The bioaccessibility of iron was determined using the procedure
of Luten et al. (1996), with suitable modifications. The ground samples
were subjected to simulated gastric digestion by incubation
with pepsin (pH 2.0) at 37 C for 2 h. Titratable acidity was measured
in an aliquot of the gastric digest, by adjusting the pH to
7.5 with 0.2 M sodium hydroxide in the presence of pancreatin–
bile extract mixture. Titratable acidity was defined as the amount
of 0.2 M sodium hydroxide required to attain a pH of 7.5. This
was followed by simulated intestinal digestion. Segments of dialysis
tubings with a molecular mass cut off of 10 kDa containing
25 ml sodium bicarbonate solution, which is equivalent in moles
to the titratable acidity determined as above, were placed in Erlenmeyer
flasks containing aliquots of the gastric digest and incubated
at 37 C in a shaking water bath for 30 min or longer until the pH
reached 5.0. The pancreatin–bile mixture was then added and
incubation was continued for 3 h or longer until the pH of the digest
reached 7.0. Five percent nitric acid was then added to the
dialysate, centrifuged at 10,000 rpm for 15 min and filtered
through Whatman No. 42 filter paper. Iron and zinc present in
the dialysate, which represents the bioaccessible fraction, were
analysed by atomic absorption spectrometry.
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