Bioaccessibility of Calcium in Legumes

A review is made of the studies on calcium bioaccessibility (BA) (fraction of calcium that is released from its food matrix in the gastrointestinal tract and thus becomes available for intestinal absorption) in legumes and the dietetic factors that condition BA. The highest calcium content always corresponds to the raw legumes, with the exception of some germinated products. In general, a decrease in calcium content is observed in the processed legumes (mainly soaking and dehulling). There are few studies on the BA of calcium in legumes. Calcium BA has been estimated by hydrochloric acid or extractability or solubility/dialysis after simulated gastrointestinal digestion. Oxalate, phytate, tannins, dietetic fiber and polyphenols are the main antinutritional components that can negatively affect calcium BA. Soaking for different periods of time, dehulling of soaked seeds, cooking and germination have been reported to lower the levels of antinutrients and increase calcium BA. Traditional legume preparation processes (soaking, germination and fermentation) can activate native phytases and substantially degrade phytic acid. Cooking (domestic or industrially) is responsible for a loss of soluble oxalate contents in legumes. Dehulling the germinating legumes is associated with significant enhancement of calcium BA.