BIOACTIVE COMPONENTS OF MILK
The cow has the special ability to extract bioactive components from its feed, mostly unsuitable for human consumption, and transfer them to its milk, or to extract components that are converted to bioactives in the rumen and other tissues. Examples are β-carotene from pasture, a portion of which is converted to vitamin A in vivo, with the provitamin and vitamin having both common and diverse nutritional properties.
Food is medicine. If that is so, then there is an increasing evidence to show that nutrition has a significant role to play in the development of various chronic diseases in human beings including obesity, insulin resistance, cancer and cardio vascular diseases. A high consumption of trans-fats and saturated fatty acids are implicated in cardio vascular diseases. The saturated fatty acids act as a double edged weapon in inducing chronic cardio vascular diseases as well as lowering insulin sensitivity leading to diabetes.
Milk and dairy products are the major source of 12:0, 14:0 and 16:0 chain fatty acids and a major share of the total fatty acid intake of the human diet. However, public health policies advocating lower intake of milk will negate the supply of essential nutrients to the body. On the contrary, milk and dairy products may confer beneficial effects like prevention of osteoporosis, cancer, atherosclerosis and degenerative disorders. Milk and other fermented dairy products are endowed with nutrients in the form of minerals, proteins, peptides, and lipids which exhibit bioactive properties with the beneficial effect of extending the longevity of the human beings.
Trans fatty acids (TFA) and bioactive lipids in milk
The U.S. Food and Drug Administration (USFDA) have for regulatory purposes defined TFA as ‘‘all unsaturated fatty acids that contain one or more isolated, that is, non-conjugated having double bonds in a trans-configuration.
Fatty acids with a conjugated bond, principally isomers of conjugated linoleic acid (CLA) in ruminant-derived foods and dietary CLA supplements, are exempt from TFA labeling regulations. Processing technologies have been developed for reducing the TFA content of edible oils and fats to meet legislative requirements.
Milk fat consists of a number of components, including 4:0, branch-chain fatty acids, trans-11 18:1, cis-9, trans-11 conjugated linoleic acid, trans-9, trans-11 18:2 CLA, vitamins A and D, beta-carotene, and sphingomyelin, that have been shown to elicit anti-mutagenic properties in a number of in vitro experiments with human cell lines and animal model studies.
The biologically active lipids and fatty acids in milk act as bio active components to safeguard the health of consumers. The total fat and the type of fat influence the incidence of cardio vascular diseases and coronary heart diseases in human beings. Saturated fatty acids play a major role in raising the total and low density lipoprotein cholesterol. Intake of myristic (14:0) and palmitic (16:0) acid results in elevated serum LDL-cholesterol level in human beings whereas consumption of stearic acid (18:0), the other major saturated fatty acid elicited a neutral response. Whole milk, cheese, and butter act as a major source of 12:0 and 14:0 and a significant amount of 16:0 in the diet.
Milk fat is a unique and relatively rich source of butyrate in the human diet, containing between 75 and 130 mmol/mol of butyric acid. Butyrate is known to exhibit anticarcinogenic effects, inhibit cell growth, promote differentiation, and induce apoptosis in various human cancer cell lines. It has also been suggested that butyrate may also prevent the invasion of tumors via inhibitory effects on urokinase. The role of butyrate as an antimutagen has been largely focused on preventing colon cancer, since butyrate is an end product of microbial fermentation of carbohydrates in the human gut. There is also some evidence to suggest that the physiological effects of butyrate may be enhanced in the presence of other bioactive compounds including retinoic acid, vitamin D and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors. The mode of action is not well understood, but it has been suggested that butyrate may mediate its effects by increased accessibility of DNA to transcription factors via inhibitory effects on histone deacetylase.
Milk has a diverse range of fatty acids containing branched chain, with length ranging from 4 to 26 carbon atoms. Scientific studies have demonstrated that several branch-chain fatty acids exhibit anti-carcinogenic properties. Oral administration of 15:0 iso at the rate of 70 mg/kg body weight over a period of 40 days was found to inhibit the growth of human prostate and liver cancer cells transplanted into the prostate and liver of mice, by 84.6% and 65.2%, respectively. Moreover, it is shown that a number of branch-chain fatty acids were effective in inhibiting the fatty acid synthesis of human breast cancer cells in vitro. The cytotoxicity of the branch chain in fatty acids was reported to be comparable to that exerted by the conjugated linoleic acid.
Poly Unsaturated Fatty Acids (PUFA) of Milk
Poly Unsaturated Fatty Acids in milk are not synthesized by the ruminant tissues and therefore, the concentration of 18:2 n-6 and 18:3 n-3 in milk is dependent on the quantity of these fatty acids absorbed and their subsequent transfer to the mammary gland. The supply of PUFA available for absorption is determined by both the amounts of PUFA in the diet and the extent of their metabolism in the rumen. In typical ration, the 18:2 n-6 concentrations in milk vary between 2 and 3 gram per 100 g fatty acids. Enriching the diet with plant oils rich in 18:2 n-6 including soybean, sunflower, or safflower oil resulted in only small increases in milk fat 18:2 n-6 content. Whereas the extruded micronized or roasted soybeans can result in higher enrichments of 18:2 n-6 in milk compared with plant oils. Linseed is the most common 18:3 n-3-rich feed ingredient other than grass or legume forages. Trials with rapeseed oil or rapeseeds which are rich in 18:3 n-3 does not result in a significant enrichment of 18:3 n-3 in milk fat.
Learn more about Conjugated Linoleic Acid and bioactive peptides in milk