Okara, soy pulp, or tofu dregs is a pulp consisting of insoluble parts of the soybean that remains after pureed soybeans are filtered in the production of soy milk and tofu. It is generally white or yellowish in color. It is part of the traditional cuisines of Japan, Korea, and China. Since the 20th century, it has been used in the vegetarian cuisines of Western nations. It is called dòuzhā or dòufuzhā in Chinese, okara in Japanese, and biji or kongbiji in Korean. Okara is the oldest of three basic types of soy fiber. The other two are soy bran and soy cotyledon/isolate fiber.
Production
Okara is a food by-product from tofu and soy milk production. In 1983 it was estimated that the annual yield for okara in Japan was approximately 70,000 metric tons. Due to its high moisture and nutrient content, okara is highly prone to putrefaction, and this has limited its commercial use.
Composition
Okara that is firmly packed consists of 3.5 to 4.0% protein, 76 to 80% moisture and 20 to 24% of solids. When moisture free, the gritty okara contains 8 to 15% fats, 12 to 14.5% crude fiber and 24% protein, and contains 17% of the protein from the source soybeans. It also contains potassium, calcium, niacin. Most of the soybean isoflavones are left in okara, as well as vitamin B and the fat-soluble nutritional factors, which include soy lecithin, linoleic acid, linolenic acid, phytosterols, tocopherol, and vitamin D. Okara contains some antinutritional factors: trypsin inhibitors, saponins, and soybean agglutinins, which cannot be easily digested. Fermentation of okara is conducive to digestion and absorption of okara nutrients, and it further improves the nutritional value. It can eliminate the bean’s odor, increase the amount of edible fiber, free amino acids, sugars, fatty acids, vitamin B12, vitamin B2, and flavoprotein.
Uses
Most okara worldwide is used as feed for livestock — especially hogs and dairy cows. Most of the rest is used as a natural fertilizer or compost, which is fairly rich in nitrogen. A small amount is used in cookery.
Human consumption
In Japan it is used in a side dish called unohana which consists of okara cooked with soy sauce, mirin, sliced carrots, burdock root and shiitake mushrooms. Okara can be used to make tempeh, by fermenting with the fungus Rhizopus oligosporus. using a tempeh starter, It can make press cake tempeh using ingredients such as brown rice, bulgur wheat, soybeans and other legume and grain combinations. Okara is also eaten as red oncom by the Sundanese people on Java in Indonesia after fermentation by Neurospora. Okara is eaten in the Shandong cuisine of eastern China by steaming a wet mixture of okara that has been formed into blocks of zha doufu. The product is sometimes used as an ingredient in vegetarian burger patties. Additional uses include processing into a granola product, as an ingredient in soysage and as an ingredient in pâtés. In Japan, there have been experiments with incorporating okara into ice cream.
Livestock consumption
Most okara is used as animal feed, especially for farms in vicinity of soy milk or tofu factories.
The product is used as an ingredient in pet foods.
As fertilizer or compost
Okara is sometimes spread on fields as a natural nitrogen fertilizer. It adds tilth to the soil. Likewise, it can be added to compost to add organic nutrients and nitrogen.
Waste/environment
When not considered foodstuff, it may be deemed 'soybean curd residue'. Some 800,000 tons of soybean curd residue is disposed annually as tofu production byproducts in Japan. As mass waste, it is a potential environmental problem because it is highly susceptible to putrefaction. The protein in SCR is of better quality than from other soy products; for example, the protein efficiency ratio of SCR is 2.71 compared with 2.11 for soymilk. The ratio of essential amino acids to total amino acids is similar to tofu and soymilk. Nevertheless, it remains a challenge to current processes to commercially extract the proteins and nutrients from SCR waste.
