Rheological properties of acid casein gels made by acidification with glucono-δ-lactone

The simultaneous effect of casein to whey protein ratio, incubation temperature and heating temperature on the rheological properties of casein solutions acidified with glucono-delta-lactone (GDL) were studied using response surface method (RSM). Gelation process was monitored by performing time sweep test. Strain and frequency sweep tests were performed to characterize the final gel (200 min after starting acidification). The experimental data on the frequency sweep tests were correlated according to the following power-law: G' = a omega(b). The (a) value is a measure of structure strength and (b) value which indicates the frequency dependency of elastic modulus (G') shows the type of structure. Strain sweep test were done to measure both linear viscoelastic range, flow point ( T-f) and yield stress (T-y) of the final gel. High incubation temperature resulted in large decrease in (a), T-f and T-y values. Increasing heating temperature gave an increase in (a), T-f and T-y values. Finally, correlations between rheological parameters from time, strain and frequency sweep tests were determined. Significant (P < 0.05) positive correlations were observed among G'(200) (G' of final gel), t(g) (the time of gelation onset after the introduction of GDL into the liquid sample), T-f, T-y, G' at T-f and (a) values. Also there were significant negative correlations between (b) and other rheological parameters such as G'(200), T-f, T-y, G' at T-f and (a).