Submitted to: British Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/10/2008
Publication Date: 4/1/2009
Citation: Jin, F., Welch, R.M., Glahn, R.P. 2009. Effects of Ascorbic Acid, Phytic Acid and Tannic Acid on Ferritin-Iron Bioavailability as Determined Using an In Vitro Digestion/Caco-2 Cell Model. British Journal of Nutrition. 101(7):972-981. Interpretive Summary: Iron is an essential nutrient and is present in many forms in foods. The ferritin form of Fe is of interest because it may represent a more bioavailable form of Fe in plant foods. This study was designed to determine if the major promoter (ascorbic acid)and inhibitor (e.g. phytate and tannic acid) of Fe uptake affect ferritin-bound Fe. An in vitro digestion/Caco-2 cell model was used for these experiments, and the ferritin-bound Fe was compared to ferrous sulfate. Ascorbic acid promoted Caco-2 cell Fe uptake in relatively similar amounts from both ferritin Fe and ferrous sulfate. Phytic acid and tannic acid both inhibited Fe uptake from ferritin-bound Fe and ferrous sulfate to a similar extent. Overall, there were no significant differences in bioavailable Fe between ferritin bound Fe and ferrous sulfate. The results suggest that Fe in the ferritin molecule is easily released during digestion and this freed Fe interacts with known promoters and inhibitors of Fe bioavailability. However, these effects may be highly dependent on the food matrix, gastric pH, and other factors. Further research is needed to completely characterize ferritin Fe bioavailability.
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.