Screening of Fermentor Yeasts for Sugarcane Wine Making and the Optimization of the Wine Manufacturing Process

• Main Authors: Daw-I Tzeng, 曾道一
• Other Authors: Andi Shau-Mei Ou
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/56954659960623662062

博士 === 國立中興大學 === 食品暨應用生物科技學系 === 96 === Yeast strains isolated from soil (Yc), pineapple (Ypa), grape peels (Yg) and liquor rice dregs collected from three wine making factories (Yr, Yp and Yk) were used as tester microbes. The purpose of the first part of this investigation was to screen for the most suitable yeast strains for making sugarcane wine. The results obtained from the compared fermentation rate, ethanol contents and ethanol tolerance all showed that strains Yr2, Yp4 and Yk2 were among the tested isolates scored the highest. Upon ethanol treatment, the survival cell counts of these 3 selected strains all decreased with the increase of ethanol concentration applied. However, in general, they could tolerate ethanol up to 12%. Using pure sugarcane juice of 24 °Brix as cultural substrate, the average ethanol contents reached peak high about 12.34% at 7 days after inoculation of these three tester strains. The yield and quality of the wine obtained suggested clearly the value of the three strains worth to be recommended for attempted sugarcane wine manufacturing. The morphological and physiological characteristics including asexual proliferation, mycelium growth, sexual reproduction, cultural characteristics, and further the confirmation by the sequence of the D1-D2 domains of the 26S rDNA gene all indicated that the three tester strains were members of Saccharomyces cerevisiae. In the second part of this study, response surface methodology was applied to explore the combined effects of cultural conditions such as sugar content, incubation temperature and medium pH on the sensory quality and ethanol contents of sugarcane wine (SCW) obtained. The results from contour plots showed that the maximum ethanol contents around 11% was obtained from the treatment with the initial sugar content at 25.0 oBrix, incubation temperature at 26.3℃ and pH at 5.5. The results of consumer tests showed that a better color acceptance of the SCW produced with initial sugar content equal to or lower than 24 oBrix was from those incubated at a higher temperature. While the applied sugar content exceeded 24 oBrix, the lower temperature appeared to be favorable for better aroma, flavor and overall preference. Statistical analysis with the central composite rotatable design (CCRD) showed that the total soluble solids of SCW produced was significantly (p<0.05) affected by the applied sugar content, pH and incubation temperature. The applied sugar content and incubation temperature appeared to affect significantly (p<0.05) the ethanol contents and aroma of SCW. Whereas the applied pH significantly (p<0.05) affected the flavor and overall preference. The overall performance regarding to the results of total soluble solids, ethanol contents, consumer preferences and the confirmative experiments all indicated that the applied sugar content at 24-26oBrix, pH at 5.5 and incubation temperature at 24-27℃ were the optimal cultural condition for SCW manufacturing. In the third part of the works, a quantitative descriptive analysis of the SCW produced by use of the tested S. cerevisiae (Yr2) strain was carried out by a panel of 8 well-trained panelists. The data obtained was used to investigate the effects of process parameters on the sensory characteristics and to analyze the correlation among the sensory properties evaluated. The increase of applied sugar content was found to be stimulatory in regarding to the aroma, alcoholic flavor, sweetness flavor and aftertaste, and decreased acidity and astringency. The applied pH appeared to affect significantly (p<0.05) the yellowness, lightness, sugarcane aroma, sweetness and acidity of SCW. Whereas the applied incubation temperature significantly (p<0.05) affected the sugarcane aroma, sweetness, acidity and sweet aftertaste of SCW. The last part of this study was aimed to examine the growth curve of yeasts, the changes of sugar contents, the yield of ethanol, organic acids and volatile compounds, and the changes of pH, acidity and color in SCW during fermentation by using tested S. cerevisiae strain. According to the results, the maximal population of S. cerevisiae reached to 8.12 log cfu/ml at the sixth day of fermentation. The maximum ethanol contents at 15.16% was obtained at the ninth day while sucrose and glucose contents of the cultural broth were almost exhausted. Citric acid was found to be the most abundant organic acids detected at the second day of fermentation, next to that was in the order lactic and succinic acids. The analysis of volatile compounds by SPME/GC-MS indicated that the concentration of alcohols, esters and acids all reached the highest level among the broth cultures at the sixth day of fermentation. The highest esters/alcohols in the wine and the most abundant amount of aroma-related compounds detected indicated that the attempted SCW fermentation by use of the tested S. cerevisiae strain is better off at the sixth day when the highest aroma quality is a primed target. The overall preference of consumer test also supports this view where that the SCWs at day six consistently showed the highest scores.