The interactions between different tastes on initiation of reflex swallow elicited by electrical stimulation in humans

The act of eating is a source of pleasure for people and is a major factor in maintaining a good quality of life. Several types of products for dysphagia patients are available to decrease aspiration of food that often accompanies daily food intake. The final goal of these products is to improve the ease of forming a food bolus and/or the safety of the swallowing process; however, tastes of products are not a major concern with initiation of swallowing. In the present study, we investigated the effect of bitter taste stimuli (quinine) and the combination of quinine and umami (monosodium glutamate: MSG) applied to the oropharynx on reflex swallows evoked by electrical stimulation to the oropharyngeal mucosa. Each of the distilled water (DW), quinine and quinine–MSG mixture solution (volume of each solutions, 100 µl) was applied 1 s prior to electrical stimulation. No swallow was evoked when each of the solutions was applied without electrical stimulation. The application of DW and lower concentration of quinine (<100 µM) did not affect the latency of reflex swallow, but 100 µM quinine application increased the latency of the reflex swallow. In addition, application of quinine–MSG mixture solution counteracted the increase in latency induced by quinine application alone. These findings suggest that MSG enhances the initiation of swallowing along with its well-known increase in appetite stimulation. Adding MSG might be effective when creating food to promote swallowing.