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World J Gastroenterol. Apr 14, 2007; 13(14): 2083-2088
Published online Apr 14, 2007. doi: 10.3748/wjg.v13.i14.2083
Gastric digestion of pea ferritin and modulation of its iron bioavailability by ascorbic and phytic acids in caco-2 cells
Satyanarayana Bejjani, Raghu Pullakhandam, Ravinder Punjal, K Madhavan Nair
Satyanarayana Bejjani, Raghu Pullakhandam, Ravinder Punjal, K Madhavan Nair, Micronutrient Research Group, National Institute of Nutrition, Indian Council of Medical Research, Jamai Osmania, Hyderabad 500007, India
Author contributions: All authors contributed equally to the work.
Supported by a grant No. BT/PR6728/AGR/02/334/2005 from the Department of Biotechnology, Government of India to KMN and RP, SB is supported by a Research Fellowship from the Indian Council of Medical Research
Correspondence to: Dr. K Madhavan Nair, Assistant Director, Micronutrient Research Group, National Institute of Nutrition, ICMR, Jamai Osmania, Hyderabad 500007, India. nairthayil@hotmail.com
Telephone: +91-40-27008921 Fax: +91-40-27019074
Received: December 8, 2006
Revised: February 2, 2007
Accepted: February 8, 2007
Published online: April 14, 2007
Abstract

AIM: To understand the digestive stability and mechanism of release and intestinal uptake of pea ferritin iron in caco-2 cell line model.

METHODS: Pea seed ferritin was purified using salt fractionation followed by gel filtration chromatography. The bioavailability of ferritin iron was assessed using coupled in vitro digestion/Caco-2 cell model in the presence or absence of ascorbic acid and phytic acid. Caco-2 cell ferritin formation was used as a surrogate marker of iron uptake. Structural changes of pea ferritin under simulated gastric pH were characterized using electrophoresis, gel filtration and circular dichroism spectroscopy.

RESULTS: The caco-2 cell ferritin formation was significantly increased (P < 0.001) with FeSO4 (19.3 ± 9.8 ng/mg protein) and pea ferritin (13.9 ± 6.19 ng/mg protein) compared to the blank digest (3.7 ± 1.8 ng/mg protein). Ascorbic acid enhanced while phytic acid decreased the pea ferritin iron bioavailability. However, either in the presence or absence of ascorbic acid, the ferritin content of caco-2 cells was significantly less with pea ferritin than with FeSO4. At gastric pH, no band corresponding to ferritin was observed in the presence of pepsin either on native PAGE or SDS-PAGE. Gel filtration chromatography and circular dichroism spectroscopy revealed a pH dependent loss of quaternary and secondary structure.

CONCLUSION: Under gastric conditions, the iron core of pea ferritin is released into the digestive medium due to acid induced structural alterations and dissociation of protein. The released iron interacts with dietary factors leading to modulation of pea ferritin iron bioavailability, resembling the typical characteristics of non-heme iron.

Keywords: Pea ferritin; Bioavailability; Caco-2 cells; Phytic acid; Ascorbic acid