Effect of gastric digestion pH on iron, zinc, and calcium dialyzability from preterm and term starting infant formulas

Iron, zinc, and calcium dialyzability from preterm and term starting infant formulas were determined after in vitro digestion, using special gastric conditions prevailing in preterm and newborn infants. Mineral dialyzability was studied using pH 2.0, 3.5, and 4.5 for gastric digestion. The effect of gastric pH was more important on iron dialyzability (FeD) and zinc dialyzability (ZnD) than on calcium dialyzability (CaD). The effect on iron dialyzability was remarkable in fluid formulations with high digestibility: FeD was 18% to 20% when gastric digestion was made at pH 2, decreasing to 3% when made at pH 4.5. In most powder infant formulas with the lowest digestibility, FeD remained close to 10% despite variations in gastric digestion pH. Percent zinc dialyzability (ZnD%) steadily decreased when gastric digestion pH increased. At each pH, percent iron dialyzability (FeD%) and ZnD% from human milk were higher than those from infant formulas. Evaluation of mineral dialyzability from these infant formulas, using a gastric digestion pH prevailing in preterm and newborn infants, can provide valuable information on mineral availability.