An in vitro evaluation system of food texture was developed using artificial tongue and a conventional uniaxial compression apparatus to mimic the tongue-palate compression. Deformation behavior of agar gels on artificial tongues from silicone rubber with three levels of elastic modulus was observed during compression by a nondeformable plate. The results were compared with the oral strategy for size reduction from sensory evaluation by human subjects. Agar gels fractured upon compression when the strain of the gels was larger than that of artificial tongue, whereas they did not when the strain of the gels was equivalent to or smaller than that of the artificial tongue. When apparent elastic modulus of artificial tongue was approximately 5.5 ¥ 10 4 Pa, fracture profile of the gels corresponded well to human tests. Results suggest that the oral strategy for size reduction might be determined by sensing the relative strain of the gels to the tongue during compression to a somewhat small strain.
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.
Ultrasound elastography as a simple and noninvasive method was used to evaluating the texture of gels. Three gellan gum gels with different mechanical characteristics and sonagel which has the similar elastic modulus to that of the human tongue were used. The combination of sonagel and gellan gels was lightly compressed and released cyclically with an ultrasound probe with 1-2 Hz. We obtained the strain for each cycle, and analyzed the results using the maximum values of strains. We found that the strain ratio between the gellan gel and the sonagel increased with the decrease of gellan gel fracture force. And also the oral strategy changes from teeth mastication to tongue-palate compression with the increase in the strain ratio. Strain obtained by ultrasound elastography is revealed as an important parameter that indicates the mechanical characteristics and even oral strategy of gels.
PRACTICAL APPLICATIONSInstrumental methods are often used for texture characterization. Normally, probes are made of metal or plastic materials that are much stiffer than foods and completely dissimilar to the tongue. As a noninvasive method, ultrasound tissue elasticity imaging has provided novel diagnostic information regarding tissue diseases. We suggest that ultrasound elastography can be used for food texture evaluation in the present study. It is possible to observe deformation behavior as the tongue-palate compression if the material whose mechanical characteristics is similar to the human tongue was used as an artificial tongue in the method.
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