Impact of process conditions on the rheological detectable structure of UHT treated milk protein–carrageenan systems

UHT treated dairy based drinks containing carrageenan to produce a weak gel type of structure are often found to vary considerably in textural properties. Target of this study was to investigate the effect of the heating temperature in the range of 120–139 °C and the filling temperature after cooling down to 4–14 °C prior to storage for 24 and 96 h at 4 °C on a system comprising milk and 400 ppm kappa-2 type of carrageenan. The textural properties and the stability of such systems mainly depend on the interaction of the carrageenan and the casein micelle surface which was assessed by means of the hysteresis loop area between the upward and downward flow curves upon variation of the shear stress. The loop area was used as a dimension for the energy required breaking down the systems’ textural structure. The hysteresis loop area was found to be significantly increased the higher the heating temperature and the lower the cooling temperature was. During storage, a further influence of the process parameters on structural development between casein and carrageenan was observed. Structure point analysis, small angle oscillatory rheology and particle size measurements were used for further explanation of the results of the hysteresis loop area. Particle size measurements indicated an aggregation phenomenon in the micellar casein dominated microdomains at increasing UHT heating temperatures. Variation of the carrageenan concentration enlightened the participation of casein dominated microdomains in the mixed system’s texture.