Karkade tea may be a rich dietary source of Mn, since the dried hibiscus calyces contain 300-950 mg/kg of this essential element. The soluble elemental content was between 55% and 85% in dependence on the plant origin and on the tea preparation procedure (temperature, leaching duration). The potential bioavailability of dissolved Mn was studied using chemical fractionation including ion exchange, liquid phase extraction and selective precipitation. Flame atomic absorption spectrometry was applied for element determination in all fractions. The main part of Mn (>90%) presents in fresh prepared tea as positively charged species with low molecular weight (free cation or labile complexes) considered as potentially bioassimilable. In vitro assessment of manganese bioaccessibility was performed using sequential enzymatic simulation of gastro-intestinal digestion in combination with operational fractionation. Under simulated intestinal conditions the bioaccessible fraction of Mn was approximative 40% from its total content. Daily drinking of 200 ml karkade tea will contribute around 9 % of RDA/RDI of this element in a potentially bioaccessible form.
The bioavailability of Mn from hibiscus infusions was compared with that of other major and trace essential elements. The percentages of low molecular weight and potentially more bioabsorbable forms of elements following simulated gastro-intestinal digestion were around 35% (Ca), 83% (Cu), 44% (Fe), 55% (Mg), 90% (K), 85% (Zn) from their total dissolved content.
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