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 4 mg/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.