PREPARATION AND NUTRITIONAL PROPERTIES OF CASEINS COVALENTLY MODIFIED WITH SUGARS - REDUCTIVE ALKYLATION OF LYSINES WITH GLUCOSE, FRUCTOSE, OR LACTOSE

Reducing sugars were attached to the e-amino lysyl residues of casein in the presence of sodium cyanoborohydride, forming stable amine linkages. At pH 8.0 and 37 °C for 120 h in the presence of 1000 M excess of sugar, the degree of modification was 80% with glucose, 62% with fructose, and 17% with lactose. Compared to native casein, these reductively formed sugar derivatives of casein were shown to have lower in vitro digestibility by a-chymotrypsin and lower nutritive values in rat feeding experiments. Severe growth depression was observed in rats fed with the glucose-derivatized casein. Addition of lysine to the diet containing glucose-derivatized casein (71 % modified) partially alleviated the growth-depressing effects. Moderate growth depression was observed in rats fed with the fructose-derivatized casein or with the lactose-derivatized casein. Since these three derivatives were not equally modified, the observed rat growth responses may be due to the decreased availability of modified lysine as well as to the nature of the attached sugar. © 1979, American Chemical Society. All rights reserved.