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Saliva is expected to be of significance for the perception of food stimuli in the mouth. Mixing the food with saliva, including breakdown and dilution, is considered to be of large importance for semi-solids as these products are masticated without chewing. It is known that there are large variations in composition of saliva originating from different glands and different subjects. In this study we investigated how variations in salivary characteristics affect sensory perception. Eighteen trained subjects participated in the study. Saliva was collected at rest and during three types of stimulation (odour, parafilm chewing and citric acid), and flow rates were determined. The collected saliva was analyzed for protein concentration, buffer capacity, mucin level and alpha-amylase activity. The salivary components measured in this study varied considerably among subjects, but also within subjects as a result of different means of stimulation. Variations in salivary components were correlated with sensory perception of a number of flavour, mouth feel and after feel attributes in the semi-solids mayonnaise and custard dessert. Total protein concentration and alpha-amylase activity were observed to correlate most strongly with texture perception.

The role of salivary alpha-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 alpha-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.

We determined the salivary flow rate in 16 healthy subjects in rest and while chewing artificial and natural foods (Parafilm, Melba toast with and without margarine, and three different volumes of breakfast cake and cheese). We also determined the duration of a chewing cycle, the number of chewing cycles until swallowing, and the time until swallowing. The physical characteristics of the foods were quantified from force-deformation experiments. The flow rates of the saliva as obtained without stimulation, with Parafilm stimulation, and with chewing on the various foods were significantly correlated. An increase in chewing cycle duration, number of chewing cycles until swallowing, and time until swallowing was observed as a function of the volume of the food. More chewing cycles were required for Melba toast than for an equal volume of cake or cheese. This may be caused by the low water and fat percentage of the Melba toast. The number of chewing cycles and the time until swallowing significantly decreased when the Melba toast was buttered. The decrease may be caused by facilitation in bolus formation and lubrication of the food due to buttering the toast. The number of chewing cycles until swallowing was not correlated to the salivary flow rate.

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.

In the oral cavity, the food is subjected to several mechanical and chemical processes. It is fractured by the teeth, diluted and broken down by saliva, heated or cooled by the ambient temperature of the mouth, formed into a bolus and finally swallowed. Numerous receptors in the oral cavity and nose respond to the initially ingested food and monitor the changes during processing. This leads to central perceptions of taste, odor, irritation and texture of the food. Most sensations associated with food texture occur only when the food is manipulated, deformed or moved across the oral receptors. In addition, people assessing the same stimulus differ in their ratings of that stimulus and their oral physiological parameters also exhibit inter-individual variations. This paper is based on the PhD thesis of one of the authors. It gives an overview of this study and includes related work of other authors. The aim of our research was to improve the understanding of oral texture perception, in particular to examine the role of oral physiological processes in oral texture perception of semisolids and to investigate whether individual differences in perception could be attributed to differences in oral physiology among subjects. The results of our study demonstrate that oral physiological parameters such as oral sensitivity, tongue movements, temperature and saliva composition are of importance for texture perception of semisolids. Many parameters of oral physiology correlate with various perceived texture attributes. This implies that intra-individual differences in texture perception could be attributed to variations in oral physiology. Oral physiology thus plays a role in texture perception of semisolids and should be taken into account in future texture research. PRACTICAL APPLICATIONS By understanding the processes in the mouth while eating, a better understanding of the sensations and the perceptions of the food can be gained. Taking for each food the relevant physiological parameter into consideration when performing and designing rheological/instrumental measurements grants more natural conditions and better predictions of sensory perception. This could save time and money on time-consuming and expensive sensory panels in the earlier steps of product development and renovation. Knowing how physiological processes highlight specific flavor/texture sensations may be useful for product development or quality control where one typically wants to focus on certain sensations and ignores others. In addition, a future application could be to tailor products for personalized nutrition, individual choices or clinical nutrition based on physiological groups. [ABSTRACT FROM AUTHOR]

The production of a sufficient amount of saliva is indispensable for good chewing. In the present study, we examined the hypothesis that adding fluid to a food will facilitate the chewing process, especially for dry foods. The effect might be larger for subjects with relatively low salivary flow rates. Furthermore, adding fluids that contain mucins or α-amylase may have a larger facilitating effect on mastication than the addition of water alone. Twenty subjects chewed on melba toast, breakfast cake, carrot, peanut, and Gouda cheese. In addition, they chewed on these foods after different volumes of water, artificial saliva containing mucins, or a solution of α-amylase had been added. Muscle activity and number of chewing strokes until swallowing were measured. The salivary flow rates of the subjects were also determined. Adding fluid to the food significantly reduced the number of chewing cycles and total muscular work (i.e. the integrated surface electromyograpy of masseter and temporalis muscles measured bilaterally, summed for all chewing cycles) until swallowing for all foods, except carrot. The largest effects were observed for melba and cake, which are dry products requiring sufficient saliva to form a coherent bolus safe for swallowing. More facilitation of the chewing process was observed after adding fluid to breakfast cake for subjects with relatively low salivary flow rates. The type of fluid had no significant effect on the chewing process. [ABSTRACT FROM AUTHOR]

Summary: The urge to swallow food could be triggered by a threshold level in both food particle size and lubrication of the food bolus. Thus, both oral physiology and product characteristics may influence the swallowing threshold. We quantified the swallowing threshold in a group of 266 healthy adult subjects (age 42±12 years) by counting the number of chewing cycles needed to prepare food for swallowing. The influence of oral physiology on the swallowing threshold was determined by measuring salivary flow rate, maximum bite force and masticatory performance. We used about 10cm3 of bread, toast, melba toast, breakfast cake, peanuts and cheese to determine the influence on the swallowing threshold of various food characteristics, e.g. hardness, moisture and fat. Furthermore, we tested the effect of buttering the bread, toast, melba toast and breakfast cake on the swallowing threshold. Salivary flow rates were significantly and negatively correlated with the number of chewing cycles of melba toast and breakfast cake. Hence, subjects with more saliva needed less chewing cycles for these dry products. Maximum bite force and masticatory performance had an influence on the swallowing threshold for the hard products only (carrot and peanut). Although significant, the correlation coefficients were less than 0.28. Thus, the oral physiology parameters explained less than 10% of the variance in the swallowing threshold. We found significantly different numbers of chewing cycles for the various foods, ranging from 17 for cake to 63 for carrot. Hard and dry products needed more chewing cycles until swallowing. Buttering the food significantly reduced the number of chewing cycles needed before swallowing. This was especially true for the dry products cake, melba toast and toast. Hard and dry products require more chewing cycles and longer time in mouth until swallowing for sufficient breakdown to take place and for enough saliva to be added to form a coherent bolus safe for swallowing. In spite of this, more saliva, higher maximum bite force and better masticatory performance were only weakly correlated with a smaller number of chewing cycles. Butter enhanced lubrication and bolus formation of dry products, thus reducing the number of chewing cycles until swallowing. In conclusion, product characteristics and to a lesser extent oral physiology significantly affect swallowing threshold. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]