From Soybeans to Tofu: The Underlying Chemistry

Tofu, a traditional Chinese food, is now popular worldwide. However, few people notice the chemistry that is involved in its production. To shed light on this, we have designed a simple demonstration for lower-level undergraduates in organic chemistry or biochemistry courses to help them understand the chemistry principles that underlie the curdling step in tofu processing. Raw soymilk is relatively stable without heating, even with the addition of coagulants. However, heat treatment denatures the soy proteins in soymilk, which makes them more amenable to coagulation. This coagulation is further promoted with salt coagulants, such as calcium gluconate, zinc gluconate, and calcium lactate. Acid coagulants such as white vinegar or grape, orange, and lemon juice can also induce coagulation due to their acidic properties. Based on our results and on previous reports, we illustrate the curdling mechanism in this work. This demonstration can also be used as an at-home experiment during lab closure situations, such as a pandemic, and can arouse students’ curiosity about the coagulation of other food proteins and the process of making alternative tofu.