Interesterification

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). 

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). 

Interesterification is a term used to describe reactions in which fatty acid esters react with free fatty acids (acidolysis), alcohols (alcoholysis), or with other fatty acid esters (transesterification). In food application, interesterification often refers to the reaction between different oils or fats with their fatty acyl groups rearranging among the molecules. 

Interesterification is conveniently achieved by an alkali methoxide-catalyzed reaction at mild temperatures (20-100°C). Microbial lipases are also widely used as biocatalysts in enzymatic interesterification. In contrast to the chemical process, the enzymatic process can be more selective if an enzyme with positional specificity is used, and it is usually much slower and more sensitive to the reaction conditions. New developments in lipase-catalyzed interesterification 

Fractionation or winterization is a process in which the more saturated molecular species in the oil are solidified during low temperature treatment and subsequently removed cold storage stability is thereby increased. When partially hydrogenated soybean oil is fractionated, the more saturated molecular species are removed to produce a clear oil that meets the requirements of a salad oil and a high-stability liquid oil. 

Various methods of laboratory scale, pilot plant processing, and batch reaction were described by Erickson (1995c). List and co-workers (1977) pioneered the development a zero trans margarine by interesterifying 80% RBD soybean oil with 20% RBD and fully hydrogenated soybean oil. The resulting product has comparable SFI to the conventional products. In a more recent study, 

A similar study of zero-trans margarine from soybean oils with modified fatty acid composition was conducted by List and co-workers (2001). A soft margarine was prepared from interesterified soybean oil with elevated stearic 

Natural fats and oils are subjected to extensive interesterification during processing. This in- 

The baking properties of lard (improvement of volume and softness of the baked goods) are improved by interesterification. The uniform distribution of palmitic acid in the triacylglycerols accounts for such an improvement. 

Furthermore, interesterification is of importance in the manufacturing of different varieties of margarine with a given composition, for example  

Melting point Prior to interesterification Single phase interesterification Directed interesterifi- cation 

Interesterification of palm oil with palm seed or coconut oil (2 1) and the use of 6 parts of this product with 4 parts of sunflower oil provides a margarine which contains 20-25% w/w of linoleic acid and does not contain hydrogenated fat. 

The most important chemical reactions for triglycerides (fats and edible oils) are hydrolysis, methanolysis, and interesterification. The other reactions, such as hydrogenation, isomerization, polymerization, and autoxidation that are primarily relevant to the processing of edible oils and fats are also discussed in this section. 

The fat or oil can be hydrolyzed into fatty acids and glycerol by treatment with steam under elevated pressure and temperature. The reaction is reversible and is catalyzed by inorganic catalysts (ZnO, MgO, or CaO) and an acid catalyst (aromatic sulfonic acid). 

Glycerides can also be hydrolyzed by treatment with alkali (saponification). After acidification and extraction, the free fatty acids are recovered as alkali salts (soaps). 

The fats and oil react with methanol to produce fatty methyl esters. Inorganic alkali, quaternary ammonium salts, and enzymes (lipase) have been used as catalysts for methanolysis in commercially practiced processes for soap manufacture. 

Interesterification causes a fatty acid redistribution within and among triglyceride molecules, which can lead to substantial changes in the 

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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. 

In addition to having the required spedfidty, lipases employed as catalysts for modification of triglycerides must be stable and active under the reaction conditions used. Lipases are usually attached to supports (ie they are immobilised). Catalyst activity and stability depend, therefore, not only on the lipase, but also the support used for its immobilisation. Interesterification reactions are generally run at temperatures up to 70°C with low water availability. Fortunately many immobilised lipases are active and resistant to heat inactivation under conditions of low water availability, but they can be susceptible to inactivation by minor components in oils and fats. If possible, lipases resistant to this type of poisoning should be selected for commercial operations. 

Lipases catalyse reactions at interfaces, and to obtain a high rate of interesterification the reaction systems should have a large area of interface between the water immiscible reactant phase and the more hydrophilic phase which contains the lipase. This can be achieved by supporting the lipase on the surface of macroporous particles. 

The role of reversed micelles in the manufacture of fine chemicals with enzymes also needs to be assessed and analysed. An outstanding example is lipase catalysed interesterification to produce cocoa butter substitute from readily available cheap materials (Luisi, 1985). This example of reversed micelles is sometimes referred to as a colloidal solution of water in organic systems. A number of water insoluble alkaloids, prostanoids, and steroids have been subjected to useful transformations (Martinek et al., 1987). Peptide synthesis has also been conducted. The advantages of two liquid phases are retained to a very great extent the amount of water can be manipulated to gain advantages from an equilibrium viewpoint. 

Fixed-bed reactors employed for lipase-catalyzed hydrolysis and interesterification reactions are highly efficient and have been used on a large scale (Table 5). The two phases may flow through the reactor in the opposite or same directions. If no solvents are used, the effect of viscosity of some substrates (i.e., oil) may be minimized by employing high temperatures which lead to faster rates of inactivation of lipases. 

At present, margarine producers are moving to use fractionation and interesterification to produce the required properties. A new technology uses lipase enzymes to rearrange fatty acids in a controlled way. 

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... 

Interaction parameters for polymer blends, 20 322 in surfactant adsorption, 24 138 Interaortic balloon pump, 3 746 Intercalated disks, myocardium, 5 79 Intercalate hybrid materials, 13 546-548 Intercalation adducts, 13 536-537 Intercalation compounds, 12 777 Intercritical annealing, 23 298 Interdiffusion, 26 772 Interdigitated electrode capacitance transducer, 14 155 Interesterification, 10 811—813, 831 Interest expense, 9 539 Interface chemistry, in foams, 12 3—19 Interface metallurgy materials, 17 834 Interfaces defined, 24 71... 

Saturated-, unsaturated fatty adds, triglyceride from interesterification products silicalite-1 2-Heptanone/ acetone [191]... 

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. 

The main current potential application of lipase-catalyzed fat-modification processes is in the production of valuable confectionery fats for instance, alternative methods of obtaining cocoa-butter equivalents by converting cheap palm-oil fats and stearic acid to cocoa-butter-like fats. The reaction is executed in a water-poor medium, such as hexane, to prevent hydrolysis. At least one commercial apphcation exists. Loders Croklaan (Unilever) has an enzymatic interesterification plant in Wormerveer, the Netherlands. Many other new potential applications of lipases have been proposed of which some will certainly be economically feasible. Examples and details can be found in chapter 9 of this book. 

The hpase activity unit (BIU, batch interesterification units) is described in publication AF 206-2 obtainable from Novo Nordisk A/S. 

Ison, A.P., Dunnill, P., Lilly, M.D., Macrae, A.R. and Smith, C.G. (1990) Enzymatic interesterification of fats Immobilization and immimogold localization of hpase on ion-exchange resins. Biocatalysis, 3, 329-342. 

Hydrolase-catalyzed enantioselective N-acylation is an important tool for the preparation of enantiopure a- and P-aminoacids. It has been observed that the reactions of many amino acid esters with ester acyl donors catalyzed by CALB is sometimes complicated by interesterification reactions. CALA has, however, emerged as a very chemoselective catalyst in favor of N-acylation of P-aminoesters. Some reviews on CALA and other hydrolases as catalysts for N-acylations of aminoesters are available [109, 126, 127]. 

R-selective interesterification Novozyme 435, acetonitrile tri-n-propylorthoformate, trace -propanol, 45 °C Remaining substrate >98% (S) at c - 60%,... 

Lipases are used to hydrolyse milk fat for a variety of uses in the confectionary, sweet, chocolate, sauce and snack food industries and there is interest in using immobilized lipases to modify fat flavours for such applications (Kilara, 1985). Enzymatic interesterification of milk lipids to modify rheological properties is also feasible. 

Release of fatty acids and some interesterification may also occur, but such changes are unlikely during the normal processing of milk. 

For interesterification to the n-butyl esters, 100 yl of n-butanol HC1 is mixed ultrasonically in the reaction vial. The solution is heated for 2 hr, 30 min in the 100°C sand bath with ultrasonic mixing every 30 min. This reaction mixture is evaporated just to dryness under nitrogen as described above. 

The dedd cells of the mycelium of Rhizopus arrhizus constitute d naturally immobilized lipdse very active in organic solvents. This immobilized enzyme was used for hydrolysis and synthesis of ester bonds triglycerides hydrolysis, and interesterification, esters and glycerides synthesis. More recently, the catalytic system has been applied in drug synthesis to the resolution of racemic esters with a good enantioselectivity. 

Organic solvents used must be compatible with the enzymatic activity, not take place in the reaction, be good solvent of the substrates, have a low cost, and be the more harmless possible. The solvents commonly used in the literature are aliphatic alkanes, or similar compounds of low polarity. Aliphatic ethers that were used in this work, show less hydrophoblcity than alkanes, and thus allow introduction of water for hydrolysis reactions. For interesterification experiments, trichloro-trifluoro-ethane was used, as water is not a substrate for the reaction (Fig. 5,). 

The interesterification of fats and oils is the only way to create new hybrid products with new physical, and especially new rheological properties. Chemical interesterification is well known, but has no position or chain specificity, and is not very clean. With lipases in micro-aqueous media, the exchange of acyl groups between the different triglycerides may be oriented, and designed according to the specificity of the enzyme. 

A single segment mycelium reactor was used with trichloro-trifluoro-ethane as solvent (Fig, 5,). For a concentration of 25% (V/V) of triglycerides, full interesterification was obtained within 1 hour of residence time. The productivity of the system can be estimated to 1.5 kg of interesterified product per hour and per kg of dry mycelium. 

Rhizopus arrhizus dead mycelium was found to be very active in organic solvents as a naturally immobilized lipase. Triglycerides hydrolysis and interesterification, esters and glycerides synthesis, natural flavour esters preparation and racemic mixtures resolution in pharmaceutical drugs synthesis are among the successfully designed processes, each of one with a specific reactional medium. 

Interesterification of edible oils is an important process for the modification of physical and functional properties, as are hydrogenation and fractionation. 

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). 

Accurate determination of the amount of solid fat in edible fats and oils is an essential requirement for process control in food industry during hydrogenation, interesterification and blending. Moreover, important physical properties, such as hardness, heat resistance, mouth-feel and flavor release, can be predicted via measurements of solid fat content at different temperatures using low resolution (low-field) NMR. 

Liang, M. T. Chen, C. H. Liang, R. C. The Interesterification of Edible Palm Oil by Stearic acid in Supercritical Carbon Dioxide. J. Supercrit. Fluids. 1998, 13, 211-216. 

Michor, H. Marr, R. Gamse, T. Schilling, T. Klingsbichel, E. Schwab, H. Enzymatic Catalysis in Supercritical Carbon Dioxide Comparison of Different Lipases and a Novel Esterase. Biotechnol. Lett. 1996b, 18, 79-84. Miller, D. A. Blanch, H. W. Prausnitz, J. M. Enzyme-Catalyzed Interesterification of Triglycerides in Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 1991, 30, 939-946. 

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