Easiness of ingestion and palatability of rice crackers for aged people were studied using compression test, electromyographic (EMG) recordings of masticatory muscles and sensory evaluation. Five types of rice crackers with different hardness were evaluated, which were Kaihatsu-type newly developed for aged people, Souka-type, Okaki-type, Niigata-type and Baby-type.
The results obtained are as follows.
1. Hardness of rice crackers was a most important factor decides whether aged subjects can ingest them.
2. Hardness (Young's modulus) of rice crackers was as follows, Souka-tupe> Okaki-type> Niigata-type> Kaihatsu-type = Baby-type. These results corresponded to the results of sensory evaluation in hardness during mastication of rice crackers by young subjects (n = 66).
3. Aged subjects were able to ingest Kaihatsu-type and Baby-type. Those Young's modulus were less than 8.56 x 10⁶N/m.
4. Young's modulus (x) of rice crackers was significantly related to sum of masseter muscle activity (y), y = 0.15x +1.52 (R² = 0.83, p <0.05). The harder rice crackers were, the more sum of masseter muscle activity increased.
5. The harder rice crackers were, the more those chewing time and sum of masseter muscle activity increased. Because those number of chewing strokes increased.
6. Hardness of rice crackers caused trouble for aged subjects at the stage of intake. Harder rice crackers tended to increase first activity of masseter muscle and burst duration per chewing.
7. Texture was the most important factor in palatability for rice crackers.
8. Both young and aged subjects evaluated that Kaihatsu-type were better than Baby-type in all items of palatability.
These results showed that Kaihatsu-type had palatability for aged people and texture properties which were easy to ingest.