Digestibility fatty acid esters

When Carroll (1958) fed fatty acids as the methyl or ethyl esters, these esters were more efficiently absorbed than the free fatty acids by the rat. However, for fatty acids in the form of triglycerides (TG) the effect was opposite for saturated and monounsaturated fatty acids. A saturated TG was less digestible than the fatty acid itself, while a TG composed of a monounsaturated fatty acid was absorbed better than its free fatty acid (Carroll and Richards, 1958). Triglyceride fatty acids also influence absorption, particularly with the poorly digested fatty acids. For example, the absorption coefficient of erucic acid was increased from 72% when fed as ethyl erucate to 80% when ethyl erucate was mixed with soybean oil (Ziemlanski et al., 1973a). Even the absorption of 22 1 in HEAR oil was improved by mixing... 

The presence of fatty acid esters in olestra bestows on it the taste and culinary properties of an ordinary fat. Yet, olestra Is not digestible like a typical fat. This is because the steric bulk of olestra renders it unacceptable to the enzymes that catalyze hydrolysis of ordinary fats. Olestra passes through the digestive tract unchanged and thereby adds no calories to the diet. As it does so, however, olestra associates with and carries away some of the lipid-soluble vitamins, namely, vitamins A, D, E, and K. Foods prepared with olestra are supplemented with these vitamins to compensate for any loss that may result from their extraction by olestra. Studies conducted since olestra s approval have demonstrated that people report no more bothersome digestive effects when eating Olean (the trademark name for olestra) snacks than they do when eating full-fat chips. 

Ester sulfonates will become more and more interesting in the future because the raw materials for their preparation are fatty acid esters which can be prepared from oils and rats, and thus from renewable resources. They can be used as possible substitutes for surfactants based on petrochemicals. Even today renewable resources play a dominant role as raw materials for surfactants, but only because of the great contribution made by soaps to the production of surfactants. If the soaps are left out of consideration as native surfactants, petrochemistry holds 65-70% of the production of synthetic surfactants [2], But for the future a further increase in the use of renewable raw materials is expected to occur in surfactant production [3]. The main reason for this development is the superior digestibility in the environment of products produced from natural materials. The future importance of the renewable raw materials becomes evident from the fact that even now new plants are cultivated or plants are modified to obtain an improved yield. A new type of sunfiower has been cultivated to obtain a higher proportion of monounsaturated oleic acid compared with doubly unsaturated linoleic acid [4]. 

Plat et al (2000) recently showed that 2.5 g/day of plant stanols as fatty acid esters consumed with a meal in one daily dose was as effective at reducing serum total and LDL cholesterol levels as the same amount divided into three doses taken throughout the day (Figure 8). This indicates that additional mechanisms at the absorptive sites of the enterocytes or within the enterocytes must play a role in the overall effect of plant sterols on cholesterol absorption. In an in vitro cell model. Field et al (1997) showed that sitosterol was taken up by Caco-2 cells less efficiently than cholesterol. Furthermore, plant sterols and stanols are absorbed into the cell walls of the digestive tract in animals (Bhattacharyya and Lopez, 1979 Sanders et al, 2000). 

Irrespective of the actual mechanisms behind the reduction of cholesterol absorption by plant sterols, solubilization into the emulsified fat phase of the food digest is a prerequisite for plant sterols to be incorporated into the micelles. The physical properties of free, crystalline plant sterols and stanols limit their applicability in foods and their cholesterol-lowering effect in many food matrices, but these limitations can be partly solved by producing fat dispersions of plant sterols or emulsifier-sterol aggregates. Currently, however, plant sterols are mainly used as fatty acid esters in functional foods. 

Although /3-oxidation is universally important, there are some instances in which it cannot operate effectively. For example, branched-chain fatty acids with alkyl branches at odd-numbered carbons are not effective substrates for /3-oxidation. For such species, a-oxidation is a useful alternative. Consider phy-tol, a breakdown product of chlorophyll that occurs in the fat of ruminant animals such as sheep and cows and also in dairy products. Ruminants oxidize phytol to phytanic acid, and digestion of phytanic acid in dairy products is thus an important dietary consideration for humans. The methyl group at C-3 will block /3-oxidation, but, as shown in Figure 24.26, phytanic acid a-hydroxylase places an —OFI group at the a-carbon, and phytanic acid a-oxidase decar-boxylates it to yield pristanie add. The CoA ester of this metabolite can undergo /3-oxidation in the normal manner. The terminal product, isobutyryl-CoA, can be sent into the TCA cycle by conversion to succinyl-CoA. 

Digestion (Section 29.1) The first stage of catabolism, in which food is broken down by hydrolysis of ester, glycoside (acetal), and peptide (amide) bonds to yield fatty acids, simple sugars, and amino acids. 

Part of the diet consists of fats, which are triglycerol esters of fatty acids (FAs). The FAs from digestion of ingested fats can be metabolized in a variety of pathways. Fragments of the original FAs are preserved in these processes and can be utilized in the biosynthesis of other molecules. It is important to note that, during metabolism, almost all FAs are broken down into two-carbon units. The only exceptions are FAs with odd numbers of carbon atoms these are relatively rare in the diet. It ean be shown further that there is a partial barrier to the incorporation of FA-derived carbon into the amino acids which constitute collagen. 

Gorreta, F., Bernasconi, R., Galliani, G., Salmona, M., Tacconi, M. T., and Bianchi, R. (2002). Wax esters of co-3 polyunsaturated fatty acids A new formulation as a potential food supplement—Digestion and absorption in rats. Lebensmittel-Wissenschaft und Technologie 35,458-465. 

No-calories fat substitutes, such as sucrose polyesters (Olestra), which are synthesized from sucrose and fatty acid methyl esters, have been widely studied and several snacks fried in this medium are available in the market place. This product has no calories since digestive enzymes are not able to break it down due to structural impairment. A major disadvantage that prevents a wide acceptance of this product is related to the gastrointestinal discomfort that may be caused to some individuals (Dobraszczyk et ah, 2006, p. 104). 

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. 

Much of the cholesterol synthesis in vertebrates takes place in the liver. A small fraction of the cholesterol made there is incorporated into the membranes of he-patocytes, but most of it is exported in one of three forms biliary cholesterol, bile acids, or cholesteryl esters. Bile acids and their salts are relatively hydrophilic cholesterol derivatives that are synthesized in the liver and aid in lipid digestion (see Fig. 17-1). Cholesteryl esters are formed in the liver through the action of acyl-CoA-cholesterol acyl transferase (ACAT). This enzyme catalyzes the transfer of a fatty acid from coenzyme A to the hydroxyl group of cholesterol (Fig. 21-38), converting the cholesterol to a more hydrophobic form. Cholesteryl esters are transported in secreted lipoprotein particles to other tissues that use cholesterol, or they are stored in the liver. 

An adult ingests about 60 to 150 g of lipids per day, of which more than n nety percent is normally triacylglycerol (formerly called triglyceride). Uhe remainder of the dietary lipids consists primarily of cholesterol, cholesteryl esters, phospholipids, and unesterified ("free") fatty acids. "The digestion of dietary lipids is summarized in Figure 15.2. 

Digestion of dietary lipids Dietary lipids DIGESTION OF DIETARY LIPIDS (p. 171) Dietary lipids consist primarily of triacylglycerol, with some cholesterol, cholesteryl esters, phospholipids, and free (nonesterified) fatty acids. 

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