Zinc transport in Caco-2 cells and zinc balance in rats: Influence of the heat treatment of a casein-glucose-fructose mixture

The effects of the heat treatment of casein in the presence of glucose-fruc tose on Zn bioavailability were studied. Changes in Zn speciation were comp ared after in vitro digestion of heated (HC) and unheated mixture (C) alone and as part of the diet. The uptake and transport of digested soluble Zn w as investigated in Caco-2 cells grown in bicameral chambers; balance studie s were done in rats fed diets containing the different samples. After in vi tro digestion, the precipitated Zn was significantly higher in HC than in C . In assays with Caco-2 cells, the amount of Zn transferred from the apical to the basolateral chamber was significantly greater when the culture medi um contained raw or heated casein. However, because a larger proportion of Zn was precipitated by in vitro digestion, Zn utilization was less efficien t in the presence of casein. rn biological experiments, food efficiency of the heated casein-glucose-fructose diet was lower, and feeding this diet in creased the urinary Zn excretion and lowered Zn absorption and retention. T he effects of browning products generated during food processing should be taken into account, especially in diets containing marginally adequate leve ls of Zn, to prevent possible deficiency.