Short-chain TAGs

Autooxidation products of triolein, trilinolein, and trilinolenin were analysed by nonaqueous RPLC with a Cjg colunrn and a acetonitrile/dichloromethane gradient and positive-ion APCl-MS [26]. Among others, mono- and dihydroxy peroxides and different types of mono- and diepoxides were observed. In a subsequent study [27], two parallel mass spectrometers, one ruiming ESl-MS, the other APCl-MS, were applied in the TAG analysis of canola oil. ESl-MS especially showed advantages over APCl-MS in the analysis of TAG oxidation products, because it yielded a more abundant intact [M+NH4]" than APCl-MS did. The ability of ESl-MS to reduce fragmentation of TAG also played an important role in the analysis of regioisomers of short-chain TAG, as reported by Kalo et al. [28]. LC-ESl-MS was also applied in the characterization of the TAG content in Malaysian cocoa butter, reported by... 

P. Kalo, A. Kemppinen, V. Ollilainen, A. Kuksis, Analysis of regioisomers of short-chain TAG by NPLC-ESI-MS-MS, Int. J. Mass Spectrom., 229 (2003) 167. 

The abundance of fatty acids in triacylglycerols (TAG) can be determined by conversion of the acyl groups into tertiary alcohols on reaction with an alkyl Grignard reagent, followed by chromatographic separation. The method was found to be of advantage over saponification and conversion to a methyl ester, especially in the determination of short-chain fatty acids, which suffer losses by volatilization. ... 

Butterfat is a mixture of more than 100,000 different triacylglycerols (TAGs) with a melting range from -40 to +40°C (109). About 400 different fatty acids (FAs) are present in butterfat, 25% of which were short-chained and 45% were long-chained saturates (110). Such variety in composition is responsible for butterfat s unique physical properties. 

Milk fat contains a number of different lipids, but is predominately made up of triacylglycerols (TAG) (98%). The remaining lipids are diacylglycerols (DAG), monoacylglycerols (MAG), phospholipids, free fatty acids (FFA) and sterols. Milk fat contains over 250 different fatty acids, but 15 of these make up approximately 95% of the total (Banks, 1991) the most important are shown in Table 19.1. The unique aspect of bovine, ovine and caprine milk fat, in comparison to vegetable oils, is the presence of high levels of short-chain volatile FFAs (SCFFA), which have a major impact on the flavor/aroma of dairy products. Most cheeses are produced from either bovine, ovine or caprine milk and the differences of their FFA profile are responsible for the characteristic flavor of cheeses produced from such milks (Ha and Lindsay, 1991). 

Lipase-catalyzed methanolysis of TAGs and methyl esterification of FFAs achieve high degree of conversion even with an equal mol of MeOFl to FAs. In addition, methyl esterification of FAs reaches nearly 90% in the presence of water and 98% on removing generated water. These reactions, therefore, become superior tools when only FAs in the raw materials (including unstable compound(s)) are converted to their esters with short-chain alcohols. There are several processes, including lipase-catalyzed conversion of FAs to their methyl (ethyl) esters, to accomplish this. 

FAs liberated from food during absorption are metabolized more easily if they are short or medium chain, i.e., C10 or below. The sn-2 monoacylglycerols can be absorbed directly. Therefore, essential or desired FAs are most efficiently utilized from the sn-2 position in acylglycerols. In accordance with this, TAGs with short-chain FAs (SCFAs) or MCFAs at the sn-1 and sn-3 positions and PEFAs at the sn-2 position are rapidly hydrolyzed with pancreatic lipase (sn-1,3-specific lipase) and absorbed efficiently into mucosal cells. SCFAs or MCFAs are used as a source of rapid energy for infants and patients with fat malabsorption-related diseases. LCFAs, especially DHA and arachidonic acid, are important in both the growth and development of an infant, while n-3 PEFAs have been associated with reduced risk of cardiovascular disease in adults (Christensen et al., 1995 Jensen et al., 1995). 

Milk fat is easily digested because of the high proportion of short-chain FA. These acids, located in the terminal position in the TAG molecule of milk fat, are hydrolyzed preferentially and transferred directly from the intestine to the liver via the portal vein. The high dispersion of fat in milk, particularly in homogenized milk, facilitates its absorption. 

Oxidation causes the formation of hydroperoxides and conjugated compounds, which by cleavage give aldehydes, alcohols, ketones, lactones, acids, esters, and hydrocarbons. Radical mechanisms lead to the formation of dimers, other oligomers, and oxidized TAG. The latter have one or more acyl group with an extra oxygen (hydroxy, keto, epoxy derivatives). Other oxidation products are TAG with short-chain fatty acyl and n-oxo fatty acyl groups. 

Structured lipids (SL) are TAG that contain combinations of short-chain fatty acids (SCFA), medium-chain fatty acids (MCFA), and long-chain fatty acids (LCFA) located in the same glycerol molecule these may be produced by chemical or enzymatic processes (29,30). These specialty lipids may be produced via direct esterification, acidolysis, and hydrolysis or interesterification. Structured lipids are developed to fully optimize the benefits of their fatty acid varieties in order to affect metabolic parameters such as immune function, nitrogen balance, and lipid clearance from the bloodstream. 

The fluorophore was modeled by two beads that are attached as a short pendant side-chain (tag). Both the absorption and emission dipole moments of the fluorophore are defined by the direction of the tag (parallel), as indicated by the vector in Fig. 19, and the fluorescence anisotropy was calculated from its orientation autocorrelation function. For simplicity, we assumed that the reorientaional motion of the fluorophore is the only source of fluorescence depolarization. We neglected energy transfer and other processes that might occur in real systems. The fluorescence anisotropy decays were interpreted using the mean relaxation time, defined as ... 

Immobilized metal ion-affinily chromatography (IMAC) was first established as a technique to fractionate proteins on solid supports based on their differential affinity towards immobilized metal ions. This differential affinity derives from the eoordination bonds formed between metal ions and certain amino acid side ehains exposed on the surface of the protein molecules. Since the interaetion between the immobilized metal ions and the side chains of amino acids has a readily reversible character, it can be used for adsorption and then be disrupted under mild conditions, usually by adding a competing agent. ° The use of this technique to purify recombinant proteins containing a short affinity-tag consisting of poly-histidine residues represent its main application (the most widespread and versatile strategy used to purify recombinant proteins). ... 

Figure 12.25h also illustrates the TIRF signal for the coumarin-tagged short chains, curve 2, as they adsorb from the mixture. Initially the short chains from the mixture are uninfluenced by the presence of the long chains, as the rise in curve 2 is compared to the rise in the 33,000 g/mol adsorption in Figure 12.25a. After this point the short chains are displaced from the surface by the incoming long chains, which continues until substantially all of the short chains are removed.

L = long chain fatty acids, M = medium chain fatty acids, S = short chain fatty acids, MAG = monoacylglycerols, DAG = diacylglycerols, TAG = triacylglycerols. Substrate specificity to acylglycerols. 

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