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.

In this study, Pediococcus pentococcus PP04 (PP04) isolated from the Northeast pickled cabbage was given to C57BL/6N mice for eight weeks, aiming to investigate the ameliorative effects of PP04 on liver injury induced by a high-fat diet. The western blot results suggested that PP04 ameliorated the increase of intestinal permeability by dramatically increasing the expressions of tight junction proteins, such as Occludin, Claudin-1 and ZO-1, which decreased hepatic lipopolysaccharides (LPS), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) concentrations to effectively alleviate the liver injury. Furthermore, PP04 relieved the high-fat diet-caused gut inflammation by the NF-κB/Nrf2 signaling pathway, which regulated the expression of inflammatory cytokines and antioxidants, to positively improve the liver injury. In addition, the 16S rDNA sequencing results inferred that PP04 had the potential to rebalance intestinal flora disorders through regulating the relative abundance of inflammation and obesity-related bacteria in mice.

Diabetic nephropathy (DN) is the most important complication in patients with diabetes. The accumulation of advanced glycation end-products (AGEs) is the main reason for the development of DN. In this study, we investigated the mechanism of buckwheat hull flavonoids to break AGEs in vitro by measuring fluorescence analysis, three-dimensional fluorescence, protein molecular weight, free amino groups, and the sulfhydryl group content. Proteomics analysis was used to determine the effect of total buckwheat hull flavonoids (TBHF) intervention on protein differential expression in the kidney of db/db mice. The results showed that buckwheat hull flavonoids were potent in breaking AGEs in vitro, and they protected mice kidneys by regulating the renal AGE-RAGE pathway. This study lays a strong experimental and theoretical foundation for the development of new lysing agents to break AGEs. The findings should make an important contribution to the field of flavonoids in improving the application of diabetic nephropathy in the diet.

Buckwheat hulls, by‐products of buckwheat processing, contain various flavonoids, but the antioxidant capacity and synergy of different flavonoids are unclear. The purpose of this study was to evaluate the antioxidant activity of flavonoid monomers and high‐flavonoid component (HBHF) in buckwheat hulls using chemical‐based assays and cellular‐based assays. Four kinds of flavonoids were identified as rutin, isoorientin, vitexin, and hyperoside from buckwheat hulls. In chemical‐based assays, rutin and HBHF showed relatively high free radical scavenging activities and total antioxidant capacities. In cellular‐based assays, however, HBHF showed much higher proliferation activity against cell damage than flavonoid monomers when HepG2 cell was oxidatively damaged by H₂O₂ or high glucose. The cytoprotective activities of flavonoid monomers and HBHF were closely associated with reducing levels of reactive oxygen species (ROS) and malondialdehyde (MDA) or increasing catalase (CAT) activity. In conclusion, buckwheat hull flavonoids are the favorable application candidates for natural antioxidants.