篩選不同來源酵母菌株製造甘蔗酒之探討

Isolation and Identification of Sugar Cane (Saccharum officinarum L.) from different sources Yeast Strains

自土壤 (Yc），鳳梨表皮（Ypa），葡萄表皮（Yg）以及由三家不同製酒工廠之廢棄酒粕（Yr, Yp 及Yk）中篩選出酵母菌株作為發酵菌種，本研究之目的根據所篩選酵母菌之發酵速率、耐乙醇能力及乙醇產率，分離及鑑定出最適合甘蔗酒製作之酵母菌株。對Yr,Yp 及Yk 等酵母菌株之耐乙醇試驗得知，隨著乙醇含量之增加，吸光值逐漸下降，生長菌數亦隨之緩慢減少，對整體菌株而言其耐乙醇度約為12%。當發酵糖度提高至24 °Brix 時，甘蔗原汁發酵終產物乙醇平均含量約為12.34%。利用不同糖度進行酒精發酵，乙醇生成率研究得知，隨著發酵糖度之增加，可溶性固形物逐漸減少，發酵產生之乙醇含量亦隨之增加，發酵糖度與乙醇含量之關係符合乙醇收量之理論值。對甘蔗酒之製作，於13 °Brix 時，Yp2 於發酵初期乙醇含量較低。對Yr1、Yr2、Yk1、Yk2 及Yp4 篩選之酵母菌而言，當發酵時間至第四天時，乙醇生成量達於最高，在24 °Brix 糖度發酵時，亦於第七天達於最高，因此對於甘蔗酒之製作，應為可用之菌株。若欲進行甘蔗酒製作時，建議最高之發酵糖度可至24 °Brix 左右。根據無性增殖特徵、菌絲型態、有性世代及培養特性等型態學及生理學特徵，並輔以酵母菌電腦鑑定程式判斷。Yp4、Yr2 及Yk2 酵母菌分離菌株應為Saccharomyces cerevisiae。

Yeast strains from soil (Yc), pineapple (Ypa), grape peels (Yg) and liquor rice dregs in three different wine making factories (Yr, Yp and Yk) were used as materials, and the purpose of this study was to isolate and identify the most suitable yeast strains for making sugar can wine based on the results of fermentation rate, ethanol yields and ethanol tolerance abilities. For the ethanol tolerance test of Yr, Yp, and Yk strains, as the concentration of ethanol increased, the absorbance decreased gradually along with the reduction of the total cell counts. In general, their ethanol tolerances are around 12% using pure sugar cane juice with 24 °Brix of sugar content as the fermenting material, and the reported average alcohol yield is about 12.34%. According to various fermentation studies, the increase of fermented sugar level and decrease of remaining total soluble solids parallel with rising of the ethanol yield. Therefore, the ethanol content is in accordance with the theoretical ethanol yield. In the initial stage of fermentation in 13 °Brix, the Yp2 strain produced a lower amount of ethanol. The ethanol yields reached the peak at the fourth day of fermentation for the isolated yeast strains Yr1, Yr2, Yk2, and Yk4. As the sugar content was raised to 24 °Brix, the ethanol yields achieved the maximum at the seventh day. Thus, these strains are recommended for sugar cane wine manufacturing. Accordingly, the suggested sugar content for wine making is around 24 °Brix. The identification of the isolated yeasts was based on their morphological and physiological characteristics including asexual proliferation, mycelium, sexual generation. and cell incubation. In addition, the computer data base helped the identification. As a result, Yp4, Yr2, and Yk2 were identified as Saccharomyces cerevisiae.