Effect of calcium and zinc concentrations and calcium source on in vitro calcium and zinc solubility in a fiber-fortified enteral formula

Abstract

The present study was carried out to evaluate the effects of simultaneous addition of increasing levels of calcium (60–210 mg/100 g formula) and zinc (1.5–3.9 mg/100 g formula) on calcium and zinc solubility in an enteral formula fortified with soy polysaccharide fiber (2.13 g/100 g formula). The solubility of calcium from various sources, added to the formula, was also examined. Solubility was estimated by the ratio of soluble calcium or zinc in the supernatant, after centrifugal separation of samples subjected to in vitro pepsin and pancreatin digestion, over the total calcium or zinc content of samples. No interaction was found between calcium and zinc levels. Zinc solubility decreased linearly from 17 to 12% with increasing calcium levels (p<0.05). Soluble calcium decreased from 18 to 13% with increasing zinc levels (p<0.01). The percentage of soluble zinc was lower as more zinc was added (p<0.01) but soluble calcium was higher as more calcium was added (p<0.01). Mono- and dibasic calcium phosphates were markedly less soluble than calcium carbonate, calcium chloride and calcium phosphate hydroxide. Results suggest a competitive effect between calcium and zinc when soy polysaccharide fiber is present. An understanding of this effect is necessary for the appropriate fortification of enteral formulas in order to maximize the proportion of minerals potentially available for absorption.