Effects of sucrose on salivary flow and composition: differences between real and sham intake.

Human saliva contains numerous salivary components that are fundamental for a healthy oral environment and the oral processing of foods. To study a possible differential influence of orosensory stimulation and metabolic activation on salivary composition, human parotid salivary flow, pH, A(280), and alpha-amylase activity were measured before, during and after real or sham (sip-and-spit) sucrose intakes. Variations in these salivary characteristics were related to perceived satiety. Sucrose, as either real or sham intake, increased salivary flow and pH and decreased A(280) before returning to pre-intake levels. Increased salivation was dependent on the sucrose concentration and was accompanied with a higher pH and lower A(280). After sucrose ingestion, the salivary alpha-amylase activity increased, while no increase occurred after sham sucrose intake. Similarly, rated satiety increased with real but not by sham sucrose intake. This indicated that salivary alpha-amylase is associated with perceived satiety controlled by caloric perception downstream of the oral cavity.

Periprandial changes of the sympathetic-parasympathetic balance related to perceived satiety in humans.

Food intake regulation involves various central and peripheral mechanisms. In this study the relevance of physiological responses reflecting the autonomic nervous system were evaluated in relation to perceived satiety. Subjects were exposed to a lunch-induced hunger-satiety shift, while profiling diverse sensory, physiological, and biochemical characteristics at 15 min intervals. Sensory ratings comprised questionnaires with visual analogues scales about their feeling of satiety, desire to eat, fullness, and hunger. Physiological characteristics included heart rate, heart rate variability, and blood pressure, while biochemical markers such as cortisol levels and alpha-amylase activity were monitored in saliva. The four sensory ratings correlated with heart rate and salivary alpha-amylase suggesting a higher sympathetic tone during satiety. Furthermore, heart rate variability was associated with age and waist-to-hip ratio and cortisol levels negatively correlated with body mass index. Finally, neither chewing nor swallowing contributed to a heart rate increase at food consumption, but orosensory stimulation, as tested with modified sham feeding, caused a partial increase of heart rate. In conclusion, after meal ingestion critical physiological alterations reveal a elevated sympathetic tone, which is a potential measure of satiety.

The taste of fat.

For many years, fat in meats have been considered to convey quality although variations in the amounts of fat were often poorly correlated with eating qualities. The contribution of fat to taste is equally controversial, because a specific 'fat taste' perception had not been characterized. The innate attraction for fats may be due to one or more of orosensory, post-ingestive and metabolic signals. This literature review suggests that taste of lipids, particularly of oxidized PUFAs and their esters, may derive from a specific fatty acid perception mechanism in human lingual papillae. Interactions of the CD36 scavenger system with the many compounds derived from fats in cooked and processed meats offer an explanation for the variety of flavors and off-flavors found in meats. The genetic variations in the presence of receptor proteins could be one of the factors related to the differences in fat preferences in different countries and between genders.

Salivary protein/peptide profiling with SELDI-TOF-MS.

In this study, large-scale profiling of salivary proteins and peptides ranging from 2 to 100 kDa was demonstrated using surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS). Results show that chip surface type and sample type critically affect the amount and composition of detected salivary proteins. Delayed processing time resulted in both increase and decrease of peak numbers consistent with proteolysis. SELDI-TOF-MS profiles also changed, depending on storage temperature, although sample processing by centrifugation and numbers of freeze-thaw cycles had a minimal impact. In conclusion, SELDI-TOF-MS offers a simple, rapid, high-throughput technique for profiling low-mass (<10 kDa) saliva proteins/peptides. We wish to use this technique to gain insight into the human saliva proteome composition and its changes over time in response to food consumption.

SELDI-TOF-MS of saliva: methodology and pre-treatment effects.

Interest in saliva as a diagnostic fluid for monitoring general health and for early diagnosis of disease has increased in the last few years. In particular, efforts have focused on the generation of protein maps of saliva using advanced proteomics technology. Surface-enhanced laser-desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) is a novel high throughput and extremely sensitive proteomic approach that allows protein expression profiling of large sets of complex biological specimens. In this study, large scale profiling of salivary proteins and peptides, ranging from 2 to 100kDa was demonstrated using SELDI-TOF-MS. Various methodological aspects and pre-analytical variables were analysed with respect to their effects on saliva SELDI-TOF-MS profiling. Results show that chip surface type and sample type (unstimulated versus stimulated) critically affect the amount and composition of detected salivary proteins. Factors that influenced normal saliva protein profiling were matrix composition, sample dilution and binding buffer properties. Delayed processing time experiments show certain new peptides evolving 3h post-saliva donation, and quantitative analyses indicate relative intensity of other proteins and peptides changing with time. The addition of protease inhibitors partly counteracted the destabilization of certain protein/peptide mass spectra over time suggesting that some proteins in saliva are subject to digestion by intrinsic salivary proteases. SELDI-TOF-MS profiles also changed by varying storage time and storage temperature whereas centrifugation speed and freeze-thaw cycles had minimal impact. In conclusion, SELDI-TOF-MS offers a high throughput platform for saliva protein and peptide profiling, however, (pre-)analytical conditions must be taken into account for valid interpretation of the acquired data.

Salivary biomarkers associated with perceived satiety and body mass in humans.

Regulation of food intake and energy homeostasis is controlled by a delicate balancing of numerous central and peripheral factors, including circulating peptide hormones. This study investigated the proteome of saliva using SELDI-TOF-MS in relation to satiety and body mass index (BMI) in humans. Within a longitudinal test session, 18 subjects were exposed to a lunch-induced hunger-satiety shift, while every 15 min collecting their whole saliva and rating their hunger and satiety. Saliva was analysed by SELDI-TOF-MS using IMAC arrays with a chromatographic copper surface (IMAC-Cu). From all subjects and time points measured, peptide and protein profiles showed 190 common peaks. Their interrelationships show that 37% of the variation was accounted for in one dimension. About 30 means had a strong association (0.70<|r|<0.95) with all subjective satiety ratings across time during the test session, and seven peaks were significantly correlated to BMI. Database MS searches indicated characterisation of some relevant metabolic peptide hormones. In conclusion, SELDI-TOF-MS on human saliva provides a valuable and noninvasive way of profiling that enables characterisation of novel and differently expressed peptides and proteins which can be used as biomarkers of satiety and overweight.

Proteomic analysis of human whole and parotid salivas following stimulation by different tastes.

Whole and parotid salivas, collected after stimulation with tastants, were analyzed by 2D electrophoresis and mass spectrometry. In whole saliva, the number of proteins affected by taste stimulation increased in the order sweet < umami < bitter < acid. Annexin A1 and calgranulin A, involved in inflammation, were over-represented after umami, bitter, and sour stimulations. Their low abundance or absence in parotid saliva after bitter stimulation suggested that they originated from other oral glands or tissues.

Relating ionisation of calcium chloride in saliva to bitterness perception.

Saliva plays a role in the perception of bitter, sour and salty tastes that are presumed to be derived from the concentration of free cations or anions ions dissolved in saliva. The role of ionisation of calcium in bitter taste was studied by determining binding in vitro mixture of saliva and protein solutions and in spit. In vitro, the addition of whey to calcium chloride solutions increased the calcium binding, pH and viscosity. The addition of saliva to these mixtures, the increased calcium binding and the induced small changes in viscosity and pH were thought not to contribute significantly to bitterness perception. Nonstimulated saliva, at pH 7.5, contained about 5 mM calcium, of which about one third was ionised. The bitter threshold of fully ionised calcium chloride in water varied between 1 and 15 mM among individuals. In spit, after tasting whey, ionised calcium was found to have increased at low, but decreased at high, calcium concentrations and varied 30% among individuals. Bitterness was related, on average, to the concentration of ionised calcium and not to the total concentration of calcium in spit. A general explicative model based on the composition of bulk saliva is discussed in relation to perception threshold and the likely importance of saliva from von Ebner's gland.

NaCl and sugar release, salivation and taste during mastication of salted chewing gum.

Salt perception impacts on food acceptability and nutrition and depends upon salt release from foods that was determined in situ during mastication of chewing gum with up to 10% (1800 mmol/kg) added NaCl. The mechanical action of chewing increased salivation, which was further increased by the presence of salt, particularly above 180 mmol NaCl/kg gum or above 100 mM NaCl in saliva. The average resting salivary flow rate was 1 ml/min, increasing to 4 and 6 ml/min with gums containing low and high salt, respectively. Thus, stimulation of salivation by salt occurred at a concentration well above the taste threshold of 20 mM NaCl. NaCl concentration in nonstimulated saliva was about 10 mM and increased to 500 mM after 30 s chewing of the 10% NaCl gum and returned to near nonstimulated levels after 4 min chewing. Changes in pH of saliva were more gradual, increasing to a maximum at about 2 min and remaining elevated after 4 min. Salty taste was related to the free chloride ion concentration in saliva irrespective of the initial salt concentration in the gum with an indication of adaptation after 3 min chewing. During chewing, salty taste increased ahead of the increase in salivary conductivity and the salt concentration in the sublingual saliva varied in a cyclic fashion about every 20 s. This is consistent with a cyclic swallowing of saliva and replacement with newly secreted saliva of low salt content and mastication releasing further salt from the gum.