Proteolytic Systems in Milk: Perspectives on the Evolutionary Function within the Mammary Gland and the Infant

  • David C. DallasEmail author
  • Niamh M. Murray
  • Junai Gan


Milk contains elements of numerous proteolytic systems (zymogens, active proteases, protease inhibitors and protease activators) produced in part from blood, in part by mammary epithelial cells and in part by immune cell secretion. Researchers have examined milk proteases for decades, as they can cause major defects in milk quality and cheese production. Most previous research has examined these proteases with the aim to eliminate or control their actions. However, our recent peptidomics research demonstrates that these milk proteases produce specific peptides in healthy milk and continue to function within the infant’s gastrointestinal tract. These findings suggest that milk proteases have an evolutionary function in aiding the infant’s digestion or releasing functional peptides. In other words, the mother provides the infant with not only dietary proteins but also the means to digest them. However, proteolysis in the milk is controlled by a balance of protease inhibitors and protease activators so that only a small portion of milk proteins are digested within the mammary gland. This regulation presents a question: If proteolysis is beneficial to the infant, what benefits are gained by preventing complete proteolysis through the presence of protease inhibitors? In addition to summarizing what is known about milk proteolytic systems, we explore possible evolutionary explanations for this proteolytic balance.


Milk Protease Digestion Mammary gland Protease inhibitor Protease activator 



Mammary epithelial cell



The authors thank Cora J. Dillard for editing this manuscript. D.C.D., N.M.M. and J.G. wrote the paper, and D.C.D. had primary responsibility for the final content. All authors read and approved the final manuscript. This project was funded in part by the K99/R00 Pathway to Independence Career Award, Eunice Kennedy Shriver Institute of Child Health & Development of the National Institutes of Health (K99HD079561) (D.C. D.).

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • David C. Dallas
    • 1
    • 2
    Email author
  • Niamh M. Murray
    • 3
  • Junai Gan
    • 1
    • 2
  1. 1.Department of Food Science and TechnologyUniversity of California, DavisDavisUSA
  2. 2.Foods for Health InstituteUniversity of California, DavisDavisUSA
  3. 3.Institute of Food and Health, School of Agriculture and Food ScienceUniversity College DublinBelfieldIreland

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