WHEY SEPARATION IN ACID SKIM MILK GELS MADE WITH GLUCONO-δ-LACTONE: EFFECTS OF HEAT TREATMENT AND GELATION TEMPERATURE

The effects of heat treatment and gelation temperature on whey separation in acid milk gels made with glucono-δ-lactone were studied using three empirical methods, two of which were developed specifically to quantify spontaneous whey separation from set acid gels. Gels were made in volumetric flasks and petri dishes and the amount of surface whey produced by gels after 16 h was compared with the amount of supernatant expressed by low speed centrifugation (100 g X 10 min) of gels made in tubes. A central composite experiment design and response surface methodology were used. Using regression analysis a second order polynomial model satisfactorily predicted the effect of heat treatment and gelation temperature on whey separation for gels made in volumetric flasks (R²= 0.89). Whey separation was significantly increased by heat treatment (P < 0.001), gelation temperature (P < 0.01) and the quadratic term for heat treatment (P < 0.01). A significant (P < 0.01) positive correlation (r = 0.71) was observed between whey separation in volumetric flasks and petri dishes. It was suggested that high heat treatments and gelation temperatures favour more rearrangements of the network just after formation, making gels unstable and sensitive to spontaneous whey separation.