Abstract
The intake of large amounts of the antinutrient oxalate can induce hyperoxaluria, an important risk factor for the development of calcium oxalate stones. The soluble and total oxalate concentrations of plants of the Fabaceae, Convolvulaceae, and Malvaceae families were determined using an HPLC-enzyme-reactor method. Sweet potato is a species of the Convolvulaceae, Fabaceae includes beans, lentils, peas, licorice and blue fenugreek, whereas okra and cocoa are species of the Malvaceae family. Total oxalate content was highest in licorice root (Glycyrrhiza glabra; 3569 mg/100 g), an important medicinal herb and sweetener in candies, blue fenugreek (Trigonella coerulea; 1246 mg/100 g) and white beans (Phaseolus vulgaris L.; 548 mg/100 g), plants of the Fabaceae family. Total oxalate content amounted to 496 mg/100 g in sweet potato (Ipomoea batatas), 619 mg/100 g in cocoa powder (Theobroma cacao) and 317 mg/100 g in okra (Abdelmoschus esculentus), the most important agricultural crops of the Convolvulaceae and Malvaceae, respectively. The findings suggested that most foods of these plant families contain high to excessively high oxalate concentrations. The consumption of these oxalate-rich plants can negatively impact calcium oxalate stone formation.
Highlights
High consumption of dietary oxalate constitutes a considerable health concern mainly due to the property of oxalic acid to form insoluble salts with divalent cations such as calcium or magnesium
Total oxalate content was highest in licorice root (Glycyrrhiza glabra; 3569.3 mg/100 g), blue fenugreek (Trigonella coerulea; 1245.9 mg/100 g) and white beans (Phaseolus vulgaris L.; 547.9 mg/100 g), species of the Fabaceae family
Total oxalate content was low in fava beans (Vicia faba), green peas (Pisum sativum), chick peas (Cicer arietinum L.) and lentils (Lens culinaris), ranging from 1.3 to 24.0 mg/100 g
Summary
High consumption of dietary oxalate constitutes a considerable health concern mainly due to the property of oxalic acid to form insoluble salts with divalent cations such as calcium or magnesium. Either based on increased intestinal absorption or high dietary intake of oxalate, is regarded as a major risk factor for calcium oxalate stone formation (Siener et al, 2003). The antinutrient oxalic acid has been shown to impair the absorption of magnesium, zinc, iron and calcium in the intestine by complexation (Kelsay & Prather, 1983; Heaney et al, 1988; Noonan & Savage, 1999; Bohn et al, 2004). The families Amaranthaceae, Chenopodiaceae and Polygonaceae comprise most of the plants with exceptionally high oxalate concentrations, e.g. spinach, sorrel, rhubarb, mangold and amaranth (Siener et al, 2006)
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