Bioavailability of calcium and zinc from cow's milk-based versus soya-based infant food

Abstract

A modified continuous flow dialysis in vitro method was used to study the availability of calcium and zinc from cow's milk-based versus soya-based infant food. First and second age infant formulae, milk for pre-schoolers and cow's milk were studied. The elemental content of the samples and dialysate fractions was determined by flame atomic absorption spectrometry. The relative availability of calcium and zinc from the soya-based first age infant formula (calcium: 31.6 ± 0.5%, zinc: 17.8 ± 1.8%), from the soya-based second age infant formula (calcium: 46.1 ± 2.1%, zinc: 20.9 ± 1.4%) and from the soya milk for pre-schoolers (calcium: 32.6 ± 0.7%, zinc: 39.7 ± 2.1%) proved to be as good as or even better than from the first age infant formula (calcium: 21.9 ± 1.4%, zinc: 23.3 ± 4.1%), from the second age infant formula (calcium: 31.0 ± 2.5%, zinc: 14.6 ± 0.7%) and from the milk for pre-schoolers (calcium: 27.7 ± 0.6%, zinc: 23.7 ± 2.8%) based on cow's milk. A similar relative availability from semi-skimmed cow's milk and soya milk was reported for calcium (31.5 ± 0.8% and 31.2 ± 1.7% respectively), as well as a much higher availability of zinc from soya milk than from cow's milk (55.7 ± 5.3% and 20.6 ± 3.0% respectively). Enrichment of soya milk with calcium results in a higher calcium availability (46.4 ± 1.9%), but a lower zinc availability (38.5 ± 2.6%) in comparison with the availability from non-enriched soya milk. The apparent absence of inhibitory effects of soya on the availability of calcium and zinc from infant food certainly is a positive finding for the about 10% of Belgian infants which are currently nourished with infant food based on derivatives of soya. According to these results no impaired calcium or zinc status should be feared for in this group of infants.