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 (νa,50) values measured with a sophisticated computer-controlled rheometer. The νa,50 values of the juices increased as thickener concentration increased, whereas their flow distances decreased. The νa,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 νa,50 values to LST flow distances revealed strong exponential relationships between the two measures (R²=0.989 and R²=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.