Foaming behaviour of liquorice (Glycyrrhiza glabra) extract

The foaming behaviour of liquorice extract was investigated using response surface methodology with concentration (0.1–0.3 w/v%) and whipping time (5–25 s) being the independent variables. A first-order kinetics was applied for the kinetic analyses of the foam collapse and foam decay rate constants were calculated. Regression equations for predicting overrun (O) and foam decay rate constant (k) were developed. Results suggest that concentration had a significant effect (P⩽0.01) on overrun and foam stability. The overrun increased with concentration and whipping time. However, the effect of whipping time on O was less pronounced. Foam stability was enhanced with the increase in concentration. The foam decay rate was observed to be mainly dependent on the concentration of sample (P⩽0.01) and decreased with the increase in concentration. The effect of whipping time on foam stability was observed to be insignificant (P⩽0.01) compared with concentration. The magnitude of changes with whipping time were observed to be more pronounced for the overrun than for the stability of liquorice extract foam.