以固定化酵母菌Saccharomyces cerevisiae發酵龍鬚菜水解液以生產生質酒精

Fermentation of Gracilaria Hydrolysate for Bioethanol Production by Immobilized Saccharomyces cerevisiae

近年來，由於石化燃料的使用造成環境汙染及溫室效應，因此尋找可替代性能源相當受到重視。台灣四面環海，擁有豐富的海洋資源，非常適合開發藻類生質能源。本研究探討以固定化菌發酵藻類水解液以生產生質酒精，發現固定化Saccharomyces cerevisiae Wu-Y2菌能有效的利用藻類水解液中之葡萄糖與半乳糖以生產酒精。使用龍鬚菜水解液，並添加Yeast extract 2 g/L為原料，固定化S. cerevisiae Wu-Y2菌在30°C下靜置培養48 小時，可獲得生質酒精4.9 g/L（酒精轉化率94%），即1g 的龍鬚菜藻粉中可產出0.25g 的生質酒精。利用掃描式電子顯微鏡可有效觀察菌株在固定化顆粒的表面與內部之生長情形，證實利用固定化菌顆粒生產酒精的可行性。在搖瓶批次培養中固定化S. cerevisiae Wu-Y2 菌可有效的利用龍鬚菜水解醣類（葡萄糖半乳糖）以生產生質酒精，且經五個批次的培養，菌株完全無弱化的現象。經過五批次培養之酒精平均產量為5.0 g/L，而每批次之酒精生產皆接近於理想轉化率（98%）。以固定化S. cerevisiae Wu-Y2 菌於反應器中進行龍鬚菜水解醣類發酵生產酒精的探討發現接種10%菌量，連續饋料及靜置培養（無曝氣）為最適生產條件。在連續饋料的實驗中以2.3mL/min 連續饋料96h，共饋料13.2L，酒精生產濃度平均為4.1 g/L，可得到的酒精總量為54.1g。因此以固定化S. cerevisiaeWu-Y2菌發酵藻類水解液以生產酒精在生質能源之發展具有相當大的潛力。

The use of fossil fuels causes environmental pollution and contributes to the greenhouse effect. Growing concern regarding the rapid depletion of fossil fuels and global warming has motivated people to seek alternative energy sources. Algae are suitable materials for bioethanol production in Taiwan, particularly because Taiwan is surrounded by the ocean and has rich marine resources. This study was conducted to investigate the fermentation of algae hydrolysate by immobilized yeast for bioethanol production. The results showed that immobilized Saccharomyces cerevisiae Wu-Y2 displayed excellent performance in the cofermentation of glucose and galactose present in algae hydrolysate. When the hydrolysate of Gracilaria cliftonii was fermented by immobilized S. cerevisiae Wu-Y2, a final ethanol concentration of 4.9 g/L (94% conversion efficiency) was achieved. Overall, 0.25 g of ethanol can be produced from 1 g of dry Gracilaria through this method. The growth of S. cerevisiae Wu-Y2 on the immobilized particles can be observed with a scanning electron microscope. Repeated batch fermentation revealed that the immobilized cells can be reused over five successive reaction cycles without any loss of biocatalytic activity. The average ethanol concentration was 5.0 g/L (more than 98% conversion efficiency in every cycle). Fermentation of Gracilaria hydrolysate by using immobilized S. cerevisiae Wu-Y2 in a bioreactor revealed that suitable conditions for ethanol production include the addition of 10% immobilized cells, continuous back-feeding, and rest cultivation (with no aeration). When the fermentation was conducted through continuous feeding of hydrolysate at 2.3 mL/min for 96 h, an overall 13.2 L of hydrolysate was added, the average ethanol concentration was 4.1 g/L, and 54.1 g of ethanol was obtained. The findings of this study revealed that Gracilaria sp. can be a potential feedstock in biorefineries for ethanol production by using immobilized S. cerevisiae.