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A simple in vitro assay for the determination of soluble iron in fortified rice analogue/natural rice blends is described. The soluble iron, measured as an indicator of iron bioavailability, is quantified by FerroZine™ colorimetry of the supernatant obtained after simulated gastric (pepsin) and intestinal (pancreatin) digestions. Method suitability was defined by assessments of linearity (R 2 average=0.9999±0.0001, and low standard residual average=+0.6±0.9 %; n=17), precision (day-to-day RSD values [n=3 days] ranged from 5.3 % to 75 % for concentrations from 0.017 to 0.585 mg per 100 g of fortified rice analogue/natural rice blend), accuracy (spike recovery=97.5±0.4 %, n=4, spiking level=0.2 to 0.8 mg/l; and linear response of the digest plot [R 2=1.0000] vs. the standard solution plot [R 2=1.0000]), and selectivity (absence of interference from Ca, Mg, Mn, and Zn; reagent blank correction for minimal bias by Cu). The assay provides for a reliable quantification of the soluble iron in fortified rice analogue/natural rice blends. The assay is regarded not as a substitute for in vivo determination of iron absorption, but instead as a tool for identifying formulation, extrusion, and storage issues that are worthy of formal in vivo study. In this connection, application of the assay to fortified rice analogue/natural rice blends and to experimental rice flour preparations has identified potential agents of iron absorption enhancement (e.g., NaFeEDTA at only 2 % of total iron), and of iron absorption inhibition (zinc).

We have reported that bone mineralization at 1 y of age correlates with the age infants started walking, weight, height and calcium intake during infancy. It is unknown if this relationship extends to a later age. We hypothesized that bone mineral content (BMC) and density (BMD) in 3-5.5 y old children are affected by calcium intake at 6-12 mos of age. We evaluated total body BMC and BMD at 3-5.5 y of age in 41 healthy children previously fed one of 3 infant formulas containing different calcium contents (A=450, B=510, C=912 mg/L calcium) at 6-12 mos of age. BMC and BMD at 3-5.5 y of age were similar among the 3 study groups despite differences in calcium intake at 6-12 mos of age. BMC for A groups were (mean-+ SFM) 29.6 +- 0.7, 29.3 +- 0.6, and 29.6 +- 0.8 g/kg body weight, respectively. There were no significant correlations between BMC or BMD and previous calcium intake. BMC and BMD were positively correlated(p