Plants constantly synthesize secondary metabolites to adapt to their environment and enable their survival and well-being. Metabolite farming is a special cultivation skill to improve the amount of metabolites that can confer health benefits. Soybean leaves are gaining considerable importance as a nutraceutical source because they are edible source, easily obtaining biomass and bioactive metabolites consisting of flavonols, isoflavones, pterocarpens and saponins. Conversely, the low concentration of isoflavones (genistein and daidzein) is a key flaw for soybean leaves to be more potent nutraceutical substance.

Aiming to industrial purpose, this study reported the most concrete method for isoflavone riched soybean leaves (IRSL). Ethylene application under the dark condition at air-sealed box led a distinctive increase of dietary isoflavones such as genistein and daidzein glycosides with 120-fold (total 25911 µg/g), which is the highest level among any plant. The metabolites changes by ethylene were systematically identified by UPLC-ESI-TOF/MS to give successfully PLS-DA score and heatmap analysis. Metabolomics analysis revealed that ethylene promoted the accumulation of isoflavones in soybean leaves selectively.

The accumulated isoflavonoid biosynthesis pathway genes were identified within the transcriptome of soyleaves tissues at 1 day after treatment of ethephon. The quantitative RT-PCR analysis of these genes indicated significantly higher expression of CHS, CHI, IFS, HID, IF7GT, and IF7MaT compared to control leaves. These findings suggest that ethylene activates a set of structural genes involved in isoflavonoid biosynthesis, thereby leading to enhanced production of isoflavones in soybean plants.

IRSL exhibited an anti-obesity effect in OVX-induced rats by decreasing weight and visceral fat accumulation. Additionally, IRSL supplementation ameliorated OVX-induced hepatic steatosis by up-regulating the expression of the fatty acid oxidation-associated genes PPARα, ACOX1, and CPT1a in the liver. Together, our observations suggest that due to its anti-obesity and liver-protective effects, IRSL may be a promising functional food resource for protecting against menopause-associated obesity.

Keywords: Metabolite Farming, Soybean Leaves, Ethylene, Isoflavone, Health Benefit

References

1. Yuk, H.J.; Song, Y.H.; Curtis-Long, M.J.; Kim, D.W.; Woo, S.G.; Lee, Y.B.; Uddin, Z.; Kim, C.Y.; Park, K.H. Ethylene Induced a High Accumulation of Dietary Isoflavones and Expression of Isoflavonoid Biosynthetic Genes in Soybean (Glycine max) Leaves. J. Agric. Food Chem. 2016
2. Xie, C. liang; Kang, S.S.; Cho, K.M.; Park, K.H; Lee, D.H. Isoflavone-enriched soybean (Glycine max) leaves prevents ovariectomy-induced obesity by enhancing fatty acid oxidation. J. Funct. Foods 2018.
3. Ban, Y.J.; Song, Y.H.; Kim, J.Y.; Baiseitova, A.; Lee, K.W.; Kim, K.D.; Park, K.H. Comparative investighation on metabolites changes in soybean leaves by ethylene and activation of collagen synthesis. Ind. Crop. Prod. 2020