High pressure effect on foaming behaviour of whey protein isolate Original Research Article

The effect of pressure-processing at 150–450 MPa for 5–25 mm on foaming behaviour of whey protein isolate (WPI) have been investigated in pH range of 5.0–7.0. Assessment of foaming properties has been based on the total foam volume (FV) produced and the foam stability (FS), and the time for loss of half the initial FV. Response surface methodology has been applied to find the regression equations for predicting the FV and FS in terms of independent variables (the intensity of pressure, the treatment time and the pH). Protein solutions (1% w/v, 50 mM phosphate buffer) were pressure-processed and foams were produced from dilute solutions of WPI (0.005% w/v) by sparging with nitrogen gas at constant flow rate (0.2±0.01 dm3/min) and constant temperature (20°C). It has been found that pH is significant (P⩽0.01) on both FV and FS; FV is influenced significantly (P⩽0.05) by pressure-intensity whereas the effect of pressure-treatment time on either FV or FS is not significant (P⩽0.05). Foaming properties of WPI were reduced as the pH approached to the isoelectric point of proteins due to enhanced aggregation. Pressurisation at high-protein concentration (2% w/v) or in high-buffer molarity (100 mM) has been observed to diminish the foaming properties of WPI.