新穎納豆產品開發之研究

Abstract

存在於黃豆中的大豆異黃酮 (isoflavone)是植物的二次代謝物，其化學結構與人體雌激素(estradiol)相似，具有雌激素活性，為一種植物雌激素(phytoestrogen)。大豆異黃酮已被證實具有預防心血管疾病、改善更年期婦女不適症狀、減緩骨質疏鬆症狀等生理功效。然而，僅有去醣基形式的異黃酮具上述活性。實驗室先前的研究由納豆產品篩選出一株納豆菌(BCRC 80517)，可將異黃酮轉換為異黃酮磷酸酯，提升其水溶性，進而大幅提升其生物可利用率。本研究以此為基礎，擬將黃豆與BCRC 80517進行固態發酵，開發一種富含異黃酮磷酸酯的黃豆發酵食品。研究首先探討黃豆最佳濕熱處理條件使malonylglucosides有效轉換為glucosides，利用電鍋蒸煮20、40、60分鐘或用高溫高壓滅菌釜分別以110°C、121°C及130°C蒸煮20、40、60分鐘；接著探討生產異黃酮磷酸酯的最適固態發酵條件，探討因子包含發酵黃豆基質顆粒大小、發酵前添加水量、接種菌液培養時間、接種菌量及碳源與無機鹽添加；最後評估納豆產品的貯藏條件，將納豆置於4°C及-20°C下進行一般貯藏試驗，以及將納豆粉置於40°C、50°C及60°C下進行加速貯藏試驗。結果顯示，將黃豆以121°C處理40分鐘，可以將glucosides佔總異黃酮含量之比例由17.0% 增加至92.4%。最適固態發酵條件為將碎粒黃豆通過10-20 mesh篩網後，加入1.5倍(w/w db)去離子水，在121°C, 1.2 kg/cm2下處理40分鐘後，接種5% (w/w db)菌齡為15 h的菌液，發酵48小時。異黃酮轉換率可達65.6 ± 2.8%，發酵後的納豆中含有258.7 ± 14.6 μmol/100 g db Daidzein-7-O-phosphate (D7P)及352.5 ± 7.7 μmol/100 g db Genistein-7-O-phosphate (G7P)。納豆在4°C下貯藏65天後，D7P及G7P的殘留率分別為55.8 ± 3.2%及63.8 ± 2.3%；在-20℃下貯藏65天後，各形式異黃酮之含量無顯著差異；納豆粉置於室溫下兩個月後，其D7P及G7P含量皆保留初始含量的80%以上。本研究開發出一種富含異黃酮磷酸酯的納豆保健食品，未來將進一歩評估此產品之生理功效。

Isoflavones are a group of plant secondary metabolites that occur mostly in the subfamily Papilionoideae of the Leguminosae. Soybean (Glycine max) is the most abundant source of isoflavones. There are 12 natural isoflavones in soybeans, consisting 3 types of aglycones (daidzein, genistein, glycitein) and their corresponding conjugates with glucose, acetylglucose and malonylglucose. The beneficial effects of isoflavones include: the reduction of serum lipids, relief of menopausal symptoms, increase of bone mineral density and chemoprevention of mammary and prostate cancer. A number of studies have revealed that the biological effects of isoflavones mainly attributed to their aglyconic forms rather than the glycosidic forms. However, many studies reported that aglycones show low bioavailability to humans because of their poor water-solubility. In the previous study of our lab, we found Bacillus subtilis BCRC80517 isolated from commercial natto products showed the capability on the biotransformation of daidzein and genistein into daidzein-7-O-phosphate (D7P) and genistein-7-O-phosphate (G7P) which have higher water-solubility. The objective of this thesis is to develop a novel functional natto product by biotransformation with Bacillus subtilis BCRC 80517. First, we investigated the optimal solid state fermentation condition of biotransformation for the production of isoflavone phosphate conjugate by BCRC 80517. The fermentation factors, which included broken soybean particle size, initial moisture content, inoculum age, inoculum volume and additional nutrients such as mineral salts, carbon sources were investigated and optimized. The optimum condition was 10-20 mesh particle size as substrate, supplemented with 1.5 (w/w db) water, autoclaved under 121℃for 40 min, and then inoculated with 5% (v/w db) inoculum, incubated at 37℃, 100% RH. The maximum biotransformation rate of isoflavone phosphate conjugate (65.6 ± 2.8%) was achieved in the condition. The fermented soybean (natto) has 168.9 ± 11.3 (μmol/100 gdb) D7P and 196 ± 18.6 (μmol/100 gdb) G7P. The results of storage test showed the content of D7P and G7P in natto remained 55.8% and 63.8% after 4℃ storage for 65 days. No significant change of D7P and G7P content in natto was observed after -20℃ storage for 65 days. The maintenances of D7P and G7P in natto powder were above 80% at room temperature withiin two months.