René A. de Wijk

Effect of bite size and oral processing time of a semisolid food on satiation.

BACKGROUND Food texture plays an important role in food intake regulation. In previous studies we showed a clear effect of viscosity on ad libitum food intake and found indications that eating rate, bite size, and oral processing time (OPT) could play a role. OBJECTIVE The objective was to determine the effect of bite size and OPT of a food on satiation, defined as ad libitum food intake. DESIGN Twenty-two healthy subjects participated in all 7 test conditions. Bite sizes were free or fixed to small bite sizes ( approximately 5 g) or large bite sizes ( approximately 15 g). OPT was free (only in combination with free bite size) or fixed to 3 or 9 s. Subjects consumed chocolate custard through a tube, which was connected to a peristaltic pump. Sound signals indicated OPT duration. RESULTS Subjects consumed significantly more when bite sizes were large than when they were small (bite size effect: P < 0.0001) and when OPT was 3 s rather than 9 s (OPT effect: P = 0.008). Under small bite size conditions, mean (+/-SD) ad libitum intakes were 382 +/- 197 g (3-s OPT) and 313 +/- 170 g (9-s OPT). Under large bite size conditions, ad libitum intakes were much higher: 476 +/- 176 g (3-s OPT) and 432 +/- 163 g (9-s OPT). Intakes during the free bite size conditions were 462 +/- 211 g (free OPT), 455 +/- 197 g (3-s OPT), and 443 +/- 202 g (9-s OPT). CONCLUSION This study shows that greater oral sensory exposure to a product, by eating with small bite sizes rather than with large bite sizes and increasing OPT, significantly decreases food intake.

Investigations on multimodal sensory integration: Texture, taste, and ortho- and retronasal olfactory stimuli in concert

Perceptual interactions between odour and oral texture were explored in a study in which a cream odour was presented ortho- or retronasally at well-defined moments whilst milk-like foods with different viscosities, produced by adding a thickener, were present in the mouth. Gaseous (odour) and liquid (texture) pulses were presented using a specially-developed computer-controlled system of air-dilution olfactometry and pumps. Odour pulses, lasting 2 s, were presented either during a 3-s period in which a liquid filled the oral cavity, during a 3-s period in which the liquid was manipulated orally or during the swallowing of the liquid. Subjects rated the intensity of overall flavour, thickness and creaminess. Perceived flavour intensity was reduced with increasing viscosity of the liquid, irrespective of whether or not the odour was presented ortho- or retronasally. The odour stimulus increased the intensities of thickness and creaminess, but only when the odour was presented retronasally that is as if the odour would have originated from the liquid. Furthermore, this enhancement was most pronounced when odours coincided with swallowing, less pronounced when odours coincided with oral manipulation and absent when presented during mouth filling. The results suggest that cross-modal interactions are the rule rather than the exception, provided that multi-modal sensory integration has occurred.

The role of intra-oral manipulation in the perception of sensory attributes.

To gain insight into the effect of oral processes on perception, we defined a set of five specific oral manipulations and investigated their effects on the perception of low and high fat versions of two semi-solid foodstuffs, vanilla custard desserts and mayonnaises. Behavior modifications ranged from simply placing the stimulus on the tip of the tongue to vigorously moving it around in the mouth. Sensory ratings for mouth-feel and flavor attributes were made 5s after placing the stimulus in the mouth, and after-feel attributes were rated immediately after swallowing. Most attributes showed a similar pattern, with lowest attribute ratings where the tongues movement was restricted and gradually increasing ratings with increasing complexity of the tongue movements. An individuals normal oral processing behavior typically resulted in the most intense sensations of flavor and mouth-feel. Residence time for all mouth-feel attributes, except prickling, was determined by the time required for tongue movements. The exact tongue movements required for sensations appeared to be related to food groups and individual foods, rather than to specific mouth-feel attributes.

The relation between saliva flow after different stimulations and the perception of flavor and texture attributes in custard desserts

Salivary flow rates were measured at rest and after three types of stimulation; odor, Parafilm chewing, and citric acid. The highest flow rate was elicited by citric acid followed by Parafilm and odor, while the lowest flow rate was unstimulated. In order to investigate whether and how the amount of saliva a subject produces influences the sensory ratings, the four types of salivary flow rates were correlated with sensory ratings of three different types of vanilla custard dessert. No significant correlation could be found between any of the salivary flow rates and the sensory ratings. A subject with a larger saliva flow rate during eating did not rate the foods differently from a subject with less saliva flow. The same pattern was seen for all types of stimulation. This finding could indicate that subjects are used to their respective amounts of saliva to such a degree that the differences in sensory ratings between subjects cannot be explained by the interindividual difference in saliva flow rate.

Relating particles and texture perception.

Practically all foods contain particles. It has been suggested that the presence of particles in food may affect the perception of sensory attributes. In the present study we investigated the effect of size and type (hardness and shape) of particles added to a CMC based vanilla custard dessert. The two types of particles included in the study were silica dioxide and polystyrene spheres, varying in size from 2 to 230 microm. Eighteen trained adults participated in the study. They rated the sensation of 17 sensory flavour and texture attributes on a 100-point visual analogue scale (VAS). The results indicate that the addition of particles increased the sensation of roughness attributes and decreased the ratings of a number of presumably favorable texture attributes (smoothness, creamy, fatty and slippery) significantly. These effects increased with increasing particle size up to 80 microm. Roughness ratings deceased for larger particles sizes. Surprisingly, even particles of 2 microm had significant effects: they increased perceived rough lip-tooth feel, and decreased slippery lip-tooth feel and smoothness of the product. The affected attributes had previously been related to lubricative properties of foods. Particles added to semi-solid foods with relatively low levels of fat seem to counteract the lubricating effects of the fat resulting in increased oral friction. In a separate study on size perception the silica dioxide particles were used. By sampling the stimuli between the tongue and palate, subjects rated the size of the particles on a 100-point scale in comparison to anchor stimuli containing no particles and particles of 250 microm. The perceived particle size significantly increased for larger particles. Furthermore, perceived particle size was negatively correlated with roughness ratings. Thus, subjects who were sensitive and perceived the particles as being relatively large reported the same stimuli to have less rough after-feel. In conclusion, particles added to a product induce large effects on texture sensations, and texture sensation is related to individual size perception.

The role of α-amylase in the perception of oral texture and flavour in custards

The role of salivary α-amylase in odour, flavour, and oral texture sensations was investigated in two studies in which the activity of salivary amylase present in the mouth of human subjects was either increased by presenting custards with added α-amylase or decreased by presenting custards with added acarbose, an amylase inhibitor. For starch-based vanilla custard desserts, amylase resulted in increased melting and decreased thickness sensations, whereas acarbose had the opposite effect, i.e., decreased melting and increased thickness. Other affected attributes included creamy mouth feel, creamy after feel, and fatty after feel. Creaminess, which is considered to be a highly desirable food quality, decreased by as much as 25% with added amylase and increased by as much as 59% with added acarbose. Neither additional amylase nor acarbose affected sensations for a nonstarch-based carboxy methylcellulose (CMC) vanilla custard dessert. This indicates that the effects of amylase on viscosity-related sensations of starch-based custards, such as perceived melting and thickness, are caused by amylase-induced breakdown of starch. Partial Least Square (PLS) analysis indicated that the effects of amylase and acarbose on perceived creaminess are not only driven by their effects on perceived melting and thickness, but also by their effects on perceived flavour.

A comparison of the effects of added saliva, α-amylase and water on texture perception in semisolids

The effect of adding saliva or a saliva-related fluid (alpha-amylase solution and water) to custard prior to ingestion on the sensory ratings of odour, flavour and lip-tooth-, mouth- and after-feel sensations was investigated. Saliva had previously been collected from the subjects and each subject received his/her own saliva. Sixteen subjects from a trained panel assessed 17 flavour and texture attributes of soy- and milk-based custard desserts. Immediately prior to administration, two different volumes (0.25 and 0.5 ml) of three different saliva-related fluids (saliva, alpha-amylase solution and water) were added to the product. The added volumes represented an approximately 33% and 66% increase of the volume of saliva present in the mouth during ingestion. The results show that addition of a fluid affected the mouth-feel attributes of melting, thickness and creamy. Melting was the only attribute on which the type of fluid had an effect, where saliva elicited a stronger melting effect than the alpha-amylase solution and water. The volume of the added fluid affected a number of attributes (thick and creamy mouth-feel and fatty after-feel). It can be concluded that in general the sensory attributes of semisolids were relatively stable. Mouth- and after-feel sensations were partly affected, while odour, flavour and lip-tooth-feel sensations were not affected by an increase in volume of saliva or other saliva-related fluid during ingestion.

Oral movements and the perception of semi-solid foods

Here we review the role of oral movements in the perception of food attributes, particularly for semi-solid and liquid foods ingested almost in ready-to-swallow form. An overview of a series of instrumental and sensory studies suggests clear links between the type of sensation and the time point of processing in the mouth. Some commonly-reported sensations, such as thickness, are relatively immediate and reflect the bulk properties of food bolus when the food is relatively intact. Others, such as fattiness and melting, reflect both bulk and surface properties and follow considerable oral processing when the food is relatively degraded. Yet others, such as fatty after-feel, are only fully developed after swallowing is complete. In addition, oral processing also plays an important role in the generation of aroma and taste sensations. Most of these in prior vivo studies have now been confirmed by in vitro work using a modified rheometer, dubbed the Structure Breakdown Cell (SBC), wherein the mechanical and enzymatic break-down of food can be monitored directly and related to sensory profiles generated by trained panelists.

Oral processing assessed by M-mode ultrasound imaging varies with food attribute.

Ultrasonic imaging was used to quantify oral movements made during the oral processing of foods while subjects assessed the intensity of the sensory attributes, thick, creamy, sweet and bitter. A series of four stimuli were prepared with high and low viscosities and high and low sweetness. Over five sessions, subjects (N=8) were asked to consume 5 ml spoonfuls of each of the stimuli while holding an ultrasound probe beneath their chin so as to produce a mid-line sagital image of the floor of the mouth and tongue. In the first session, subjects were asked to swallow the sample. In subsequent sessions, subjects were asked to rate one of the attributes, thickness, sweetness, creaminess or bitterness, in random order. The resulting video recordings were subjected to an image-processing algorithm to quantify the amount of intra-oral manipulation performed. The results demonstrated that oral movements varied with attribute, especially in the period during which the bulk of the food is typically processed and the following swallowing phase. The foods sweetness affected oral movements especially during the bulk phase, whereas the foods viscosity primarily affected movements during the following swallowing and clearance phases.

ANS Responses and Facial Expressions Differentiate between the Taste of Commercial Breakfast Drinks

The high failure rate of new market introductions, despite initial successful testing with traditional sensory and consumer tests, necessitates the development of other tests. This study explored the ability of selected physiological and behavioral measures of the autonomic nervous system (ANS) to distinguish between repeated exposures to foods from a single category (breakfast drinks) and with similar liking ratings. In this within-subject study 19 healthy young adults sipped from five breakfast drinks, each presented five times, while ANS responses (heart rate, skin conductance response and skin temperature), facial expressions, liking, and intensities were recorded. The results showed that liking was associated with increased heart rate and skin temperature, and more neutral facial expressions. Intensity was associated with reduced heart rate and skin temperature, more neutral expressions and more negative expressions of sadness, anger and surprise. Strongest associations with liking were found after 1 second of tasting, whereas strongest associations with intensity were found after 2 seconds of tasting. Future studies should verify the contribution of the additional information to the prediction of market success.