On the nature of the Ca binding to the hull of nixtamalized corn grains

Corn hull is composed of cellulose, hemicelluloses and a minor fraction of lignin. Hemicelluloses are acidic polysaccharides which could explain the relatively large ability of the corn hull to retain Ca during the cooking of corn in a saturated solution of Ca(OH)₂. In order to shed light in this sense the Ca binding to the hull of alkaline cooked corn grains was studied using EDS, pH titration, IR and ¹³C CP/MAS NMR techniques. For short cooking times, prior to hull degradation, Ca is retained in the corn grain according to the following order: hull>germ>endosperm. The acidic groups of hemicelluloses (mainly uronic acids) are the responsible for Ca retention in the corn hull. The amount of Ca retained by the hull approximately is 4mg/g. On the alkaline cooking the hull is progressively degraded and loses its ability to retain Ca because the hemicelluloses fraction passes to the cooking liquor.