Abstract
Okara is a white-yellow fibrous residue consisting of the insoluble fraction of the soybean seeds remaining after extraction of the aqueous fraction during the production of tofu and soymilk, and is generally considered a waste product. It is packed with a significant number of proteins, isoflavones, soluble and insoluble fibers, soyasaponins, and other mineral elements, which are all attributed with health merits. With the increasing production of soy beverages, huge quantities of this by-product are produced annually, which poses significant disposal problems and financial issues for producers. Extensive studies have been done on the biological activities, nutritional values, and chemical composition of okara as well as its potential utilization. Owing to its peculiar rich fiber composition and low cost of production, okara might be potentially useful in the food industry as a functional ingredient or good raw material and could be used as a dietary supplement to prevent varied ailments such as prevention of diabetes, hyperlipidemia, obesity, as well as to stimulate the growth of intestinal microbes and production of microbe-derived metabolites (xenometabolites), since gut dysbiosis (imbalanced microbiota) has been implicated in the progression of several complex diseases. This review seeks to compile scientific research on the bioactive compounds in soybean residue (okara) and discuss the possible prebiotic impact of this fiber-rich residue as a functional diet on eubiosis/dysbiosis condition of the gut, as well as the consequential influence on liver and kidney functions, to facilitate a detailed knowledge base for further exploration, implementation, and development.
Highlights
Soybean is labeled as one of the essential crops across the globe and is native to Asia, and has been under cultivation for over thousands of years there
The authors suggested that the main components of okara, i.e., dietary fiber and protein, could be attributed with the total lipids and cholesterol decreased in the liver and plasma, and the fecal output increase in high-fat-fed hamsters, and might play an essential role in the prevention of hyperlipidemia and could as well be used as value-added ingredient for functional food preparation
The results showed that rats fed 2.5% pectin for two weeks displayed increased plasma glucagon-like peptide-2 (GLP-2) and increased cecal short-chain fatty acids (SCFAs)
Summary
Soybean is labeled as one of the essential crops across the globe and is native to Asia, and has been under cultivation for over thousands of years there. Soybean and its by-products are evidenced in the literature as a rich source of phytochemicals/bioactive compounds, i.e., non-nutrient components of a plant with health-promoting functions and qualities These compounds include, but are not limited to, lunasin, lectin, phytic acids, saponins, omega-3-fatty acids, phytates, trypsin inhibitors, proteins, peptides, Bowman-Birk’s protease inhibitor, phytosterols, and isoflavones, mainly daidzein, genistein, and glycitein [1,43,44]. A recent study suggests that it is vital to put into account all potential effects of fermentation on the molecular weights of peptides, amino acids profile as well as the inhibitory activity of trypsin, since they play a role in impacting the overall functional characteristics including solubility and foaming properties, as well as the bioactivity of residual soy content [1,46].
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