AN OPTIMIZATION MODEL FOR MASTICATION AND SWALLOWING IN MAMMALS

Mammalian mastication is a process combining simultaneous food comminu tion and lubrication. The initiation of swallowing, which is voluntary , has been thought to depend on separate thresholds for food particle size and for particle lubrication. Instead of this duality, we suggest that swallowing is initiated when it is sensed that a batch of food p articles is binding together under viscous forces so as to form a bolu s. Bolus formation ensures that when the food mass is swallowed, it wi ll pass the pharyngeal region safely without risk of inhaling small pa rticles into the lower respiratory tract. Crucial for bolus formation is food particle size reduction by mastication. This allows the tongue to pack particles together tightly by pressure against the hard palat e. A major function of salivation is to fill the gradually reducing sp aces between particles, so increasing viscous cohesion and promoting b olus formation. If swallowing is delayed, excessive saliva floods the bolus, separating particles and reducing cohesion. Swallowing then bec omes more precarious. Our model suggests that there is an optimum mome nt for a mammal to swallow, defined in terms of a peak cohesive force between food particles. The model is tested on human mastication with two foods, brazil nut and raw carrot, which have very different partic le size breakdown rates. The peak cohesive force is much greater with brazil nuts but both foods are predicted to be swallowed after similar numbers of chews despite the very different food particle size reduct ions achieved at that stage. The predicted number of chews to swallow is in broad agreement with published data.