Bioactive components, in vitro digestibility, microstructure and application of soybean residue (okara): a review

Abstract

Okara is a by‐product of soymilk production with a rich nutritional profile, particularly in proteins, fibers, lipids, and bioactive components. Okara has the potential for value‐added production and utilization—choices that, at the same time, deliver on the promise of increased economic advantages along with a reduction in environmental pollution. Research on bioactive constituents, in vitro digestibility and structural aspects (microstructure and infrared spectroscopy) suggests its potential as an ingredient with high bioactive components and digestibility score, along with varied structural strength, which may be of great importance to the food industry while developing new products with okara integration. Further, various food formulations made from the addition of okara flour also suggested the potential of this low‐cost waste ingredient to enhance the nutritional value and address the various health‐related issues such as obesity, diabetes and hyperlipidemia diseases. Therefore, this mini review summarizes the existing literature with a view to establish an extensive knowledge base for the composition and utilization of okara. In addition, structural and digestibility aspects of okara are also highlighted as they may determine the quality and acceptability of the product.

Prebiotic Impacts of Soybean Residue (Okara) on Eubiosis/Dysbiosis Condition of the Gut and the Possible Effects on Liver and Kidney Functions

“…However, the chemical composition is dictated by the method of soy processing or extraction, thus the quantity of water-soluble components obtained from ground soybeans and whether the residual extractable constituents have been extracted or not, and the cultivar of soybean used. Varied cultivars differ in lipid and crude protein contents, fatty acids compositions, and lipoxygenase activities [ 46 , 47 ]. Moreover, the variation in the nutritional profile of both wet and dry soybean residue has been attributed to cultivar differences, the incidence of sunshine, analysis methods, and the production or processing conditions used.…”

“…Hence, the characteristics of water-soluble constituents may vary owing to the raw material used [ 48 , 49 ]. However, this lies beyond the scope of this review and, hence, interested readers can refer to these articles [ 10 , 47 , 50 , 51 , 52 ]. The sequence and procedures for processing the beans are as well very essential and it dictates the fate of all water-soluble extract in the beans.…”

“…In the Chinese way, the soaked beans are rinsed, and the raw beans are then ground and the residue is then filtered off with water, and then heat the extract; in the Japanese system, the soaked beans are first cooked prior to grinding and filtering [ 7 , 30 , 46 ]. Figure 1 displays the schematic illustration of the steps involved in processing soy milk and the production of soybean residue/okara [ 46 , 47 , 52 ].…”

“…An antioxidant is classified as an organic compound, which when available in small concentration/quantity in contrast with an oxidizing substrate, can significantly combat that substrate’s oxidation [ 92 ]. Although the term officially defines compounds that react with oxygen, it can also adhere to compounds that guard and/or protect against free radicals (i.e., molecules with unpaired electrons) that deny these radicals from harming healthy cells [ 47 ]. Daidzein and genistein are the strongest soy isoflavones for antioxidant activity.…”

Bacterial and Fungal Microbiota Associated with the Ensiling of Wet Soybean Curd Residue under Prompt and Delayed Sealing Conditions

“…A significant amount of soybean curd residue (SCR) is generated as a by-product from the manufacturing of tofu, a traditional Asian food prepared by coagulating soy milk. The sum of SCR in China, Korea, and Japan is approximately 3.9 million tons per year, equivalent to the annual amount of tomato pomace generated globally [ 2 , 3 ]. Although the low dry matter (DM) content (about 200 g/kg) of wet SCR poses a challenge to its handling and transportation, its high crude protein content (about 250 g/kg DM) makes it an attractive ingredient for use in animal feed.…”