Esters in milk

Schwartz, H.E., Anzion, C.J.M., Van Vliet, H.P.M., Copius-Peereboom, J.W. Brinkman, U.A.T. (1979) Analysis of phthalate in sediments from Dutch rivers by means of high performance liquid chromatography. Int. J. environ, anal. Chem., 6, 133-134 Scott, R.C., Dugard, P.H., Ramsey, J.D. Rhodes, C. (1987) In vitro absorption of some o-phthalate diesters through human and rat skin. Environ. Health Perspect, 74, 223-227 Shaffer, C.B., Carpenter, C.P Smyth, H.F., Jr (1945) Acute and subacute toxicity of di(2-ethylhexyl) phthalate with note upon its metabolism. J. ind. Hyg. Toxicol., 27, 130-135 Sharman, M., Read, W.A., Castle, L. Gilbert, J. (1994) Levels of di-(2-ethylhexyl) phthalate and total phthalate esters in milk, cream, butter and cheese. Eood Addit Contam., 11, 375-385... 

Table 1.5. Alcohols, Carbonyls, Acids, and Esters in Milk.

DC Woollard, H Indyk. The distribution of retinyl esters in milks and milk products. J Micronutr Anal 5 35-52, 1989. 

Sharman, M., Readn, W. A., Castle, L., and Gilbert, J. Levels of di-(2-ethylhexyl) phthalate and total phthalate esters in milk, cream, butter and cheese. Food Additives and Contaminants, 11, 375-385 (1994). 

CH3 [CHJb-COOH. M.p. 31 5"C, b.p. 268-270 C. A fatty acid, occurring in wool as the potassium salt, as esters in fusel oil, and as glycerides in cows and goats milk and coconut and palm oils. 

Uses Determining fat content in milk solvent for alkaloids, fats, oils manufacturing isovaleric acid, isoamyl or amyl compounds, esters, mercury fulminate, artificial silk, smokeless powders, lacquers, pyroxylin photographic chemicals pharmaceutical products microscopy in organic synthesis. 

Zhu J, Phillips SP, Feng YF, Yang X (2006) Phthalate esters in human milk concentration variations over a 6-month postpartumtime. Environ Sci Technol 40 5276-5281... 

Cholesterol (Appendix 3C) is the principal sterol in milk (>95% of total sterols) the level ( 0.3%, w/w, of total lipids) is low compared with many other foods. Most of the cholesterol is in the free form, with less than 10% as cholesteryl esters. Several other sterols, including steroid hormones, occur at trace levels. 

Most of the sterols and sterol esters, vitamin A, carotenoids and squalene in milk are dissolved in the core of the fat globules but some are probably present in the membrane. 

Vitamin A activity is present in milk as retinol, retinyl esters and as carotenes. Whole cows milk contains an average of 52 fig retinol and 21 fig carotene per 100 g. The concentration of retinol in raw sheep s and pasteurized goats milks is 83 and 44 fig per 100 g, respectively, although milks of these species are reported (Holland et ai, 1991) to contain only trace amounts of carotenes. Human milk and colostrum contain an average of 58 and 155 fig retinol per lOOg, respectively. In addition to their role as provitamin A, the carotenoids in milk are reponsible for the colour of milk fat (Chapter 11). 

Gas chromatographic methods have been successfully used for the determination of penicillin molecules bearing neutral side-chains in milk and tissues (95, 97), but cannot be used for amphoteric -lactams. Gas chromatography of penicillin residues is further complicated by the necessity for derivatization with diazomethane. This derivatization step is particularly important because it not only leads to formation of the volatile penicillin methyl esters but also improves their chromatographic properties (thermal stability and decreased polarity). Using a fused-silica capillary column in connection with a thermionic nitrogen-selective detector, excellent separation and sensitivity figures were obtained. 

About one-tenth of the P in milk (i.e., about 100 mg/liter) is in the form of water-soluble organic esters of orthophosphoric acid. A list of such esters that have been detected in milk is presented in Table 1.8. Most of them are sugar phosphates and constituents of phospholipids. Reported concentrations of some of the compounds vary considerably, and complete quantitation of the group has not been made. 

Timmen and Dimick (1972) characterized the major hydroxy compounds in milk lipids by first isolating the compounds as their pyruvic ester-2,.6-dinitrophenylhydrazones. Concentrations as weight percent of the compounds from bovine herd milk lipids were 1,2-DGs 1.43, hydroxyacylglycerols 0.61, and sterols 0.35. Lipolysis tripled the DG content. The usual milk fatty acids were observed, except that the DGs lacked 4 0 and 6 00, again indicating that these lipids were in part intermediates in milk lipid biosynthesis. With the large hydrazone group... 

Iverson and Sheppard (1977) have compared the method above, substituting sodium butoxide for sodium methoxide to H2S04 and boron trifluoride-catalyzed butyrolyses. Butyl esters were used by these and other investigators to improve the resolution of short chain esters and to reduce their volatility. They recommend the boron trifluoride method for preparation of butyl esters of milk fatty acids, although the other catalysts gave satisfactory results. Analysis of methyl esters resulted in lower values for the short chain fatty acids. 

The number of fatty acids and related compounds in milk lipids grew from 16 in 1959 (Jenness and Patton, 1959) to 142 in 1967 (Jensen et al. 1967) to over 400 in 1983. However, there are only 10 fatty acids of quantitative importance. The amounts (weight percent) as butyl esters prepared by three methods of esterification were determined by Iverson and Sheppard (1977). Because of the widely differing molecular weights of the fatty acids (4 0-18 0), fatty acid compositions of ruminant milk fats are often presented as a mole percent. The nutritionist needs the data calculated in yet another manner weight of fatty acid/100 g or 100 ml of edible portion. Analyses of food fatty acids should always be accompanied by the fat content so that the actual weights of the fatty acids and be calculated. A compilation of this type was made by Posati et al. (1975). Since these analyses were done with methyl esters, the contents of 4 0 are low. Data from Feeley et al. (1975), obtained from careful analyses, are more reliable, and USDA Handbook 8-1 (Posati and Orr 1976) has data for many milk and dairy products. 

Deman and Deman (1983) have investigated the determination of trans unsaturation in milk fat by infrared analysis and found values of 7.4% (winter) to 9.9%(summer) when the TGs were analyzed. These are higher than the quantities found by infrared analysis of methyl esters of the fatty acids. These quantities are isolated total trans bonds and do not give an estimate of the positional and polyunsaturated isomers which are present. The trans contents obtained by Deman and Deman are higher than the 4% found by Smith et al. (1978). 

Frankel, E. N. and Tarassuk, N. P. 1956A. The specificity of milk lipase. I. Determination of the lipolytic activity in milk toward milk fat and simpler esters. J. Dairy Sci. 39, 1506-1516. 

The most common analytical technique for the analysis of FFAs and their breakdown products has been chromatography. HPLC has been used for the analysis of FFAs (Christie, 1997 Lues et ah, 1998 Zeppa et ah, 2001). Analysis of short-chain fatty acids (C2-C4) may be relatively simple (Zeppa et ah, 2001). However, the analysis of long-chain fatty acids (>C6) may require derivatization. They are extracted using solvents, converted to bromophenacyl esters, and analyzed by reverse-phase HPLC. GC (with sample preparation and derivatization) has been the method of choice for analysis of fatty acids. An ideal but difficult procedure is to extract FFAs from the aqueous phase and organic phase and combine them (IDF, 1991). The challenge is to overcome the effects of partitioning and extraction of compounds that interfere with the analysis. ISO and IDF have detailed some of the extraction methods for lipids and liposoluble compounds in milk products (ISO, 2001b). Several other methods, which are mainly different in the extraction and derivatization steps, were reviewed by Collins et ah (2004). 

The major dietary sources for preformed vitamin A are vertebrate animal products that are rich in vitamin A esters (liver, kidney, oil, dairy products, and eggs). Liver and oil, particularly from fish, are the major dietary sources of preformed vitamin A. Levels in milk and eggs depend on dietary retinoid and carotenoid intake. Freshwater fish are a source of vitamin A2 (3,4-dehydroretinol), which shows reduced vitamin A activity. Levels of retinal in food are very low, whereas retinoic acid has not been found. 

The quantitative determination of individual isomers of tram-18 1 fatty acids in milk fat is not straightforward. It involves a multi-stage analytical procedure (i.e., transesterification of milk fat, argentation TLC of the fatty acid esters to separate the civ-isomers and tram-isomers, followed by capillary GC). This method gives an almost complete separation of the 13 individual tram-18 1 isomers, from A4 to A16 (Precht and Molkentin, 1996). 

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