ARS | Publication request: OXALATE REDUCES CALCIUM AVAILABILITY IN THE PADS OF THE PRICKLY PEAR CACTUS THROUGH FORMATION OF CALCIUM OXALATE CRYSTALS

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 2004
Publication Date: February 20, 2004
Citation: Mcconn, M.M., Nakata, P.A. 2004. Oxalate reduces calcium availability in the pads of the prickly pear cactus through formation of calcium oxalate crystals. Journal of Agricultural and Food Chemistry. 52(5): 1371-1374.

Interpretive Summary: Many plant foods contain substances that affect the ability of the human body to absorb certain nutrients. Therefore just because we eat a particular nutrient does not mean that it will be absorbed. This is especially true in the case of calcium. In many plant foods the calcium is bound by oxalate. Oxalate binds the calcium in a state that renders it unavailable for absorption by humans. The authors show that although prickly pear cactus leaves are enriched in calcium, the calcium is in the form of calcium oxalate crystals and therefore is not readily available for absorption. Thus, this study emphasizes that the nutritional quality of a food is not just determined by the amount of a nutrient present, but also the form of the nutrient in the food.

Technical Abstract: The pads (nopales) of the prickly pear cactus are considered a good source of minerals and other nutrients based on compositional analysis. In this study, we take this analysis a step further by assessing the availability of selected minerals in nopales using an in vitro digestion and dialysis method. The results obtained suggest that although nopales is enriched in a number of minerals, its tissue calcium is not freely available. Microscopic analysis, energy dispersive x-ray microanalysis, and oxalate measurements suggest that this reduction in available calcium is a result of its sequestration in the form of calcium oxalate crystals. The issue of mineral availability in plant foods is important when considering the dependence of many populations around the world on plant foods as their main source of minerals and other nutrients.