Structures, Biological Activities and Action Mechanisms of Secondary Metabolites from Soybean: A Review

Soybean, Glycine max, is an annual herbaceous plant of the family Leguminosae, which contains not only high-quality proteins and oils but also a large number of bioactive secondary metabolites, such as isoflavones and saponins. Soybean secondary metabolites have been widely recognized for their unique structures and multiple biological activities. In this article, an overview of recent progress on the major soybean secondary metabolites and their biological activities is presented based on Web of Science and PubMed. Twelve soybean isoflavones have been identified, which exerts health benefits such as preventing cardiovascular diseases, anti-osteoporosis, antioxidant, anti-inflammation, anti-tumor, anti-stroke, and hypoglycemic, neuroprotective and hepatoprotective functions through regulating mitogen activated protein kinase (MAPK), nuclear factor kappa-B (NF-κB), phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), and nuclear factor erythroid 2-related factor 2 (Nrf2). Totally 30 soybean saponins have been identified and demonstrated to possess anti-inflammation, antioxidant, anti-obesity, anti-diabetic, anti-tumor functions and preventive effects against cardiovascular disease. Their mechanisms of action involve the toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88)/NF-κB, MAPK, Janus kinase (JAK) and Nrf2 signaling pathways. These soybean secondary metabolites, due to their different structures, have different bioactivities. The major bioactivity of soybean isoflavones is phytoestrogenic activity, while soybean saponins mainly exert anti-tumor and anti-inflammatory activities. This review aims to provide the basis for the in-depth mining of soybean secondary metabolites and lay the foundation for further development of soybean resources.