Contribution of Umami Substance to Swallowing

Abstract

Reflecting progressive aging of society, many special diets for patients suffering from swallowing disorders (i.e. dysphagia diets) have been developed. Texture modification for less risk of aspiration is one of the important elements in dysphagia diets from the viewpoint of safety assurance. However, no attempt has been done to add chemicals to such diets to facilitate swallowing initiation. For this, sensory inputs from the oropharynx play an important role in swallow initiation. Animal studies showed that stimulation by umami taste is effective stimulus of this area. Therefore, to study the effect of umami taste on swallow initiation in humans, we examined the effect of application of Monosodium L-Glutamate (MSG) solution as an umami taste to the oropharynx on the latency of the swallow reflex evoked by electrical stimulation of the oropharynx. Distilled water (DW) and 0.15 M sodium chloride (NaCl) solution (saline) were used as vehicles of MSG. Each of the DW, saline, 0.1 M MSG dissolved with DW (MSGDW) and 0.1 M MSG dissolved with saline (MSG-saline) were slowly injected approximately 1 s prior to electrical stimulation. The amount of each solution was 0.1 ml. No swallow was evoked when each of the solutions was applied to the posterior wall of the oropharynx without electrical stimulation, and the subjects could not discriminate the solutions. Results showed that application of DW to the oropharynx shortened the latency of the swallow reflex, but saline application elongated the latency of the reflex. Also, application of MSG-saline solution counteracts the elongation of the latency induced by saline application. This counteractive effect of MSG was concentrationdependent. Above findings suggest that using MSG as a food additive with NaCl (i.e. salty taste) may serve not only as a flavor enhancer but also as an enhancer of swallow initiation.