Microstructure and surface properties of ice cream and frozen yogurt

The synergy of yogurt bacteria as dairy starters and surface-active entities was studied. The premise of multiple bacteria cells functioning as particles and contributing to the triphasic stability of frozen yogurt and ice cream emulsions is unique. Frozen yogurt and low fat ice cream mixes were prepared with an added high shear mixing step for initial foam generation prior to freezing. The main objective was to create a finely whipped foam of evenly distributed air cells and then frozen in state for a finished low fat product with better mouth feel. Dairy starters were incorporated as fermenters, as discrete entities, or exopolysaccharide producers to evaluate their effect on texture. The foaming ability of three starter strains was compared. The mixes were evaluated for surface activity, and flow profile when subjected to extreme high and low shear premixing. High shear mixing lowered the surface tension of the frozen yogurt mix from an average of 45.8 ± 2.9 mN/m to 38.4 ± 0.78 mN/m. The foaming capacity of frozen yogurt mixes subjected to high shear was the most stable compared to cultured and uncultured milk. The viscoelastic behavior of the mixes was compared to finished products and the trend showed mixes that were subjected to high shear whipping increased viscosity after draw compared to non-whip samples. In low fat ice cream mixes, high shear mixing did not affect the growth of ice crystals subjected to heat shock, nor prevented the growth of air cells. The microstructures of frozen yogurt and ice cream were examined by an exploratory replica casting method. When a replica of the surface morphology of ice cream was cast, it enabled the evaluation of ultrastructures at ambient temperature conditions. A freeze substituted dehydration method was also explored, and micrographs obtained were compared with the more established method of cryogenic scanning electron microscopy.