Table 1.
Overview of proteins and peptides in mature human milk with presumed functions or activities in addition to being a source of amino acids to breast fed infants.
| Protein | Human Milk Concentration (mg/L) | Molecular Weight (kDa) | Human Milk Concentration (µmol/L) | Bioactivity a | Bioactivity in Cell or Animal Models (1) or in Clinical Trials (2) | Resistance to Digestion |
|---|---|---|---|---|---|---|
| β-casein | 3000–5000 [21] | 24 | 125–208 | peptides | (1) casein phosphopeptides support Ca absorption [11], (1) β-casomorphins act as opioid receptor ligands [22] (2) β-casomorphins appear in infant plasma [23] |
casein phosphopeptides detected in ileostomy fluids of adults [24] |
| κ-casein | 1000–3000 [21] | 30 | 33–100 | protein/peptides | (1) inhibition of H. pylori adhesion to gastric mucosa cells [14] (1) glycomacropeptide shows bifidogenic and pathogen inhibiting effects in the gut and anti-inflammatory effects after absorption [12] |
κ-caseinglycopeptide detected in the duodenum of adults after milk consumption [25] |
| α-lactalbumin | 1800–3100 [26] | 14 | 129–221 | peptides | (1) activity against gram positive bacteria [13] (1) immunostimulation by GLF peptides [27] (2) increased serum Fe [28] |
slower digested than caseins, but no intact α-lactalbumin detected in infant faecal samples [27] |
| lactoferrin | 1200–3000 [29] | 77 | 16–39 | protein/peptides | (1) antimicrobial and immunomodulating effects, influence on iron absorption in various models [30] (1) antimicrobial activity of lactoferricin H and B [31] (1) bifidogenic activity [32] (2) beneficial effects [33] |
detected in fecal samples of breast fed infants [34] |
| haptocorrin | <0.7–7 | 68 | <0.01–0.1 (age 4 months) [35] | protein | (1) bacteriostatic effect of porcine haptocorrin [36] (1) contribution to Vit-B12 absorption [37] |
in vitro resistance to proteolysis for porcine haptocorrin [36] |
| lysozyme | 50–250 [38] | 15 | 3–17 | protein | (1) cleavage of cell wall of gram positive bacteria [19] | resistant to peptic digestion, but susceptible to tryptic digestion [39] |
| secretory IgA | 500–1000 [38] | 420 | 1–2 | protein | (1) antibody, antimicrobial activity [18] | secretory IgA detected in fecal samples of breast fed infants [34] |
| bile-salt stimulated lipase | 100–200 [40] | 120–140 | <1–2 | protein | (1) lipolytic activity [41] (2) increased long chain fatty acid absorption [42] (1) inhibits the attachment of Norwalk virus-like particles to its cellular ligand [43] |
stable at pH > 3 [44] |
| osteopontin | 60–220 [45] | 60 | 1–4 | protein/peptides | (1) altered intestinal gene expression in rhesus monkeys [46] (2) less fever and altered cytokine pattern [47] |
human and bovine osteopontin are partially resistant to proteolysis by infant gastric juice at pH 4 [41] |
a Bioactivity ascribed to intact protein or derived peptides.