Triacylglycerols substitutes

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. 

Monounsaturated fats Triacylglycerols containing primarily fatty acids with one double bond are referred to as monounsaturated fat. Unsaturated fatty acids are generally derived from vegetables and fish. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL cholesterol, but increase HDLs. This ability of monounsaturated fats to favorably modify lipoprotein levels may explain, in part, the observation that Mediterranean cultures, with diets rich in olive oil (high in monounsaturated oleic acid), show a low incidence of coronary heart disease. 

Solvent-free enzymatic interesterification of milk fat alone or with other fats or fatty acids provides the most acceptable route for modification of the triacylglycerol structures in milk fat and further research and development in this field is expected to provide physical and physiological benefits. From a nutritional perspective, it is of interest to examine the effects of randomized milk fat on serum cholesterol. Christophe et al. (1978) reported that substitution of native milk fat with chemically-randomized interester-ified milk fat reduced cholesterol levels in man. However, others found that there was no effect on serum cholesterol levels in man as a result of substitution of ezymatically randomized milk fat (De Greyt and Huyghebaert, 1995). Further studies are required to determine if interesterilied milk fat provides a nutritional benefit. 

Diets high in fat content lead to a large amount of stored fat, ultimately causing an individual to be overweight. One recent attempt to reduce calories in common snack foods has been to substitute fake fats such as olestra (trade name Olean) for triacylglycerols. 

As SCO are usually triacylglycerols that can account for over 90% of the total lipid in the microbial cell, this makes them potential substitutes for plant oils and animal fats, although clearly their economic potential will rest on their intrinsic value. It is to be emphasized, however, that an SCO will only complete with other commercial sources if it can be shown to be better in some respect or cheaper than the traditional source. 

Stadler, P., Kovac, A., Haalck, L., Spener, F. and Paltauf, F. (1995) Stereoselectivity of microbial lipases. The substitution at position sn-2 of triacylglycerol analogs influences the stereoselectivity of different microbial lipases. Eur. J. Biochem. 227, 335-343... 

A high-carbohydrate diet results in substantial elevation of plasma VLDL concentration. A high-cholesterol diet alters the composition of VLDL, with cholesterol esters substituting for triacylglycerol as core components, and leads to a marked increase in apo E synthesis. 

Fig. 5. Pathway depicting how flux through phosphatidylcholine (product of reaction 3) can promote acyl group diversity in plant triacylglycerols. Production of 18 2 (boxed) at the sn-2 position and its transfer to TG is used as a sample modification. Other fatty acid alterations may be substituted. Enzymes 1, glycerol-3-phosphate acyl-CoA acyltransferase and lysophosphatidic acid acyl-CoA acyltransferase 2, phosphatidic acid phosphatase 3, diacylglyceroliCDP-aminoalcohol aminoalcoholphosphotransferase 4, 18 l-desaturase or other fatty acid modifying enzyme 5, phosphlipid diacylglycerol acyltransferase 6, diacylglycerol acyltransferase 7, acyl-CoA phosphatidylcholine acyltransferase or phospholipase plus acyl-CoA synthetase.

Test Articles and Dosing. The DAG oil (Econa Oil, Kao Corporation, Biological Science Laboratories, Tochigi, JAPAN) used in this study was prepared from rapeseed oil in the presence of lipase, and was 90% DAG (w/w). The ratio of 1,2-DAG to 1,3-DAG was 3 7. Triacylglycerol oil was prepared from a mixmre of rapeseed, soybean, and safflower oils. This mixture was used to match the major fatty acid composition of the DAG and TAG oils as closely as possible. The intended use of the DAG oil product is as a component in cooking, as a substitute for other oils. 

Thia fatty acids represent non-p-oxidizable fatty acid analogues in which a S atom substitutes for the P-methylene group in the chain. They are known to reduce serum tri-acylglycerol and cholesterol. The hypolipaemia is detectable within 3 hours of administration and is explained initially by an increase in mitochondrial P-oxidation and a decrease in triacylglycerol secretion, followed by an increase in activity of peroxisomal P-oxidation enzymes after 12 hours. ... 

Skorve, J, Rustan, A.C. Berge, R.K. 1995. Lipids 30 987-994. Effects of non-beta-oxidizable suUur-substituted fatty acid analogues on synthesis and secretion of triacylglycerol and cholesterol in cultured rat hepatocytes. 

Fatty Acids and Triacylglycerols 1028 THE CHEMISTRY OF... Olestra and Other Fat Substitutes 1032... 

The most common substituted fatty acids found in plants are the monohy droxy derivatives, though polyhydroxy acids, keto acids, epoxy acids, di-carboxylic acids and even to-fluoro acids (Ward et al., 1964) are known. The 2-hydroxy derivatives of common fatty acids are found esterified in cerebro-sides, ceramides, and phytoglycolipid in high amounts. In seed oils they occur in triacylglycerol. All known 2-hydroxy acids are d isomers. The 3-hydroxy acids, which are important intermediates in both fatty acid synthetase and )8-oxidation pathways, rarely accumulate. However, ricinoleic (12-hydroxyoleic) acid accounts for 90% of the fatty acids of commercial... 

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