No significant differences in firmness were detected between samples (Table 3) and there was a low correlation between sensory firmness and fat level (Table 4). The texture of ice creams where the levels of fat and total solids have been lowered (ice creams similar in composition to LF and FF) has been reported to be firmer than for samples of higher fat and total solids (Bodyfelt et al., 1988). This is due to the higher levels of ice and hence the lower levels of crystallized milk fat, which is a softer component than ice. The modified starch used in the reduced fat samples was effective in mimicking the firmness of samples of higher fat content. The firmness of the second trial for FF (not included in the statistical comparison) is of note in that the panellists assigned a high value (11.8), suggesting that it was not able to inhibit the formation of ice crystals as was the case with the other samples.
When the inclusion of modified starch results in undesirable ice cream firmness, as was the case for the second FF sample, the behaviour of the individual starch polymers is most likely responsible. For a starch-based fat replacer to be highly functional in ice cream, the modified amylose and amylopectin chains must interact with water/ice and other constituents in the ice cream. It is probable that the starch polymers in the firmer products are interacting to form gelled starch particles. Such gelled particles would increase the resistance of the samples to deformation by the tongue thereby contributing to the higher firmness intensities obtained during sensory testing. If, on the other hand, the modified amylose and amylopectin chains are able to align at the air cell, milk fat and ice crystal interfaces, the force required by the tongue to flatten the ice cream sample will be reduced. It would appear that the main source of modified starch used in this study was able to perform this function and thereby produce ice cream products whose sensory firmness was not significantly different from that of regular fat ice cream.