Food and nutrition.pdf

232 Milkfrom separating out of the milk. The milk is pumped at high pressuresthrough very narrow tubes, breaking up the fat globules throughturbulence and cavitation. A greater number of smaller particles possessmore total surface area than a smaller number of larger ones, and theoriginal fat globule membranes cannot completely cover them.Casein micelles are attracted to the newly-exposed fat surfaces; nearlyone-third of the micelles in the milk end up participating in this newmembrane structure.The casein weighs down the globules and interferes with theclustering that accelerated separation. The exposed fat globules are brieflyvulnerable to certain enzymes present in milk, which could break downthe fats and produce rancid flavors. To prevent this, the enzymes areinactivated by pasteurizing the milk immediately before or duringhomogeniza tion.Homogenized milk tastes blander but feels creamier in the mouththan unhomogenized; it is whiter and more resistant to developing offflavors. Creamline, or cream-top, milk is unhomogenized; it mayor maynot have been pasteurized. Milk which has undergone high-pressurehomogenization, sometimes labeled as "ultra-homogenized," has a longershelf life than milk which has undergone ordinary homogenization atlower pressures. Homogenized milk may be more digestible thanunhomogenized milk.Concerns exist about the health effects of consuming homogenizedmilk. Work by Kurt A. Oster, M.D. in the 1960s through the 1980ssuggested a link between homogenized milk and arterosclerosis, due tothe release of bovine xanthine oxidase (BXO) from the milk fat globularmembrane (MFGM) during homogenization. While Oster's work has beenwidely criticized, it is apparent that homogenization introduces changesthe MFGM and the exposure of its proteins, and the effects of these changeson food safety have not been thoroughly investigated.Nutrition and HealthThe composition of milk differs widely between species. Factors suchas the type of protein; the proportion of protein, fat, and sugar; the levelsof various vitamins and minerals; and the size of the butterfat globulesand the strength of the curd are among those than can vary. For example:• Human milk contains, on average, 1.1% protein, 4.2% fat, 7.0%lactose (a sugar), and supplies 72 kcal of energy per 100 grams.• Cow milk contains, on average, 3.4% protein, 3.6% fat, and 4.6%lactose, 0.7% minerals and supplies 66 kcal of energy per 100grams. See also Nutritional value further on.Donkey and horse milk have the lowest fat content, while the mills of