The effect of pressure-processing at 150-450 MPa for 5-25 mm on foaming beh
aviour 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 rime 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 independe
nt variables (the intensity of pressure, the treatment time and the pH). Pr
otein solutions (1% w/v, 50 mM phosphate buffer) were pressure-processed an
d 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 dm(3)/min) and const
ant temperature (20 degrees C). It has been found that pH is significant (P
less than or equal to 0.01) on both FV and FS; FV is influenced significan
tly (P less than or equal to 0.05) by pressure-intensity whereas the effect
of pressure-treatment time on either FV or FS is not significant (P less t
han or equal to 0.05). Foaming properties of WPI were reduced as the pH app
roached to the isoelectric point of proteins due to enhanced aggregation. P
ressurisation at high-protein concentration (2% w/v) or in high-buffer mola
rity (100 mM) has been observed to diminish the foaming properties of WPI.
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