Bioactive Proteins in Milk

Human milk contains a wide variety of proteins that contribute to its unique qualities. Many of these proteins are digested and provide a well-balanced source of amino acids to the rapidly growing infant. Some proteins, such as bile-salt stimulated lipase, amylase, β-casein, lactoferrin, haptocorrin and α1-antitrypsin assist in the digestion and utilization of micro- and macronutrients from the milk. Several proteins with anti-microbial activity, such as immunoblobulins, κ-casein, lysozyme, lactoferrin, haptocorrin, -lactalbumin and lactoperoxidase are relatively resistant against proteolysis in the gastrointestinal tract and may, in intact or partially digested form, contribute towards the defense of the breast-fed infant against pathogenic bacteria and viruses. Prebiotic activity, such as promoting the growth of beneficial bacteria like Lactobacilli and Bifidobacteria,  may also be provided by human milk proteins.  This type of activity can limit the growth of several pathogens by decreasing intestinal pH. Some proteins and peptides have immunomodulatory activities, such as cytokines and lactoferrin, whereas others, like IGF, EGF, and lactoferrin, are likely to be involved in the development of the intestinal mucosa and other organs of the newborn. Together, breast milk proteins assist in providing adequate nutrition of the breast-fed infant, while at the same time aiding in the defense against infection and facilitating optimal development of important physiological functions in the newborn.