Relationship of Heating and Cooling Condition to Hardness of Tofu

Studies on the preparing conditions of soybean milk for Tofu making (Part II)

Abstract

Tofu-gel prepared with soybean milk which was heated at 100°C for long time, was softer than usual preparations. This is due to the oxidation of sulfhydryl groups of soybean protein during the heating. Blowing nitrogen gas into soybean milk before heating increased the hardness of the gel by preventing the oxidation of sulfhydryl groups. Protein solution immediately cooled to 60-70°C had much more sulfhydryl groups than that cooled to 80-90°C, and the tofu-gel prepared with the former protein solution was harder. Soybean milk obtained by filtering the mash heated at 60-80°C, was higher in yield than that obtained from the mash heated at 100°C or unheated. From these experimental results reasonable heating process of soybean milk for tofu making are as follows, after heating mask at 70°C, filter it to get soybean milk, heat the soybean milk at 100°C and cool to 70°C for coagulation.