Iron release from spinach: effects of treatment on levels of iron (II) and iron (III) released in vitro

The release of iron from spinach, under in vitro conditions to mimic stomach conditions was investigated to determine the levels of iron (II) and iron (III) expected to be present in chyme that would enter the small intestine if a diet containing spinach alone were consumed. In the presence of hydrochloric acid only (0.01 M) and no pepsin, the average percentage release was 22% for fresh spinach, 33% for frozen and 45% for vacuum-dried. The maximum release occurred at 1 h in all cases other than fresh spinach which showed a gradual increase over a 4 h experimental period. The effect of pepsin on the rate of release was also investigated, with maximum releases of 26% when pepsin was present at 0.06%, and 41% at 0.19% pepsin. In all cases, only Fe(aq)2+ could be stated to be released: there were no significant differences observed between values observed for Fe(aq)2+ and total iron [Fe(aq)2++Fe(aq)3+] analyses [using 1,10-phenanthroline complexation, λmax=510 nm (ϵ=10900 M−1 cm−1)]. The absolute release, in the presence of hydrochloric acid only, in μmols g−1 (dry matter) was consistent throughout eight shop-bought fresh spinach batches, with no correlation of release to total% Fe, leading to the conclusion that free inorganic Fe(aq)2+ only is released, not iron contained within non-haem proteins. The higher values for frozen, vacuum-dried and in the presence of 0.19% pepsin may be indicative of some breakdown of cellular structures.