Fatty acids lipase catalyzed reactions

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. 

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). 

Recent studies have attempted to improve the efficiency of epoxidation under milder conditions that minimize the formation of byproducts. Chemo-enzymatic epoxidation uses the immobilized lipase from Candida antartica (Novozym 435) (56) to catalyze conversion of fatty acids to peracids with 60% hydrogen peroxide. The fatty acid is then self-epoxidized in an intermolecular reaction. The lipase is remarkably stable under the reaction conditions and can be recovered and reused 15 times without loss of activity. Competitive lipolysis of triacylglycerols is inhibited by small amounts of fatty acid, allowing the reaction to be carried out on intact oils (57). Rapeseed oil with 5% of rapeseed fatty acids was converted to epoxidized rapeseed oil in 91% yield with no hydroxy byproducts. Linseed oil was epoxidized in 80% yield. Methyl esters are also epoxidized without hydrolysis under these conditions. 

Yamane, T. Lipase-catalyzed synthesis of structured triacylglycerols containing polyunsaturated fatty acids monitoring the reaction and increasing the yield. In Enzymes in Lipid Modification Bornscheuer, U.T., Ed. Wiley-VCH Weinheim, Germany, 2000 148-169. 

FIGURE 13.1 Lipase-catalyzed reactions and production of MAG using the reactions. FA, fatty acid MAG, monoacylglycerol TAG, triacylglycerol FAEE, fatty acid ethyl ester EtOH, ethanol. 

In the food area, due to the characteristics of oleic acid mentioned above and the specificity of lipases by the type and positions of fatty acid on the glycerol, it is possible to synthesize lipids rich in oleic acid with improved physicochemical, nutritional and biological properties (Lin and Huey, 2009 Sellami et al., 2012 Farfan et al., 2013). The lipase-catalyzed reaction between oleic acid and phytosterols also produces sterol esters with higher solubility, which contributes to practical applications in food products (Pan et al., 2012). 

Lipase-catalyzed reactions are accelerated by Ca + ions since the liberated fatty acids are precipitated as insoluble Ca-salts. 

Ju, Y-H, Huang, F-H and Fang, C-H (1998) The incorporation of -3 polyunsaturated fatty acids into acylglycerols of borage oil via lipase-catalyzed reactions. J. Am. Oil Chem. Soc., 75, 961-965. 

Based on the substrates involved in the lipase-catalyzed reactions, they can be classified into different categories esterification, hydrolysis, acidolysis, alcoholysis and interesterification (1). Direct esterification reaction may be enqjloyed for the preparation of stmctured lipids by reacting free fatty acids with glycerol. However, this process is not commonly used in stmctured lipid production. The major problem is that the water molecules are formed as a result of the esterification reaction. The water molecules so produced need to be removed in order to prevent the hydrolysis of the product. Hydrolysis is the... 

Lipase-catalyzed reactions do not necessarily require water as the second reactant. An immobilized enzyme is often stable in anhydrous media (Sharma et al 2001) and can use different alcohols as the secondary acceptors of fatty acids. The concentration of alcohol is relatively low and cannot be treated as a constant. Consequently, the reaction obeys the bisubstrate ping-pong mechanism (Cheirsilp et al 2008 Mitchell et al., 2008 Xiong et al., 2008) as shown in Figure 14.3. The corresponding equation of the reaction rate in the absence of products is ... 

The metabolic breakdown of triacylglycerols begins with their hydrolysis to yield glycerol plus fatty acids. The reaction is catalyzed by a lipase, whose mechanism of action is shown in Figure 29.2. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine residues, which act cooperatively to provide the necessary acid and base catalysis for the individual steps. Hydrolysis is accomplished by two sequential nucleophilic acyl substitution reactions, one that covalently binds an acyl group to the side chain -OH of a serine residue on the enzyme and a second that frees the fatty acid from the enzyme. 

Lipase is an enzyme which catalyzes the hydrolysis of fatty acid esters normally in an aqueous environment in living systems. However, hpases are sometimes stable in organic solvents and can be used as catalyst for esterifications and transesterifications. By utihzing such catalytic specificities of lipase, functional aliphatic polyesters have been synthesized by various polymerization modes. Typical reaction types of hpase-catalyzed polymerization leading to polyesters are summarized in Scheme 1. Lipase-catalyzed polymerizations also produced polycarbonates and polyphosphates. 

The lipase-catalyzed fatty acid ester hydrolysis and the lipoxygenation of free polyunsaturated fatty acids are involved in the same lipid degradation pathway. They are respectively the first and second reaction in the lipoxygenase pathway (Fig. 3) [87-91]. The pathway produces volatile products of considerable importance in food technology including Cg[92, 93] or Cg- 94—96 aldehydes and alcohols from polyunsaturated fatty... 

Recently [63], we studied the behavior of two-enzyme system catalyzing two consecutive reactions in a macroheterogeneous medium (modified Lewis cell). The system consisted of lipase-catalyzed hydrolysis of trilinolein and subsequent lipoxygenation of liberated fatty acids (Fig. 3). Our approach compared the kinetic behavior of coupled enzymes in the Lewis cell with the sequential study of separated phenomena presented before ... 

It, thus, appears that the capacity to catalyze reactions of transesterification and esterification is a characteristic of various hydrolases (Chapt. 3). Apart from the carboxylesterases discussed here, lipoprotein lipase has the capacity to synthesize fatty acid ethyl esters from ethanol and triglycerides, or even fatty acids [127]. Ethanol, 2-chloroethanol, and other primary alcohols serve to esterify endogenous fatty acids and a number of xenobiotic acids [128-130]. In this context, it is interesting to note that the same human liver carboxylesterase was able to catalyze the hydrolysis of cocaine to benzoylecgonine, the transesterification of cocaine, and the ethyl esterification of fatty acids [131]. 

Lipases are enzymes of the hydrolase family and, in nature, hydrolyze fatty acid esters in aqueous environment. It is worth recalling that the hydrolysis of esters is a reversible reaction. Chemists thus often use lipases to catalyze the reverse reaction, i.e., the esterification and the ROP of lactones. In 1993, the groups of Kobayashi [91] and Knani [92] reported independently the hpase-catalyzed ROP of sCL and 8-valerolactone. The aliphatic polyesters were functionalized by a carboxylic group at one chain-end and a hydroxyl group at the other chain-end. Accordingly, the polymerization was initiated and terminated by water present in the reaction media. 

The natural substrates of lipases are triglycerides and, in an aqueous environment, lipases catalyze their hydrolysis into fatty acids and glycerol. In anhydrous media, lipases can be active in the reverse reaction [19]. In fact, in the acylation step, acids, lactones, (cyclic) carbonates [20, 21], cyclic amides [22, 23], (cyclic) thioesters [24, 25], and cyclic phosphates [26] have been found to act as suitable acyl donors. In the deacylation step, apart from water, lipases also accept alcohols [27], amines [28, 29], and thiols [30] as nucleophiles although the specificity of lipases is lower for amines and thiols than for water and alcohols [31]. 

Hydrolases, which catalyze the hydrolysis of various bonds. The best-known subcategory of hydrolases are the lipases, which hydrolyze ester bonds. In the example of human pancreatic lipase, which is the main enzyme responsible for breaking down fats in the human digestive system, a lipase acts to convert triglyceride substrates found in oils from food to monoglycerides and free fatty acids. In the chemical industry, lipases are also used, for instance, to catalyze the —C N —CONH2 reaction, for the synthesis of acrylamide from acrylonitril, or nicotinic acid from 3-pyridylnitrile. 

It is clear that the water activity is of crucial importance for the equilibrium yield in a reversed hydrolysis reaction. As expected, the equilibrium yield increases with decreasing water activity. This has been shown, for example, for the condensation of glucose and octanol [62], esterification of lysophospholipids with fatty acids [29, 63], and in normal lipase-catalyzed esterification reactions [64, 65]. The same situation is observed in ionic liquids [66]. 

Fatty acids of sugars are potentially useful and fully green nonionic surfactants, but the lipase-mediated esterification of carbohydrates is hampered by the low solubility of carbohydrates in reaction media that support lipase catalysis in general. Because the monoacylated product (Figure 10.8) is more soluble in traditional solvents than is the starting compound, the former tends to undergo further acylation into a diester. In contrast, the CaLB-catalyzed esterification of glucose with vinyl acetate in the ionic liquid [EMIm][BF4] was completely selective. The reaction became much faster and somewhat less selective when conducted in... 

Hydrolytic enzymes such as lipases catalyze hydrolysis of esters in aqueous media, but when used in non-aqueous media such as organic solvents, ionic liquids and supercritical fluids, they catalyze reverse reactions the synthesis of esters. For example, lipases in natural environment catalyze the hydrolysis of fatty acid esters as shown in Figure 6(a). However, when they are used in organic solvents, they catalyze the esterification reaction (Figure 6(b)). 

Hydrolytic enzymes can also catalyzed the esterification of alcohols or acids with hetero atoms.1617 Some examples for the reactions of phosphorous and sulfur compounds by lipases are shown in Figure 16. By the repeated enantioselective acylation and hydrolysis of a hydroxyl phosphonate and its acetate with lipase AH, phosphonic acid analogue of carnitine (essential cofactor of fatty acid metabolism), (A)-phosphocarniiine, and its enantiomer were synthesized as shown in Figure 16 (b). 

Lipase is known to catalyze esterification through an acyl-intermediate formed between the fatty acid substrate and the enzyme. Free enzyme can bind fatty acid to produce either this intermediate or the ester product. With a high concentration of alcohol, the acyl-intermediate will be consumed, and the enzyme may then start to bind product and catalyze its hydrolysis, thereby reversing the reaction. When present in an excess of fatty acid, however, most of the enzyme is found in the acylated form, preventing it from binding the product (15,16). 

Energy production from triacylglycerols starts with their hydrolysis into free fatty acids and glycerol. Enzymes called lipases, which catalyze the reaction, carry out this hydrolysis. 

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