A comparison of low-intensity ultrasound and oscillating rheology to assess the renneting properties of casein solutions after UHT heat pre-treatment

Ultrasonic and oscillating rheological methods were applied to investigate the effects of heat pre-treatment at Ultra-High-Temperatures on the rennet gel formation of a whey-protein-free casein solution. By comparison, the ultrasonic velocity was found to be sensitive to measure the enzymatic hydrolysis by rennet and the following aggregation process, but not as sensitive to detect the formation of a casein gel. In contrast, the oscillating rheological method was not sensitive enough to detect the enzymatic hydrolysis, but more suitable to characterize the formed gel network. A linear correlation was found between the coagulation times determined by these two methods.