The effect of the addition of heat denatured whey proteins (frozen; nonfrozen
and enzymaUcally hydrolyZed) to C(Ni milk on the quality of yoghurt was Investigated. Results revealed that addition of whey proteins extended duration of incubation time from 3 hours for control to 4 hours In the treated samples. The control samples showed the highest degree of curd syneresis and curd firmness in comparison with the treated samples. The water holding capacity of yoghurt made with whey proteins increased slightly compared with the control. However. total volatile organic acids; diacetyl and non protein nitrogen (NPN) were markedly Increased In yoghurt fortified with whey proteins. These values increased with Increasing whey protein concentration. Great differences in the sensory properties were observed with the addition of denatured whey proteins. Control samples had the highest score followed by the ones with added hydrolyzed whey proteins; nonfrozen whey proteins and froz.en whey proteins. Cold storage at 7'C for 7 days resulted in a decrease In \he pH of all samples after 3 days and then remained constant up to 7 days. Curd firmness and volatile organic acids showed an increase during the storage perfod while. diacetyl increased after 3 days, then decreased after 7 days.