Crack expansion dynamics of freeze-dried soybean curd during rehydration

• Published in: FOOD SCIENCE AND TECHNOLOGY RESEARCH Vol. 30; no. 3; pp. 295 - 303
• Main Authors: Hirakawa, Mai, Teshima, Hideaki, Ikuta, Tatsuya, Takahashi, Koji
• Format: Journal Article
• Language: English
• Published: Tsukuba Japanese Society for Food Science and Technology 2024; The Japanese Society for Food Science and Technology; Japan Science and Technology Agency
• Subjects: Body temperature; Breakage; Cracks; environmental scanning electron microscopy; Food processing; Freeze drying; freeze-dried foods; High temperature; Moisture content; morphology; Rehydration; Scanning electron microscopy; soybean curd; Soybeans; Stress concentration; Temperature requirements; Tofu; Water content; Water temperature
• ISSN: 1344-6606; 1881-3984
• DOI: 10.3136/fstr.FSTR-D-23-00230

In contrast to the freeze-drying process, the rehydration process of freeze-dried foods remains unclear. This study investigated the rehydration of freeze-dried soybean curd, also known as tofu, and elucidated its breakage mechanism during rehydration, which impairs texture. The rehydration of freeze-dried tofu was observed at different water temperatures (20, 40, 70, and 100 °C), with the required rehydration time found to decrease with increasing water temperature. Furthermore, tofu was found to absorb water faster in cracks formed during production than in the porous body. Crack expansion was observed only in high-temperature water, leading to breakage of the tofu. Environmental scanning electron microscopy revealed that tofu expanded when a sufficient amount of water was absorbed. Accordingly, crack expansion in high-temperature water is attributed to the stress concentration at the tip of the crack, which is caused by differences in the rehydration rate and resulting stiffness between the porous body and cracks.