Combination-moderate electric field (MEF) processing successfully increases the iron content of kale by ~ 160 × as compared to untreated kale, but it is unknown whether this kale better delivers iron. It is also not known how combination-MEF treatments impact other nutritionally relevant bioactive kale compounds. This study aimed to (1) determine intestinal delivery of iron from the iron-enriched kale leaf following in vitro digestion and (2) assess ascorbic acid (AA), carotenoid, and α-tocopherol (i.e., vitamin E) concentrations in the combination-MEF treated kale. AA, carotenoids and α-tocopherol were separated and quantitated from non-polar kale extracts using high-performance liquid chromatography-diode-array detection (HPLC–DAD). Iron-enriched kale, hemoglobin, and FeSO4 were digested in vitro, and the digesta was centrifuged, filtered, diluted 16x, and applied to confluent Caco-2 cells. The combination-MEF treated kale increased cell ferritin 4.4 × and 1.8 × relative to FeSO4 and hemoglobin, respectively. The combination-MEF treatment decreased β-carotene and lutein by 3–4 ×, produced no change in α-tocopherol, and increased AA 3 ×, as compared to untreated kale. In conclusion, combination-MEF treated kale is a potentially excellent source of dietary iron for those at risk of iron deficiency, and the combination-MEF treatment merits further investigation for its ability to enrich other vegetables with iron.
Li et al. (Thu,) studied this question.