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

The effects of heat treatment and gelation temperature on whey separat ion in acid milk gels made with glucono-delta-lactone were studied usi ng three empirical methods, two of which were developed specifically t o quantify spontaneous whey separation from set acid gels. Gels were m ade in volumetric flasks and petri dishes and the amount of surface wh ey produced by gels after 16 h was compared with the amount of superna tant expressed by low speed centrifugation (100 g x 10 min) of gels ma de in tubes. A central composite experiment design and response surfac e methodology were used. Using regression analysis a second order poly nomial model satisfactorily predicted the effect of heat treatment and gelation temperature on whey separation for gels made in volumetric f lasks (R-2 = 0.89). Whey separation was significantly increased by hea t treatment (P < 0.001), gelation temperature (P < 0.01) and the quadr atic term for heat treatment (P < 0.01). A significant (P < 0.01) posi tive correlation (r = 0.71) was observed between whey separation in vo lumetric flasks and petri dishes. It was suggested that high heat trea tments and gelation temperatures favour more rearrangements of the net work just after formation, making gels unstable and sensitive to spont aneous whey separation.