Electromyography was used as a noninvasive and unobtrusive technique to characterise chewing patterns for a range of foods. Differences between subjects for a variety of aspects of chewing sequence are recorded for a range of foods (carrot, apple, roast pork, salami, biscuit and toast). Identifiable subgroups of subjects differing in chewing behaviour existed within the random sample of 52 dentate subjects. The five subgroups accounted for 52%, 21%, 11%, 10% and 6% of the sample population. Major discriminating factors between the behavioural groups lie in their chewing time and the muscle work rate during chewing. Sensory ratings for firmness and rubberiness of model foods differed significantly between the subjects exhibiting different chewing behaviours. Chewing behaviour may influence consumers’ perceptions about the texture of a food.

The ripening characteristics of modified tomatoes (Lycopersicon esculentum Mill cv Ailsa Craig), which express antisense RNA to polygalacturonase (PG) and thus have very low activity of this enzyme, were compared with control fruit. Previous studies of these fruits showed that although PG activity was reduced to approximately 1% of that in untransformed tomatoes, this reduction had no effect on softening. Further detailed mechanical assessments have now been performed which revealed small, but significant differences in the fruit ripening characteristics between control and antisense fruits. Compression along the polar axis of the PG antisense fruit was significantly reduced relative to the control. Deformation at failure (h), 'modulus' (M), coefficient of compression ( K J , and coefficient of shear (K,) values from probe tests along the equatorial axis also indicated that the antisense fruit was firmer. Although these significant differences in texture properties were observed between the antisense fruit and the control, they were quite limited in extent, as compared to the normal evolution observed during ripening. Scanning electron microscope studies on the subexocarpic region of the pericarp showed that cell wall separation was reduced in the ripe antisense tomatoes, and this may explain the change in mechanical properties. Optical measurements made with both Hunter Color Difference (Hunter Lab Ltd, Fairfax, VA, USA) and Micromatch 2000 (ICS Texicon Ltd, Altrincham, UK) spectrophotometer systems showed that the 'a' (green/red) component of colour of the antisense tomatoes was increased relative to that of the control samples. The effect of PG on softening and of cell wall breakdown on mechanical and optical properties is also considered.

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