The effects of food viscosity on bite size, bite effort and food intake.

Two studies investigated the effect of a food's viscosity on bite size, bite effort and food intake using a standardized protocol in which subjects sipped through a straw every 20 s for a period of 15 min from one of two products, a chocolate-flavored dairy drink and a chocolate-flavored dairy semi-solid, matched for energy density. In the first study, subjects consumed 47% more from the liquid than from the semi-solid to reach the same degree of satiation, with larger bite sizes for the liquid throughout the 15 minute period (8.7+/-0.45 g) compared to the semi-solid (5.8+/-0.3 g, p<0.01). In the second study bite effort was eliminated by using a peristaltic pump to present the products every 20 s. Oral processing time before swallowing was set at 5 s (both products) or 8 s (semi-solid). With the elimination of bite effort and a standardized oral processing time, subjects consumed as much from the semi-solid as from the liquid to reach the same degree of satiation. Bite size for liquids started relatively small and grew gradually over successive bites, whereas the bite size for the semi-solid food started relatively large and became gradually smaller. The latter effect was even more pronounced when the oral processing time was increased from 5 to 8 s. In conclusion, semi-solids resulted in smaller bite sizes and lower intake than liquids, but these differences disappeared when differences in bite effort were eliminated.

Effect of bolus size on chewing, swallowing, oral soft tissue and tongue movement.

Simultaneous 3D articulograph and ultrasonograph techniques were used to monitor the chewing, swallowing, oral soft tissue and tongue movements of six subjects whilst consuming varying numbers (1, 2 and 4) of a confectionery product. Modifying the number of confectionery units had a variable effect on chewing, swallowing and oral soft tissue movements during the start of the chewing sequence. The distance, range and velocity of chin movement were significantly lower when 1 confectionery unit was consumed compared with 2 and 4 during the middle stage of the chewing sequence. Significant differences in modioli movement were observed during the initial stages of chewing allowing the identification of a working and non-working side, whilst no differences in thyroid cartilage movement were noted over the whole chewing sequence. Increasing the number of confectionery units caused a significant increase in the index of tongue movement during the end of the eating sequence, although the mean index of tongue movement over the total chewing sequence remained constant. Jaw movement correlated with tongue movement, where for all samples, gape decreased linearly as the chewing sequence progressed, reflected in a similar decline in the index of tongue movement. The lack of differences in the index of tongue movement observed over the start and middle of the chewing sequence as a consequence of the number of confectionery units consumed suggested that the change in the physical properties of the bolus had a greater effect on the index of tongue movement than the change in bolus size.

Is fat perception a thermal effect?

It has been generally assumed that fat is detected by its flavour and by its lubrication of the oral mucosa. A recent study reported a correlation of -.99 between perceived temperature of a product and its fat content. This was significantly higher than correlations of sensory scores for fat flavour, mouthfeel, and afterfeel. This suggested a third detection mechanism; fat may be detected via its effect on the thermal conductivity of the food. In 3 studies, thermal sensitivity in humans was investigated to verify whether oral thermal receptors are sufficiently rapid and accurate to play a role in the perception of fats. The thermal sensitivity of the lips and oral mucosa of the anterior and middle one-third of the tongue were assessed using a Peltier device. Subjects detected 0.5 Hz fluctuations in temperature of 0.08'C on the lower lip, 0.26 degrees C and 1.36 degrees C at the tip and dorsum of the tongue, demonstrating that the lips are sufficiently sensitive to detect small differences in temperature. In two further experiments subjects ingested custards and mayonnaises and then spat out samples after 5, 10, or 20 sec. The temperature of the food and oral mucosa was measured before and after spitting and the rates of heating were calculated. Results suggest assessment of thermal conductivity of food may be used to assess fat content.

Contribution of the cheeks to the intraoral manipulation of food.

The role of the teeth in chewing has been studied extensively; however, less attention has been paid to soft tissue function. In this study the process of mixing within the bolus and the contribution of the cheeks to this process were investigated using a test food constructed from two differently colored chewing gums. A cheek guard was placed into either the left the or right buccal sulcus. Eighteen dentate subjects were instructed to chew four samples of gum for 30 strokes, two samples with the cheek guard in place and two without. Upon completion, the gum was removed from the mouth and its length was measured. The bolus was then placed into a plastic bag and flattened. Pairs of flattened samples chewed with and without the cheek guard in place were then assessed by five judges who were asked to identify which of each pair was most mixed. Inhibition of the cheek during chewing resulted in significantly longer samples, which were also less mixed.

Sensory correlation of glucose levels in a starch-based semi-solid model system before and after alpha-amylase breakdown.

In this study a diabetic glucose monitor was used to measure the glucose content of 40 model vanilla custard desserts, these were compared with sensory ratings from a trained quantitative descriptive analysis panel. Stimuli varied in starch type, concentration and homogenisation but had identical sugar, flavour and fat contents. Despite this, mean sensory ratings of sweetness varied from 21 to 43 on a 100-point scale. Glucose levels in the stimuli were measured, in vitro, before and after the addition of 0.1% whole human saliva to the product. In all cases glucose concentration increased after the addition of saliva as starch was converted to glucose. There were highly significant correlations of some odour, flavour, mouth feel and after-feel attributes with glucose concentration. The correlation of sweet flavour with glucose concentration was higher in unmodified stimuli than in stimuli with added saliva, suggesting that sweetness is perceived soon after ingestion. Additional glucose produced through starch breakdown appeared to have a relatively small impact on the sensory scores of the stimuli.

Instrumental and sensory quantification of oral coatings retained after swallowing semi-solid foods.

After a mouthful of food has been swallowed, some food material is always retained in the mouth. With semi-solid foods this is in the form of a coating that adheres to the oral mucosa. The amount and location of this material may play an important role in food sensations. In this study two quantitative methods of describing the coatings, generated by a set of 16 model custards varying in degree of lubrication (fat content) and degree of viscosity (starch concentration) are investigated. In the first method, a trained quantitative descriptive analysis panel (N=8) was instructed to take single mouthfuls of semi-solid foods, swallow and then rinse twice for 5s with water and spit out. The turbidity of the rinse water was then measured. During the same session, sensory assessments of the products were obtained. In the second method the thickness of the coating on the anterior and middle one-thirds of the tongue was quantified using a pair of opto-electronic reflectance sensors mounted on a probe which was placed on the tongue, one sensor measuring the anterior part of the tongue the other the posterior (middle third) of the tongue. Turbidity of the first rinse related strongly to the food's viscosity, as well as to sensory attributes associated with the food's fat content and viscosity, such as perceived thickness, creaminess and fattiness. Turbidity of subsequent rinses related primarily to fat content. These results indicate that turbidity of rinse water is a useful tool in fundamental (e.g., food texture research) as well as applied research (e.g., product development and quality assurance in food industry). Reflectance varied primarily with fat content and did not relate well to sensory attributes.

Do tastants have a smell?

The stimuli used in taste research are usually considered to be odourless. This was tested in two experiments with aqueous solutions of two representative compounds for each of the five taste qualities including umami. In the first experiment elderly and young subjects rated the intensity and pleasantness of three concentrations of the stimuli, while wearing or not wearing a noseclip. Saliva production was also measured. Blocking olfaction only influenced salivation for umami. It reduced taste intensity ratings, but as in an earlier experiment with the same compounds in food products, this effect was stronger in the young, who also liked the stimuli better wearing the noseclip. In the second experiment, another group of young people tried to detect the odours of the tastants dissolved in demineralized, double-distilled or Evian water. A considerable number of subjects could regularly detect seven of the ten tastants by olfaction and the extent to which they did correlated significantly with the reduction in taste intensity ratings for the different tastants found in the first experiment. We suggest that most tastants can be smelled and that this smell contributes to taste intensity ratings.

Abrasives in foods and their effect on intra-oral processing: a two-colour chewing gum study.

In this study we suggest that the presence of abrasives in food items lead to physiologic responses that reduce the amount of tooth loss because of abrasion. Subjects were presented with two pairs of two-colour chewing gum, one sample had 0.5 g of an abrasive powder added. Subjects were instructed to chew for 10 or 20 chewing strokes and then remove the gum. After removal the chewing gum was placed in a plastic bag and flattened. Each pair of gums was compared on the basis of the amount of mixing observed. In all cases the addition of the abrasive powder resulted in slower chewing and less mixing. Salivary flow rate increased from a resting value of 0.6 to 0.9 mL min(-1) when stimulated by the non-abrasive gum to 1.1 mL min(-1) with the abrasive gum. This difference was significant (P < 0.05). We conclude that when abrasive particles are detected in the mouth, less bolus manipulation is performed and more saliva is secreted. These responses would have the effect of reducing loss of tooth substance at the expense of reduced cominution of the food.

Simulated digestion status of intact and exoskeletally-punctured insects and insect larvae: a spectroscopic investigation.

In this study, we tested the hypothesis that puncturing the chitin exoskeleton of insect and insect larvae food sources aids the ingress of digestive fluids and increases the rate of digestion and energy uptake in insectivorous mammals. For this purpose 10 crickets (Acheta domesticus) and 10 mealworms (Tenebrio molitor larvae) were divided into two groups of 5; one group was punctured using a small blade to mimic the effect of a single bite, the remainder serving as controls. The insects were then individually immersed in 5 ml of a 1 x 10(-2) mol.dm(-3) solution of hydrochloric acid (pH 2.0) for a period of 2 h in order to mimic digestion in the stomach. The matrix was then centrifuged and the supernatant fluid subjected to spectrophotometric and high-resolution proton (1H) NMR analysis. Electronic absorption spectra of these supernatants revealed that puncturing the exoskeleton of mealworms and crickets gave rise to substantial elevations (up to 14-fold) in the concentrations of UV-absorbing biomolecules (p < 0.025 for both species). The 400-MHz 1H NMR profiles of supernatants derived from mealworm and cricket specimens with punctured exoskeletons contained a wide variety of prominent biomolecule resonances, whereas those from unpunctured (control) insects contained signals of a much lower intensity, ascribable only to selected biomolecules. We conclude that puncturing the cuticle of insects and insect larvae prior to swallowing confers significant nutritional advantages over swallowing prey whole.

The influence of density and material on oral perception of ball size with and without palatal coverage.

The size of a bolus determines how it will be manipulated in the mouth and swallowed. Ten healthy individuals assessed the size of ball bearings of five sizes (4-11 mm diameter) and four materials with different densities in order to investigate the effect of weight on oral size perception. To study the role of the tongue and palate, the experiment was performed with and without a custom-made plastic palate. The results revealed that size itself determines size perception, and that material and weight are negligible factors. An illusional effect in the direction of under-estimation was found for the ball bearings, especially for the small sizes up to 8 mm diameter. While wearing a plastic palate a significant improvement (P<0.05) occurred; the participants performed better and there was less under-estimation. An explanation for this could be that only a minor part of the total area of the ball bearing touches the palate and is hence detected, while the tongue alone is more compliant and thereby able to sense the ball's whole size.

"The first bite of the cherry": Intra-oral manipulation prior to the first bite in humans.

The breakdown of food in the mouth during mastication can be described in terms of two parameters: a breakage function, which describes the fragmentation of food after a bite, and a selection function which defines the probability of particle fracture. The non-zero value of the selection function depends on the manipulation of food particles by the tongue. Little, however, is known about this. As a first step, this study investigated the manipulation of wax sheets of differing sizes and shapes by the tongue after ingestion. It was found that subjects tended to orientate rectangular and square wax wafers so that the long axis of the particle was parallel to the tooth row, independent of the initial orientation given when they were introduced into the mouth. Circular wafers were randomly oriented relative to initial orientation. If this could be extrapolated to the start of mastication, then it suggests that the tongue tends to align food particles so that the post-canines produce close to the greatest surface area possible by fragmenting them along their longest axis.

Saliva tannin interactions.

Many plant foods contain tannins, compounds that bind proteins, such as mammalian enzymes. Although described as tasteless, tannins can be detected orally by their astringency. However, the actual mechanism of oral detection and the effect of tannins on mastication and swallowing have been little investigated. Here, we show from in vitro tests that tannic acid, a common standard in tests used to detect tannins, significantly reduces the lubricating qualities of human saliva both by decreasing its viscosity and increasing friction, both factors lending support to the notion that astringency is a tactile phenomenon. From the literature, it is clear that this effect depends on the presence of salivary proline-rich proteins (PRP). In a mammalian context, ingestion of tannin-rich foods in a species with salivary PRP will be signalled by interference with bolus formation during mastication while the increase in friction may also be detectable and lead to increased tooth wear if the signal is ignored. In a human context, cross-cultural preferences for tannin-rich beverages such as tea, coffee and red wine at the end of meals may be explained by reduction in adhesion of food particles to the oral mucosa allowing their rapid oral clearance.

Bolus dimensions in normal chewing.

Samples of 17 different types of chewing gum weighing between 0.3 and 22 g were presented to eight subjects. After chewing the samples for between 20 and 100 strokes the boluses of gum were removed from the mouth and their length was measured. Bolus length increased with weight from 0.3 to 4 g, but remained constant between 4 and 18 g at which point it began to increase once more. The range of sizes associated with this plateau is similar to the range of sizes of natural bites with other foods.

Computer aided gnathosonic analysis: distinguishing between single and multiple tooth impact sounds.

Watt developed a classification of tooth contact sounds that distinguished between the short sharp, reproducible sounds heard when the teeth meet simultaneously and the dull prolonged, poorly reproducible sounds heard when tooth contacts are sequential. However, when a large occlusal prematurity, for instance a high restoration, is introduced, tooth contact sounds are also short sharp and highly reproducible. In this study, a method of distinguishing single from multiple tooth contact sounds is described, based on an analysis of the phase and amplitude of sounds detected by headphones placed over the ears.

Quantitative evaluation of the effect of bolus size and number of chewing strokes on the intra-oral mixing of a two-colour chewing gum.

One of the major aims of the dental profession is the maintenance of oral function, specifically chewing ability. However, there are no generally accepted measures of chewing ability or even general agreement as to what level of tooth loss is deemed to require clinical intervention. There is therefore a need for simple objective tests of oral function. In this study a modification of the two-colour chewing gum test devised by Liedberg & Owall (1991, 1995) is described. In this test chewing gum containing two contrasting colours is chewed. On removal from the mouth the bolus is placed in a transparent plastic bag, flattened and a digital image is taken. Several image processing techniques are described and evaluated as measures of the amount of mixing present in the chewed gum. Flattening the gum was found to increase the accuracy of subjective evaluation, which was similar to that achieved by the image processing techniques.

Food properties that influence neuromuscular activity during human mastication.

The rate of breakdown of food in mastication depends on the ratio of two mechanical properties of the food--the toughness and modulus of elasticity (Agrawal et al., 1997)--a result which can be predicted by an analysis of the energetics of fracture. The work input to produce food fragmentation is provided by the masticatory muscles, the activity levels of which depend on sensory feedback from the mouth. Here, we test the hypothesis that the activity of a representative of this musculature is modulated by the above combination of food properties. The surface electrical activity (EMG) of the anterior temporalis muscles of ten human subjects was recorded while subjects chewed standardized volumes of 15 food types. The integrated EMG in these muscles was highly significantly related to the square root of the ratio of the above two food properties. Significant correlations were found between this food property index and integrated EMG, both when data for all chews and all subjects were lumped together (r = -0.86; p < 0.0001) and when correlation coefficients between the index and EMG were plotted for each chew made by each subject. Except for two subjects in the first chew, these coefficients reached and maintained highly significant levels throughout the masticatory sequence. Thus, a clear relationship between the electrical activity of a jaw-closing muscle and the mechanical properties of food has been found for the first time.

Subjective assessment of temporomandibular joint sounds.

If it could be shown that the human ear was sufficiently sensitive to describe TMJ sounds, there would be no need to use sophisticated electronic equipment to analyse the sounds. To test this, the ability of normal listeners to distinguish the subtle changes in position, pitch, duration and latency present in TMJ sounds is measured using triangle tests to determine the just-noticeable differences. The results suggest that the human ear is a rather poor instrument for describing subtle differences in the position, duration and latency of TMJ sounds, but is capable of detecting small differences in frequency. It is therefore doubtful that the human ear can distinguish the reciprocal click associated with disc displacement with reduction from clicks due to defects of form on the basis of their relative position in the envelope of movement.

Autocorrelation of acoustic signals from the temporomandibular joint.

Although there have been many investigations of TMJ sounds in the time and frequency domains, no previous reports have been found of investigations of the autocorrelation spectra of these sounds. In the present study, TMJ sounds were digitized at 1.7 kHz and 300 ms samples containing either clicks (single short duration sounds), crepitus (long duration continuous sounds) or creaks (a series of two or more clicks) were selected. These samples were compared with sounds of known origin: tooth impact sounds, frictional sounds elicited by scratching the head, and bruxing sounds resulting from stick-slip friction as teeth were slid against one another under high pressure. There were clear qualitative and quantitative differences between the autocorrelation spectra of the three types of TMJ sounds. Clicks were similar to tooth impact contact sounds, creaks were similar to the bruxing sounds, and crepitus was similar to the scratching sounds. The repetition rate of creaks was 16 Hz (s.d. 9 Hz), this being similar to the resonance of the mandible about the condylar axis. It is suggested that the creaks are due to stick-slip friction in the lower joint compartment of the TMJ.

Physical mechanisms involved in the genesis of temporomandibular joint sounds.

Several different mechanisms are potentially capable of generating sounds in the temporomandibular joint (TMJ). These include impact, sliding and stick-slip friction, fluid dynamic effects and the release of elastic strain energy. It is the aim of this paper to provide a framework with which to separate sounds resulting from the different underlying causes. Each mechanism is described and its relevance to TMJ sounds and clinical significance discussed. Since it is not possible to observe these mechanisms in vivo the arguments are based mainly on analogies which are used to make predictions of the characteristic acoustic signatures of the sounds produced by these different mechanisms. In particular the changes in the characteristics of the sounds as parameters such as mandibular speed and loading are stressed. It is suggested that single short duration sounds (clicks) are due to impact, multiple short duration sounds (creaks) to stick-slip friction and defects of form and long duration sounds (crepitus) to simple sliding friction. Several other mechanisms which have no obvious clinical significance but which are capable of producing similar sounds are also described and methods of distinguishing them from the sounds that do have clinical implications are discussed.

Techniques for rapid quantitative assessment of activity levels in small-group tutorials.

Two techniques for the rapid quantitative analysis of student participation in small-group teaching were investigated. In the first approach an observer, who also acted as a 'critical friend', recorded the length of individual contributions using a computer keyboard as a simple timing device. In the second approach, small-group sessions were recorded with a portable stereophonic audiotape recorder. The teacher was recorded on one channel, all students on the other. A computer program produced automated analysis of these small group interactions by computing relative amount of speech on each channel. Simple analysis produced automatically by the programs revealed the overall style of the tutorial--variably 'mini-lectures' by teachers with very little participation by the student body, rapid 'question and answer' sessions with about equal teacher/student body involvement or 'mini-presentations' by students with the teacher offering sparse comments in the manner of a facilitator. By presenting results in a graphic format, teachers can be given rapid objective feedback on their teaching style. Coupled with short verbal/non-verbal quizzes at the end of tutorials and information from other assessments, the value of using levels of participation as a measure of the efficiency of such small-group sessions can itself be assessed.