Fatty acid esters, hydrolysis

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... 

The pH is adjusted to the desired value with an aqueous solution of NaOH or HCl, depending on the value that needs to be reached. The pH of the nanoemulsion is generally adjusted to 7-8 to allow physiological compatibility and maintain emulsion physical integrity by minimizing fatty acid ester hydrolysis of MCT-LCT and phospholipids. ... 

Olestra is prepared by a solvenfless transesterification process in which sucrose is treated with methyl ester of fatty acids in the presence of sodium methoxide between 100—180°C for 14 hours (68). The manufacturing process involves removal of the unreacted fatty acid esters by enzymic hydrolysis... 

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 cholesterol required for biosynthesis of the steroid hormones is obtained from various sources, it is either taken up as a constituent of LDL lipoproteins (see p. 278) into the hormone-synthesizing glandular cells, or synthesized by glandular cells themselves from acetyl-CoA (see p. 172). Excess cholesterol is stored in the form of fatty acid esters in lipid droplets. Hydrolysis allows rapid mobilization of the cholesterol from this reserve again. 

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. 

Fig. 22 Initial reaction steps for fatty acid ester decomposition, represented by ethyl butanoate, which can decompose via thermolysis (pyrolysis), oxidation, or hydrolysis.

There are many enzymes that have a specific binding site Ca in the active center and for which Ca has an essential role in catalysis. An example of a Ca -dependent enzyme is phospholipase A2. Phosphohpase A2 catalyses the hydrolysis of fatty acid esters at the 2 position of phosphohpids (see Fig. 5.24), whereby Ca plays an essential role. The enzyme has two Ca ions boimd tightly at the active center. One of the two Ca ions is directly involved in catalysis. It binds the substrate in the groimd state and also helps to neutralize charge in the transition state of ester hydrolysis. The second Ca ion is assigned a role in stabilization of the transition state, in addition to a structural fimction (White et al., 1990). 

The analysis of essential fatty acids involves hydrolysis of the ester bonds and subsequent formation of the fatty acid methyl esters, which can be separated by gas chromatography (GC) [10]. By accident, the plasmalogens are hydrolysed in the same reaction and the methylation reaction transforms them into dimethylacetals, which appear in the GC run of the fatty acid methyl esters [4]. 

Increased plasmalogen levels have not been observed. Erroneously low red cell levels can be encountered when the transmethylation process has not been completed. Breaking the ether lipid bond of the plasmalogens requires more energy than hydrolysis of the fatty acid esters. Evaluation of the plasmalogen levels should not be done after a blood transfusion. Donor erythrocytes will be present for up to 120 days following a transfusion. 

Enzymatic Hydrolysis Reactions of Esters. Xenobiotic compounds containing esters or other acid derivatives in their structures (e.g., amides, carbamates, ureas, etc., see Table 17.3) are often readily hydrolyzed by microorganisms. To understand how enzymatic steps can be used to transform these substances, it is instructive to consider the hydrolases (i.e., enzymes that catalyze hydrolysis reactions) used by organisms to split naturally occurring analogs (e.g., fatty acid esters in lipids or amides in proteins). The same chemical processes, and possibly even some of the same enzymes themselves, are involved in the hydrolysis of xenobiotic substrates. 

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)). 

Conventional ring-opening polymerization of cyclic anhydrides, carbonates, lactones, and lactides require extremely pure monomers and anhydrous conditions as well as metallic catalysts, which must be completely removed before use, particularly for medical applications. To avoid these difficult restrictions, an enzymatic polymerization may be one of the more feasible methods to obtain the polyesters. This method was first reported by two independent groups (Kobayashi [152] and Gutman [153]) who showed that lipases, enzymes capable of catalyzing the hydrolysis of fatty acid esters, can polymerize various medium-sized lactones. 

Raw materials. It is possible to use any fatty acid as a feed material for sulphonation but economic considerations dictate that oleochemical material be preferred. Fatty acids are readily obtained from vegetable and animal oils and fats which are fatty acid triglycerides. These are transesterified to generate glycerol and three moles of a fatty acid ester, normally a methyl ester. The methyl ester can be distilled to give a specific cut and the fatty acid finally isolated by hydrolysis or hydrogenation of the ester. It is common to use animal fats (tallow) in which case the dominant C chains are 16 and 18. 

This enzyme catalyzes the specific hydrolysis of the fatty acid ester located on the C-2 carbon position of an sn-3 phosphoglyceride. The reaction occurs as shown in Figure 4-6 using 6phosphatidylcholine as the model substrate. 

Fatty alcohols are obtained by direct hydrogenation of fatty acids or by hydrogenation of fatty acid esters. Typically, this is performed over copper catalysts at elevated temperature (170°C-270°C) and pressure (40-300 bar hydrogen) [26], By this route, completely saturated fatty alcohols are produced. In the past, unsaturated fatty alcohols were produced via hydrolysis of whale oil (a natural wax occurring in whale blubber) or by reduction of waxes with sodium (Bouveault-Blanc reduction). Today, they can be obtained by selective hydrogenation at even higher temperatures (250°C-280°C), but lower pressure up to 25 bar over metal oxides (zinc oxide, chromium oxide, iron oxide, or cadmium oxide) or partially deactivated copper chromite catalysts [26],... 

Figure 2. Relative rates of hydrolysis of fatty acid esters of different chain lengths hy pancreatic lipase (10)...

Oleochemical Route. Oleochemicals. Oleochemicals are chemicals derived from oils or fats. They are analogous to petrochemicals, which are chemicals derived from petroleum. The hydrolysis or alcoholysis of oils or fats form the basis of the oleochemical industry. The hydrolysis of the triglycerides composing oils and fats produces fatty acids and glycerol. If oils or fats are made to react with an alcohol instead of with water, the process is alcoholysis, and the products are fatty acid esters and glycerol. 

In the DOD, phytosterols are present in both the free and esterified forms with fatty acids. Therefore, the first step in the extraction of phytosterols is conversion of phytosterol fatty esters into free phytosterols. This is achieved either by hydrolysis or trani-esterification. Hydrolysis could be carried out under strong basic conditions (saponification with further acidulation), under strong acidic conditions, or under chemical or enzyme (specific or nonspecific) catalyzation. Re-esterification of phytosterols occurs during methyl ester distillation as a result of the high temperatures involved therefore, a further trani-esterification step for free sterols is required. Esterification of phytosterols or trani-esterification of sterol fatty acid esters is the second step in this process. Methanol is the most commonly used alcohol, and it leads to methyl esters, which are characterized by a higher volatility, however, other Ci to C4 alcohols may also be used. Esterification and trans-esterification of fatty acids or phytosterols can be catalyzed by metal alcoholates, or hydroxide, by organic catalysts, or by enzymes (Table 7). 

Recently, geranylgeranylhydroquinone (22.6) and a mixture of fatty acid esters 22.7 have been isolated from L. lignyotus (23). Clearly, these phenols are biogenetically related to flavidulols A-C and to compound 22.1. Compound 22.6 could also be obtained by hydrolysis of the esters 22.7. The acids esterified in 22.7 were identified by GC-MS analysis of the mixture of methyl esters obtained by transesterification (23). Interestingly, the free hydroquinone 22.6 has previously been isolated from the sponge ireinia muscarum (123) and from plants of the genus Phacelia (124). 

We should note, however, that incorporation of a substrate into a micelle will accelerate its reaction with a micelle counterion only if the substrate is bound at the micellar surface, since ionic reagents cannot, apparently, penetrate into the micellar core. Thus, the hydroxyl ion-catalyzed hydrolysis of long-chain fatty acid esters of 3-nitro-4-hydroxybenzenesulfonic acid was inhibited by incorporation into micelles no matter whether these were uncharged, anionic, or cationic (68). 

Lipase is an enzyme which catalyzes the hydrolysis of fatty acid esters normally in an aqueous environment in living systems. On the other hand, some lipases are stable in organic solvents and can be used... 

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