Attractive Textures

Taste is not the only thing that matters to us about our food. The sensations it provides as we chew and swallow it are also important. Chewing enhances the release of flavour as well as
being pleasurable in itself. People are more likely to eat a particular food if they enjoy chewing it.

Dr Wendy Brown of the Institute of Food Research is investigating the process of chewing and swallowing to see how different foods differ and how their attractive properties might best be mimicked by
synthetic substitutes, such as vegetable protein used as a substitute for meat for example.

Chewing occurs out of sight and makes it difficult to study without disrupting the process. The answer to this developed at the institute's laboratory in Reading has been to use recordings of tiny
electrical signals produced by working muscles: electromyography, to record the level of activity of the different muscles of the face that control the movement of the jaw.

Dr Brown has used this technique to measure and plot differences in the ways in which we chew different foods. The results are now helping to identify the aspects that are most important to us in our
enjoyment of them. This will help to develop more appropriate quality control tests for the textures of different foods. It will also help food manufacturers to provide the most attractive and
appropriate chewing textures for their products.

The effort involved in chewing generally declines over the chewing sequence but the rate and extent of the decline depend on which food is being chewed.

Not surprisingly, foods which are softer require less chewing. But there are fewer obvious differences. For example even relatively tender meat is perceived as tough because it continues to offer
resistance to chewing over long periods, whereas raw carrot is perceived as crunchy because although it is quite hard to chew at first it soon breaks down into small fragments which are relatively
easy to masticate.

"It is these progressive changes that convey our perception of the different textures of different foods'', says Dr Brown. "To give another example, biscuits offer an initial crisp texture which
collapses quickly under relatively low chewing forces. But as chewing goes on, and the biscuit absorbs moisture from saliva, more effort is required again, this time to knead and combine the crumbs
into a bolus, for swallowing''.

The combination of electromyographs and jaw movement monitoring has made it possible to distinguish different types of chewing over a period as well as different degrees of effort. When we start to
chew our food most of the effort goes in vertical, up-and-down jaw movement. But as chewing continues it becomes predominantly horizontal before swallowing occurs.

Different foods elicit different patterns of horizontal and vertical effort in chewing. "For example, for raw apples and carrots, very little effort occurs during the horizontal phase of chewing,
showing that the effort is all going into teeth clenching. With biscuits, too, the teeth do move sideways but in a way that requires very little effort and is probably associated with separating
biscuit crumbs to assist in moisture uptake''.

This research has shown that, without us being aware of it though we are conscious of the pleasure it gives us, we constantly match our chewing action to the type of food we are eating, and also to
continuous changes in its size, shape and consistency.

When it comes to monitoring the "chewability'' properties of food, in ways that could be used in quality control, attributes that are important early in the chewing sequence, such as crispness, are
potentially easy to measure and monitor. They could be checked by simple procedures such as bending or compressing food samples.

But some other attributes, such as crunchiness or toughness, are judged subjectively over quite long periods of chewing, during which the properties of the food being chewed change. These attributes
will be much harder to measure instrumentally.