Characterization of protein stabilized foam formed in a continuous shear mixing apparatus

A continuous shearing apparatus was employed to make sodium caseinate stabilized foams which was characterized by bubble size, apparent viscosity, foam volume fraction and liquid holdup profile. The bubble size of the foam was smaller for higher rotational speed of the rotor, lower ionic strength, pH away from pI, higher xanthan gum concentration and room temperature and did not vary significantly with air–liquid ratio. Bubble size at different gum concentrations correlated well with dimensionless Weber number. The foam volume fraction was higher at higher values of rotational speed, air–liquid ratio, xanthan gum concentrations and at pH 7 and 9. The evolution of liquid holdup profile indicated faster syneresis at higher ionic strength, higher temperature and lower air–liquid ratio. Collapse of the foam caused by syneresis was more pronounced at higher ionic strengths and higher temperature. The foam produced at pH 6 was drier with liquid holdup less than 0.26. The foam exhibited shear thinning behavior with the apparent viscosity of foam increasing initially with time as a result of syneresis followed by a decrease at longer times due to coarsening of bubble size. The presence of emulsion droplets decreased foam stability.