The effect on human salivary flow rate of the temperature of a gustatory stimulus

Oral Temperature and pH Influence Dietary Nitrate Metabolism in Healthy Adults

This study tested the hypothesis that the increases in salivary and plasma [NO₂^-] after dietary NO₃^- supplementation would be greater when oral temperature and pH were independently elevated, and increased further when oral temperature and pH were elevated concurrently. Seven healthy males (mean ± SD, age 23 ± 4 years) ingested 70 mL of beetroot juice concentrate (BR, which provided ~6.2 mmol NO₃^-) during six separate laboratory visits. In a randomised crossover experimental design, salivary and plasma [NO₃^-] and [NO₂^-] were assessed at a neutral oral pH with a low (T_Lo-pH_Norm), intermediate (T_Mid-pH_Norm), and high (T_Hi-pH_Norm) oral temperature, and when the oral pH was increased at a low (T_Lo-pH_Hi), intermediate (T_Mid-pH_Hi), and high (T_Hi-pH_Hi) oral temperature. Compared with the T_Mid-pH_Norm condition (976 ± 388 µM), the mean salivary [NO₂^-] 1-3 h post BR ingestion was higher in the T_Mid-pH_Hi (1855 ± 423 µM), T_Hi-pH_Norm (1371 ± 653 µM), T_Hi-pH_Hi (1792 ± 741 µM), T_Lo-pH_Norm (1495 ± 502 µM), and T_Lo-pH_Hi (2013 ± 662 µM) conditions, with salivary [NO₂^-] also higher at a given oral temperature when the oral pH was increased (p < 0.05). Plasma [NO₂^-] was higher 3 h post BR ingestion in the T_Mid-pH_Hi, T_Hi-pH_Hi, and T_Lo-pH_Hi conditions, but not the T_Lo-pH_Norm and T_Hi-pH_Norm conditions, compared with T_Mid-pH_Norm (p < 0.05). Therefore, despite ingesting the same NO₃^- dose, the increases in salivary [NO₂^-] varied depending on the temperature and pH of the oral cavity, while the plasma [NO₂^-] increased independently of oral temperature, but to a greater extent at a higher oral pH.

Addition of chocolate milk to diet corresponds to protein concentration changes in human saliva

Salivary proteins have the potential to alter oral sensory perception of foods. In rodents, dietary polyphenol exposure increases salivary concentrations of polyphenol-binding proteins and several cystatins, which correlate with less aversion to polyphenol-rich solutions. If similar salivary shifts occur in humans, then increasing dietary polyphenols may improve orosensory experience of polyphenol-rich foods. We hypothesized that small dietary changes, focused on polyphenols, would increase expression of salivary binding proteins for polyphenols and thus suppress unpleasant polyphenol sensations. However, analogs of salivary polyphenol-binding proteins are found in foods. Thus, we also hypothesized that food-sourced analogs of these salivary proteins would mitigate changes in saliva and sensation. Human subjects (N=55) alternated weeks of consuming a low polyphenol diet and then a regular diet plus a polyphenol-rich chocolate milk (almond, containing no polyphenol-binding proteins, or bovine, containing polyphenol-binding proteins). Statistical analyses revealed both chocolate milk interventions corresponded to changes in relative expression of 96 proteins and calculated concentration of 146 proteins (both after correction for false discovery rate), out of 1,176 proteins identified through proteomics. Of the proteins that changed, proline-rich proteins and cystatins were noticeable, which reflects prior work in animal studies. Subjects rated all chocolate milks as less flavorful after the bovine chocolate milk intervention week compared to low polyphenol weeks, but generally sensory changes were minimal. However, the results confirm that dietary changes coincide with salivary changes, and that some of those changes occur in proteins that have potential to influence oral sensations.

Invited review: Astringency in whey protein beverages

Astringency is the sensation of mouth drying and puckering, and it has also been described as a loss of lubrication in the mouth. Astringency is perceived as an increase in oral friction or roughness. Astringency caused by tannins and other polyphenols has been well documented and studied. Whey proteins are popular for their functional and nutritional quality, but they exhibit astringency, particularly under acidic conditions popular in high acid (pH 3.4) whey protein beverages. Acids cause astringency, but acidic protein beverages have higher astringency than acid alone. Whey proteins are able to interact with salivary proteins, which removes the lubricating saliva layer of the mouth. Whey proteins can also interact directly with epithelial tissue. These various mechanisms of astringency limit whey protein ingredient applications because astringency is undesirable to consumers. A better understanding of the causes of whey protein astringency will improve our ability to produce products that have high consumer liking and deliver excellent nutrition.

Salivary functions in mastication, taste and textural perception, swallowing and initial digestion

Saliva exerts multiple functions in relation to the initial digestive processes taking place in the upper parts of the gastrointestinal tract. Ingestion of food and beverages, in turn, is a strong stimulus for secretion of saliva with a differential composition depending on the neuronal stimulation pattern. This review paper provides insight into the mechanisms by which saliva acts in relation to taste, mastication, bolus formation, enzymatic digestion and swallowing. Also, the protective functions of saliva including maintenance of dental and mucosal integrity will be discussed as they indirectly influence the digestive process. The final part of this study focuses on the implications of xerostomia and salivary gland dysfunction on gastrointestinal functions.

The Effects of Tooth Brushing on Whole Salivary Flow Rate in Older Adults

Objectives

(1) To determine whether manual (MTB), or electric, tooth brushing (ETB) modulates whole salivary flow rate in older adults who are free of systemic disease. (2) To determine the duration of the brushing-related modulation of salivary flow rate. (3) To compare salivary flow rate modulation associated with MTB and ETB.

Method

Twenty-one adults aged 60 years and older participated in two experimental sessions during which they used a manual, or electric, toothbrush to brush their teeth, tongue, and palate. Whole salivary flow rates were determined using the draining method before, during, and after brushing. Differences in salivary flow rates across time periods, and between conditions, were examined using paired samples t-tests applying a Holm-Bonferroni sequential procedure (p_corr < 0.0045). The relationship between tooth brushing and age with respect to maximum salivary flow rate increase was examined using Pearson's correlation coefficient (p < 0.05).

Results/Conclusion

Whole salivary flow rates increased during, and for up to 5 minutes following, tooth brushing in adults aged 60 years and older who were free of systemic disease. The salivary effects of MTB and ETB were not significantly different. A moderate, positive correlation was observed between tooth-brushing-related maximum salivary flow rate increase and age.

Measurement of saliva flow rate in healthy young humans: influence of collection time and mouthrinse water temperature

The aim of the current study was to determine if unstimulated saliva flow (measured in μl min^-1 ) is affected by different durations of sample collection and by temperatures of mouthrinse water used before sample collection. In randomized order, participants provided 10 samples of unstimulated saliva at time points ranging from 1 to 6 min after rinsing with different temperatures of water (10, 20, and 30°C). Data were analysed by one-way anova with post-hoc tests. Test-retest reliability was assessed using Bland-Altman plots and correlation coefficients. A larger volume of saliva was obtained over a longer collection time. No significant difference in saliva flow rate was observed between collection times [mean: 364 (95% CI: 332-397) μl min^-1 ]. Although rinsing with different temperatures of mouthrinse water resulted in no significant difference in saliva flow rates as a result of the mouthrinse water temperatures, 60% of the participants had a higher saliva flow rate after rinsing with mouthrinse water at a temperature of 10°C compared with mouthrinse water at 20 and 30°C, suggesting large individual variation (range: 24-420 μl min^-1 ). These findings provide justification for using saliva collection times of 1-6 min during sampling of unstimulated saliva. The large individual variations in saliva flow rate in response to different mouthrinse water temperatures suggest that standardization, control, and reporting of mouthrinse water temperature is warranted.

Influence of five neutralizing products on intra-oral pH after rinsing with simulated gastric acid

The aetiology of dental erosion may be of both extrinsic and intrinsic origin. The aim of the present study was to test the ability of various neutralizing products to raise the low intra-oral pH after an erosive exposure, in this case to gastric acid, which was simulated using hydrochloric acid (HCl). Eleven adults participated. They rinsed with 10 ml of 10 mM HCl (pH 2) or 10 ml of 100 mM HCl (pH 1) for 1 min, after which the pH was measured intra-orally for up to 30 min at four sites (two approximal, one buccal, and the dorsum of the tongue). After rinsing with the two acid solutions (pH 1 and pH 2), the following products were used: (i) antacid tablet; (ii) gum arabic lozenge; (iii) mineral water; (iv) milk; and (v) tap water (positive control). The negative control was no product use. The five test products were used for 2 min after the erosive challenge. All the products produced an initially higher pH compared with the negative control. The antacid tablet resulted in the greatest and most rapid increase in pH, followed by the lozenge. In dental practice, the use of any of the neutralizing products tested, especially the antacid tablet, could be recommended in order to increase the intra-oral pH after an erosive challenge.

Saliva characteristics and individual sensitivity to phenolic astringent stimuli

Astringency sensation is due to interactions between salivary proteins and phenols and is based on an increased-friction mechanism. Modifications to the profile of salivary proteins and their concentration could affect tannin/protein reactions and hence the intensity of perceived astringency. Salivary characteristics of 65 subjects were compared after abstention from phenol-containing food and immediately after ingestion of tannic acid. The effect of stimulation on saliva characteristics was expressed in terms of D value, computed as the arithmetic difference between values found in saliva samples from the 2 conditions. Based on D values, subjects were clustered in two groups. Cluster 1 (Cl1, 53 cases) was characterized by low D values thus indicating that the basal saliva condition was quickly restored in these subjects. Cluster 2 (Cl2) was composed of 12 subjects whose basal salivary condition was not quickly restored, particularly in terms of salivary protein concentration and profile and saliva haze-forming capacity. Sensory data showed that subjects capable of maintaining constant saliva characteristics were less sensitive to astringent stimuli than subjects in which the same stimulations induced significant saliva modifications. The results suggest that a large proportion of the population are able to maintain their salivary protein concentration and simultaneously intercept and inactivate dietary tannins.

Oral hydration, parotid salivation and the perceived pleasantness of small water volumes

Previous studies have suggested that the preference for drinking cold water is increased when the drinker has a dry mouth. In a first experiment, we investigated whether a positive shift in preference would occur for small water volumes (0.75 ml and 1.5 ml) at 8, 16 or 25 degrees C, delivered into a mouth that had been dried using a warmed airflow, versus a normally hydrated mouth. Subjects rated the perceived wetness (or dryness) of their mouth, and the perceived pleasantness (or unpleasantness) of the water samples, using a labeled magnitude scale. Cooler water samples were preferred, and consistent with previous research, this preference was slightly enhanced when the subject's mouth was dried. The coldest water sample led to significantly wetter mouthfeel than the other two less cold samples, consistent with the possibility that the coldest water increased the rate of salivation. However, a second experiment found that although the rate of parotid salivation was increased if the mouth had been dried using a warm airflow, the different water temperatures did not induce different rates of parotid salivation. This indicates that enhanced preference for cold water when the mouth is dry is not invariably based in the reward gained from mouth rewetting via increased parotid saliva flow.

Assay of gastrin and somatostatin in gastric antrum tissues of children with chronic gastritis and duodenal ulcer

AIM: To study the expressions of gastrin (GAS) and somatostatin (SS) in gastric antrum tissues of children with chronic gastritis and duodenal ulcer and their role in pathogenic mechanism.

METHODS: Specimens of gastric antrum mucosa from 83 children were retrospectively analyzed. Expressions of GAS and SS in gastric antrum tissues were assayed by the immunohistochemical En Vision method.

RESULTS: The expressions of GAS in chronic gastritis Hp+ group (group A), chronic gastritis Hp- group (group B), the duodenal ulcer Hp + group (group C), duodenal ulcer Hp- group (group D), and normal control group (group E) were 28.50 + 4.55, 19.60 + 2.49, 22.69 + 2.71, 25.33 + 4.76, and 18.80 + 2.36, respectively. The value in groups A-D was higher than that in group E. The difference was not statistically significant. The expressions of SS in groups A-E were 15.47 + 1.44, 17.29 + 2.04, 15.30 + 1.38, 13.11 + 0.93 and 12.14 + 1.68, respectively. The value in groups A-D was higher than that in group E. The difference was also not statistically significant.

CONCLUSION: The expressions of GAS and SS are increased in children with chronic gastritis and duodenal ulcer.

Thermally evoked parotid salivation

Parotid salivation is known to be influenced by the temperature of liquids moved around the mouth. Here we investigated the ability of non-liquid thermal stimuli to change the rate of salivation. Unilateral parotid saliva was collected using a Lashley Cup from 12 normally hydrated subjects. Thermal stimuli were delivered through a copper tube, in which temperature-controlled water flowed, resting statically on the anterior tongue. During separate trials, the tube was 10, 22, or 44 degrees C, or the resting temperature of the tongue (or hypothenar of the hand, the control site). On each trial, the unstimulated salivation rate was first measured for 6 min while the subject remained seated with the mouth closed. Subsequently, salivation was measured for 6 min during application of the thermal stimulus. The tube was then removed for 1-2 min before the next trial. During the trials, subjects repeatedly rated the subjective temperature of the tongue (or hypothenar) and its perceived wetness/dryness. Stimulated salivation, expressed as a proportion of the previously measured unstimulated salivation, differed among body sites and temperatures (P<0.03). A significant increase in salivation was seen only for the 10 degrees C stimulus applied to the tongue. Wetness ratings and salivation rates were positively correlated, albeit weakly. These results demonstrate that temperature-evoked changes in parotid salivation do not require the unique spatiotemporal dynamics of the tongue and jaw movements in wetting the oral mucosa.

Influence of drinking method on tooth-surface pH in relation to dental erosion

The aim of this investigation was to study the intraoral pH response on tooth surfaces in relation to dental erosion during and after drinking a sugar-free cola-type soft drink. Six different methods of drinking were tested in a randomized order: holding; short-sipping; long-sipping; gulping; nipping; and sucking. Two methods of pH measurement were used in two series of individuals. In the first series, pH was measured by using the microtouch method in 12 healthy adults at three dental erosion-prone sites: 11 palatally; 11 buccally; and at the mesiobuccal cusp tip of 16. In the second series, pH was measured by using the telemetric method in 6 healthy individuals, producing continuous recordings of pH by means of a glass electrode in a specified approximal area. The two series showed similar results, although the telemetric method generally recorded larger pH falls. Holding the drink in the mouth before swallowing led to the most pronounced pH drop, followed by the long-sipping method. Gulping resulted in only a small decrease of pH. No differences among the three intraoral sites were found when analyzed by using the microtouch method. The conclusion from this study is that the drinking method strongly affects tooth-surface pH and thereby the risk for dental erosion. It therefore seems appropriate to include advice on the method of drinking in dietary counseling related to dental erosion.

Is there a parotid-salivary reflex response to fat stimulation in humans?

The perception of fats in foods may involve gustatory, olfactory or textural cues. There is contradictory evidence as to whether the orosensory perception of fat is as a basic quality of taste or related to the physical characteristics of fat. A dose-response reflex parotid-salivary secretion has, however, been shown for the accepted basic taste qualities. The aim of this study was to establish whether varying fat concentration in two food types causes an associated dose-response reflex parotid secretion in humans. Parotid salivary flow was recorded using Lashley cups and cannulae connected to an instantaneous flow meter. Gustatory stimuli were achieved using 3 ml of skimmed (0.1% fat), semi-skimmed (1.7% fat) or full (3.6% fat) milk (Sainsbury) or 5 g of extra-light (5% fat), light (16% fat) or original (24% fat) cream cheese (Kraft). No significant differences in salivary flow rate were shown within the milk group (n=10, P=.93) or within the cream-cheese group (n=11, P=.82). Furthermore, no correlation was observed between increasing fat concentration and flow within either the milk (P=.98) or the cream-cheese group (P=.69; Pearson Product Moment Correlation). These results do not support the hypothesis that there is a fat-specific dose-response parotid reflex.