Seong Khaw Teik, Katakura Yoshio, Ninomiya Kazuaki, Bito Yohei, Katahira Satoshi, Kondo Akihiko, Ueda Mitsuyoshi, Shioya Suteaki
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Appl Microbiol Biotechnol. 2006 Nov;73(1):60-6. doi: 10.1007/s00253-006-0454-y. Epub 2006 May 13.
In the direct ethanol fermentation of raw starch by arming yeast with alpha-amylase and glucoamylase, it is preferable to use a flocculent yeast because it can be recovered without centrifugation. Three types of arming yeast system, I (nonflocculent), II (mildly flocculent), and III (heavily flocculent), were constructed and their fermentation performances were compared. With an increase in the degree of flocculation, specific ethanol production rate for soluble starch decreased (0.19, 0.17, and 0.12 g g-dry-cell(-1) h(-1) for systems I, II, and III, respectively), but that for raw starch did not decrease as much as expected (0.06, 0.06, and 0.04 g g-dry-cell(-1) h(-1) for systems I, II and III, respectively). Microscopic observation revealed that many starch granules were captured in the yeast flocs in system III during the direct ethanol fermentation of raw starch. It was suggested that the capture of starch granules increases apparent substrate concentration for amylolytic enzymes in arming yeast cell flocs; thus, the specific ethanol production rate of system III was kept at a level comparable to those of the other systems.
通过用α-淀粉酶和糖化酶武装酵母来直接发酵生淀粉生产乙醇时，最好使用絮凝酵母，因为它无需离心即可回收。构建了三种类型的武装酵母系统，即系统I（非絮凝型）、系统II（轻度絮凝型）和系统III（重度絮凝型），并比较了它们的发酵性能。随着絮凝程度的增加，可溶性淀粉的比乙醇生产率下降（系统I、II和III分别为0.19、0.17和0.12 g g-干细胞（-1）h（-1）），但生淀粉的比乙醇生产率下降幅度不如预期（系统I、II和III分别为0.06、0.06和0.04 g g-干细胞（-1）h（-1））。显微镜观察表明，在生淀粉直接乙醇发酵过程中，系统III的酵母絮凝物中捕获了许多淀粉颗粒。这表明淀粉颗粒的捕获增加了武装酵母细胞絮凝物中淀粉分解酶的表观底物浓度；因此，系统III的比乙醇生产率保持在与其他系统相当的水平。
