Texture Evaluation of Soft Gels with Different Fracture Strains using an Artificial Tongue

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Abstract
The structure of soft foods with similar fracture forces may be destroyed by compression between the tongue and palate or mastication during natural oral processing. Our objective was to identify the mechanical properties determining the oral strategy for the initial size reduction of soft gels. Three gellan gels with an equivalent fracture force and different fracture strains were evaluated by instrumental compression testing and sensory evaluation. In addition, a combination of a gellan gel and a sonagel, which has an apparent elastic modulus similar to that of the human tongue, was subjected to a compression test and ultrasound (US) elastography. The fracture profile of the gellan gel on the sonagel in the instrumental compression test corresponded to the oral strategy. The strain ratio of the gellan gel to the sonagel observed in US elastography had a high linear correlation with the reciprocal of the apparent elastic modulus of the gellan gel. The oral strategy of gels changes from tongue–palate compression to mastication with increasing apparent elastic modulus or decreasing the relative strain against the sonagel. The results reveal that the apparent elastic modulus influences the oral strategy for the natural consumption of gels although a threshold value was not clearly determined in conventional compression testing using hard materials.Practical Applications: An appropriate care food that can be consumed using compression between the tongue and hard palate without chewing is increasingly required in an aging society. Instrumental methods are often used for texture characterization of such foods. Probes are usually made of metal or materials that are much stiffer than foods and completely dissimilar to the tongue. Ultrasound (US) elastography can detect the strain ratio between food gels and a sonagel, which is used as an artificial tongue in this study. We suggest that the strain ratio obtained from US elastography can be used to evaluate the deformation behavior of soft foods and a soft material whose mechanical characteristics are similar to those of the human tongue. As the strain ratio was highly correlated with the reciprocal of the apparent elastic modulus measured using conventional compression testing, the modulus was an important parameter for selecting the tongue compression.

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