Dephosphorylation of sodium caseinate, enzymatically hydrolyzed casein and casein phosphopeptides by intestinal alkaline phosphatase: implications for iron availability

Milk Proteins and Iron Absorption: Contrasting Effects of Different Caseinophosphopeptides

“…Indeed, we believe that the previous results are conflicting only in appearance: cow milk proteins have different functional properties concerning mineral metabolism; ␤-casein and its CPP enhance Fe absorption, whereas ␣ S -casein-rich fractions or their CPP inhibit it (12,13). The impairing effect of releasing Fe from the Fe-␤-CPP complex at the brush border membrane level suggests, as previously shown (10), that its uptake by the mucosa occurs in a bound form.…”

“…Hydrolysis of cow milk proteins enhances Fe absorption (5), but previous studies suggested that not all caseins are equal in their interactions with Fe. Whereas CPPs derived from ␤-casein enhance Fe absorption and bioavailability in experimental and human studies (9 -11), CPPs derived from whole caseins or from ␣ s1 -casein-enriched fractions seem to exert an opposite effect (12)(13)(14). The confirmation of such functional differences between milk proteins could have significant consequences on infant nutrition, because breast milk is rich in ␤-casein but has no ␣-casein.…”

“…Then, 1 mL of Fe solutions was added to the top compartment of the insert, and plates were placed on an incubator (37°C, low oscillations) for 2 h. After incubation, uptake into cell monolayers was stopped by addition of ice-cold spDMEM, and the transepithelial resistance was measured. Solutions were removed by aspiration, and monolayers were incubated once with 500 mol of 1 mM bathophenanthroline disulfonic acid and 5 mM sodium hydrosulfite solution to remove surface-bound Fe (12). Cell monolayers then were rinsed twice with Hank's buffer solution salt without Ca and Mg and solubilized with 0.1% triton (2 mL) .…”

“…Hydrolysis of whole caseins improves Fe absorption (5), but caseinophosphopeptides (CPP) released by the enzyme digestion of different caseins give conflicting results; the two main cow milk caseins are ␣ S -and ␤-caseins; binding Fe to CPP of ␤-casein or to hydrolyzed ␤-casein improves its absorption and its bioavailability in rats and in humans (9 -11); however, CPP derived from the hydrolysis of whole casein or fractions enriched with ␣ S -casein CPP inhibit Fe absorption (12)(13)(14).…”

“…The objectives of this study were to evaluate the absorption of Fe complexed to CPP purified either from ␤-casein or from ␣ s1 -casein and to determine the effect of an inhibitor of intestinal alkaline phosphatase (Na 2 WO 4 ) (12,15). The study used two models, the in vivo perfused rat intestinal loop and a human colon adenocarcinoma cell line culture (Caco-2), which is predictive of human Fe bioavailability (16).…”