OSCILLATORY RHEOLOGICAL STUDY OF THE GELATION MECHANISM OF WHEY-PROTEIN CONCENTRATE SOLUTIONS - EFFECTS OF PHYSICOCHEMICAL VARIABLES ON GELFORMATION

The thermal gelation of a commercially available whey protein concentr ate was studied by oscillatory rheometry using a Bohlin rheometer. Gel ation time increased with decreasing protein concentration with a crit ical protein concentration (at infinite gelation time) of 6.6 %. The e ffect of temperature in the range 65-90-degrees-C on gelation time was described by an Arrhenius equation with an activation energy of 154 k J/mol. Gelation time was a minimum at pH 4.6, the isoelectric region o f the whey proteins. Small additions of NaCl or CaCl2 dramatically dec reased gelation time. Higher protein concentrations always produced hi gher storage modulus (G') values after any heating time. Loss modulus (G'') v. time curves exhibited maxima at relatively short times for pr otein concentrations of 30 and 35 %. G' values for 10% protein concent ration increased with temperature for heating times up to 59.5 min. G' values at 59.5 min for 25 % protein concentration were higher at 78-d egrees-C than at either 85 or 90-degrees-C. The results are discussed in terms of current theories for biopolymer gelation.