Interactions of polysaccharide stabilisers with casein aggregates in stirred skim-milk yoghurt

The stabilisation mechanisms of low-methoxy pectin, λ-carrageenan, guar gum, locust bean gum and xanthan in stirred yoghurt were investigated using dynamic oscillatory rheometry and water holding capacity measurements. As the level of low-methoxy pectin and λ-carrageenan increased, the stabilisation mechanism was consistent with the model of casein aggregates passing through a region of bridging flocculation, followed by partial steric stabilisation. For guar gum, locust bean gum and xanthan, the results were consistent with depletion flocculation at a low concentration of stabiliser, and trapped aggregated casein within a viscous polysaccharide solution at higher concentrations. A peak was observed for the phase angle of guar-stabilised yoghurt as a function of frequency, from 4.5 to 0.2 Hz as guar increased from 0.5 to 5 g L−1 for 1-day yoghurt, and from 4.5 to 2.2 Hz as the yoghurt containing 0.5 g L−1 guar gum was aged from 1 to 42 days. Results are interpreted with an understanding that the rheological behaviour is affected by the pre-sharing conditions of the stirred yogurt.