Interesterification catalyst

Interesterification with chemical catalysts Interesterification with specific lipases Enzymic enhancement... 

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. 

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]. 

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). 

The catalyst is efficient in ester synthesis and in interesterification. It is able to catalyze ester formation with both primary and secondary alcohols. 

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. 

Lipase catalyzed reactions take place in the neat oil or in a nonpolar (usually hydrocarbon) solvent. The efficiency depends on the amount of water, solvent (if present), temperature, and ratio of reactants. A factorial approach can be used to optimize the conditions (32). In interesterification reactions, 1,3-specific enzymes give control over product composition that is not possible using chemical catalysts. For example, starting with SOS and OOO, chemical interesterification produces aU eight possible isomers (see Table 5). Enzymatic interesterification does not exchange fatty acids at the sn-2 position, and it will result in only two additional molecular species, OOS and SOO. In more realistic situations, chemical and enzymatic interesterification may produce the same or a similar number of molecular species, but in different proportions (31). 

Although interesterification will occur in the absence of added catalysts at sufficiently high temperatures, catalysts are employed by industry to speed this reaction, reducing reaction time and the sample degradation that occur at elevated temperatures. The most commonly used inorganic catalysts are alkaline ones such as sodium methoxide, sodium ethoxide, sodium or potassium metal, and alloys of sodium and potassium. Catalyst concentrations of 0.05% to 0.1% are employed. As the catalysts will react with water, free fatty acids, and oxidized compounds, it is important to use clean, dry feedstocks. Reaction temperatures are generally kept below 100°C. The reactions can be mn in batch or continuous formats. In batch mode, the reaction times are typically less than an hour. 

Interesterification by chemical or enzymatic catalyst Domestication of wild crops... 

The production of fat spreads as an alternative to butter led to an increased demand for solid fats. For the most part, this demand has been met by the use of partially hydrogenated vegetable oUs (Section 8.3), but concern about the health effects of trani-unsaturated acids has raised interest in an alternative way of producing fats with the required melting behavior. This can be achieved by interesterification of blends of natural or fractionated fats. Products obtained in this way will probably contain more saturated acids than their partially hydrogenated equivalents, but they will have no trans-acids. This section is devoted to interesterification carried out under the influence of a chemical catalyst (177, 186, 187). Similar reactions with enzymes are discussed in the following section. 

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). 

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 is conveniently achieved by using alkali metal methylates as a catalyst. Microbial lipases are also used as biocatalysts in enzymatic interesteiification. In contrast to the chemical process, the enzymatic process can be more selective if an enzyme with positional specificity is used, but this reaction is usually much slower and more sensitive to reaction conditions. Recent developments in lipase-catalyzed interesterification have resulted in new industrial applications of this process (255). Nevertheless, the high costs of enzymes and process equipment may limit widespread adoption of this process. 

Lipase catalysis constitutes an alternative to the method of interesterification using chemical catalysts. Products of different physical properties may be obtained, according to lipase specificity (99,100). 

In addition to moisture, FFAs and peroxides also will poison the catalyst. For successful interesterification, most of the crude oil impurities must be removed, and refining operations should be performed beforehand. 

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

Microbial lipases may be used as biocatalysts for interesterification. Lipase-assisted interesterification offers possibilities for transformation of lipids beyond those possible using chemical interesterification (11). Enzymatic interesterihcation has several advantages over the chemical-assisted reactions, such as mild reaction conditions leading to reduced energy consumption and less thermal damage to reactants and products, the possibility of lipase specificity toward their natural substrates, as well as high catalytic efficiency. Lipase-catalyzed interesterihcation reactions, in contrast to those carried out with chemical catalysts, yield different types of products depending on the specihcity of the lipase used. 

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