Editing Milk (section)

===Proteins===
Normal bovine milk contains 30–35&nbsp;grams of protein per liter, of which about 80% is arranged in casein [[micelles]]. Total proteins in milk represent 3.2% of its composition (nutrition table).

====Caseins====
{{Main|Casein}}
The largest structures in the fluid portion of the milk are [[casein|"casein micelles"]]: aggregates of several thousand protein molecules with superficial resemblance to a surfactant [[micelle]], bonded with the help of nanometer-scale particles of [[calcium phosphate]]. Each casein micelle is roughly spherical and about a tenth of a micrometer across. There are four different types of casein proteins: αs1-, αs2-, β-, and κ-caseins. Most of the casein proteins are bound into the micelles. There are several competing theories regarding the precise structure of the micelles, but they share one important feature: the outermost layer consists of strands of one type of protein, [[k-casein]], reaching out from the body of the micelle into the surrounding fluid. These kappa-casein molecules all have a negative [[electrical charge]] and therefore repel each other, keeping the micelles separated under normal conditions and in a stable [[colloid]]al [[suspension (chemistry)|suspension]] in the water-based surrounding fluid.<ref name="On Food and Cooking"/><ref name="chem">{{cite web |last=Goff |first=Douglas |url=https://www.uoguelph.ca/foodscience/book-page/raw-milk-quality |title=Raw milk quality |work=Dairy Science and Technology |publisher=University of Guelph Food Science, Guelph, Ontario, Canada |access-date=February 8, 2011 |year=2010 |archive-url=https://web.archive.org/web/20141231022516/http://www.uoguelph.ca/foodscience/book-page/raw-milk-quality |archive-date=December 31, 2014 |url-status=live}}</ref>

Milk contains dozens of other types of proteins beside caseins and including enzymes. These other proteins are more water-soluble than caseins and do not form larger structures. Because the proteins remain suspended in [[whey]], remaining when caseins coagulate into curds, they are collectively known as ''whey proteins''. [[Lactoglobulin]] is the most common whey protein by a large margin.<ref name="On Food and Cooking"/> The ratio of caseins to whey proteins varies greatly between species; for example, it is 82:18 in cows and around 32:68 in humans.<ref name=Applications2017>{{cite book |title=Handbook of Milk of Non-Bovine Mammals |chapter=Potential Applications of Non-Bovine Mammalian Milk in Infant Nutrition |editor1-first=Young W. |editor1-last=Park |editor2-first=George F.W. |editor2-last=Haenlein |editor3-first=William L. |editor3-last=Wendorff |first1=Shane V. |last1=Crowley |first2=Alan L. |last2=Kelly |first3=John A. |last3=Lucey |first4=James A. |last4=O'Mahony |page=630 |date=2017 |publisher=John Wiley & Sons Ltd. |edition=2nd |doi=10.1002/9781119110316.ch13 |isbn=978-1-119-11031-6}}</ref>

{| class="sortable wikitable" style="margin:auto"
|+Ratio of caseins to whey proteins in milk of nine mammals<ref name=Applications2017/>
|-
! Species !! Ratio
|-
| Human || 29.7:70.3 – 33.7:66.3 
|-
| Bovine || 82:18
|-
| Caprine || 78:22
|-
| Ovine || 76:24
|-
| Buffalo || 82:18
|-
| Equine || 52:48 
|-
| Camel || 73:27 – 76:24
|-
| Yak || 82:18
|-
| Reindeer || 80:20 – 83:17
|}