An approach to saving energy in Kori-Tofu processing

Consumption of energy was analysed on a kori-tofu plant which processed 6 t of soybeans per day, involving 13 unit operations such as wet-milling, extraction-denaturation of soy protein, coagulation, compression, thawing, and waste-water treatment. Total energy consumption per kg of the dry kori-tofu was 35.4–27.1 MJ of fuel energy and 8.3 MJ of electrical energy. The extraction-denaturation of soy protein consumed twice as much thermal energy as the drying. The waste-water treatment consumed more electrical energy than the whole manufacturing process including the freezing and aging.

Next the reduction of the thermal energy consumption in the extraction-denaturation of soy protein was attempted. The point was to reduce the amount of the extraction water that must be heated to at least 90°C for denaturation of the soy protein. Decrease in the yield of extracted protein was overcome by using multi-extraction. The coagulation was not affected if the ratio of bound calcium to soy protein was controlled at a certain level. The consolidation became easier but its operation had to be adjusted to obtain the same quality of the consolidated cake. The series of investigations suggested that the thermal energy consumption in the extraction-denaturation of soy protein could be reduced to less than one half of the current energy consumption by only improving the extraction-denaturation of soy protein. Cost for a partially optimized sub-system is also discussed.