tranj -margarines by random (252) or directed interesterification of mixtures of unhydrogenated and fully hydrogenated soybean oils and other fats (253). To produce these products, a liquid oil and completely hydrogenated hardstock are interesteiified, so that proper plasticity can be obtained. Oils that contain considerable amounts of palmitic acid favorably influence crystallization and polymorphic form of the interesterified fat blends (254). 

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