Editing Casein (section)

===A1/A2 beta caseins in milk===
{{Main|A2 milk}}

A1 and A2 beta-casein are [[Single-nucleotide polymorphism|genetic variants]] of the beta-casein milk protein that differ by one [[amino acid]]; a [[proline]] occurs at position 67 in the [[Peptide sequence|chain of amino acids]] that make up the A2 beta-casein, while in A1 beta-casein a [[histidine]] occurs at that position.<ref name="truswell">{{cite journal | vauthors = Truswell AS | title = The A2 milk case: a critical review | journal = European Journal of Clinical Nutrition | volume = 59 | issue = 5 | pages = 623–631 | date = May 2005 | pmid = 15867940 | doi = 10.1038/sj.ejcn.1602104 | doi-access = free }}</ref><ref>{{cite journal|vauthors=Truswell AS|date=2006|title=Reply: The A2 milk case: a critical review|journal=[[European Journal of Clinical Nutrition]]|volume=60|issue=7|pages=924–5|doi=10.1038/sj.ejcn.1602454|doi-access=free}}</ref> Due to the way that beta-casein interacts with [[enzymes]] found in the digestive system, A1 and A2 are processed differently by [[digestive enzymes]], and a seven-amino [[peptide]], beta-[[casomorphin]]-7, (BCM-7) can be released by digestion of A1-beta-casein.<ref name="truswell"/>

The A1 beta-casein type is the most common type found in cow's milk in Europe (excluding Italy and France which have more A2 cows), the United States, Australia, and New Zealand.<ref name=EFSA/>

Interest in the distinction between A1 and A2 beta-casein proteins began in the early 1990s through [[Epidemiology|epidemiological]] research and animal studies initially conducted by scientists in New Zealand, which found correlations between the prevalence of milk with A1 beta-casein proteins and various chronic diseases.<ref name="truswell"/> The research generated interest in the media, among some in the scientific community, and entrepreneurs.<ref name="truswell"/>  A company, A2 Corporation, was founded in New Zealand in the early 2000s to commercialize the test and market "A2 Milk" as premium milk that is healthier due to the lack of peptides from A1.<ref name="truswell"/> A2 Milk even petitioned the [[Food Standards Australia New Zealand]] regulatory authority to require a health warning on ordinary milk.<ref name="truswell"/>

Responding to public interest, the marketing of A2 milk, and the scientific evidence that had been published, an independent review published in 2005 found no discernible difference between drinking A1 or A2 milk on the risk of contracting chronic diseases.<ref name="truswell" /> The [[European Food Safety Authority]] (EFSA) reviewed the scientific literature and published a review in 2009 found no identifiable relationship between chronic diseases and drinking milk with the A1 protein.<ref name="EFSA">{{Cite journal|last=EFSA|author-link=European Food Safety Authority|date=2009|title=Review of the potential health impact of β-casomorphins and related peptides: Review of the potential health impact of β-casomorphins and related peptides|journal=EFSA Journal|volume=7|issue=2|pages=231r|doi=10.2903/j.efsa.2009.231r|doi-access=free}}</ref>