Composition, Nutrition, and Utilization of Okara (Soybean Residue)

Okara is a by-product generated during tofu or soymilk production processes. It contains about 50% dietary fiber, 25% protein, 10% lipid, and other nutrients. The huge quantities of okara produced annually pose a significant disposal problem. Extensive studies have been done on the chemical composition, nutritional values, and biological activities of okara and on its potential utilization. Due to its high fiber content and low production costs, okara is a good raw material and rich source for preparing fiber and could also be used as a dietary supplement to prevent diabetes, obesity, and hyperlipidemia. Chemical or enzymatic treatment, fermentation, extrusion, high pressure, and micronization can increase the content of soluble fiber of okara, which improves its nutritional quality and processing properties. Fresh okara putrefies quickly due to its high moisture content, so it should be dried as early as possible. This review focuses on the application of okara in the food industry as partial replacement for wheat or soy flour to increase fiber and protein contents of foods. Okara can also be used as a fermentation substrate to produce a variety of products (natto, fibrinolytic enzymes, α-glucosidase inhibitor, β-fructofuranosidase, edible fungi, iturin A, chitosan, alcohol, etc.) for human consumption and nonfood production. In addition, the application of okara in feed and environmentally friendly material has also been documented.