Impact of soy protein dispersibility on the structural and sensory properties of fat-free ice cream

Soy protein can be an effective fat replacer in ice cream due to its contribution to the viscosity and foaming ability. In this study, we investigated the individual effect of soy protein particle size and mix viscosity on the physical, rheological, tribological and sensory properties of fat-free ice cream. Particle size was varied by homogenization and subsequent separation of the dispersible and non-dispersible fractions. Three series of ice cream mixes were made in which (i) particle size and viscosity were varied, (ii) particle size was varied with a constant viscosity, and (iii) the ratio between the dispersible and non-dispersible protein fractions, particle size and viscosity were varied. The results showed that dispersible protein particles (0.25 mu m) led to lower hardness and higher scoopability as their presence was related to increased overrun and reduced non-air thickness between the air cells. In comparison, large non-dispersible particles (3.8-145 mu m) enhanced the melting resistance and stability of ice cream by forming a network in the serum phase. Therefore, the size of the protein particles determined their functionality in ice cream. Based on sensory evaluation, samples with a protein particle size of approximately 4 mu m showed a relatively denser texture, a lower melting rate and better lubrication behavior (lower friction), as well as a sensory profile similar to that of full-fat ice cream. This study indicates that both textural and sensory properties of fat-free ice cream can be improved by manipulating the size of plant proteins and mix viscosity.