Effect of ultrasonic treatment on the rheological property and microstructure of tofu made from different soybean cultivars

• Ultrasonic-treated tofu had the rheological property different from the heat-treated tofu.
• The rheological property of tofu were affected by the sonication time and temperature.
• Ultrasonics is a time-effective method for tofu making as compared to current technology.

Effect of high intensity ultrasound (HIUS) treatment on the rheological property and microstructure of tofu made from yellow and black soybeans was investigated. Raw soymilk was either heated at 95 °C for 10 min, or HIUS treated at 25 and 50 °C for 5, 15, and 30 min, and then was coagulated by adding Glucono-δ-lactone (GDL) to produce tofu. Results showed that HIUS denatured the soy protein and was confirmed by the changes in protein surface hydrophobicity. The HIUS-treated soymilk and the heat-treated soymilk expressed different gelation behaviors, which led to distinct rheological property and microstructure in the final products. The network of tofu prepared with HIUS-treated soymilk was constructed by thicker strands in a loose arrangement. The rheological property and microstructure of HIUS-treated tofu can be modified by changing the sonication time and temperature. The tofu made form soymilk with HIUS at 25 °C for 15 min gave the best rheological property.Industrial relevanceTofu is a widely accepted and commonly manufactured soy product in Asia. The worldwide tofu consumption is increasing due to its unique texture and health benefits. However, the thermal process of soymilk during tofu making is time and energy consuming. HIUS is a more efficient and environment-friendly technology that can be commercially applied as an energy and labor saving alternative to the conventional thermal treatment. The rheological property and microstructure are two important parameters for the gel texture evaluation. This research paper presents a comparative study between soymilk treated by heating and by HIUS using yellow soybean and black soybean to produce tofu with unique rheological property. Finding in this research gave the primary knowledge for further application of HIUS on tofu processing.