Impact of disperse microstructure on rheology and quality aspects of ice cream

Abstract

Oscillatory thermo-rheometry (OTR) was used to correlate rheological properties with the microstructure and quality characteristics of ice cream. In a rotational rheometer (plate–plate geometry) the rheological behavior of ice cream was studied, performing oscillatory measurements at low deformation amplitudes for three different temperature ranges corresponding to important consumer properties of ice cream. The ice crystal microstructure determined the rigidity and “scoopability” of ice cream at low temperatures (−20°C to −10°C). The higher the overrun and the smaller the connectivity of ice crystals, the smaller were the measured storage and loss moduli G′ and G″. The slope of the variations in G′ and G″ with temperature in the range between −10°C and 0°C were correlated with the sensory impression of coldness. Decreasing overrun levels led to steeper slopes and correspondingly to a more pronounced impression of coldness. The microstructures of air and fat phases had also a significant impact on the rheology and the sensorial “creaminess” of ice cream especially in the molten state (0–10°C). With increasing overrun levels, ice cream showed increasing storage and loss moduli at temperatures higher than 0°C. Smaller air bubble sizes and increased fat globule aggregation in low temperature extruded (LTE) ice cream led to higher values of G″ in comparison to conventionally hardened (Freezer) ice cream. Sensorial studies demonstrated a close correlation between loss moduli G″ measured in the OTR-test and the ice cream quality parameters scoopability and creaminess. The improved scoopability and increased creaminess of LTE ice cream in comparison to Freezer ice cream was measured quantitatively by a decrease of G″ at a temperature of −15°C and a increase of G″ for ice cream in the molten state.