Correlations of sensations of hardness and springiness of agar and gelatin gels with mechanical properties in human participants

Objectives: It is unclear which mechanical properties of foods cause the texture sensation in humans. This study aimed to investigate the relationship between unilateral compression measurements and the sensations of hardness and springiness in gels.

Methods: Three different concentrations of agar and gelatin gels were prepared by the addition of agar (1%, 2%, and 3%) and gelatin (4%, 8%, and 16%) to water or apple juice. In a stress-rupture test, stress-strain curves were obtained by the application of uniaxial compression with a disc plunger at a compression rate of 10 mm/s. The hardness, springiness, and palatability of the gels were evaluated by 12 healthy volunteers using a visual analog scale.

Results: The sensation of hardness was positively correlated with the sensation of springiness for the agar and gelatin gels. Palatability decreased as hardness increased for both gels. In terms of mechanical properties, the sensation of hardness was only significantly correlated with the initial elastic modulus, while the sensation of springiness was correlated with the late elastic modulus and other mechanical properties such as fracture strain, time, and stress.

Conclusions: These results suggest that sensations of hardness and springiness are produced in the initial and late stages, respectively, during the food-crushing process using the tongue, palate, and teeth.