A method for in vitro determination of calcium, iron and zinc availability from first-age infant formula and human milk

A method for in vitro determination of available calcium, iron and zinc content from infant food after digestion was evaluated. This method introduced Bn intraluminal digestive phase, adapted to the gastrointestinal conditions of infants younger than 6 months of age, prior to continuous flow dialysis of the resultant gastric digest. Precautions handling the method were discussed and enzymatic parameters were defined. Ruggedness of the method was determined from the availability of calcium, iron and zinc at different gastrointestinal conditions. Availability of all three elements was higher at gastric pH of 2 (20.0 +/- 1.1% for calcium, 4.06 +/- 0.66% for iron and 17.5 +/- 1.3%, for zinc), than from the normal procedure (pH 4) (15.6 +/- 1.2% for calcium, 1.18 +/- 0.26% for iron and 8.2 +/- 0.9% for zinc). At pH 5, however, calcium availability appeared to be lower (11.7 +/- 1.0%) (P < 0.05). The intestinal pH also had a major influence on the availability. At low intestinal pH (5.5), availability was 40.5 <plus/minus> 2.3% for calcium, 3.01 +/- 0.58% for iron and 26.8 +/- 1.8% for zinc, which was higher compared with the normal procedure (P < 0.05). Moreover, other factors, such as digestion time, mixing and filtration pressure, also affected the availability. Recovery tests yielded mean values of 94 <plus/minus> 3% for calcium, 109 +/- 9% for iron and 106 +/- 4% for zinc. Mean intra- and inter-batch precision of the availability procedure was 4.1 CV% and 6.6 CV% for calcium, 14.5 CV% and 19.2 CV% for iron, and 4.0 CV% and 13.6 CV% for zinc. The method provides adequate accuracy, acceptable precision and good recovery. It offers the advantage of being simple, rapid and inexpensive, since it takes only 1 day to run the whole availability procedure (including four replicates per sample), and the low costs of the dialysis equipment. It can therefore be considered as suitable for predicting the availability of essential elements from foods used during the first months of infancy.