One of the major functions of chewing is to prepare food for safe swallowing by mixing it with saliva and by grinding large particles into small fragments. Due to this fragmentation, the surface area of the food is increased yielding a more efficient breakdown by enzymes in the mouth and later in the gastrointestinal tract. Furthermore, food comminution facilitates and influences the release of flavour.
The overall process of comminution will be clarified for foods which form a loose aggregation of particles, in particular dealing with results from an artificial test food (the silicone rubber Optosil®). Traditionally chewing is started on batches of 4 cm3 Optosil particles, for example on 8 cubes of 8 mm. Following various numbers of chews, N, up to 225 ones while suppressing swallowing, the particle size distribution by weight is characterized by the median particle size, X50, and the broadness, b, of the distribution, using curve-fitting with the Rosin-Rammler equation. The log(X50)-log(N) relationship has a reversed sigmoid shape. The b-log(N) relationship shows initially a pronounced decrease in b and a weak increase following a shallow minimum. For understanding these characteristics in the relationships, two underlying processes of food comminution are considered, (1) selection, the chance that a food particle will be placed between the teeth and comminuted, or at least damaged by the teeth, and (2) breakage, the process by which selected particles are fractured between the teeth into fragments of variable size.
Regarding testing chewing ability, a determination of X50 is problematic during a first range of 10-20 chews when chewing is started on batches of 8 Optosil cubes of 8 mm. It will be outlined how test conditions can be improved by choosing a different initial particle shape (half-cubes rather than cubes) and by reducing the initial number of particles.
