Milk is the first food for man and, for its nutritional characteristics (including those of its derivatives), it is confirmed as one of the fundamental products for human nutrition in all ages. There are various types of milk which differ in terms of fat content: whole milk with a content of at least 3.5%; semi-skimmed milk with a fat content of between 1.5% and 1.8%; skimmed with a content of less than 0,5%. Milk is a food with good nutritional value, thanks to its chemical composition, and good food value. In fact, it contains on average 32 grams of proteins per liter, a fair amount of vitamins of the B group and, among the mineral salts, the primacy is certainly due to calcium. But milk proteins are not just a complete source of the nine essential amino acids that humans can not synthesize. Apart from casein, some as such are also provided with biological action: many of them are responsible for the protective effect on the breastfeeding baby. Excluding antibodies (immunoglobulins), here is a list of the most abundant bioactive proteins in milk.
These glycoproteins are very resistant to gastric degradation and protect against various micro-organisms. The purified mucins from maternal milk, MUC1 and MUC4, and cervical mucus of pregnancy (MUC2, MUC5AC, MUC5B and MUC6), inhibit HIV-1 in an in vitro test. Milk also has minor mucins such as MUC15 (PAS3), a highly glycosylated protein associated with the fat cell membrane of bovine milk (MFGM). In addition to fractions containing fats such as MFGM and buttermilk, MUC15 is also present in fractions without fat, such as skimmed milk and whey.
Butyrophylines (PAS 5)
They serve to correct the secretion of lipid cells in milk, but they seem to play a role in regulating certain immune functions. They constitute a large family of structurally similar trans-membrane proteins from the super-family of immunoglobulins. Although the main member of this family is linked to lactation, by participating in the secretion, formation and stabilization of milk fat globules, it can also have a cell surface receptor function. In general, butyrophilins are now known to modulate T lymphocyte selection, their differentiation, their co-stimulatory responses and the determination of cell fate.
This protein promotes the formation of subcutaneous fat, thus participating in a relevant way to the physiology of cutaneous and subcutaneous tissues. Increased perlipin 2 activity increases insulin resistance, thereby promoting type 2 diabetes. Decreased perlipin 2 expression decreases fatty liver while increasing perlipin expression is associated with various metabolic diseases such as type 2 diabetes, insulin resistance, heart disease. Furthermore, its expression was found to be related to other age-related diseases. The analysis of body fluids such as urine and blood in patients with different types of cancer, such as lung adenocarcinoma, colorectal cancer and Burkitt’s lymphoma, showed an increase in adipofilin levels.
Lactoaderin (PAS6 / 7)
Lactaderin is an important component of the milk fat membrane in milk. Inhibits the infectivity of rotavirus, or those responsible for many forms of gastroenteritis. The inhibitory activity against HRV infection of human lactaderin was identified for the first time by Yolken et al. (1992). In addition, a previous clinical study indicated a correlation between human lactaderin in breast milk and morbidity due to rotavirus gastroenteritis in young children. Lactaderin binds to MA104 cells through the αvβ3 integrin, which is known as one of the rotavirus cell receptors. Therefore, the interaction between lactaderin and cell surface components is probably important for its antiviral activity.
Important component of the immune system of mammals, with antimicrobial activity against numerous microorganisms, anti-inflammatory, antiviral and antitumor activity. Lactoferrin hydrolyses RNA and shows the properties of specific secretory ribonucleases of pyrimidine. In particular, by destroying the RNA genome, this protein inhibits the reverse transcription of the retroviruses that cause breast cancer in mice. Lactoferrin has been shown to have positive effects on bone health. It has reduced the formation of osteoclasts, which means a decrease in pro-inflammatory responses prone to promote bone loss. This means that it could be an active component of milk, apart from calcium, to counteract the appearance of osteoporosis. The human colostrum has the highest concentration, followed by human milk, then cow’s milk (150 mg / L).
Lactoperoxidase (LPO) is an antimicrobial protein secreted by mammary, salivary, and other mucosal glands. It is an important member of the heme-peroxidase enzymes and of the primary peroxidase enzyme present in animal tissues. It is one of the most important whey enzymes capable of forming powerful bactericidal molecules, oxidizing chloride anions through hydrogen peroxide. Thiocyanate (SCN-) is one of the most important substrates of the enzyme, because it produces hypothiocyanate (OSCN-). Hypothiocyanate is a powerful oxidizing antibacterial agent; in this way, lactoperoxidase exerts a significant antibiotic activity in milk. The concentration of LPO in cow’s milk is about 30 mg / L depending on the season, the diet, the birth and the breeding season.
Xanthine oxidase (XOS / XDH)
This enzyme is known classically because it synthesizes the final product of DNA catabolism, namely uric acid. In milk, however, it is involved in the secretion of the lipid globule and then acts as a defense protein as it regulates some oxidation-reduction reactions. One of these is the production of superoxide during its enzymatic activity, a free radical that has a bactericidal effect.
Bioactive substances are also present in the lipid and carbohydrate components of milk. Four of these are the most important.
This short-chain fatty acid (SCFA) directly inhibits cell growth of various tumors, which can prevent colon cancer. As a cell growth inhibitor, it has a direct effect on enzymes (histone deacetylases) of the cell nucleus. SCFA acids modulate the functions of different systems, such as intestinal, cerebral, endocrine and blood, serving as a key factor in regulating metabolic disorders and immunity. These actions are mainly performed through the activation of surface receptors, such as GPR41, GPR43 and GPR109a. The effects of SCFA have been demonstrated in influencing systemic autoimmune responses and participating in different phases of the inflammation process.
CLA (conjugated linoleic acid)
Whole cow’s milk contains an average of 3.5% fatty acids and of these about 0.5% is represented by CLA. The main isomer is rumenic acid, cis9-trans11, which can represent from 79% to 94% of the total CLA of milk. It has anti-inflammatory potential but above all anti-tumor, as it inhibits the growth of human cancer cells. It also improves immune function and lean mass and leads to a reduction in atherosclerosis. It seems that some strains of Lactobacillus and Bifidobacterium present in the human intestine can contribute to its partial internal synthesis. Other actions demonstrated by CLA are regulator of pancreatic function (insulin), immuno-modulatory and contrasting the formation of atherosclerotic plaques.
This phospholipid has an important anti-tumor action, in particular as regards the cell growth of colon carcinoma. It becomes part of the cell membranes, but from its enzymatic cleavage it produces ceramide. This, in turn, is the real one responsible for the chemopreventive action through a type of programmed cell death called apoptosis. The other product of hydrolysis is phospho-choline, which is a nutrient of nerve cells; it can be used to synthesize acetylcholine and phospholipids in the brain, being a source of phosphorus for brain metabolism.
Glycans are characteristic components of milk and each species has unique patterns of specific carbohydrates. Human milk is unusually rich in glycans, with the main components such as lactose and oligosaccharides, which account for respectively 6.8% and 1% of milk. In breast milk, the presence and patterns of these glycans vary according to the stage of lactation. Human milk contains larger amounts and more complex structures of soluble oligosaccharides than any other mammalian milk; the average amounts range from 7g/L in mature milk to 23 g/L in colostrum. Many human milk glycans inhibit pathogens from binding to the intestinal mucosa. Glycans also directly stimulate the growth of beneficial microbiota bacteria; these mutualists and their fermentation products can, in turn, inhibit pathogens, inflammation and fermentation products can be absorbed and used as a source of calories in the diet.
There is enough to change your mind about petty information and unjustified demonization of “Mr Milk”.
- edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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