含水溶性大豆異黃酮發酵液之脫水試驗及熱安定性研究

Abstract

大豆(Glycine max)中含有豐富的異黃酮 (Isoflavones)，其具有植物性類雌激素(phytoestrogens)的活性。先前有研究指出攝食大豆異黃酮有助於減少低密度脂蛋白，增加高密度脂蛋白，可降低冠狀動脈硬化及心血管發生之風險。大豆異黃酮依化學結構可分成4類12種，而其中以不帶醣基之異黃酮 (aglycones) 有較佳之生理活性，但由於aglycones的水溶性不佳，導致生物可利用率 (bioavailability) 不佳。本研究室於先前篩選出FC-10菌株，可將daidzein 及 genistein 轉化成高水溶性的磷酸化異黃酮 daidzein 7-O-phosphate (D7-P) 和 genistein 7-O-phosphate (G7-P) ，並且已建立實驗室規模生產及回收 D7-P 與 G7-P 水溶性大豆異黃酮的程序。本研究利用噴霧乾燥法將發酵液進行乾燥，探討其噴霧乾燥操作之最適條件，並針對水溶性異黃酮於不同型態之安定性進行探討。本研究分為三部分，第一部分比較離心與微過濾對發酵液之除菌效果、回收率以及發酵液之熱安定性，結果顯示以離心及微過濾方式除菌所得之水溶性異黃酮回收率分別為93.4%以及95.3%，除菌之液體的OD600分別為0.088及0.060，因此以微過濾方式除菌較佳；總水溶性異黃酮發酵液於4℃儲藏7天後仍保有95.6%之回收率。第二部分探討噴霧乾燥最適條件以及噴乾粉末之水分含量，結果顯示噴霧乾燥之最佳條件為：入口溫度140℃、出口溫度80℃，水溶性異黃酮的保留率為98.2%，不同噴乾條件下水分含量範圍在0.30%到0.36%之間。第三部分探討水溶性異黃酮於噴乾粉末中降解之動力學，結果顯示 D7-P，G7-P 以及總水溶性異黃酮在噴乾粉末中的降解為一級反應，半衰期分別為169.1、301.4以及192.5天，活化能分別為13.3、14.1以及13.4 (kcal/mole)。噴乾之水溶性異黃酮粉末在25℃儲藏下會於62天後降解至原有含量之80%。

Isoflavones are a class of phytoestrogens. They are plant-derived phenolic compounds with estrogenic activity. Previous studies have revealed that the intakes of isoflavones could achieve to decrease significantly in serum LDL cholesterol and increase in serum HDL cholesterol, which reduce the risk of cardiovascular disease in human body. A number of reports have shown that the biological effects of isoflavones were mainly attributed to their aglyconic forms rather than the glycosidic forms. However, plenty of studies reported that aglycones show low bioavailability due to their poor water solubility. In our previous work, a FC-10 strain showed capabilities on the biotransformation of daidzein and genistein into water soluble conjugated form namely, daidzein-7-O-phosphate and genistein-7-O-phosphate. Moreover, the recovery procedure for the said water soluble isoflavones from bioconversion broth was also established. In this study, we developed the process of the harvested fermentation broth by means of spray drying. We also investigated the stability of the water soluble soy isoflavones during spray dry and storage. The result revealed that for bacterial biomass removal the process of microfiltration showed more efficient than that of centrifugation, and their recoveries of total water soluble isoflavones were 95.3% and 93.4%, respectively. The results of storage test showed the content of D7-P and G7-P remained 95.6% of their origin at 4℃ for 7 days. The optimal condition of spray drying process were determined as the flow rate of 2.87 mL/min with inlet and outlet temperature as for 140℃ and 80℃, respectively. The recovery of total water soluble isoflavones was 98.2% after spray-dried. The water content of the spray-dried powder under different spray drying processes ranged from 0.30% to 0.36%. D7-P, G7-P and total water soluble isoflavones showed first order degradation during storage. Their t0.5 were 169, 301, 193 days and Ea were 13.3, 14.1, 13.4 kcal/ mole respectively. According to our results, with a storage at 25℃ for 62 days, total water soluble isoflavones in spray-dried powder would degrade into 80% of their original content.