Effect of pH of food emulsions on their continuous foaming using a mechanically agitated column

A continuous process for the production of foamed food from an emulsion was studied at pH values in the range of 4.2 to 6.6 using an apparatus which simulates the behaviour of an industrial scraped surface heat exchanger. The effect of pH on the rheological properties of the emulsion showed that the consistency factor (k) and the viscoelastic shear modulus (G′) of the emulsion could be increased by a factor of 5 when pH was decreased from 6.6 to 4.2 due to a change of colloidal interactions between proteins and texturing agents. An increase of rotational speed of impeller from 200 rotations per minute to 800 rpm resulted in a reduction in mean bubble diameter (d32) in foams for a given emulsion. At a fixed rpm, the mean bubble diameter and the bubble size distributions increased with decreasing pH. On the other hand, the solidity of the foam was decreased by an increase in pH from 4.2 to 6.6. Weber number (We) explains that foaming is the combined effect of process parameters and physicochemical properties of the emulsion. We numbers at pH 6.6 and 5.2 were 0.6 and 1.1, respectively, representing the minimum and the maximum in the pH range studied. This variation of We number with pH could be observed probably because the viscoelastic character of the continuous phase was ignored for bubble division.