A recent study published in Physiology & Behavior investigated how human saliva responds, minute by minute, to continuous exposure to a food smell..
The study examined not only the amount of saliva produced, but also changes in total protein concentration, α-amylase activity and salivary protein profiles, aiming to understand how exposure time and sample collection duration may influence the results obtained in sensory stimulation studies.
The body starts responding before we eat
The familiar “mouthwatering” sensation triggered by the smell of appealing food is part of what is known as the cephalic phase response. resposta de fase cefálica.
Before food even enters the mouth, sensory cues such as smell can trigger physiological responses that help prepare the body for food intake and digestion.
Food odours are particularly relevant because the olfactory system is directly connected to brain regions involved in the regulation of autonomic functions, including salivary secretion. secreção salivar.
Although increased salivation in response to food cues has been known for a long time, there is still less information about an equally interesting question: can saliva composition also change when we simply smell food? a composição da saliva também pode mudar quando apenas cheiramos um alimento?
A minute-by-minute study
To investigate these temporal changes, 12 healthy adults, aged between 20 and 46 years, participated in the study.
A strawberry food aroma was used as the olfactory stimulus. It had been previously selected because it was familiar, moderately intense and able to evoke a mouthwatering sensation.
Saliva was collected in consecutive one-minute periods:
- t0: before exposure to the aroma;
- t1–t5: during five consecutive minutes of exposure to strawberry odour;
- t10: após um período de cinco minutos sem o estímulo.
This approach allowed the researchers to observe the salivary response minute by minute, rather than combining several minutes into a single sample.
Figure 1. Experimental design of the study. Saliva was collected before exposure to strawberry aroma (t0), during five consecutive minutes of stimulation (t1–t5), and again after five minutes of recovery without stimulation (t10). Source: Simões et al. (2026), Physiology & Behavior.
The first few minutes may be especially important
During the first minute of exposure to strawberry aroma, the researchers observed a tendency towards an increase in salivary flow rate.
The mean value increased from approximately 0.64 mL/min at baseline to 0.74 mL/min during the first minute of exposure.
At the same time, total protein concentration showed a tendency to decrease, from around 570 µg/mL to 494 µg/mL.
However, these overall changes were not statistically significant and should therefore be interpreted as trends rather than confirmed general effects.
Salivary α-amylase activity also showed no statistically significant changes across the different stimulation periods.
Even so, the results suggest something important: some salivary responses to food odours may be rapid and transient, making the timing of sample collection particularly relevant.
Some salivary proteins responded differently
In addition to salivary flow, total protein concentration and α-amylase, the researchers also analysed the salivary protein profile.
Different protein bands were identified using SDS-PAGE. Some showed a characteristic pink-violet staining potentially associated with proline-rich proteins (PRPs).
These proteins are particularly interesting in the context of food because they participate in interactions between saliva and different food components and may also influence certain sensory properties during oral processing.
Some of these bands showed changes during the first minutes of odour exposure.
Band L, at approximately 22 kDa, showed significantly higher intensity during the second minute.
Band M, around 19 kDa, showed higher values during minutes 1, 2 and 3 compared with baseline levels.
Band N also showed variation over time, although individual comparisons did not reveal significant differences.
Figure 2. Temporal evolution of the mean intensity of bands L, M and N, potentially associated with proline-rich proteins (PRPs). Asterisks indicate statistically significant differences compared with baseline levels. Source: Simões et al. (2026), Physiology & Behavior.
It is important to note that not all of these bands were directly identified by mass spectrometry. For this reason, the authors refer to them as bands potentially corresponding to proline-rich proteins.
Could smell help prepare the oral environment?
Proline-rich proteins play important roles in interactions between saliva and food components.
The transient increase observed in some of these bands during exposure to food odour raises an interesting possibility: the body may begin preparing the oral environment even before food enters the mouth.
Salivary responses to food-related stimuli are regulated by the autonomic nervous system. While parasympathetic activity is particularly associated with salivary flow, sympathetic stimulation may have a stronger influence on the secretion of protein-rich saliva.
In this study, the absence of major changes in salivary flow combined with changes in some protein bands suggests that the effect of food smell may be more closely related to the qualitative composition of saliva than simply to the amount produced.
Collecting saliva for too long may hide the response
One of the main conclusions of the study relates to the methodology used in saliva research.
Collection duration varies considerably between studies. Some experiments collect saliva for only a few seconds, while others continuously collect samples for several minutes.
This may create a problem.
If a change occurs only during the first or second minute, combining all saliva produced during five minutes into a single sample may dilute or hide that early response.
The researchers therefore analysed the results as though samples were progressively accumulated over increasingly longer periods.
Figure 3. Cumulative measurements of salivary flow rate, total protein concentration and α-amylase enzymatic activity over progressively longer periods of exposure to the stimulus. Source: Simões et al. (2026), Physiology & Behavior.
The results showed that increasing collection duration did not necessarily make salivary changes easier to detect.
On the contrary, longer collection periods may average together different stages of the response and therefore mask rapid changes or transient peaks.
For this reason, when the aim is to study early salivary responses to a sensory stimulus, shorter collection intervals may be more appropriate.
Does saliva return to baseline after five minutes?
After five minutes of exposure to strawberry aroma, participants remained for another five minutes without any olfactory stimulus.
A new saliva sample was then collected.
Overall, salivary flow rate, total protein concentration and α-amylase activity showed values similar to those observed before stimulation.
The bands potentially associated with PRPs also no longer showed the differences observed during odour exposure.
Figure 4. Salivary flow rate and total protein concentration before odour exposure (t0), during the final minute of strawberry stimulation (t5), and after five minutes of recovery without stimulation (t10). Source: Simões et al. (2026), Physiology & Behavior.
These findings suggest that many responses triggered by olfactory stimulation are temporary and reversible over a relatively short period.
However, not all salivary components behaved in exactly the same way. One protein band containing albumin remained significantly elevated after the recovery period.
This suggests that five minutes may be sufficient for some salivary parameters, but not necessarily for all of them, particularly when specific proteomic outcomes are being investigated.
Collection time is also part of the experiment
This study highlights an important methodological point.
When studying saliva, it is not enough to decide what to measure.
It is also essential to carefully define when to measure and how long to collect the sample.
A longer collection period may provide a larger volume of saliva for analysis, but it may also hide changes that occur only during the earliest moments following a stimulus.
Studies investigating salivary responses to food-related cues should therefore take the dynamic nature of saliva into account and adapt collection protocols to the specific phenomenon being investigated.
When studying saliva, timing matters.
A first step towards better understanding responses to food smell
The study also has some important limitations.
Only one food-related olfactory stimulus — strawberry aroma — was tested, and there was no control condition involving either no odour or a non-food odour.
It is therefore not yet possible to determine whether the observed changes are specific to strawberry aroma, represent a more general response to food odours, or are partly related to the repeated saliva collection procedure itself.
Even so, the findings show that the salivary response to sensory stimulation may be far more dynamic than a single sample can reveal.
Even before we begin eating, the smell of food may be associated with rapid changes in the oral environment — and some of these changes may disappear only a few minutes later.
Understanding this dynamic may contribute to more precise experimental protocols and help deepen our knowledge of the relationships between saliva, sensory perception, eating behaviour and physiological responses to food.
Reference
Simões, C., Castelo, P. M., Costa, A. I., & Lamy, E. (2026). Salivary protein changes over time in response to food smell – methodological implications. Physiology & Behavior, 115457.
