Salivary protein changes over time in response to food smell - methodological implications

Although salivation triggered by smell is well documented less is known about potential changes at protein composition level. Methodological variability in saliva collection may be a limitation. Therefore, there is a need to set a best period for saliva collection in studies focused on assessing pre-ingestive salivary responses to smell. The aim of the present study was to assess continuous salivary responses triggered by the exposure to a food odorant (strawberry) over a 5-minute period. A total of 12 healthy-adults collected saliva samples at 1-minute intervals: immediately before (t0, no odorant, basal levels) and during five minutes exposure to an odorant (t1, t2, t3, t4 and t5). After a 5-minute break/wash period a new saliva collection was made (t10). Temporal changes in salivary responses among the different one-minute interval were evaluated for flow rate, alpha-amylase enzymatic activity and variations in salivary protein profile. A tendency for increased salivation and decreased protein concentration was observed at the first minute of exposure, although no statistically significant differences were observed in any stimulation minute. However, 5-minute continuous saliva collection fails to capture the early rise in flow rate during the initial minute(s) of stimulation. Bands potentially corresponding to proline-rich proteins increased after 2 minutes of stimulation, but this effect was transient. In conclusion, extended saliva collection times may mask salivary responses to smell. From a methodological perspective, these findings may have important implications for the design of experiments addressing sensory stimulation.