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.
Highlights
Soybean (Glycine max (L.) Merr.) is a large portion of major grain production, along with corn, wheat, and rice [1]
Deinococcus geothermalis amylosucrase (DGAS) fused with 6× histidine appeared as a single band with a molecular mass of about 73 kDa (Figure 1b), which is in good agreement with the estimated molecular mass of DGAS
DGAS was considered to be free of protein toxicity because it was not harmful to E. coli
Summary
Soybean (Glycine max (L.) Merr.) is a large portion of major grain production, along with corn, wheat, and rice [1]. Isoflavones, a subgroup of flavonoids, are well-known plant secondary metabolites that are found mainly in the plant families Fabaceae or Leguminosae, including soybean [2,3]. Isoflavones in soybeans are present mainly in conjugated forms [4]. Soy isoflavones are classified as acetylisoflavones, malonylisoflavones, non-acylated isoflavone glucosides, and isoflavone aglycones (IFAs), depending on the side groups attached to the isoflavone skeleton [5]. IFAs have antioxidant properties, interact with epigenetic modifications, and exhibit estrogen-like activities [3]. Dietary IFAs can be metabolized to equol (4’,7-isoflavandiol), which has significant estrogenic activity in the intestine [6]. Soy isoflavones exist naturally in conjugated forms rather than as aglycones; for example, daidzein [7-hydroxy-3-(4-hydroxyphenyl)chromen-4-one], glycitein [7-hydroxy-3-(4-hydroxyphenyl)-6-methoxychromen-4-one], and genistein [5,7-dihydroxy-3-(4hydroxyphenyl)chromen-4-one] [5].
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