| Summary: | 碩士 === 國立臺灣大學 === 農業化學研究所 === 103 === Isoflavones are a group of plant secondary metabolites that occur mostly in soybean (Glycine max). There are 4 types of isoflavones found in soybeans, consisting of isoflavone aglycones and their corresponding conjugation forms (malonyl glucosides, acetyl glucosides and glucosides). Due to the similar chemical structure between isoflavone aglycones and estradiol, aglycones were referred to be a class of phytoestrogens. Among all types of soy isoflavones, aglycones have been reported as the bioactive forms. However, aglycones have shown low bioavailability owing to their poor water solubility. In our previous study, Bacillus subtilis var. natto BCRC 80517 showed the capability to convert isoflavone aglycones into isoflavone 7-O-phosphates which are highly water-soluble. Glucosides would be deglycosylated into their corresponding aglycones then further converted into isoflavone 7-O-phosphates. However, malonyl glucosides could only be deglycosylated into their corresponding aglycones without forming phosphate conjugates. The aim of this work was to figure out the reason why malonyl glucosides contribute to the failure of biotransformation by BCRC 80517. Firstly, we found that there was no significant effect on the bacterial growth while BCRC 80517 cultivated with malonyl glucosides. Then, we explored whether the hydrolysate of malonyl glucosides by β-glucosidase impact on the phosphorylation of aglycones by BCRC 80517. The results revealed that neither malonic acid nor glucose 6-malonate could inhibit the production of isoflavone 7-O-phosphates during the biotransformation. Moreover, the metabolites from the culture broth of BCRC 80517 with malonyl glucosides showed no inhibition on the phosphorylation of aglycones, either. And meanwhile, we found that the biotransformation performance varied considerably by the growth status of BCRC 80517 cells. The biotransformation rate was the most efficient when the bacteria grew at the exponential phase of growth, and the performance of biotransformation decreased gradually along with the bacterial growth. Besides, the results from comparing the deglycosylation efficiency between malonyl glucosides and glucosides of soy isoflavone by Bacillus subtilis var. natto BCRC 80517 revealed that malonyl glucosides were carried out more slowly than glucosides. Therefore, we concluded the dominant factors of the phosphate esters of isoflavone not being generated by the biotransformation with malonyl glucosides of soy isoflavone would be highly related to inferior substrate specificity with deglycosylation and the attenuation of phosphorylation along with the bacterial growth.
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