Mono-and diacylglycerols

The presence of partial glycerides in olive oil is due either to incomplete triacylglycerol biosynthesis or hydrolytic reactions. In virgin olive oil, the concentration 

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Olid carbon is asymmetric. The various acylglycerols are normally soluble in benzene, chloroform, ether, and hot ethanol. Although triacylglycerols are insoluble in water, mono- and diacylglycerols readily form organized structures in water (discussed later), owing to the polarity of their free hydroxyl groups. 

FIGURE 25.20 Triacylglycerols are formed primarily by the action of acyltransferases on mono- and diacylglycerol. Acyltransferase in E. coli is an integral membrane protein (83 kD) and can utilize either fatty acyl-CoAs or acylated acyl carrier proteins as substrates. It shows a particular preference for palmitoyl groups. Eukaryotic acyltransferases nse only fatty acyl-CoA molecnles as substrates. 

In positive ion mode, the characteristic peaks representative of the binding media were fatty acids from lead soaps (of palmitic acid at m/z 461 463 and of stearic acid at m/z 489 491). Other peaks corresponding to mono- and diacylglycerol cations, protonated stearic acid or its acylium ions could be found in the spectra of the reference products but not in the paint sample. The spectrum of lead white egg tempera paint exhibits peaks of phosphocholine (m/z 184) and protonated ketocholesterol (m/z 401). These peaks were not found in the spectrum from the cross-section. In negative ion mode, the spectrum of the oil... 

Lipids are easily detected in negative ion mode on account of the peaks of deprotonated stearic, palmitic and arachidic acids. In positive ion mode, mono- and diacylglycerol are also detected. All these lipids show the same distribution all over the sample. An interesting point is the predominance of stearic acid. This could be consistent with the use of shea butter or karite in the recipe of the patina, products commonly used in West Africa. 

The physiological functions of carboxylesterases are still partly obscure but these enzymes are probably essential, since their genetic codes have been preserved throughout evolution [84] [96], There is some evidence that microsomal carboxylesterases play an important role in lipid metabolism in the endoplasmic reticulum. Indeed, they are able to hydrolyze acylcamitines, pal-mitoyl-CoA, and mono- and diacylglycerols [74a] [77] [97]. It has been speculated that these hydrolytic activities may facilitate the transfer of fatty acids across the endoplasmic reticulum and/or prevent the accumulation of mem-branolytic natural detergents such as carnitine esters and lysophospholipids. Plasma esterases are possibly also involved in fat absorption. In the rat, an increase in dietary fats was associated with a pronounced increase in the activity of ESI. In the mouse, the infusion of lipids into the duodenum decreased ESI levels in both lymph and serum, whereas an increase in ES2 levels was observed. In the lymph, the levels of ES2 paralleled triglyceride concentrations [92] [98],... 

Farooqui A. A., Wallace L. J., and Horrocks L. A. (1991). Stimulation of mono- and diacylglycerol lipase activities in ibotenate-induced lesions of nucleus basalis magnocellularis. Neurosci. Lett. 131 97-99. 

Yang, B., Harper, W.J., Parkin, K.L., Chen, J. 1994, Screening of commercial lipases for production of mono and diacylglycerols from butteroil by enzyme glycerolysis. Int. Dairy J. 4, 1-13. 

Hydroxyl number (OHN). This number reflects the content of hydroxy fatty acids, fatty alcohols, mono- and diacylglycerols, and free glycerol. 

Parameters that affect crystallization may influence either the thermodynamic behavior or the crystallization kinetics (or both). Parameters that influence lipid crystallization include chemical composition, subcooling, cooling rate, agitation, minor components of fats (mono- and diacylglycerols, polar lipids, etc.), and scale of operation. The effects of these parameters on lipid crystallization will be reviewed briefly in this section. More detailed information about the effects of these parameters on lipid nucleation and crystal growth may be found elsewhere (4, 24, 28, 54). 

Moisture promotes the splitting of triacylglycerols to form free fatty acids, mono- and diacylglycerols (Figure 1), which result in increase of refining losses directly related to the free fatty acid content of oUs and fats. Essentially, hydrolysis... 

Improvement of the deodorizer design by the installation of baffles and demisters in the vapor chimneys has significantly reduced entrainment losses to 0.1-0.2% in chemical refining. For steam refining, an additional loss directly proportional to the FFA content has to be taken into account. For most oils (soybean oil, pahn oil, etc.), NOL is exclusively due to mechanical carry-over. However, in lauric oils, part of the NOL is a consequence of effective evaporation of volatile short-chain mono- and diacylglycerols (30). (Table 13). This distillation loss of NOL is inherently due to the deodorization conditions, but is not affected by the deodorizer design. 

Oil acylglycerols Ethoxilated mono- and diacylglycerol Water dispersable, skin conditioninig and moisturizing, skin, body and hair care... 

Gas chromatographic analyses are useful not only to determine if an unusual amount of mono- and diacylglycerol sexists, but also if contaminants or adulterants are found in the oil. 

The partial hydrolysis of the triacylglycerol to mono and diacylglycerol is called Hydrolytic rancidity. The hydrolysis is hastened by the presence of moisture, warmth and lipases present in fats or air. In fats like butter which contains a high percentage of volatile fatty acids, hydrolytic rancidity produces disagreeable odour and taste due to the liberation of the volatile butyric acid. Butter becomes rancid more easily in summer. 

The various classes of minor constituents can be divided into two groups. The first group consists of fatty acid derivatives such as mono- and diacylglycerols, phospholipids, waxes and esters of sterols. The second group includes classes of compounds not related chemically to fatty acids hydrocarbons, aliphatic alcohols, free sterols, tocopherols, chlorophylls, carotenoids and polar compounds such as tyrosol and hydroxytyrosol. 

Yamaguchi, S., and Mase, T. 1991. High-yield synthesis of monoglyceride by mono- and diacylglycerol lipase from Penicillium camembertii U-150. J. Ferment. Bioeng. 72 162-167. 

Farooqui, A.A., Anderson, D.K., Flynn, C., Bradel, E., Means, E.D., and Horrocks, L.A. (1990) Stimulation of mono- and diacylglycerol lipase activities by bradykinin in neural cultures. Biochemical and Biophysical Research Communications 166 1001-1009. 

The opposite process takes place during the germination (Section 11.5.2), so that lipids of germinating seeds may also contain mono- and diacylglycerols as TAG degradation products. 

Mono- and diacylglycerols are present in egg yoUc lipids at 1.5 to 2.2% (Evans et al., 1967). Holopainen (1972) cited contents of 6.7% but this seems to be too high. Mono- and diacylglycerols primarily occur in the HDL fraction of the granules (5.8 to 8.5% in the lipids of the HDL fraction). In the lipids of the LDL fraction from plasma, only low concentrations of 0.4 to 0.7% were found (Tsutsui and Obara,... 

At frying temperatures (160 to 200°C), the moisture escaping from the food hydrolyzes triacylglycerols (TAG) to FA, glycerol, and mono- and diacylglycerols. 

Lipid components comprised 96% TAG with 4% other lipid constituents (e.g., phospholipids, sterols, mono- and diacylglycerols). 

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