Table 3.
Properties of minor human milk fat globule membrane (MFGM) proteins.
| Protein | Molecular weight (kDa) | Location in milk fraction | Function | Difference with bovine MFGM | Change over lactation | Glycosylated (Y/N) | Resistance to digestion |
|---|---|---|---|---|---|---|---|
| Carbonic anhydrase 6 | 35 | MFGM | Acid neutralizer, antibacterial component, and growth factor | Not specified | No significant change reportedc, or 8-fold higher in colostrum MFGM than the MFGM in mature milke | Y | Not specified |
| Milk alkaline phosphatase (AP) | 86 | MFGM | Immune system | Not specified | Not specified | Y | Not specified |
| Lysozyme | 17 | Predominantly in whey and to lesser extent in MFGM | Antibacterial component, immune system | Higher in human than in bovine MFGM (P < 0.05)b | Higher at later stages of lactationa,c | Y | Not detected in feces of breastfed infantsi; resistant to pepsin, but susceptible to trypsinj |
| Lactoferrin | 78 | Predominantly in whey and to lesser extent in MFGM | Antibacterial component, immune system | Higher in human than in bovine MFGM (P < 0.05)b | No significant change reportedc; however, higher in early milk than in mature milkf | Y | 4-9 % of ingested lactoferrin detected in feces of breastfed infantsi |
| Osteopontin (OPN) | 41-75 | Predominantly in whey and to lesser extent in MFGM | Antibacterial component, immune system | Lower in human than in bovine MFGM but not significant (P > 0.05)b | No significant change reporteda,c; but in bovine milk, higher in early milk MFGMd | Y | Partially resistant to proteolysis when incubated with infant gastric juice in vitrok |
| α-Lactalbumin | 16 | Predominantly in whey and to lesser extent in MFGM | Antibacterial component, immune system | Higher in human than in bovine MFGM (P < 0.05)a | Higher in mature human MFGM than colostrum MFGMa; or no change reportedc. | Y | Digested in the small intestine, releasing bioactive peptides and essential amino acidsl |
| Immunoglobulins (e.g., IgA α-chain C region) | 37-38 | Predominantly in whey and to lesser extent in MFGM | Antibacterial component, immune system | A wider range of Ig present in human MFGM; IgA is more enriched in human than in bovine MFGMb | IgG H chain, Ig heavy chain variable region, polymeric immunoglobulin receptor and immunoglobulin J chain were higher in colostruma | Y | Resistant to digestion and survived intact to the stoolm |
| Toll-like receptors (e.g.,TLR2, 4) | ~90 | MFGM | Antibacterial component, immune system | Higher TLR2 in human than in bovine MFGMg | Higher TLR4 in mature milk MFGM than in colostrum MFGMh | Y | Not specified |
| Clusterin | 52 | MFGM | Antibacterial component | Higher in human than in bovine MFGM (P < 0.05)b,g; but another study reported lower quantity in human than in bovine MFGMa | No significant change reporteda; but in bovine, colostrum MFGM has significantly higher quantity than mature MFGMb | Y | Resistant to gastric hydrolysisn |
| Tenascin | 241 | Whey and MFGM | Antibacterial component | Not specified | Significantly higher in colostrum MFGM than in mature MFGM (P < 0.05)a,c | Y | Resistant to gastric hydrolysisn |
a
Yang et al. (99),
b
Hettinga et al. (1),
c
Liao et al. (97),
d
Reinhardt and Lippolis (100),
e
Karhumaa et al. (110),
f
Rai et al. (111),
g
Lu et al. (107),
h
Cao et al. (98),
i
Davidson and Lonnerdal (112),
j
Hamosh (113),
k
Demmelmair et al. (114),
l
Layman et al. (115),
m
Demers-Mathieu et al. (116), and
n
Dallas et al. (117).
Note that the study by Reinhardt and Lippolis (100) used bovine MFGM.