Compression test of soft gellan gels using a soft machine equipped with a transparent artificial tongue

A soft machine system (texture analyzer equipped with an artificial tongue) was developed to analyze the occurrence of fractures in soft food gels compressed between the tongue and hard palate. Artificial tongues were newly designed with a modulus similar to that of a somewhat tense human tongue, using transparent urethane gels. A model of soft foods that are easy or difficult to crush with the tongue was prepared using gellan gums at different concentrations. A piece of gellan gum gel was uniaxially compressed on an artificial tongue with the flat probe of a texture analyzer. The food gel and artificial tongue were deformed, leading to the fracturing of food gels alone. During compression-induced fracture, the softer food gels exhibited a lower force, lower displacement, and lower true stress than the harder gels on all artificial tongues. The fracture probability of gellan gels was lower for the combination of harder food gels and softer artificial tongues, as softer materials can deform to a larger extent. Fracture displacement of food gels was increased as the modulus of the artificial tongue decreased; however, the fracture force did not differ significantly. These results suggest that an artificial tongue with elastic modulus values similar to those of the actual human tongue is suitable for determining the fracture behavior of foods during compression between the tongue and hard palate.