Speciation of zinc in pumpkin seeds (Cucurbita pepo) and degradation of its species in the human digestive tract

Pumpkin seeds are one of the foodstuffs recommended in diets which do not contain other Zn-rich sources. The main objectives of this work were to get information on Zn and its species in pumpkin seeds, and their possible degradation in the human gastrointestinal tract, indicative of Zn bioaccessibility. A sequential analytical approach was applied, focusing on total Zn, spatial Zn distribution, extractability, speciation and bioaccessibility of Zn and its species. It was shown that water extracts of pumpkin seeds exhibit a specific Zn species fingerprint with ca. 30% of a low-MW fraction (0.5–2 kDa) and ca. 60% of an intermediate/high-MW fraction (10–20 kDa). Digestion of Zn species under simulated stomach conditions proved that Zn species identified in plant extracts were completely decomposed to Zn2+. The subsequent digestion under intestinal conditions showed that Zn becomes less accessible, indicating that antinutrients like naturally present phytate may be responsible for complex formation in the small intestines, thus reducing the potential for Zn bioavailability.