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Tactile senses hold key to texture perception: Study

By Nathan Gray , 29-Nov-2010

Tactile textures perceived by the tongue and mouth cavity are the main sense responsible for the perception of texture and mouth-feel, according to new research.

It is thought that texture is mainly perceived by the tongue, the parodontal ligament, and tissues lining the oral cavity (known as tactile or mechano-reception), however the authors noted that there may also be kinaesthetic and thermal information and feedback from the oral musculature (known as proprioception).

The study, led by Dr Alexander Kutter, tested which senses have the most influence over texture perception by numbing certain senses with topical anaesthetic whilst comparing samples of vanilla custard with differing textures. The findings, published in Food Quality and Preference, suggest such mechano-sensors in the mouth “are almost exclusively responsible for the sensation of mouth-feel.”

“It has been shown that the proprioception of the tongue has no influence on the perception of the thickness of semi-solid foods, but that the mechano-sensors contribute predominantly to this sensation. This disproves statements made in the literature that claim the opposite,” wrote Dr Kutter and co workers, from the University of Erlangen-Nuremberg, Germany.

They stated that the effect of the rheology of the food on mechano-sensors, has a high impact on the perceived thickness, noting that such issues can now be more accurately addressed during product development.

Sensory evaluation

According to the authors, although sensory tests are already a common tool in the food industry and research, the way in which we perceive the texture and mouth-feel of liquid and semi-solid foods are “still far from being completely understood.”

They note that whilst taste perception is provided solely by specialised receptors on the tongue, texture perception is thought to be a multi-modality of processes based on a number of different sensory systems.

Dr Kutter and colleagues explained, the complex property of ‘texture’ itself “is the result of numerous physical parameters, mechanical stresses and deformations interacting with these sensory systems.”

They added that sensory attributes such as ‘consistency’ and especially ‘creaminess’ are, multidimensional in nature: “which might be ascribed to the fact that more than one sensory system is included in the process of thickness evaluation.”

The new study investigated the impact of two sensory systems (proprioception of the tongue and the tactile senses) on the perception of thickness of semi-solid foods.

“The question to be answered within this work was whether one of the two systems … determines the oral perception of the thickness,” wrote the researchers.

“The idea to achieve this goal was to eliminate the influence of one of these two systems and thus generate comparable data about the remaining sensitivity to texture.”

Study details

Assessments without anaesthesia revealed that that we are able to distinguish small differences in viscosity (100 per cent vs. 95 per cent sample).

The researchers reported that anaesthesia of the palate (reducing proprioception) decreased texture recognition quality. However, after total topical anaesthesia of the oral cavity (numbing tactile senses), they observed that subjects “could hardly distinguish whether there was sample already in their mouth or not.”

“Assuming that the proprioception of the tongue alone is responsible for the sensation of thickness, then anaesthesia of the palate should have nearly no effect (the palate itself has not proprioception). The opposite was the case,” wrote the researchers.

They added that if the tactile senses are the main cause of the thickness perception, then total topical anaesthesia would further decrease the recognition quality, as was seen. leading to the conclusion that tactile senses “are the only reason for perceiving thickness.”

“Even if the proprioception has an effect, it should be negligible,” added the researchers.

“As this study was carried out with a homogeneous semi-solid food (custard), further research will investigate the effect of anaesthesia on the perception of particle-loaded foodstuffs, so that the influence of the particle shape on the perceived grittiness can be extracted, as it is the sum of tactile sensations,” they added.

Source: Food Quality and Preference
Published online ahead of print, doi: 10.1016/j.foodqual.2010.09.006
“Impact of proprioception and tactile sensations in the mouth on the perceived thickness of semi-solid foods”
Authors: A. Kutter, C. Hanesch, C. Rauh, A. Delgado