THE EFFECT OF DIGESTIVE ENZYMES ON THE BINDING AND BACTERIOSTATIC PROPERTIES OF LACTOFERRIN AND VITAMIN B12 BINDER IN HUMAN MILK

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Abstract
Human milk contains unsaturated lactoferrin and vitamin B12 binding protein. These proteins may exert antibacterial effects in the intestine of the breast-fed infant, but the effect of the intestinal environment on the antibacterial effect of these proteins was not described. In this study human milk was treated with pepsin and trypsin, and the influence of digestion on Fe and vitamin B12 binding capacity, bacterial uptake of Fe and vitamin B12 from milk and bacteriostatic effect was studied. Pepsin digestion had no effect on vitamin B12 binding capacity, the ability of bacteria to take up vitamin B12, or the growth inhibitory effect on a vitamin B12-dependent strain. In contrast, pepsin digestion (or low pH alone) released Fe from milk and abolished its bacteriostatic effect. Trypsin digestion slightly reduced the molecular size of the vitamin B12 binding protein without releasing free vitamin B12; the bacteriostatic effect on a vitamin B12- dependent organism [Escherichia coli] was abolished. In contrast, trypsin digestion did not affect Fe binding or bacteriostatic effects attributable to lactoferrin. The findings support an in vivo bacteriostatic role for lactoferrin in the breast-fed neonate''s intestine but do not support a similar role for the vitamin B12 binding protein.