Development Of Vacuum Drying Technology Of Alcohol Fermentation Active Dry Yeast

Dry yeast cells having activity have advantages in aspects of stable fermentation, good infruit flavor, short period for fermentation, and thus have wide market and great potential inapplication。However, the dry yeast agents currently used are mainly imported. Therefore, ithas high value in screening and producing local yeast agents that has specific suitability todifferent grape varieties, processing locations and different types of wine. Furthermore,processing the obtained yeasts into dry agents is helpful to solve the problems in practicalapplication, such as tending to contamination, difficult for storage and easy mutation. And, itis helpful to produce high quality wine with local properties. The work has also significancein pushing forward the development of yeast industry and solving the dependence of abroaddry yeast agents and the similarity of Chinese wine produced in different places.A strain of Saccharomyces cerevisia Nx11424, a yeast strain isolated from local site inChina was used throughout the study. Experiments were carried out in aspects of optimizationof medium and cultivation conditions, isolation and concentration of yeast cells from theculture, optimization of complex protective agents and development of vacuum dryingtechnology. Finally, dry yeast agents were obtained and its stability and activity was tested.The obtained major results were listed as follows.(1) By comparing the results of different media, YEPD was selected as the medium usedin following studies. According to the results of the single-factor design, the best nutrients forcell growth were obtained as sucrose for carbon source, soybean sprout and peptone fornitrogen source, KH2PO4for mineral ions, and inositol. After analysis using response surfacemethodology, the medium used for yeast growth was optimized as sucrose56.80g/L, soybeansprout153.25g/L, peptone16.37g/L, KH2PO43.05g/L, and inositol91.49mg/L. Under theoptimal conditions, mass of yeast reached to10.78g/L, being1.7fold of that before theoptimization. The conditions for cultivation was optimized at28℃, pH4.8, and180r/min. Inaddition, the method for collection yeast cells was optimized as centrifugation for10min at4000r/min, under which the recovery of yeast cells was more than95%.(2) After optimization, the protective agents for vacuum drying was obtained as sucrose100g/L, lactose120g/L, mycose100g/L, and sorbitol80g/L. The optimal carrier for making dry yeast agents was obtained as egg white powder.(3) After optimization, the vacuum drying conditions were obtained as39℃, vacuum0.07MPa, and protective to wet yeast cells ratio of2.98:1. The ratio of active yeast in the yeastpowder obtained under the optimal conditions was86%, with quality indexes of active yeastamount8.25×1010cfu/g and water content3.6%, reaching the level of high quality dryyeast powder.