PREPARATION AND PROPERTIES OF ACID-INDUCE D GEL OF WHEY-PROTEIN

Preparation and theological properties of acid-induced gel of whey pro tein were investigated, using whey protein isolate (WPI) and glucono-d elta-lactone (GDL) as an acidulant. A 6% WPI solution, pH 7.0, was hea ted at 65-90 degrees C in the absence of acidulant, then cooled to roo m temperature for obtaining partially heat-denatured WPI solution. The solution was incubated at 20-50 degrees C in the presence of GDL. Dur ing incubation, the WPI solution denatured by heating to a certain ext ent was found to form gel below pH 5.8, whereas undenatured WPI soluti on did not. The pH of the resultant finally reached 4.3 after incubati on. Rheological properties of the acid-induced gel were dependent on t emperature and time of the heat treatment of WPI solution, GDL concent ration, and incubation temperature. HPLC analysis indicated the format ion of aggregates in heated WPI solution, and scanning electron micros copy showed the presence of finer network structure of whey protein ag gregates in acid-induced gel with higher incubation temperature. It wa s concluded that both the formation of whey protein soluble aggregates by heating and a decrease of negative charge on the surface of the ag gregates arising from a decrease of pH during incubation caused gelati on.