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 forlower-level undergraduates in organic chemistry or biochemistry coursesto help them understand the chemistry principles that underlie thecurdling step in tofu processing. Raw soymilk is relatively stablewithout heating, even with the addition of coagulants. However, heattreatment denatures the soy proteins in soymilk, which makes themmore amenable to coagulation. This coagulation is further promotedwith salt coagulants, such as calcium gluconate, zinc gluconate, andcalcium 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 curdlingmechanism in this work. This demonstration can also be used as anat-home experiment during lab closure situations, such as a pandemic,and can arouse students' curiosity about the coagulation ofother food proteins and the process of making alternative tofu.