利用芋頭農業資材以嗜高溫酵母菌Kluyveromyces marxianus K21醱酵生產生質乙醇

Abstract

自工業革命以來人類對於化石燃料的需求日益漸增，其中主要以石油為主。而石油最主要的用途是作為交通運輸工具之燃料。然而，大量利用化石燃料會導致溫室氣體含量增加，進而造成溫室效應及全球暖化。為解決大量燃燒造成空氣汙染及預防能源危機，世界各國開始研發替代燃料，而生質乙醇是生質能源中具有高效能及低環境汙染特性之一種再生能源。 根據不同生質乙醇的原料可分為糖質、澱粉質及纖維素原料。利用澱粉質原料有許多優勢，包括可醱酵糖含量高、生產乙醇的效率較高、操作流程上較簡單等。但澱粉質原料因其多為糧食而備受爭議；第二代生質能源則以纖維素原料為主之農業資材，但其水解條件嚴苛、水解醣利用有限且水解後含有呋喃等抑制物質，因此希望能找尋一種以澱粉為主之農業資材作為乙醇生產之原料。本實驗所用之芋頭為台灣重要作物之一，每年產量約為40,000噸，其主要被製作成糕餅、甜點及小吃等。芋頭農業資材 (taro agricultural resource, TAR)是帶有芋頭澱粉的外皮，主要由芋頭酥工廠所提供，於本研究的目的是利用芋頭工廠所丟棄之芋頭廢棄物，經過前處理及酵素性水解，並利用替代氮源去評估取代酵母萃取物 (氮源) 製造出更具有經濟價值和環保的培養基並應用在生產生質乙醇上。其次，探討培養基最適化包括不同濃度的芋頭農業資材、鹽類離子濃度、接菌量及培養基過濾，利用耐高溫酵母菌K21在不同溫度下分別以分開酵素水解與發酵 (separated hydrolysis and fermentation, SHF) 和同步糖化醱酵 (simultaneous saccharification and fermentation, SSF)，最後利用最適化的條件放大至5 L生物反應器進行醱酵。其結果顯示在搖瓶中利用170.17 g/L TAR可水解出約100 g/L的葡萄糖，混入9 g/L的玉米麩粉 (corn gluten meal, CGM) 及鹽離子後不過濾為最理想之培養基，接著以5%接菌量在40oC下以SSF進行醱酵，可得到最大乙醇濃度48.98 g/L，產率為2.23 g/L/h，理論產率為95.85%，而以相同條件放大到5 公升生物反應器中可得最大乙醇濃度43.78 g/L，產率為2.19 g/L/h，理論產率為85.66%。

The demand for fossil fuels has significantly increased since the beginning of industrial revolution. Petroleum, one of the most important types of fossil fuel, is predominantly being used as car’s fuel. Fossil fuel dependence leads to the increase of greenhouse gas, resulting in more severe greenhouse effect and global warming. In order to lessen the amount of air pollution due to fossil fuel burning and to alleviate the energy crisis, many countries began to develop alternative fuels. Bioethanol is one of the high efficient and low environmental impact bioenergy sources. The raw materials that produce bioethanol can be divided into sugar, starchy and lignocellulose materials. Using starchy materials for bioethanol production have many advantages, such as rich in fermented sugar, high efficiency of ethanol production, simple operation and so on. Most of starchy materials are foods and have lot of controversies. Second generation bioethanol are using lignocellulosic materials. These materials have some properties, such as harsh hydrolysis conditions, fewer fermented sugar, and lot of inhibition substances. If we can find a kind of starchy agricultural resource, it can compensate for the disadvantages of both. Taro is one of the most important crops in Taiwan and annual output about 40,000 tons, which serves as main ingredient of different types of food products such as pastries, snacks, and dessert. In this study, we used taro agricultural resource (TAR), which is provided by taro pastries factory to perform our experiment. The received TAR was mainly composed of taro’s skins that contain many starch residues. We pretreated and enzymatically hydrolyzed TAR. Various alternative nitrogen sources were evaluated as substitute nitrogen source of yeast extract for producing more economic and environmental friendly medium for ethanol production. Subsequently, we are going to discuss about the factors of modification medium, such as TAR loading amount, ions concentration, inoculum and medium filtration. The modification medium is followed by using thermotolerance yeast K21 to separate hydrolysis fermentation (SHF) and simultaneous saccharification fermentation (SSF) under different temperature. Our ultimate goal is scale-up to 5L bioreactor to make sure of conditions can produce ethanol efficiently by using TAR. The flask scale result showed the optimizing medium was using 170 g/L TAR which can hydrolyze about 100 g/L glucose and added 9 g/L CGM and salt without filtration. The optimizing medium was inoculated 5% K21 under 40oC by SSF can carry out the maximum ethanol concentration (48.98g/L) and productivity (2.23g/L/h). The result of maximum ethanol concentration and productivity were 43.78 g/L and 2.19 g/L/h, respectively in 5L bioreactor under the optimizing condition.