Submitted to: British Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/8/2008
Publication Date: 4/1/2009
Citation: Jin, F., Frohman, C., Glahn, R.P., Thannhauser, T.W., Welch, R.M. 2009. Effects of Ascorbic Acid, Phytic Acid and Tannic Acid on Iron Bioavailability from Reconstituted Ferritin Measured by an In Vitro Digestion/Caco-2 Cell Model. British Journal of Nutrition. 101(7):312-316. Interpretive Summary: A model for digestion has been developed in our lab that uses a simulated digestion and Caco-2 epithelial tissue cell culture monolayer to imitate the intestinal lining and absorption of minerals into our bodies. The model was used to test whether iron in ferritin (an iron storage protein found in plants and animals) would be more readily used by the body as opposed to iron sulfate (commonly used as an iron supplement) using both inhibitors and enhancers of iron absorption. The results suggest that ferritin is broken down during digestion and as a result iron from the ferritin reacts with the inhibitors and promoters similar to iron sulfate.
Technical Abstract: The effects of ascorbic acid, phytate and tannic acid on Fe bioavailability from Fe supplied as ferritin was compared to FeSO4 using an in vitro digestion/Caco-2 cell model. Horse spleen ferritin (HSF) was chemically reconstituted into a plant-type ferritin (P-HSF). In the presence of ascorbic acid (AA; molar ratio of Fe:AA, 1:20), significantly more Fe was absorbed from FeSO4 (~303%), HSF (~454%) and P-HSF (~371%) compared to ferrous sulfate or ferritin without AA. Phytic acid (PA; molar ratio of Fe:PA, 1:20), significantly reduced Fe bioavailability from FeSO4 (~86%), HSF (~82%) and P-HSF (~93%) relative to FeSO4 or ferritin controls. Fe bioavailability was significantly decreased (~97%) from both FeSO4 and ferritin samples by tannic acid (TA; molar ratio of Fe:TA, 1:1). AA was able to partially reverse the negative effects of PA (molar ratio of Fe:PA:AA, 1:20:20) on Fe bioavailability but did not reverse the inhibiting effects of TA (molar ratio of Fe:TA:AA, 1:1:20) on Fe bioavailability from ferritin and FeSO4. Overall, there were no significant differences in bioavailable Fe between P-HSF, HSF or FeSO4. Furthermore, the addition of AA (a known promoter) or the inhibitors, PA and TA, or both, did not result in significant differences in bioavailable Fe relative to FeSO4. The results suggest that Fe in the ferritin molecule is easily released during in vitro digestion and this freed Fe interacts with known promoters and inhibitors of Fe bioavailability.