From milk fat

In milk approximately 90% of the yellow color is because of the presence of -carotene, a fat-soluble carotenoid extracted from feed by cows. Summer milk is more yellow than winter milk because cows grazing on lush green pastures in the spring and summer months consume much higher levels of carotenoids than do cows ham-fed on hay and grain in the fall and winter. Various breeds of cows and even individual animals differ in the efficiency with which they extract -carotene from feed and in the degree to which they convert it into colorless vitamin A. The differences in the color of milk are more obvious in products made from milk fat, since here the yellow color is concentrated. Thus, unless standardized through the addition of colorant, products like butter and cheese show a wide variation in shade and in many cases appear unsatisfactory to the consumer. 

Parodi (1976) determined the distribution of double bonds in cis and trans octadecenoic fatty acids from milk fat and bovine adipose tissue. About 95% of the 18 1 is the cis-9 isomer. Parodi detected the cis-12, -13, and -14 isomers, fatty acids not observed by Hay and Morrison (1970). The 18 1 content of Australian butterfat has varied throughout the season from 17.3 to 24.9 M%, with isolated trans unsaturation from 4.3 to 7.6 M%,... 

Milk fat contains both keto (oxo) and hydroxy fatty acids, and earlier identifications are discussed by Jensen et al. (1967), Morrison (1970), and Kurtz (1974). In a more recent and careful study, Weihrauch et al. (1974) isolated 60 oxo acids from milk fat and positively and tentatively identified 47 with the aid of mass spectrometry. These data are presented in Table 4.9. About 85% (weight) of the oxo acids were stearates, mostly the 13-isomer, and 20% were palmitates, largely the 11-isomer. Of the unsaturated oxo acids, the 9-oxo, 12-ene, and 13-oxo, 9-ene were the predominant species. Other unsaturated oxo acids which are not listed in Table 4.9 but which were possibly present, are 15 1, 16 2, 17 1, 17 2, 17 3, 18 2, 18 3, 19 1, 19 2, and 20 1. 

Parodi, P. W. 1974A. The composition of a high melting glyceride fraction from milk fat. Aust. J. Dairy Sci. 29, 20-22. 

Schwartz, D. P. 1972. Methods for the isolation and characterization of trace components from milk fat. J. Am. Oil Chem. Soc. 49 312A, Abstr. 96. 

Market milk and some products manufactured from milk sometimes possess a flavor described as rancid . This term, as used in the dairy industry, denotes implicitly the flavor due to the accumulation of the proper concentrations and types of free fatty acids hydrolytically cleaved from milk fat under the catalytic influence of the lipases normally present in milk. 

Imam, A., Laurence, D. J. R. and Neville, A. M. 1981. Isolation and characterization of a major glycoprotein from milk-fat-globule membrane of human breast milk. Biochem J. 193, 47-54. 

Patton, S. 1982. Release of remnant plasma membrane from milk fat globules by Triton X-100. Biochim. Biophys. Acta 688, 727-734. 

Figure 9.3 Gas chromatogram of methyl esters prepared from milk fat on a 2.4-m stainless steel column, 25% EGS on 42/60 mesh Chromosorb, thermal conductivity detector, injector 325°C, detector 225°C, column 200°C(10).

Usually, mobile phases of acetonitrile and acetone have been used in the analysis of TG from milk fat, most often in isocratic elution (114,115) and in gradient eiution, and they provide a resolution of 50 chromatographic peaks (Numela). One of the main difficulties in the analysis of TG is the identification of the chromatographic peaks, because of the small number of mixed TGs in a pure state. Bornaz et al. (115) and Dotson et al. (114) identified butterfat chromatographic peaks from the relationship between the retention time and the theoretical carbon number according to the model proposed by El-Hamdy and Perkins (87). An alternative method is the fractionation of total TG in milk fat by reversed-phase HPLC and analysis of the fatty acids in each fraction (116,117). 

Two saturated fatty acids, pentadecanoic acid (15 0) and heptadeca-noic acid (17 0), in adipose tissue (Baylin et al., 2002) and serum lipids (Smedman et al., 1999 Sun et al., 2007a Wolk et al., 1998) have been proposed and validated as biomarkers of dietary ruminant fat intake, that is, mainly from milk fat and to lesser extent from ruminant meat. The human body is unable to synthesize fatty acids with an uneven number of carbon atoms, whereas ruminal microbes of cows have this ability (Wu and Palmquist, 1991). To measure the content of 15 0 and/or 17 0 in plasma lipids or adipose tissue is consequently a way to estimate the milk fat intake. It is known that the proportion of 15 0 and 17 0... 

Yoon, S. H. Nakaya, H. Ito, O. Miyawaki, O. Park, K. H. Nakamura, K. Effects of Substrate Solubility in Interesterification with Riolein by Immobilized Lipase in Supercritical Carbon Dioxide. Biosci. Biotechnol. Biochem. 1998, 62, 170-172. Yu, Z. R. Rizvi, S. S. H. Zollweg, J. A. Enzymatic Esterification of Fatty Acid Mixtures from Milk Fat and Anhydrous Milk Fat with Canola Oil in Supercritical Carbon Dioxide. Biotechnol. Prog. 1992, 8, 508-513. 

It is obvious that many of these volatiles contribute to the aroma generated from milk fat by heating. In 1967, Kinsella et al. emphasized the flavor capabilities of milk fat and outlined a scheme for their utilization (7). The lactones and methyl ketones are... 

YOOETAL. Processing Parameters and Volatile Compounds from Milk Fat 115... 

Cholesterol is present in milk at a level of 0.25-0.46%. The interest in removing cholesterol from milk fat has been driven primarily by consumer concern about the possible link between cholesterol and heart disease. Although there is still some debate about the causal relationship between dietary cholesterol and heart disease, a marketing position has been created for low-cholesterol products and this has spurred interest in examining alternative ways of cholesterol removal in the 1980s and 1990s (Schlimme, 1990). A number of physical, chemical and biological processes have been used to reduce the level of cholesterol in milk fat (Boudreau and Arul, 1993). Cholesterol-reduced butter has been introduced on the market in Europe (Anon, 1992). 

The efficiency of supercritical CO2 for removing cholesterol is temperature- and pressure-dependent. Removal of about 90% cholesterol from milk fat was achieved using bench-scale supercritical CO2 extraction using an ascending pressure profile (Bradley, 1989). With multistage supercritical CO2 extraction, more than 90% cholesterol can be removed from milk fat (Anon, 1989). 

Micich et al. (1992) demonstrated that polymer-supported saponins could be used to remove cholesterol from milk fat and that the polymers could be regenerated by solvent extraction without loss of cholesterol-binding capacity. 

Bradley, R.L. Jr. 1989. Removal of cholesterol from milk fat using supercritical carbon dioxide. J. Dairy Sci. 72, 2834-2840. 

Lawrence et al. (1967) reported some preference for long-chain triglycerides by a P. fragi lipase but for short-chain triglycerides by a lipase from Micrococcus freudenreichii. Temperature may have an influence on the apparent specificity of lipolysis, with relatively more short-chain and unsaturated fatty acids being released from milk fat at lower temperatures. This appears to be a reflection of the physical state of the substrate (Alford and Pierce, 1961 Sugiura and Isobe, 1975). 

Lipase preparations from numerous microorganisms, including those mentioned above, have been used in the synthesis of dairy (buttery or cheesy) flavors from milk fat (Arnold et al., 1975 Kilara, 1985) or to enhance flavor development in ripening cheese (Fox, 1988). These include lipases from Rhizomucor (Mucor) miehei (Moskowitz et al., 1977 Huge-Jensen et al., 1987), Achromobacter lipolyticum (Khan et al., 1967), Aspergillus niger... 

Choi, I.W., Jeon, I.J., Smith, J.S. 1994. Isolation of lipase-active fractions from ultra-high temperature-processed milk and their patterns of releasing fatty acids from milk fat emulsion. J. Dairy Sci. 77, 2168-2176. 

Sundheim, G., Bengtsson-Olivecrona, G. 1987b. Hydrolysis of bovine milk fat globules by lipoprotein lipase inhibition by proteins extracted from milk fat globule membrane. J. Dairy Sci. 70, 1815-1821. 

Bills et al. (1963) used pre-treated Amberlite resin dispersed in hexane to isolate FFAs from milk. Fat was removed from the resin using hexane, absolute ethanol and methanol and the FFAs were esterified prior to analysis by GC. Needs et al. (1983) extracted lipids from milk by using ether and the FFAs were isolated using a strong basic anion exchange resin (Amberlyst 26, BDH Ltd, Poole Dorset, UK). The FFAs were methylated and resolved by GC. McNeill et al. (1986) also used Amberlyst resin to isolate FFAs in conjunction with silicic acid to remove phospholipids. Extracted FFAs were then analyzed by GC. This method was used by McNeill and Connolly (1989) to quantify FFAs in a number of semi-hard cheeses. 

Lipolytic rancidity is normally enzymatic, the enzymes responsible usually coming from bacteria or moulds. The effect of lipolytic rancidity is that the level of free fatty acid rises. The effect of this on the product depends very much upon the nature of the free fatty acid liberated. Low levels of free butyric acid from milk fat tend to enhance a toffee by giving it a more buttery flavour, whereas lipolysis of a lauric fat such as HPKO gives free lauric acid, which is an ingredient of, and tastes of, soap. This effect is very unpleasant. 

Thompson AK, Mozafari MR, Singh H (2007) The properties of liposomes produced from milk fat globule membrane material using different techniques. Lait 87 349-360... 

Romero, P., Rizvi, S.S.H., Nelly, M.L., and Bauman, D.E. 2000. Concentration of conjugated linoleic acid from milk fat with a continuous supercritical fluid processing system. J. Dairy Sci. 

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