Effect of Thermal Processing on Endogenous and Added Iron in Canned Spinach

The effect of thermal processing on endogenous and added iron in canned spinach puree was investigated. Eight different sources of iron were evaluated for their distribution of iron forms, or “iron profile” after four treatments. The treatments included: control, unprocessed, processed, and processed with ascorbate. Iron endogenous to raw spinach was 93% in the insoluble form whereas iron added to spinach varied widely in degree of insolubility. For certain iron sources, processing increased the proportion of insoluble as well as ferrous iron over what was present in unprocessed spinach. Processing with ascorbate also increased ferrous iron in some cases. One iron source, ferric EDTA, was exceptional as it was affected minimally in all four treatments. The effects of foods and processes on iron chemistry may help explain the large variations in iron absorption observed from various foods and diets.