DECREASED CITRATE IMPROVES IRON AVAILABILITY FROM INFANT FORMULA: APPLICATION OF AN IN VITRO DIGESTION/CACO-2 CELL CULTURE MODEL

Authors: Glahn, Raymond; LAI, CINDY - CORNELL UNIVERSITY; HSU, JEAN - CORNELL UNIVERSITY; Thompson, John; Van Campen, Darrell

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: We have applied an in vitro digestion/cell culture model to the assessment of Fe availability from human milk and a generic cow milk-based infant formula. This model combines simulated stomach and intestinal digestion with measurement of Fe uptake by human intestinal epithelial cell mono- layers. Experiments were designed to determine the availability of iron from human milk relative to infant formula, and to determine if known promoters of iron absorption would increase cell iron uptake and availability from the infant formula. In addition, we sought to determine if decreasing the citrate concentration in the infant formula would increase the iron uptake. Although approximately twice as much iron was in solution from digests of the infant formula relative to that of human milk, less or equal iron was taken up from the infant formula relative to the human milk digest. As a result, the iron in the human milk digest could be considered more available than the iron from the infant formula. These results are qualitatively similar to human studies. Addition of known iron uptake promoters (ascorbic acid, cysteine, cysteinyl glycine and glutathione) to infant formula did not enhance iron uptake from the infant formula digest, indicating that the iron in the infant formula existed predominantly in a tightly bound unavailable form(s). By reducing the amount of citric acid in the infant formula, we were able to improve iron uptake from by 46%. These results suggest that in order to maximize iron availability from milk based infant formula, optimal levels of citrate should be determined. This study is an example of how this model can be used to improve the nutritional quality of a food such as infant formula.

Technical Abstract: We have applied an in vitro digestion/cell culture model to the assessment of Fe availability from human milk and a generic cow milk-based infant formula. This model combines simulated peptic and intestinal digestion with measurement of Fe uptake by Caco-2 cell monolayers. Prior to digestion, FeSO4, extrinsically labeled with 59FeSO4 was added to infant formula or human milk to achieve a total Fe concentration of 10 or 200 mol/L. Experiments were designed to determine the availability of iron from human milk relative to infant formula, & to determine if known promoters of iron absorption would increase Caco-2 cell iron uptake & availability from the infant formula. In addition, we sought to determine if decreasing the citrate concentration in the infant formula would increase the iron uptake. Although approximately twice as much iron was in solution from digests of the infant formula relative to that of human milk, less or equal iron was taken up from the infant formula relative to the human milk digest. As a result, the iron in the human milk digest could be considered more available than the iron from the infant formula. These results are qualitatively similar to in vivo studies. Addition of known iron uptake promoters to infant formula did not enhance Caco-2 cell iron uptake from the infant formula digest, indicating that the iron in the infant formula existed predominantly in a tightly bound unavailable form(s). Enzymatic pretreatment of the infant formula to decrease the citrate concentration from 4.64 to 1.53 mmol/L resulted in a 64% increase of iron in solution, which corresponded to a 46% increase in the cell iron uptake. These results suggest that in order to maximize iron availability from cow milk-based infant formula, optimal levels of citrate should be determined.