Salivary protein profiles and sensitivity to the bitter taste of caffeine.

The interindividual variation in the sensitivity to bitterness is attributed in part to genetic polymorphism at the taste receptor level, but other factors, such as saliva composition, might be involved. In order to investigate this, 2 groups of subjects (hyposensitive, hypersensitive) were selected from 29 healthy male volunteers based on their detection thresholds for caffeine, and their salivary proteome composition was compared. Abundance of 26 of the 255 spots detected on saliva electrophoretic patterns was significantly different between hypo- and hypersensitive subjects. Saliva of hypersensitive subjects contained higher levels of amylase fragments, immunoglobulins, and serum albumin and/or serum albumin fragments. It also contained lower levels of cystatin SN, an inhibitor of protease. The results suggest that proteolysis occurring within the oral cavity is an important perireceptor factor associated to the sensitivity to the bitter taste of caffeine.

Variability of human saliva composition: possible relationships with fat perception and liking.

Saliva is the medium that bathes the taste receptors in the oral cavity and in which aroma and taste compounds are released when food is eaten. Moreover saliva contains enzymes and molecules that can interact with food. To date, little research has been devoted to the intra- and inter-individual variabilities of these components and their inter-relationships. The first aim of this work was to study intra- and inter-individual variabilities over time in the composition of molecules likely to interact with food in the mouth, with particular focus on molecules that might interact with fat. The second aim was to try to relate this composition to a liking for fat and its perception. Stimulated and unstimulated saliva from 13 subjects was collected in the morning and afternoon on three occasions at 4-month intervals. Saliva characteristics such as flow, protein concentration, lipolysis, proteolysis, amylolysis, lipocalin concentration, lysozyme activity, total antioxidant status and uric acid concentrations were measured, as well as the liking for and perceived fattiness of a fat solution. The results showed that for most of the measured characteristics, intra-subject variability in saliva composition was smaller than inter-subject variability, with remarkable stability over time (8 months) in terms of flow, lypolysis, proteolysis and total antioxidant status. Relationships were found between some of these characteristics (lipolysis, lipocalin and flow) and fat-liking or perception, showing that the composition of saliva may play an important role in fat perception and liking.

Inter-individual variability of protein patterns in saliva of healthy adults.

In order to document inter-individual variability in salivary protein patterns, unstimulated whole saliva was obtained from 12 subjects at 10 am and 3 pm of the same day. Saliva proteins were separated using two-dimensional gel electrophoresis, and semi-quantified using image analysis. One-way ANOVA was used to test the effects "time of sampling" and "subject". Data were further explored by multivariate analyses (PCA, hierarchical clustering). Spots of interest were identified by mass spectrometry (MALDI-TOF MS/MS and nanoLC ESI-IT MS/MS). A dataset of 509 spots matched in all gels was obtained. There was no diurnal statistical effect on salivary patterns while inter-individual variability was high with 47 spots differentially expressed between subjects (p<1%). Clustering of these spots revealed that subjects could be discriminated first based on several proteins participating to the non-specific immune response (cystatins, lipocalin 1, parotid-secretory protein and prolactin-induced protein). Independently, subjects were also differentiated by their level of proteins originating from serum and involved in the immune system (complement C3, transferrin, IgG2), as well as the relative abundance of enzymes involved in carbohydrates metabolism (amylase and glycolytic enzymes). Inter-individual variability should be accounted for when searching for salivary biomarkers or when studying in-mouth biochemical mechanisms.