Potential of bulk acoustic wave (BAW) process analytical technology to monitor acid-induced skim milk coagulation

Acid-induced milk coagulation is a key processing step in the manufacture of dairy products i.e. yoghurt, and could benefit from process analytical technologies for monitoring the kinetics of milk coagulation. This study evaluates a novel, bulk acoustic wave (BAW) sensor technology to monitor acid-induced (glucono-delta-lactone (GDL)) coagulation of skim milk. The effects of GDL concentration (2.5, 3 and 3.5%) and temperature (22, 31 and 40 degrees C) on skim milk coagulation kinetics were evaluated using rheometry and the BAW sensor. A parameter tAVg, determined from acoustic viscosity (AV), was established to monitor the onset of gelation. Changes observed in tAVg at the onset of gelation were due to changes in particle size of samples at pH -5.3 and -5.2. A positive linear relationship (R2 = 0.97) were found between gelation point (G ' > 1 Pa) and tAVg, and was capable to monitor early stages of gel formation.