Dairy lipids content

High levels of citric acid may cause problems with fructose or glucose. In these cases, the use of anion-exchange minicolumns (Alternate Protocol 1) or GC can be used to overcome this problem. For samples that are high in lipid content (e.g., dairy products) and are thus difficult to dissolve, use warm water for dispersion. 

Table 9.3 Lipid contents of yeasts isolated from New Zealand dairy drains (from Davies and Holdsworth, 1992)...

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. 

Bachman, K. C. and Wilcox, C. J. 1976. Factors that influence milk cholesterol and lipid phosphorus Content and distribution. J. Dairy Sci. 59, 1381-1387. 

Nielsen et al. (1996b) reported significant accumulation of OS in dairy spreads compared to butter. The concentration of OS was 4 times higher in dairy spreads than in butter after storage at 4°C for 13 weeks, and 7-keto was the dominant oxidation product, at 1.3 and 5.7 pg/g lipid in the stored butter and dairy spread, respectively. This difference in stability is undoubtedly related to the high content of PUFA in dairy spreads. 

Although significant strides have been directed at reducing fat content in food products, certain lipid ingredients and sources of fatty acids are used to enhance the health and nutritional quality of foods. For example, CLA isomers were enriched in both dairy and nondairy products to convey its anticancer and antiobesity effects that were reported repeatedly in animal studies (39). Sources of n-3 PUFAs are also added directly to infant formula to provide sufficient DHA for normal development of the nervous system during early infancy. In the United States, DHA was approved by the FDA in 2001 to be added into infant formula (40, 41). 

Plants contain no cholesterol. In animals cholesterol synthesis occurs in many cells, but most cholesterol synthesis occurs in the fiver. Food products from animals contain cholesterol, and the average adult consumes around 450 milfigrams (0.016 ounces) per day. Dairy products and egg yolks are particularly rich in cholesterol. Diets low in fat content and high in vegetables, especially those containing polyimsaturated lipids, can help to lower plasma cholesterol levels. Many physicians recommend that their patients try to maintain cholesterol levels below 200 milfigrams per deciliter. 

Oxidation of milk fat is one of the most important factors limiting the keeping qnality of dairy prodncts. Lipid oxidation yields hydroperoxides that decompose to a broad group of carbonyl componnds, which can contribnte to off-flavors in dairy prodncts. The oxidative stability of fat depends on its composition. Compared with many edible fats, milk fat is relatively resistant to oxidation because of its low PEFA content, and high proportion of satnrated FA, and the presence of natural antioxidants, principally a-tocopherol and P-carotene. Milk fat from the summer contains... 

Most of the lipids in the diet, which we usually refer to as fats, are triglycerides. We get them from meats and fish, vegetables and vegetable oils, and dairy products. They may be solid fats or oils, and they may incorporate saturated or unsaturated fatty acids (Section 12.3). The fat content of some common foods is shown in Figure 16.2. 

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