Iron and zinc in hydrolised fractions of human milk and infant formulas using an in vitro method

The development of an in vitro method to simulate new-born digestion and to study iron and zinc bioavailability from human milk and cowʹs milk based infant formulas was carried out. Enzyme treatment was conducted in two stages involving (1) pepsin at pH 5.0 followed by (2) pancreatin at neutral pH, where the incubation times were kept short to mimic the fast transit in the infantʹs gastrointestinal tract. Solubility of trace elements was used to express bioavailability, and so analytes were determined in the fractions obtained after centrifugation by flame atomic absorption spectrometry (FAAS) using a high performance nebulizer. The results were compared to those obtained by performing gastric digestion at pH 2.0 for an adult, using various incubators to treat the sample and centrifugation or ultracentrifugation to separate soluble fractions. No differences in iron bioavailability from breast milk and infant formulas at different pHs could be detected due to the variability of the infant formulas analysed. However, zinc bioavailability from breast milk samples was higher than those obtained from infant formulas at the new born gastric pH.