Tongue Pressure - A Key Limiting Aspect in Bolus Swallowing

Food oral processing is very basic activity of human life, providing individuals with pleasure, enjoyment and serving their needs for social interaction. Dysphagia describes a disorder affecting the safety and/or efficiency of swallowing. To manage this reduced ability, dysphagic individuals are often prescribed a diet having specific ranges of mechanical properties. As a result, a number of sectors such as food, pharmaceutical and health care industries are eagerly searching for fundamental knowledge in order to design food for vulnerable population. This thesis addresses this gap and aims to investigate the relationship between the mechanical properties of bolus swallowing (e.g. rheology, bolus manipulations, perceived ease / difficult of initiation swallowing and perceived bolus flow behaviour) along with oral pressures (i.e. generated by the tongue) recorded in healthy subjects. This area of oral processing is researched mostly from a clinical point of view and thus knowledge in oral processing from sensory view point is currently limited as shown in the literature review. In this study, some of existing clinical researches were extended using relevant techniques (such as maximum isometric tongue pressure, oral volume and oral residence time). Findings from this thesis demonstrated a strong correlation between sensory perception of bolus (e.g. ease / difficult of swallowing, ease of break-swallow, bolus flow) and subjective measurement of tongue pressure in context of ready-to-swallow food bolus with different rheological properties. Further experiments were conducted to mechanically characterise a range of viscoelastic and pastry food systems and measure the intra-oral pressures applied when breaking these foods. Data analysis showed that a positive correlation existed between tongue strength and oral food handling. From our results, we can conclude that individual’s capacity in tongue pressure generation needs to exceed a certain limit in order to perceive ease in swallowing bolus and also to perceive a bolus flow behaviour. However, such correlation was not seen for individuals with reduced capability in generating MITP. These results support the aim that both the oral physiological conditions (MITP) and the rheological properties of the food (bolus) are important factors that influence the bolus manipulations and comfortable oral handling as well as perceived ease of initiating bolus flow.