the firmness of ice cream is related to its structure. The air cells of ice cream structure are essentially spherical although there is some distortion due to fat and ice crystal formation (Prentice, 1992). The material surrounding these air cells is a non-Newtonian fluid containing clumps of fat (up to 80%) and small ice crystals. In fat reduced ice cream products, it is clear that the rheology of the composite fluid surrounding the air cells will be altered due to the reduction in the fat clumps which predominate the composite fluid of conventional ice cream structure.
There were no differences in firmness values obtained with the plunger for the FF, L and RF samples; the LF value, however, was higher (Table 5). A similar trend was seen with the tackiness values, which measure the negative force when the plunger is withdrawn from the sample (Table 5). There was also a good correlation between sensory firmness and both firmness and tackiness values obtained with the plunger attachment (Table 6).