Department of Food Science and Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
ABSTRACT: This paper presents the results of studies concerned with the preparation of fresh food foams based on egg white and various hydrocolloids including Iranian gum tragacanth, guar and xanthan gums at different concentrations (0.002-0.040% w/w). The basic physical parameters of the obtained foams such as overrun, stability and morphology of gas bubbles were measured. Viscosity measurements were also performed, and Power law model was applied to describe the flow behavior of gum solutions. The addition of hydrocolloids into the egg white solution had a deteriorative effect on the foam expansion but enhanced the foam stability. In addition, ANOVA showed that by increasing the concentration of the hydrocolloids in egg white solution significantly decreased the overrun and foam drainage (p<0.05). The stability of egg white foam in the presence of gum tragacanth was lower than xanthan gum and higher than guar counterpart. However, higher overrun was observed for tragacanth when compared to xanthan. Optical microscopy also showed smaller bubbles for foams which stabilized with tragacanth or xanthan in comparison with larger ones in the case of guar gum that stabilized the egg white foam. Rheological measurements also showed a pseudoplastic behavior for gum solutions at higher concentrations.