Guinard et al. (1997) also performed indentation tests on ice cream with the fat level ranging from 8.73% (32.49% total solids) to 19.3% (53.16% total solids). Using the TA-XT2 Texture Analyser their results showed the force of deformation for their low fat–low solids sample to be greater than five times the force measured from their high fat–high solids sample. This demonstrates the contribution that the presence of ice crystals can make to the detection of firmness.
As an alternative to determining ice cream firmness using a plunger attachment, as has been the case in most previous studies (Specter and Setser, 1994 and Guinard et al., 1997), a knife attachment was also used to evaluate both firmness and tackiness (Table 5). The only difference with the knife attachment was that the fat free sample had a lower firmness value than the regular fat product. A correlation between the tackiness using the knife attachment and the sensory firmness was also noted, but the correlation coefficient was lower the with the plunger (Table 6). Once again, the second F sample proved to be much firmer with firmness and tackiness values of 284 and −33.7 N, respectively. The inability of this one trial to prevent ice crystal formation points out the importance of raw product quality in this process.
From these results it is clear that the presence of modified starch can overcome the problem of increased ice crystal volume in reduced fat ice cream products and provides a product with firmness values equivalent to those of regular fat ice cream.