Mouth-state dependent changes in the judged pleasantness of water at different temperatures

Distinguishable short-term effects of tea and water drinking on human saliva redox

Food consumption can alter the biochemistry and redox status of human saliva, and the serving temperature of food may also play a role. The study aimed to explore the immediate (3 min) and delayed (30 min) effects of hot tea (57 ± 0.5 °C) ingestion and cold tea (8 ± 0.5 °C) ingestion on the salivary flow rate and salivary redox-relevant attributes. The saliva was collected from 20 healthy adults before, 3-min after and 30-min after the tea ingestion. The hot or cold deionised water at the same temperatures were used as control. The salivary flow rate and redox markers in hot tea (HBT), cold tea (CBT), hot water (HW) and cold water (CW) group were analysed and compared. The results demonstrated that neither the black tea nor the water altered the salivary flow rate; the black tea immediately increased the salivary thiol (SH) and malondialdehyde (MDA) content while reduced salivary uric acid (UA) significantly. The tea ingestion showed a tendency to elevate the ferric reducing antioxidant power (FRAP) in saliva, although not significantly. The water ingestion decreased the MDA content immediately and increased the UA level significantly. Cold water was found to induce a greater delayed increase in total salivary total protein (TPC) than the hot water. In conclusion, the black tea ingestion affects the redox attributes of human saliva acutely and significantly, while the temperature of drink makes the secondary contribution.

Whey Protein Derived Mouthdrying Found to Relate Directly to Retention Post Consumption but Not to Induced Differences in Salivary Flow Rate

Whey protein is fortified into beverages to provide functional benefits, however, these beverages are considered mouthdrying. To date whey protein derived mouthdrying has not been quantified using a 'physical measure' in parallel with rated perception. Saliva flow could also relate to whey protein derived mouthdrying, however this has not been previously tested as an intervention. Accordingly, volunteers (n = 40) tested mouthdrying in different whey beverages and the sensory profile was evaluated by a trained sensory panel (n = 10). Volunteers also rated mouthdrying combined with collection of saliva samples post beverage consumption to measure retention to the oral cavity. To modulate saliva flow rate, volunteers both chewed on parafilm (to increase saliva flow) and used cotton wool (to remove saliva) before tasting beverages and rating mouthdrying. Both the volunteers and sensory panel rated whey protein beverages (WPB) as significantly more mouthdrying than the control beverage (whey permeate). The significantly higher rating of mouthdrying from the volunteers coincided with significantly higher protein concentration in saliva samples post WPB consumption, supporting mucoadhesion as the mechanism. Modulating saliva flow did not lead to any difference in rated mouthdrying and future work would be beneficial to evaluate further the influence of natural variation in salivary flow rate.

A Study of Multi-Sensory Experience and Color Recognition in Visual Arts Appreciation of People with Visual Impairment

Visually impaired visitors experience many limitations when visiting museum exhibits, such as a lack of cognitive and sensory access to exhibits or replicas. Contemporary art is evolving in the direction of appreciation beyond simply looking at works, and the development of various sensory technologies has had a great influence on culture and art. Thus, opportunities for people with visual impairments to appreciate visual artworks through various senses such as hearing, touch, and smell are expanding. However, it is uncommon to provide an interactive interface for color recognition, such as applying patterns, sounds, temperature, or scents. This review aims to convey the visual elements of the work to the visually impaired through various sensory elements. In addition, to open a new perspective on appreciation of the works, the technique of expressing the color coded by integrating patterns, temperature, scent, music, and vibration was explored, and future research topics were presented.

At what stage in the drinking process does drinking water affect attention and memory? Effects of mouth rinsing and mouth drying in adults

Drinking water is important for health and there is an agreement that drinking water facilitates certain cognitive processes. However, the mechanism underlying the effect of drinking water on cognition is unknown. While attention performance is improved by even a very small drink, memory performance seems to require larger drinks for performance enhancement. This suggests that attention could be affected earlier in the drinking process than memory. We aimed to elucidate further the mechanism involved by investigating the stage during the drinking process influencing performance on cognitive tasks. To this end, we compared mouth rinsing and mouth drying. Mouth rinsing was expected to result in improved attention performance and would suggest that the mechanism responsible is located in the mouth and occurs early in the drinking process, before swallowing. Eighty-seven adults participated in either a treatment (mouth rinsing or mouth drying) or control (no intervention) condition. They were assessed at baseline and 20 min later after intervention on measures of visual attention, short-term memory, subjective thirst and mood. Our results showed that mouth rinsing improved visual attention, but not short-term memory, mood or subjective thirst. Mouth drying did not affect performance. Our results support the hypothesis that different mechanisms underlie the effect of drinking water on different cognitive processes. They suggest that merely sipping water, as opposed to having a large drink, can improve attention.

The Role of Pitch and Tempo in Sound-Temperature Crossmodal Correspondences

We explored the putative existence of crossmodal correspondences between sound attributes and beverage temperature. An online pre-study was conducted first, in order to determine whether people would associate the auditory parameters of pitch and tempo with different imagined beverage temperatures. The same melody was manipulated to create a matrix of 25 variants with five different levels of both pitch and tempo. The participants were instructed to imagine consuming hot, room-temperature, or cold water, then to choose the melody that best matched the imagined drinking experience. The results revealed that imagining drinking cold water was associated with a significantly higher pitch than drinking both room-temperature and hot water, and with significantly faster tempo than room-temperature water. Next, the online study was replicated with participants in the lab tasting samples of hot, room-temperature, and cold water while choosing a melody that best matched the actual tasting experience. The results confirmed that, compared to room-temperature and hot water, the experience of cold water was associated with both significantly higher pitch and fast tempo. Possible mechanisms and potential applications of these results are discussed.

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.

Infusing pleasure: Mood effects of the consumption of a single cup of tea

Tea has historically been associated with mood benefits. Nevertheless, few studies have empirically investigated mood changes after tea consumption. We explored immediate effects of a single cup of tea up to an hour post-consumption on self-reported valence, arousal, discrete emotions, and implicit measures of mood. In a parallel group design, 153 participants received a cup of tea or placebo tea, or a glass of water. Immediately (i.e. 5 min) after consumption, tea increased valence but reduced arousal, as compared to the placebo. There were no differences at later time points. Discrete emotions did not differ significantly between conditions, immediately or over time. Water consumption increased implicit positivity as compared to placebo. Finally, consumption of tea and water resulted in higher interest in activities overall and in specific activity types compared to placebo. The present study shows that effects of a single cup of tea may be limited to an immediate increase in pleasure and decrease in arousal, which can increase interest in activities. Differences between tea and water were not significant, while differences between water and placebo on implicit measures were unexpected. More servings over a longer time may be required to evoke tea's arousing effects and appropriate tea consumption settings may evoke more enduring valence effects.

The influence of ice slushy on voluntary contraction force following exercise-induced hyperthermia

This study aimed to investigate the effect of exercise-induced hyperthermia on central fatigue and force decline in exercised and nonexercised muscles and whether ingestion of ice slushy (ICE) ameliorates fatigue. Eight participants (5 males, 3 females) completed 45 s maximal voluntary isometric contractions (MVIC) with elbow flexors and knee extensors at baseline and following an exercise-induced rectal temperature (Trec) of 39.3 ± 0.2 °C. Percutaneous electrical muscle stimulation was superimposed at 15, 30 and 44 s during MVICs to assess muscle activation. To increase Trec to 39.3 °C, participants cycled at 60% maximum power output for 42 ± 11 min in 40 °C and 50% relative humidity. Immediately prior to each MVIC, participants consumed 50 g of ICE (-1 °C) or thermoneutral drink (38 °C, CON) made from 7.4% carbohydrate beverage. Participants consumed water (19 °C) during exercise to prevent hypohydration. Voluntary muscle force production and activation in both muscle groups were unchanged at Trec 39.3 °C with ICE (knee extensors: 209 ± 152 N) versus CON (knee extensors: 255 ± 157 N, p = 0.19). At Trec 39.3 °C, quadriceps mean force (232 ± 151 N) decreased versus baseline (302 ± 180 N, p < 0.001) and mean voluntary activation was also decreased (by 15% ± 11%, p < 0.001). Elbow flexor mean force decreased from 179 ± 67 N to 148 ± 65 N when Trec was increased to 39.3 °C (p < 0.001) but mean voluntary activation was not reduced at 39.3 °C (5% ± 25%, p = 0.79). After exercise-induced hyperthermia, ICE had no effect on voluntary activation or force production; however, both were reduced from baseline in the exercised muscle group. Peripheral fatigue was greater than the central component and limited the ability of an intervention designed to alter central fatigue.

Water restriction and fluid temperature alter preference for water and sucrose solutions

The role of diet temperature in ingestive behavior is poorly understood. We examined the importance of stimulus temperature and water-restriction state on the preference for and intake of water and sucrose. Using custom-designed equipment that allows us to monitor and maintain solution temperatures during testing (±0.1 °C), we conducted a series of 2-bottle preference tests (10 °C water vs. sucrose 10-40 °C) and brief access tests (10-40 °C water and sucrose). Water-restricted rats preferred cold water over any sucrose concentration (0.0-1.0 M) if the sucrose was 30 or 40 °C, whereas the same rats preferred sucrose at all concentrations and temperatures when unrestricted suggesting that the water-restriction state interacts with temperature preference. In a series of brief-access tests using a Davis Rig (MS-180), rats reduced licking to cold sucrose compared with 20 °C sucrose, suggesting that unlike water, cold temperature reduced the palatability of sucrose.

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.

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.

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.

Dietary restraint and heightened reactivity to food

Previously, studies have explored the relationship between dietary behavior and salivary reactivity to food. Despite this, it remains unclear which behaviors are associated with enhanced reactivity. One problem is that measures of behavior have not been compared directly. In particular, it is unclear whether elevated reactivity is associated with measures of dietary restraint or with measures of failed dietary control and a tendency to overeat. To address this problem, we compared the association between salivary reactivity and scores on the subscales of the Three-Factor Eating Questionnaire (restraint, disinhibition, and hunger). Estimates of reactivity were derived from the difference between a baseline saliva measure and a similar measure taken in close proximity to hot pizza. Our second aim was to explore how salivary reactivity changes after a meal. Female participants (N=40) were tested before and after a lunch (cheese sandwiches). All tended to show reactivity to pizza before but not after lunch. No significant differences were associated with the disinhibition or hunger subscales. However, prelunch reactivity was significantly greater in those participants with high scores on the restraint scale. This does not appear to be related to reported levels of hunger before lunch. Rather, it may reveal an intrinsic difference between the reaction of restrained and unrestrained eaters to food.

Effects of mouth dryness on drinking behavior and beverage acceptability

In humans, the association between mouth dryness and thirst has been examined in a variety of contexts. Typically, drinking behavior produces a concomitant reduction in unpleasant dry mouth sensations. Evidence is reviewed for a mechanism that influences the termination of drinking behavior by metering this change. Drinking behavior causes a progressive increase in parotid saliva flow. Thus, one possibility is that satiety results from a decrease in the reward associated with mouth wetting during a drinking episode. Beverages can differ in their satiating ability. This variability may be related to their mouth-wetting characteristic, and may be reflected in a shift in their acceptability when the mouth becomes dry. Physically drying the mouth appears to increase the acceptability of beverages that are either cold or acidic. It may be significant that two important determinants of mouth wetting are temperature and acidity. Cold or acidic beverages are also likely to be regarded as 'thirst-quenching.' Thus, shifts in acceptability, 'thirst quenching' and satiety may all be related to the mouth-wetting properties of a beverage. The extent to which this coincidence is meaningful warrants further investigation. However, if a common underlying process exists, then this may help to elucidate reasons for voluntary dehydration and aberrant drinking behavior in the elderly.

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

In the first study, whole saliva was collected from ten adults during stimulation with sour, carbonated, sweet and water stimuli in the form of 5-ml of ice at about -10 degrees C or of liquids at 0, 8, 20 or 37 degrees C. Parotid saliva was also collected in response to ice or infusion into the mouth of the liquids at different temperatures. Another group of ten adults also collected whole saliva in response to water at 20 degrees C, with or without the presence in the mouth of an acrylic cube of dimensions similar to those of the ice. In a second study, 20 adults collected whole saliva in response to stimulation with 5 ml of water and of an astringent stimulus at 0, 8, 37 and 70 degrees C. In the first study, flow rates fell in the order sour, carbonated, sweet and water and flow rates in response to stimuli in the form of ice were very significantly higher than in response to the corresponding liquids at the four different temperatures. With the sour stimulus, liquids at 0 and 8 degrees C elicited higher flow rates than liquids at 20 or 37 degrees C. Although the presence in the mouth of the acrylic block increased the flow rate of whole saliva, the increase was only about 30% of that achieved with ice. In the second study, the astringent stimulus was a more effective salivary stimulus than water; flow rates were significantly higher in response to liquids at 0 and 8 degrees C than at the higher temperatures and flow rates in response to liquids at 37 degrees C were significantly lower than with the other temperatures. In summary, stimuli in the form of ice were the most effective and liquids at 37 degrees C were least effective in stimulating salivary flow.

Role of cold receptors and menthol in thirst, the drive to breathe and arousal

Menthol is widely used in candy, chewing gum, toothpastes, cigarettes and common cold medications. Menthol has been shown to stimulate cold receptors in the mouth and nose. The present paper puts forward the hypothesis that menthol, by its effects on oral and nasal cold receptors, may influence thirst, the drive to breathe, and arousal. The satisfying effects of menthol on thirst and breathing, together with an effect on arousal, may explain the popularity of menthol and account for the very large amount of menthol-containing products that are consumed each day.