Site Specific and Processing Effects on Oxalate–Mineral Ratios in Hibiscus from Kwilu Province / DR Congo
Publication Date : 27/07/2026
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Abstract :
This study examines the mineral composition and the oxalate-to-calcium, magnesium, and iron molar ratios in five Hibiscus species, considering both their provenance and traditional processing methods. Mineral analysis revealed the presence of Ca, Mg, K, P, Fe, Se, and trace amounts of Zn. The highest iron content was recorded in Hibiscus acetosella red shield (HARS) from Idiofa (0.71 g/100 g of dry material), while the lowest occurred in H. acetosella cranberry (HAC) from Kikwit (0.09 g/100 g). Selenium levels were greatest in HARS from Kikwit (0.53 g/100 g) and lowest in H. cannabinus (HC) from Idiofa (0.04 g/100 g). Potassium was most abundant in H. sabdariffa var. altissima (HSA) from Kikwit (0.96 g/100 g). The highest Ca and Mg concentrations were found in HSA and H. sabdariffa var. sabdariffa (HSS) from Kikwit, with 0.33 g/100 g Ca and 0.28 g/100 g Mg, respectively. Molar oxalate/Ca ratios were below 1 for all species except HC, indicating generally good calcium bioavailability. In contrast, oxalate/Fe ratios exceeded 1 in all species except HSA, suggesting limited iron bioavailability. Sun‑drying increased oxalate–mineral molar ratios despite previously reported reductions in oxalate content, and oven‑drying caused an even greater increase. Prolonged soaking of dried leaves resulted in substantial mineral losses and a marked rise in oxalate–mineral ratios. Conversely, the traditional use of artisanal potash reduced these ratios, thereby enhancing mineral bioavailability.
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