Fats, hydrolysis

Ester hydrolysis is common in biological chemistry, particularly in the digestion of dietary fats and oils. We ll save a complete discussion of the mechanistic details of fat hydrolysis until Section 29.2 but will note for now that the reaction is catalyzed by various lipase enzymes and involves two sequential nucleophilic acyl substitution reactions. The first is a trcinsesterificatiori reaction in which an alcohol gioup on the lipase adds to an ester linkage in the tat molecule to give a tetrahedral intermediate that expels alcohol and forms an acyl... 

Amide hydrolysis is common in biological chemistry. Just as the hydrolysis of esters is the initial step in the digestion of dietary fats, the hydrolysis of amides is the initial step in the digestion of dietary proteins. The reaction is catalyzed by protease enzymes and occurs by a mechanism almost identical to that we just saw for fat hydrolysis. That is, an initial nucleophilic acyl substitution of an alcohol group in the enzyme on an amide linkage in the protein gives an acyl enzyme intermediate that then undergoes hydrolysis. 

Diels-Alder reaction, 493 El reaction, 391-392 ElcB reaction, 393 E2 reaction, 386 Edman degradation, 1032 electrophilic addition reaction, 147-148. 188-189 electrophilic aromatic substitution, 548-549 enamine formation, 713 enol formation, 843-844 ester hydrolysis, 809-811 ester reduction, 812 FAD reactions. 1134-1135 fat catabolism, 1133-1136 fat hydrolysis, 1130-1132 Fischer esterification reaction, 796 Friedel-Crafts acylation reaction, 557-558... 

Lipase from Aspergillus sp. Milk fat hydrolysis (rich in saturated fatty acids) Oil-phosphate buffer (1/2) 35.7 101... 

The use of homogenized milk for cheesemaking has been reviewed by Peters (1964). The advantages of homogenized milk in the manufacture and ripening of cheese are (1) lower fat losses in whey and therefore a higher yield, (2) reduced fat leakage of cheese at room temperatures, and (3) increased rate of fat hydrolysis and, therefore, desired flavor production in blue cheese. 

Stadhouders, J. and Veringa, H. A. 1973. Fat hydrolysis by lactic acid bacteria in cheese. Neth. Milk Dairy J. 27, 77-91. 

Production of Fatty Acids by Fat Hydrolysis in a Membrane Reactor... 

Adsorption of FFAs on various solid supports, usually after solvent extraction, has led to the development of the best methods for quantifying all the FFAs present in a product. Some of these in which the FFAs are quantified by GC are now regarded as reference methods (Anderson et al., 1991). In some earlier solid adsorption methods, hydrolysis of the fat occurred on the support and overestimated the true FFA level (Stark et al., 1976). However, methods have been developed using deactivated alumina (Deeth et al., 1983) or ion exchange resins (Needs et al., 1983 Spangelo et al., 1986 de Jong and Badings, 1990) in which fat hydrolysis does not occur. 

Bachman, K.C., Hayen, M. J., Morse, D., Wilcox, C. J. 1988. Effect of pregnancy, milk yield, and somatic cell count on bovine milk fat hydrolysis. J. Dairy Sci. 71, 925-931. 

In seeds, lipases may cause fat hydrolysis unless the enzymes are destroyed by heat. Palm oil produced by primitive methods in Africa used to consist of more than 10 percent of free fatty acids. Such spoilage problems are also encountered in grains and flour. The activity of lipase in wheat and other grains is highly dependent on water content. In wheat, for example, the activity of lipase is five times higher at 15.1 percent than at 8.8 percent moisture. The lipolytic activity of oats is higher than that of most other grains. 

When lauric CBS are exposed to moisture and fatsplitting enzymes (lipase), there is a danger of fat hydrolysis and the liberated lauric acid has a distinct... 

Calcium salts of long-chain fatty acids (33.14) are the reaction products between calcium and long-chain fatty acids of vegetable and/or animal origin. They shall contain a maximum of 20% lipid not bound in the calcium salt form and the percent total fat shall be indicated. The unsaponifiable matter (exclusive of calcium salts) shall not exceed 4% and moisture shall not exceed 5%. If an antioxidant is used, its common name must be indicated on the label. Before conducting an assay for total fats, hydrolysis of the calcium salts should be performed to liberate the lipid fraction. 

Continuous Process. The continuous countercurrent, high-pressure fat-splitting process, more popularly known as the Colgate-Emery process, is the most efficient of the current methods of fat hydrolysis. The high temperature and pressure used permit short reaction time. Full countercurrent flow of oil and water produces a high degree of splitting without the need of a catalyst. However, a catalyst may be used to increase reaction rate further. 

The major use of rendered fats is in the production of tallow soaps and in the area of fat hydrolysis, sphtting triglycerides into fatty acids, and byproduct glycerine. As the soap-making industry grew and became more refined, the quality standards and specifications for animal fat became more precise to meet the soap industry s need. The specihcations and terminology, from the soap industry, form the basis for the quality standards and characteristics used today. 

Bile salts are required for supporting the activity of pancreatic lipase as well as for maintaining the polar products of fat hydrolysis in solution. While in the lumen of the small intestine, a fraction of the bile salts is modified by the bacteria present If the taurine or glycine rnoictics are removed by microbial enzymes, they are replaced in the liver after reabsorption of the bile salts in the distal ileum. 

The entire process of heat generation from brown fat, called nonshivering thermogenesis, is regulated by norepinephrine. (In shivering thermogenesis, heat is produced by nonvoluntary muscle contraction.) Norepinephrine, a neurotransmitter released from specialized neurons that terminate in brown adipose tissue, initiates a cascade mechanism that ultimately hydrolyzes fat molecules. The fatty acid products of fat hydrolysis activate the uncoupler protein. Fatty acid oxidation continues until the norepinephrine signal is terminated or the cell s fat reserves are depleted. 

Of these reactions, the fat hydrolysis into glycerol an fatty acids is quite important in systems containing biological materials ... 

Time-temperature indicators are used for products where the storage and transport in appropriate conditions is very important. This indicator informs on the difference between the optimal temperature and the actual temperature and how long a product was exposed to inappropriate temperature conditions. An indicator must be able to monitor one or more conditions chill temperature, frozen temperature, temperature abuses, partial, or full history. The principle operation is based on the polymerization reaction or enzymatic fat hydrolysis or diffusion of the chemically modified dye from encapsulation layer. i Color change must be correlated to food shelf-life. The time-temperature indicator could be placed as a label or as a small packaging in shipping containers (Figure 61.3). 

There is a further commercially important step associated with soap manufacture, namely glycerol recovery. Glycerol is a by-product of saponification or fat hydrolysis and represents a valuable credit in the overall economics of soap production. 

---