In vitro availability of calcium, iron, and zinc from first-age infant formulae and human milk

Background: Variation in the bioavailability of calcium (Ca), iron (Fe). an d zinc (Zn) occurs because of interactions of food components in the gastro intestinal microenvironment. Bioavailability is preferably determined by in vivo tests, but these are expensive, labor-intensive, time consuming, and often unethical. As an alternative, in vitro methods can be used to predict bioavailability of nutrients from foodstuffs. Methods: A continuous-flow dialysis model with preliminary intraluminal dig estive phase, adapted to the gastrointestinal conditions of infants younger than 6 months, was used. Human milk was the reference standard. Ca, Fe, an d Zn content of samples and dialysates after digestion were analyzed by ato mic absorption spectrometry. Results: Ca availability is similar in human milk (13.1% +/- 0.8%), whey (1 3.3% +/- 1.2%), and soy-based formulae(13.0% +/- 1.2%: P > 0.05), and highe r in casein-predominant formula(21.2% +/- 0.6% P < 0.05). Availability of F e is highest in human milk (8.12% +/- 0.27%: P < 0.05). Fe availability in whey (1.28% +/- 0.28%) and soy formulae (1.48% +/- 0.28%) is similar (P > 0 .05), but availability is lower in casein-predominant formula (0.48% +/- 0. 22%; P < 0.05). Zn availability is also highest in human milk (13.1% +/- 0. 7%; P < 0.05). However, Zn availability is similar in whey (6.7% +/- 0.6%) and casein formulae (8.5% +/- 1.6%: P > 0.05), but lower in soy formula (2. 3% +/- 0.4%; P < 0.05). Conclusions: Our observations are in agreement with previous data from in v ivo studies in term infants. This in vitro procedure is an inexpensive, sim ple, rapid, and reliable method that predicts the bioavailability of Ca, Fe , and Zn in foods.