以共固定糖化菌及Saccharomyces cerevisiae生產甘藷生質酒精

Abstract

生質酒精開發應用已成為現今再生能源發展方針，甘藷易於栽培且各地均可種植，十分適宜作為能源作物。目前以澱粉為原料轉化生成酒精，仍多採用水解與醱酵分離之二階段製程，若能藉由共固定系統同時進行兩項步驟，將可降低生產成本、提高酒精產量。 本研究利用糖化菌與Saccharomyces cerevisiae所組成之共固定系統，以批次醱酵將甘藷澱粉轉化生成酒精，並探討最適醱酵條件。當固定化酵母於添加6%酒精之10% glucose YPD培養時，最大醱酵效率80.23%，酵母生存能力95.70%，較游離細胞高，耐糖性試驗亦具同樣結果，可見固定化確實可提升酵母之耐受性。Aspergillus oryzae及Monascus purpureus有較高之α-amylase活性(8.43, 7.65 U/mL)及glucoamylase活性(12.22, 10.42 U/mL)。當A. oryzae菌絲與S. cerevisiae共固定化時，膠體硬化時間15分鐘、 pH 4.0、溫度30℃及轉速150rpm條件下，培養13天可得最大酒精濃度3.05%(v/v)，YE/s值為0.31。若以M. purpureus菌絲與S. cerevisiae進行共固定，其最佳膠體硬化時間60分鐘，於pH 4.0、溫度30℃及轉速150rpm條件下培養13天，最大酒精濃度3.17%(v/v)，YE/s值為0.37。 當混合糖化菌與S. cerevisiae共固定化時，A. oryzae與M. purpureus以比例2:1混合，醱酵11天可得最大酒精濃度3.84%(v/v)及YE/s值0.39; 若A. oryzae與 M. purpureus以比例1:2共固定化，醱酵9天可得最大酒精濃度4.08%(w/v)及YE/s值0.41。顯示混合糖化菌與酵母之共固定化有助於提升酒精產量及縮短醱酵時間。

The development and application of bioethanol is the main set goals of Taiwan’s renewable energy policy in recent years. The properties of sweet potato including its easy growth and adaptation to many farming conditions have made it to be considered as a major energy crop. Presently, ethanol fermentation processes from starchy materials normally involves two stages, hydrolysis and fermentation. Therefore, direct ethanol from starch by co-immobilization would both reduce production cost and increase ethanol yield. This study investigated the bioethanol production from sweet potato by co-immobilization of saccharolytic molds (Aspergillus oryzae, Monascus purpureus) and Saccharomyces cerevisiae under batch fermentation and optimal parameters for fermentation were analyzed to obtain maximum ethanol production. The results showed that immobilized yeast cells had the maximum fermentation rate of 80.23% and 95.70% cell viability when cultivated under 10% glucose YPD and 6% ethanol. This indicates immobilization enhances the ethanol tolerance capacity of yeast cells, and glucose tolerance test had the same. The α-amylase activities of A. oryzae and M. purpureus were 8.43 and 7.65 U/mL whereas the glucoamylase activities were 12.22 and 10.42 U/mL, respectively. During the co-immobilization of S. cerevisiae with A. oryzae or M. purpureus, the optimal hardening time of gel beads were 15 and 60 min, the bioethanol production were 3.05 and 3.17%(v/v), and YE/s were 0.31 and 0.37 at pH 4, 30℃ and 150 rpm for 13 days of fermentation, respectively. In co-immobilization of S. cerevisiae and mixed molds while A. oryzae and M. purpureus mixed ratio was 2:1, the bioethanol production was 3.84%(v/v), and YE/s was 0.39 after 11 days of fermentation, whereas A. oryzae and M. purpureus mixed ratio was 1:2, the bioethanol production was 4.08%(v/v), and YE/s was 0.41 after 9 days of fermentation. This study demonstrated that co-immobilization of S. cerevisiae and mixed molds would both reduce fermentation time and increase ethanol yield.