Abstract
Taste and smell perceptions diminish in older age, impacting upon quality of life and nutrition, yet the causes of taste loss are largely unknown. Transient receptor potential channels (TRP) found on the oral mucosa are also involved in oral sensations including cooling and burning and may contribute to the eating experience of older people. Older adults often have reduced salivary flow and the physical properties of saliva may change, but the role of saliva in oral sensations of older adults is yet to be elucidated. Here, the effect of older age on subjective (perception) and objective (stimulated salivary response) measures of TRP stimulants, odors, and basic tastants was investigated. Whole mouth saliva was collected from younger (mean age 24 years) and older adults (mean age 72 years) following stimulation of taste [mono sodium glutamate (MSG) and caffeine], olfaction (menthol), and TRP receptors (capsaicin). Participants rated perceived intensity of each stimulus, and salivary properties were assessed. Older age was associated with 15% lower umami taste and 26% lower menthol odor perception, coupled with 17% lower salivary response to MSG. Interestingly, there were no differences for perception of TRP stimulants, so chemo-sensation was not affected by age. Younger adults had four times greater elasticity (Spinnbarkeit) with MUC7 levels almost double and 66% greater resting salivary flow rate. Stimulated salivary responses in the younger group were also higher compared to the older group, with changes in protein and viscoelasticity in response to taste and TRP stimulation. These results show the impact of older age upon taste and smell sensation which may lead to changes in the physical and compositional properties of saliva in response to taste/odor stimulation. Measurement of stimulated salivary flow and rheology provides an objective measure of taste in addition to subjective perceptions which can be influenced by participant bias. Chemo-sensation may be retained with age and trigeminal stimuli such as chili could be employed in future studies to enhance meals for an age group at risk of malnutrition. Alteration in salivary properties due to advanced age could impact on ability to taste due to poor diffusion of tastants and reduced oral surface protection.
Highlights
There is a link between age and the decline of taste acuity, often coupled with decreased olfactory sensation, retro nasal (Stevens and Cain, 1986)
The older group had a significantly lower unstimulated whole mouth saliva (UWMS) salivary flow rate, 0.55 ± 0.06 g/min compared to 0.83 ± 0.10 g/min in the younger group (p = 0.044) (Figure 2A)
Saliva was secreted as a reflex response to stimulus including taste and smell, and so stimulated whole mouth saliva (SWMS) flow rate was calculated as an objective measure of taste response
Summary
There is a link between age and the decline of taste acuity, often coupled with decreased olfactory sensation, retro nasal (via the mouth) (Stevens and Cain, 1986). Sensory loss can have serious implications for the health and quality of life of an elderly individual. Their nutritional status may be impaired as a result of reduced food intake because of reduced enjoyment when eating (Schiffman, 1997). Taste loss may result in unhealthy eating behaviors such as increased salt intake to heighten flavor in meals (Stevens et al, 1991) or eating more sugary foods (Gilmore and Murphy, 1989). Loss of sense of smell can lead to difficulty in detecting out of date foods, or failure to notice smoke or a gas leak (Boyce and Shone, 2006)
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