Texture Discrimination of Agar Gels in Rats

Food texture is a pivotal factor influencing consumer preference, acceptance, and eating experience. Although human sensory studies have underscored the importance of the sensations of springiness and hardness in mastication and swallowing, the underlying mechanisms remain unknown due to the lack of an animal model. We therefore hypothesized that rats can discriminate textures based on mechanical properties-springiness and hardness-independent of taste, odor, and visual cues. To investigate texture perception, we evaluated rats' discrimination of agar gels using a conditioned texture aversion paradigm with a two-bottle preference test. Agar gels at 1%–3% concentrations were cut into 5 mm cubes or strained through a 100-mesh sieve to form paste. In the two-bottle preference test comparing 1% and 3% agar cubes, the conditioned stimulus (CS) applied to the cubes induced selective aversion to the CS cubes, but the CS applied to the paste form eliminated this aversion. Moreover, to exclude taste or odor cues, gelatin cubes with physical properties similar to those of the 3% agar cubes were prepared, and conditioning with these gelatin cubes induced aversion to the 3% agar cubes. To eliminate visual cues, resin cubes resembling agar cubes were prepared; however, conditioning with the resin cubes did not produce aversion to agar cubes. These results indicated that aversion learning to the agar cubes was acquired based on textures rather than taste, odor, or visual properties. The newly developed experimental system offers a valuable framework for exploring mechanisms of food texture perception and guiding the development of texturally optimized food products.