Flavor Identification and Intensity: Effects of Stimulus Context

Is food preference innate instinct driven or human's free will?

The question whether food preference decisions are controlled by innate instincts, or a conscious decision-making process is still open. The answer to this question is important not only for neuroscientists, psychologists, and philosophers but also for food scientists and developers. Looking from different perspectives involved in food preference decisions could not only settle a long ongoing debate but also pave the way to understand why people prefer to eat what they eat.

Dysgeusia: A review in the context of COVID-19

Background

Taste disorders in general, and dysgeusia in particular, are relatively common disorders that may be a sign of a more complex acute or chronic medical condition. During the COVID-19 pandemic, taste disorders have found their way into the realm of general as well as specialty dentistry, with significance in screening for patients who potentially may have the virus.

Types of Studies Reviewed

The authors searched electronic databases (PubMed, Embase, Web of Science, Google Scholar) for studies focused on dysgeusia, ageusia, and other taste disorders and their relationship to local and systemic causes.

Results

The authors found pertinent literature explaining the normal physiology of taste sensation, proposals for suggested new tastes, presence of gustatory receptors in remote tissues of the body, and etiology and pathophysiology of taste disorders, in addition to the valuable knowledge gained about gustatory disorders in the context of COVID-19. Along with olfactory disorders, taste disorders are one of the earliest suggestive symptoms of COVID-19 infection.

Conclusions

Gustatory disorders are the result of local or systemic etiology or both. Newer taste sensations, such as calcium and fat tastes, have been discovered, as well as taste receptors that are remote from the oropharyngeal area. Literature published during the COVID-19 pandemic to date reinforces the significance of early detection of potential patients with COVID-19 by means of screening for recent-onset taste disorders.

Practical Implications

Timely screening and identification of potential gustatory disorders are paramount for the dental care practitioner to aid in the early diagnosis of COVID-19 and other serious systemic disorders.

Interactions of Lemon, Sucrose and Citric Acid in Enhancing Citrus, Sweet and Sour Flavors

Flavorants such as lemon extract that activate olfactory receptors may also evoke or enhance flavor qualities such as sour and sweet that are typically considered gustatory. Similarly, flavorants such as sucrose and citric acid that activate gustatory receptors may enhance flavors such as citrus that are typically considered olfactory. Here, we ask how lemon extract, sucrose, and citric acid, presented separately and together, affect sweet, sour, and citrus flavors. We accomplished this by testing, in the same 12 subjects, lemon extract and sucrose (Experiment 1), lemon extract and citric acid (Experiment 2), and lemon extract, sucrose, and citric acid (Experiment 3). Results showed that both lemon extract and citric acid increased the ratings of citrus and sour intensity. Lemon extract did not affect sweet, but citric acid did, mainly in Experiment 3. Sucrose systematically increased only sweet intensity and modulated the effect of lemon extract on sour. The most robust multiquality effect was the enhancement of sour by lemon extract. These outcomes suggest, first, a role played by experience with the statistical associations of gustatory and olfactory flavorants and, second, that lemon flavor is complex, having citrus and sour qualities that may not be fully separable in perception.

Contextual Effects in Judgments of Taste Intensity: No Assimilation, Sometimes Contrast

Judgments of taste intensity often show contextual contrast but not assimilation, even though both effects of stimulus context appear in other sense modalities, such as hearing. Four experiments used a paradigm that shifts the stimulus context within a test session in order to seek evidence of assimilation in judgments of the taste intensity of sucrose and, for comparison, the loudness of 500-Hz tones. Experiment 1 found no assimilation in taste using three response scales, magnitude estimation, labeled magnitude, and visual analog, but did find evidence of contrast. Experiments 2 and 3 found no clear evidence of either assimilation or contrast in taste, but found consistent evidence of assimilation in loudness. Experiment 4 found no assimilation in loudness, however, when the intervals between successive stimuli increased from about 6 to 30 s in order to match the interval used with sucrose in Experiments 1 to 3. Taken together, these findings suggest that the assimilation found in intensity judgments in other sensory modalities may not appear in taste perception because of the slower rates presenting of taste stimuli.