Colour and consistency of semi-solid dairy desserts: Instrumental and sensory measurements

Colour and consistency of seven commercial samples of vanilla dairy desserts were studied. All samples showed the typical spectral curve for yellow–orange coloured materials, with maximum reflectance values at wavelengths longer than 550 nm. Significant differences in the values of the colour parameters were found between samples. Flow behaviour of samples was characterised as time-dependent and shear-thinning. Data from the upward flow curves were fitted to the Herschel–Bulkley model and the values of yield stress (σ0), flow index (n), and apparent viscosity at 10 s−1 (η10) were obtained. From the oscillatory rheological measurements, the values of storage modulus (G′), loss modulus (G″), loss angle tangent (tan δ) and complex viscosity (η∗) were determined. Significant differences between samples were found for all rheological parameters. Sensory ranking tests were performed by 42 assessors to evaluate perceptible differences both in the colour and in the consistency of the samples. Correlations between sensory and instrumental data were determined using the Spearman correlation coefficient. Results showed a significant positive correlation between sensory colour and parameter a∗ (red component) and significant negative correlations with parameters L∗ (brightness) and h∗ (hue). The yield stress was the flow parameter showing the best correlation with oral thickness and both the storage modulus at 1 Hz and the complex viscosity at 7.95 Hz (50 rad s−1) were the viscoelastic parameters best correlated with this sensory property.