|a英文題名:Characteristics of ethanol fermentation and emulsifying properties of its mannoproteins of Saccharomyces cerevisiae mutant with ability of over-expression mannoproteins
|a甘露糖蛋白是酵母菌細胞壁的主要成分之一，由5-20％的蛋白質和80-90％甘露糖共價結合至D-葡萄糖及N - 乙醯基葡糖胺，其在葡萄酒中具有穩定酒石酸、改善色澤和香氣等功能，在食品加工中則可作為生物乳化劑。本研究目的為篩選具大量表現甘露糖蛋白能力之釀酒酵母菌（Saccharomyces cerevisiae），並探討此菌株作為葡萄酒菌酛之潛力及其甘露糖蛋白作為生物乳化劑之效果。將酵母菌以UV光照射或加入化學誘導劑誘導酵母菌產生突變，篩選出具大量表現甘露糖蛋白活性之菌株後，進行酒精耐受性及酒精轉化率之測試，再將其作為發酵台灣巨峰葡萄之菌酛，進行葡萄酒主成分分析及消費者喜好性感官品評。本研究篩選出一株表現甘露糖蛋白能力最佳之化學突變株，命名為S. cerevisiae CM8，其細胞壁中glucose/mannose之比例為1: 3.6(野生株為1：2.1)；細胞壁中甘露糖蛋白的含量為386.8 mg /g，野生株為340.1mg /g。突變株之酒精耐受性較野生株較佳，且經長時間培養(72hr)，其菌數量顯著高於野生株。此外，在酒精轉化率的結果中，突變株在培養72小時後達到與野生株相同生產率(66 %)，因此顯示S. cerevisiae CM8作為紅酒發酵菌酛的潛力。由化學突變株生產的紅葡萄酒(CM-wine)其主成分分析含有137.4 mg / L的酒石酸酯，1174.73 mg/ L的總多酚和403.75mg/ L的單寧，與野生株生產之葡萄酒（SC-wine）中的酒石酸酯(146.9 mg /L)及單寧(310 mg /L)具有顯著差異(p < 0.05)。然而在CM-wine中，單寧含量雖比SC-wine高，但感官品評的結果顯示，CM-wine的消費者喜好度高於SC-wine，CM-wine的消費者喜好度高於SC-wine，同時CM-wine的澀味程度確實低於SC-wine。萃取突變株細胞壁中甘露糖蛋白，並以之作為生物乳化劑的結果顯示，當甘露糖蛋白與棕櫚油混合後，具有良好的乳化穩定性(60 %E24)，甚至高於卵磷脂的乳化穩定性(52 %E24)。因此本研究結果表明，獲得之釀酒酵母突變株(S. cerevisiae CM8)可作為紅葡萄酒發酵之菌酛，由於其細胞壁具較高含量之甘露糖蛋白，所以可有效降低酒石酸的形成及紅葡萄酒的澀味並穩定葡萄酒的顏色，也因此可釀造高品質之葡萄酒。此外，其細胞壁中所含之甘露糖蛋白確實具有作為生物乳化劑的商業價值。|uMannoprotein found in the cell wall of Saccharomyces cerevisiae is composed of 5–20% protein and 80–90% mannose and responsible for most cell surface properties of yeast. The mannoprotein is generally link mannose to protein through covalent bond and associated to the residues of D-glucose and N–acetylglucosamine. Numerous studies have clearly proven the multiple applications of mannoprotein, such as wine quality improvers and stabilizers bio-emulsifier. In this study, yeast mutants were generated by UV light irradiation or chemical mutagen. Killer-9 toxin was used to screen mannoprotein over-expression strains, and then the selected strain with the lowest glucose/mannose ratio in its cell wall was used to ferment Kyoho grape (Vitis vinifera L.) for wine production. One chemical induced mutant (CM8) was selected as the starter and the ratio of glucose/mannose in its cell wall was 1/3.6 (wild-type strain is 1: 2.1). Mannoprotein content in the cell wall of CM8 was 386.8 mg/g while the content in the wild-type strain was 340.1 mg/g. Alcohol tolerance of CM8 was better than that of the wild-type strain, and the cell count of CM8 was significantly higher than that of the wild strain after 72 hr incubation. In addition, after 72 hr incubation, the alcohol conversion rate of CM8 was the same as that of the wild strain. These results showed that CM8 has the potential to serve as a wine fermentation starter. Red wines produced by CM8 (CM-wine) contained 137.4 mg/L tartaric esters, 1.01 g/L titratable acidity, 1174.73 mg/L total phenolics and 403.75 mg/L tannins. The tartaric esters content in CM-wine was significant lower than that in red wine produced by the wild strain (SC-wine) (146.9 mg/L), but the tannin content in CM-wine (403.75mg/ L) was higher than that in SC-wine (310 mg /L). However, the results of sensory evaluation showed that CM-wine had higher consumer preference than SC-wine. Moreover, the astringency degree of CM-wine indeed lower than the SC-wine. The mannoproteins extracted from the cell wall of CM8 had a good emulsion stability (60 %E24) when mixed with plam oil, even higher than the emulsion stability of lecithin (52 %E24). Therefore, this study concluded that S. cerevisiae mutant strain CM8 could serve as a wine fermentation starter to produce high quality of red wine. It had high mannoproteins in its cell wall, and thus, it could effectively reduce the formation of tartaric acid and the astringency of the wine, and increase the stability of wine color. In addition, the mannoprotein extracted from CM8 had the potential to be a commercial bio-emulsifier.
|aCharacteristics of ethanol fermentation and emulsifying properties of its mannoproteins of Saccharomyces cerevisiae mutant with ability of over-expression mannoproteins