Yield stress for initial firmness determination on yogurt

Yield stress and apparent residual stress were measured in laboratory-made yogurts containing different gum concentrations and in seven retail yogurts. Yield stress exhibited significant correlation (p < 0.001) with the sensory initial firmness perceived by trained panelists in both laboratory-made (r = 0.99) and retail (r > 0.97) yogurts. Apparent residual stress was significantly correlated with sensory viscosity for retail yogurts (r > 0.90). The yield stress had more power to detect differences in initial firmness (lower CV(%)), thus requiring fewer samples and was considered a good predictor of the sensory initial firmness perceived by panelists. The use of yield stress also avoids the need for training panelists and conducting sensory panels, and facilitates data analysis by eluding relative scales and lack of homogeneous variances associated with sensory panelists. Additionally, the determination of the yield stress and residual stress offer the potential to manufacture yogurts with targeted yield stress (Pa) and viscosity properties as identified by consumer panels.