Alkali cold gelation of whey proteins. Part II: Protein concentration.
The effect of the whey protein isolate (WPI) concentration on the sol-gel-sol transition in alkali cold gelation was investigated at pH 11.6-13 using oscillatory rheometry. The elastic modulus increases quickly with time to reach a local maximum (G'max), followed by a degelation step where the modulus decreases to a minimum value (G'min). Depending on the pH, a second gelation step will occur. At the end of the first gelation step around G'max, the system fulfilled the Winter-Chambon criterion of gelation. The analysis of the maximum moduli with the protein concentration shows that (i) there is a percolation concentration above which an elastic response is observed (approximately 6.8 wt %); (ii) there are two concentration regimes for G''max and G''max above this concentration, where we have considered power-law and percolation equations; (iii) there is a crossover concentration between the two regimes (at approximately 8 wt %) for both G'max and G''max when both moduli are equal, and this value is constant under all conditions tested (G'max=G''max approximately 4 Pa). Therefore, alkali cold gelation is better represented using two concentrations regimes than one, as observed for other biopolymers.
Biological Systems Engineering, University of WisconsinMadison, 460 Henry Mall, Madison, Wisconsin 53706, USA. rubenmp@cantab.net
Ruben
R
Mercadé-Prieto
Sundaram
S
Gunasekaran
D005782:Gels / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008894:Milk Proteins / Q000737:chemistry*; D044367:Phase Transition; D012972:Sodium Hydroxide / Q000737:chemistry*; D000067816:Whey Proteins
D005782:Gels; D008894:Milk Proteins; D000067816:Whey Proteins; D012972:Sodium Hydroxide; D006046:Gold