臺灣博碩士論文加值系統

當以蔗糖做為唯一碳源時,酒精生產菌Zymomonas mobilis ATCC 10988的
醱酵效率, 決定於培養基中蔗糖的濃度和蔗糖的水解產物葡萄糖的累積濃
度。本文利用外加的固定化轉化■與菌體本身的競爭反應來適當控制醱酵
液中蔗糖和單糖的濃度, 發現可以有效的提高此酒精生產菌的醱酵效率。
本研究中所使用的固定化擔體為天然的無機矽氧化物--河沙和有機合成高
分子--甲基丙烯醯胺-N,N'亞甲基雙丙烯醯胺共聚合物。結果發現合成共
聚合物經乙二胺修飾和戊二醛活化後為最佳之固定化擔體, 於蔗糖濃度
0.8M,pH5與30℃之下每克固定化轉化■的活性為6900Ｕ。除此之外實驗結
果也顯示轉化■經固定化後對熱有較高的穩定性。 Z. mobilis批次醱酵
的結果顯示, 隨著培養基中蔗糖濃度的增加, 副產物果聚糖和山梨醣醇的
累基量將會上升, 同時造成酒精的收率急速下降。當起始蔗糖濃度為200
g/l時, 酒精的收率只有理論值的百分之五十七左右。在Z. mobilis-固定
化轉化■的批次聯合反應系統中,培養基起始的蔗糖濃度固定為200g/l,
實驗結果顯示, 當固定化轉化■添加量較多時可快速降低蔗糖濃度所以只
有微量果聚糖產生, 但此時系統中所累積的高濃度葡萄糖和果糖會使山梨
醣醇的濃度增加。當固定化轉化■添加量較少時,蔗糖濃度的減低速率較
為緩慢, 果聚糖的產生量稍為增加, 但山梨醣醇的濃度則明顯下降。批次
聯合反應的最佳結果為添加0.2g固定化轉化■, 酒精收率從0.29g/g提高
到0.40g/g(理論值的80％)。這個收率值也比Z. mo- bilis以混糖(等量葡
萄糖和果糖)醱酵的酒精收率高,顯示此聯合反應系統也比蔗糖水解加酒精
醱酵兩階段操作還要有效率。在連續操作的聯合反應系統中, 本實驗所穫
得的最佳結果為稀釋率等於0.2(1/h), 此時酒精的生產率為10.5g/l/h,而
收率則和批次聯合反應相似。實驗結果也顯示, 固定化酵素的加入, 醱酵
液中蔗糖濃度低, 菌體所催化的蔗糖水解與果聚糖生成速率都明顯降低,
表示酵素蔗糖-6-果糖基轉移■為蔗糖誘導性蛋白質本研究最後也推導Z.
mobilis醱酵的動力學以及蔗糖為基質的Z. mobilis / 固定轉化■聯合反
應系統之動力學等模式。模式中的參數值也由實驗結果與模式的配合求得
。

In this work, immobilized invertase was added into the
fermenter in order to compete with microorganims for the
hydrolysis of sucrose, the accumulation of monosccharides in
the broth was thus controlled and the ethanol yield was
enhanced. Results from batch fermentations of Z. mobilis showed
that the formations of by-products; i.e., sorbitol and levan,
were associ- ated with an higher sucrose concentration in the
medium.The for- mation of by-products was suggested to be the
reason for low ethanol yields from sucrose. As the sucrose
concentration in the feed was 200g/l, the ethanol yield became
only 57％ of its thro- retical value. In a combined Z. mobilis/
immobilized invertase system with 200 g/l sucrose as
substrates. It was found when 0.2g immobilized invertase
(activity 2100Ｕ/g)was added to a 1.2 liter batch fermenter,
the ethanol yield was increased from 0.29 to 0.40 g/g (80％ of
the theoretical value). High ethanol yields we also obtained
from continuous cultures.When 0.2 g immobilized invertase was
added, the dilution rate for the maximum ethanol productivity
(10.5g/l/h) was determined as 0.2. Experimenal data showed that
increasing the addition of immobilized invertase led to a low
concentration of sucrose in the culture and lower rate of levan
formation and sucrose hydrolysis,both were catalyzed by the
extracellular exzyme levansucrase.It could be concluded that
the levansucrase secreted by Z. mobilis is a sucrose inducible
enzyme. In this work,the kinetic models of Z. mobilis
fermentation and combined Z. mobilis/immobilized invertase
system were also developed. Parameters used for model
simulation were estimated from fitting the experimental data
with these kinetic models.