**Enrichment of Polyglucosylated Isoflavones from Soybean Isoflavone Aglycones Using Optimized Amylosucrase Transglycosylation**

**Young Sung Jung 1,**†**, Ye-Jin Kim 2,**†**, Aaron Taehwan Kim 1, Davin Jang 2, Mi-Seon Kim 2, Dong-Ho Seo 3, Tae Gyu Nam 4, Chan-Su Rha 1, Cheon-Seok Park <sup>2</sup> and Dae-Ok Kim 1,2,\***


Academic Editor: Josefina Aleu Received: 6 December 2019; Accepted: 30 December 2019; Published: 1 January 2020

**Abstract:** Isoflavones in soybeans are well-known phytoestrogens. Soy isoflavones present in conjugated forms are converted to aglycone forms during processing and storage. Isoflavone aglycones (IFAs) of soybeans in human diets have poor solubility in water, resulting in low bioavailability and bioactivity. Enzyme-mediated glycosylation is an efficient and environmentally friendly way to modify the physicochemical properties of soy IFAs. In this study, we determined the optimal reaction conditions for *Deinococcus geothermalis* amylosucrase-mediated α-1,4 glycosylation of IFA-rich soybean extract to improve the bioaccessibility of IFAs. The conversion yields of soy IFAs were in decreasing order as follows: genistein > daidzein > glycitein. An enzyme quantity of 5 U and donor:acceptor ratios of 1000:1 (glycitein) and 400:1 (daidzein and genistein) resulted in high conversion yield (average 95.7%). These optimal reaction conditions for transglycosylation can be used to obtain transglycosylated IFA-rich functional ingredients from soybeans.

**Keywords:** *Deinococcus geothermalis*; glycosyltransferase; *Glycine max* (L.) Merr.; HPLC/MS; isoflavone aglycone-rich extract; isoflavone α-glucoside
