Nanoencapsulation of Tea Catechins in Casein Micelles: Effects on Processing and Biological Functionalities

This thesis focuses on the interactions between milk proteins (caseins) and tea catechins and the consequences of the interactions on the renneting properties and digestion of casein micelles as well as on the biological functionality of the mixture, as measured using intestinal cell models. The binding of epigallocatechin-gallate (EGCG) to casein micelles was quantified using HPLC and fluorescence quenching, and it was shown that a substantial amount of EGCG can be incorporated in the casein micelles. At concentrations < 2.5 mg/ml milk, most of the EGCG added to milk was associated with the caseins. The formation of EGCG-casein micelles complexes not only delayed the gelling point of milk, but they also affected the structure formation of the gels. EGCG is known to have antiproliferative activity on colon cancer cells. Although nanoencapsulation of EGCG in casein micelles may have some advantages, such as protecting this bioactive compound from degradation, it may also affect the bioavailability of EGCG. To test this hypothesis, the effect of nanoencapsulation of EGCG in casein micelles on the biological functionality of EGCG was tested by evaluating the cytotoxity and proliferation behaviour of HT-29 colon cancer cells. It was demonstrated that nanoencapsulation did not affect the bioefficacy of EGCG. Similar experiments were also carried out on rat colonic cells, a normal line and its cancerous tranformed line. For this study, nanoencapulated EGCG was subjected to in vitro digbefore absorption. The results showed that EGCG-casein binding did not affect the digestion of the milk proteins. In this case, the bioefficacy of EGCG was not diminished as well. In addition, studies on normal cell lines demonstrated the specific effect of EGCG on cancer cells, favoring normal cell survival whether EGCG was isolated or complexed with milk. These experiments bring further evidence that milk can be employed as an appropriate platform for the delivery of bioactive compounds.