Relationship between Apparent Viscosity and Line-Spread Test Measurement of Thickened Fruit Juices Prepared with a Xanthan Gum-based Thickener

The flow behaviors of three thickened fruit juices (orange, apple, and grape juice) prepared with a commercial instant xanthan gum (XG)-based thickener that is marketed in Korea were investigated at different thickener concentrations (1.0%, 1.5%, 2.0%, 2.5%, 3.0%, and 3.5%) and setting times (5 and 30 min) using a rheometer and a line-spread measurement method. The flow distance values measured by the line-spread test (LST) were compared with the apparent viscosity (${\eta}_{a,50}$) values measured with a sophisticated computer-controlled rheometer. The ${\eta}_{a,50}$ values of the juices increased as thickener concentration increased, whereas their flow distances decreased. The ${\eta}_{a,50}$ values at the 30-min setting time were much higher than those at the 5-min setting time, indicating that the setting time before serving or consuming thickened juices can affect viscosity values. Plots comparing ${\eta}_{a,50}$ values to LST flow distances revealed strong exponential relationships between the two measures ($R^2$=0.989 and $R^2$=0.987 for the 5- and 30-min setting times, respectively). These results indicate that the LST can be a suitable instrument for evaluating the viscosity of thickened fruit juices prepared with different XG-based thickener concentrations and setting times for the dysphagia diet.