Tofu is a traditional food invented in China. There are many varieties of tofu today, and their nutritional content varies depending on the processing method.
Traditional tofu is made from ground soybeans with bittern or gypsum as a coagulant. The former is called Northern tofu, and the latter is called Southern tofu. Because Southern tofu uses less gypsum, it is softer (what people call tender tofu), while tofu made with bittern is relatively firmer (what people call firm tofu). Lactone tofu is made using glucono-delta-lactone as a coagulant and water-retaining agents like trehalose and plant gums. Since it does not require pressing and dehydration, the yield is high. It is widely popular for its pure white, delicate texture, moist mouthfeel, and lack of the bitter taste found in Northern and Southern tofu. However, lactone tofu itself has poor structural strength, making it unsuitable for dishes that require methods like flipping and stirring during cooking.
Tofu produced using Japanese techniques—Silken tofu and Momen tofu—are actually Southern tofu and Northern tofu, respectively. The former uses a very fine silk-screen cloth for filtering, resulting in a finer and especially tender tofu. The latter uses a slightly coarser cotton cloth, resulting in a thicker, more substantial tofu.
Soybeans themselves are rich in protein, but it is not easily digested and absorbed by the human body. In processed tofu, the way peptide chains fold within the protein molecule changes, and the structure becomes less dense, greatly increasing the absorption rate of nutrients. The digestibility of cooked soybeans is only 65.3%, while for tofu it reaches 92% to 96%. Furthermore, processed tofu removes the beany flavor and adds a unique aroma.
The nutritional content of tofu made by different methods varies. The protein, fat, calcium, and magnesium contents are highest in Northern tofu, followed by Southern tofu. This is mainly related to the different water content and coagulants used in each type: bittern's main components are calcium chloride and magnesium chloride, while the chemical composition of gypsum is calcium sulfate. Both add beneficial minerals to the tofu. Therefore, tofu not only supplements the body's protein but is also a good source of calcium and magnesium. The coagulant for lactone tofu contains no calcium or magnesium. Selenium, vitamin B1, and niacin content are highest in Southern tofu.
Tofu is the best source of plant protein for people, earning it the reputation of "plant meat." Tofu produced by traditional methods also provides abundant calcium and magnesium for humans. Calcium is an essential element for various physiological and biochemical processes in the body. It maintains the integrity of cell membranes, participates in nerve and muscle activities, and is the main component of bones and teeth. It is the material basis for the growth and development of children and adolescents and for preventing and treating osteoporosis in middle-aged and elderly people. Eating 200 grams of firm tofu can meet one-third of the daily calcium requirement. Magnesium helps relax the tension of arterial vessels, aids in lowering blood pressure, prevents cardiovascular and cerebrovascular diseases, and strengthens bones and teeth. Bean products also contain phospholipids and isoflavones and are cholesterol-free, so tofu is a truly healthy food.
The nutritional value of tofu is similar to that of milk. For people who cannot drink cow's milk due to lactose intolerance or who avoid meat and poultry to control chronic diseases, tofu is the best substitute.