Influence of heat treatment of casein in presence of reducing sugars on Znsolubility and Zn uptake by Caco-2 cells after in vitro digestion

The effect of the heat treatment of casein in presence of reducing sugars o n some aspects of Zn availability was investigated. Samples were prepared b y mixing casein with glucose-fructose, and were used unprocessed (C) or hea ted (HC). Changes in Zn speciation after the in vitro digestion of the samp les, both as part of a diet and in isolation, were studied. The uptake of s oluble Zn from the digested samples was investigated in Caco-2 cells. After in vitro digestion, the percentage of precipitated Zn was significantly hi gher with the HC sample, both when digested alone and as a part of the diet . In assays with Caco-2 cells, a significant decrease in Zn uptake was obse rved when the uptake buffer contained the sample C digest, by comparison wi th the control buffer, without casein digest. When the digested heated mixt ure was added, Zn uptake by the cells was significantly lower than in eithe r of the two other cases. It may be concluded that the heat treatment of ca sein in the presence of glucose-fructose has a negative effect on Zn availa bility because, after in vitro digestion, Zn insolubilization was enhanced and Zn uptake by the enterocyte was impaired, compared with the unheated mi xture. In addition, the usefulness of Caco-2 cells in this kind of research has been shown.