Does processing of a powder or in-bottle-sterilized liquid infant formula affect calcium bioavailability?

Processing of infant formulas can induce Maillard reaction or lactose isomerization, among other changes. These reactions were evaluated with furosine and lactulose, respectively. Protein alteration was assessed with sodium dodecylsulfate-polyacrylamide gel electrophoresis. Repercussions on calcium bioavailability in powder and in-bottle-sterilized liquid infant formulas were studied. Lactulose, advanced Maillard-reaction products, and denatured proteins were higher in liquid infant formula. After in vitro digestion, soluble non-dialyzed calcium was significantly higher in liquid than in powder infant formula, but there were no differences in dialyzed insoluble calcium. Two-week-old rat pups drank the powder or liquid infant formula for 7 d. Food intake and final body weight were significantly lower in those fed liquid formula. Accordingly, the intake, apparent absorption, and retention of calcium were measured; the percentages of retention versus absorption and retention versus intake were significantly lower, although calcium digestibility (percentage of absorption versus intake) was higher. These results show that, although calcium in the sterilized infant formula was available in vitro and was absorbed more efficiently in vivo, it was poorly used by suckling rats. The low acceptability of this formula and the interaction of calcium with lactulose and advanced but absorbable Maillard-reaction products might explain the results. Thus, for calcium bioavailability, we recommend the powder instead of the conventional sterilized infant formula.