Instrumental Uniaxial Compression Test of Gellan Gels of Various Mechanical Properties Using Artificial Tongue and Its Comparison with Human Oral Strategy for the First Size Reduction

Abstract

Instrumental compression test using artificial tongue was carried out to compare the fracture profile of gels with the first oral strategy for size reduction by humans (termed as the first size reduction). Gellan gel samples, whose size and shape were the same as those of artificial tongue, were prepared in a wide mechanical range and were compressed uniaxially on artificial tongue at crosshead speed of 10 mm/s. When apparent Young's modulus of artificial tongue was approximately 55 kPa, fracture probability of gels corresponded to the ratio of subjects who decided to use tongue‐palate compression instead of mastication. This was applicable to the gels whose fracture strain was below 65% but not to the gels whose fracture strain was above 70% within the range of fracture stress tested; approximately 30–100 kPa. Fracture strain should be a critical initial mechanical parameter that relates to the decision of oral strategy. Practical Applications There is an increasing demand for texture‐controlled foods that can be consumed by tongue‐palate compression without the need of mastication as the number of people having oral deficiency is expanding. It is proved that instrumental texture evaluation method that the authors developed is applicable to a wide range of food texture, particularly for viscoelastic gels, with some changes of instrumental operation condition if necessary, providing a simple method for assessing textural acceptability of food products for consumption without using human subjects. From an industrial point of view, this method can contribute to the texture design of food products that are comfortable to eat and thus to the improvement of quality of life for those people. From a scientific point of view, this method can contribute to better understanding of the physiology of human tongue‐palate compression as an oral strategy for size reduction, particularly during consumption of solid or semi‐solid foods.

A Pilot Study on Ultrasound Elastography for Evaluation of Mechanical Characteristics and Oral Strategy of Gels

“…Food texture is a very important cue for human decision‐making to choose an appropriate oral strategy for size reduction, either for tongue–palate compression (for soft foods) or teeth mastication (for hard foods) (Takahashi and Nakazawa ; Arai and Yamada ; Ishihara et al . ). The oral strategy changes from tongue–palate compression to teeth mastication with increasing fracture force in our study.…”

“…A similar conclusion was drawn by Ishihara et al . () in which they observed deformation profiles of gels (agar gels or gellan gels) and an artificial tongue (prepared from silicone rubber) using instrumental compression by the artificial tongue, and found that the strain ratio between gels and artificial tongue increased with the decrease of gel fracture force. US elastography is based on the fact that compression produces strain in various tissues and magnitude of the strain is lower in harder tissues than that in softer tissue.…”

“…A similar observation was made by Ishihara et al . (), where they used three kinds of artificial tongue to investigate the deformation behavior of gels on it at a crosshead speed of 10 mm/s. They reported that the fracture strains of agar and gellan gels increased with fracture force or elastic modulus.…”

“…The process for the preparation and the concentration referred to Ishihara et al . () are shown in Table . We obtained cylindrical gellan gels of different sizes (20 mm in diameter and 10 mm in height and 56 mm in diameter and 10 mm in height).…”

“…Ishihara et al . () developed an in vitro evaluation system of tongue compression of food. They used an artificial tongue made of silicone rubber with three levels of elastic modulus and a conventional uniaxial compression apparatus to mimic tongue–palate compression.…”