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Format:
Print
Author:
Smith, Casey Ryan
Dept./Program:
Animal Science
Year:
2004
Degree:
Ph. D.
Abstract:
Human milk is the best choice for infants, with a nutrient balance, content of growth-promoting substances, and immunological protection against disease forming the rationale behind this recommendation. However, there are instances when breast feeding is not possible, including: premature and milk-sensitive infants, inborn errors of metabolism, breast-feeding failure, and insufficient milk syndrome. Deficiencies of trace elements are rare in breast fed infants, however, infants who consume formula low in iron and zinc may experience a deficiency of these nutrients. Poor solubility and bioavailability of iron, as well as zinc, in commercial infant formula warrants fortification at levels that greatly exceed those observed in human milk in order to assure adequate nutrition. The goal of these experiments was to investigate the solubility and relative bioavailability of organic mineral salts of iron and zinc (ferrous gluconate and zinc gluconate) against inorganic mineral salts (ferrous sulfate and zinc sulfate) in whey protein dominated (40:60 casein:whey ratio) liquid and powdered infant formula.
In addition, the impact of additional antioxidants, specifically vitamins C and E, on the solubility and bioavailability of iron and zinc in infant formulas prepared with organic and inorganic mineral salts of iron and zinc was investigated. An in vitro digestion/Caco-2 cell model was used to examine the relative bioavailability of iron and zinc from the formulas. Initial experiments indicated that there was no difference in the solubility of iron or zinc in formulas prepared with organic or inorganic mineral salts, at 43.4% and 42.6% of iron, and 29.6% and 27.3% of zinc, respectively, found in the serum fraction of whey protein dominated liquid infant formula. Further experiments investigating the reducing power on iron by the antioxidant nutrients ascorbic acid and vitamin E indicated no improvement in solubility by vitamins C or E.
The next set of experiments examined the solubility and bioavailability of iron and zinc in whey protein dominated powdered infant formula. The solubility of iron was significantly higher in formula prepared with inorganic mineral salts, at 39.1% vs. 35.5% total iron in the serum fraction, with no difference in zinc solubility, at 39.5% vs. 38.3%, in formulas prepared with organic and inorganic mineral salts of zinc, respectively. In addition, vitamins C and E at levels exceeding the RDA significantly decreased the solubility of selected mineral salts of iron and zinc in formulas prepared with organic or inorganic mineral salts. Relative bioavailability of iron and zinc from organic or inorganic mineral salts, and with additional antioxidants, was not different when the in vitro digestion/Caco-2 cell model was employed. Future research should address the low solubility of trace minerals in infant formula, to improve the nutritional quality and competitive position of these products.