Interesterification processes

Natural fats and oils can be used directly in products, either individually or as mixtures. In many cases, however, it is necessary to modify their properties, particularly their melting characteristics, to make them suitable for particular applications. Therefore, the oils and fats industry has developed several modification processes using enzyme technology. In particular, lipases (and lately cutinases), phospholipases and pectinases can be used for interesterification processes, ester syntheses and in olive-oil extraction. 

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). 

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 Solid Fat Index (SFI) estimates the percent of solids in a semisolid fat on the basis of changes in volume with temperatures. This is of importance in fat hydrogenation and interesterification processes. 

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 processes involving the use of metal catalysts are employed random and directed. 

Interesterification is done by two methods chemical and enzymatic. The cost for making interesterified producs is very similar for both processes. The enzymatic interesterification process is becoming more popular because it is environmentally friendly. 

Continuous interesterification processes exist but to date none have been commercialized. Interesterification is generally performed in small batches by specialty processors. An alternate method of increasing interest is directed interesterification using enzymes. The process is generally applied to palm-oil-based materials such as cocoa butter substitutes and to coconut oils. There is some concern about the effectiveness of interesterification with physical refined oils as low levels of FFA must be present or the reaction will not proceed as planned (5). Although not a hazardous process, interesterification is often included in the hydrogenation section of the refinery because of the similarity of the reactors. 

The one food product that may be influenced the most by trans-fat concerns is margarine. Obviously, margarine must be a solid product, and this product cannot be replaced by liquid oils with improved stability. The most probable replacement for hydrogenation for margarine oils is interesterification. A chemical interesterification system is depicted in Figure 4. Although the chemical interesterification process is over 50 years old, it is coming back into popularity to process low frani-solid products. 

One must understand that the interesterification process, chemical or enzymatic, is of no value in making heavy-duty frying fats. The high percentage of unsaturated oil, even with interesterification and addition of near-zero IV fat to provide plasticity, is still unstable under heavy-stress frying conditions. 

The interesterification process has not found any significant application to CNO itself. The most important property of CNO and HCNO is their short plastic range and interesterification does not improve this very significantly. Nevertheless, some interesting products can be made by interesterfication of blends of CNO or PKO with palm oil and palm stearin to produce margarine fats, and these are described under PKO. 

More often, lipolytic enzymes are replacing chemical catalysts in the interesterification process, as well as effectively regulating the process parameters. 

The chemistry of polyol surfactants is reviewed by Benson (1967), and interesterification processes are described by Sonntag (1982). Synthetic procedures for monoglycerides are dealt with in Chapter 7. 

These changes can be further modified if the interesterification process is carried out at a lower temperature (0-40 C), so that fully saturated glycerides (S3) crystallize from the reaction mixture. This is called directed interesterification. Crystallization disturbs the equilibrium in the liquid phase so that more S3 forms and again separates producing, finally, more S3 and U3 and less of the mixed glycerides. This usually causes an increase in the melting range of the fat. Such reactions are slower and may take up to 24 hours. 

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. 

Except for perhaps the manufacture of cocoa butter substitutes, enzymatic interesterification processes have been confined to laboratories and pilot plants. The reasons are partially due to the relatively low value of products from these processes and more importantly to the many difriculties in solving the engineering problems of bioreactor designs for efficient, continuous processes. Application of biotechnology and computer aided techniques in bioreactor designs are consequently used to find solutions to these problems. The ultimate aim is to produce cost effident process designs for manufacturing products of even subtle value at competitive production costs to chemical catalysis. 

Table 12.6 Example of immobilized lipases and reactor types used in interesterification processes...

The solid liquid ratio of acylglycerols is of importance in fat hydrogenation and interesterification processes (cf. 14.4.3). This ratio can also be assessed using the Solid Fat Index by measuring the expansion of the fat, i. e. the volume increase of a fat during its transition from solid to liquid and by H-NMR spectroscopy (cf. 14.5.1). 

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