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A2 milk is cow's milk that contains only the A2 type of beta-casein protein rather than the more common A1 protein commonly found in regular milk. A2 milk is branded by the A2 Milk Company and sold mostly in Australia, New Zealand and the United Kingdom. While the company marketing A2 milk claims that milk containing A1 proteins is harmful, there is no scientific evidence that A2 milk has benefits over normal milk.〔1 February 2009, EFSA review of scientific literature on A1 and A2 milk, (Review of the potential health impact of β-casomorphins and related peptides )〕 A1 and A2 beta-casein are genetic variants of the beta-casein milk protein that differ by one amino acid. The A1 beta-casein type is the most common type found in cow's milk in Europe (excluding France), the USA, Australia and New Zealand. A genetic test, developed by the A2 Milk Company, determines whether a cow produces the A2 or A1 type protein in its milk. The test allows the A2 Milk Company to give licenses to milk producers once these producers prove their cows produce only A2 beta-casein protein in their milk, to the exclusion of the A1 beta-casein protein type. ==Background== Cows' milk is about 87 percent water and 13 percent solids—the solids being a combination of fat, carbohydrates in the form of lactose, minerals and protein. The major component of the milk proteins is casein; in turn about 30-35 percent of the casein (equivalent to two teaspoons in a litre of milk) is beta-casein, of which there are several varieties, determined by the genes of the cow. The most common of these variants are A1 and A2 (named for the order in which they were identified by scientists), with the sole difference between the two being one of the 209 amino acids that make up the beta-casein proteins: a proline occurs at position 67 in the chain of amino acids that make up the A2 beta-casein, while in A1 beta-casein a histidine occurs at that position. Studies in cells found that digestive enzymes that cut up proteins interact with beta-casein precisely at that location, so that A1 and A2 beta-casein proteins are processed differently. A seven-amino peptide, beta-casomorphin-7, (BCM-7) can be cut away from the A1-beta-casein protein by those enzymes, but the enzymes cannot cut the A2 protein at that location, so BCM-7 is not formed from A2 proteins. Studies in humans have not consistently found that BCM-7 is formed in the human digestive system.〔Clemens RA. (Milk A1 and A2 peptides and diabetes ). Nestle Nutr Workshop Ser Pediatr Program. 2011;67:187-95. doi: 10.1159/000325584. Epub 2011 Feb 16. PMID 21335999〕 BCM-7 can also be created during the fermentation of milk or through the process by which cheese is made; those same processes can also destroy BCM-7.〔 Scientists believe the difference originated as a mutation that occurred between 5000 and 10,000 years ago—as cattle were being taken north into Europe—when the proline at position 67 was replaced by histidine, with the mutation subsequently spreading widely throughout herds in the western world through breeding. The prevalence of the A1 and A2 beta-casein protein varies between herds of cattle, and also between countries and provinces. While African and Asian cattle continue to produce only A2 beta-casein, the A1 version of the protein is common among cattle in the western world.〔 The A1 beta-casein type is the most common type found in cow's milk in Europe (excluding France), the USA, Australia and New Zealand.〔 On average, more than 70 percent of Guernsey cows produce A2 milk, while among Holsteins and Ayrshires between 46 and 70 percent produce A1 milk. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「A2 milk」の詳細全文を読む スポンサード リンク
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