Screening Of Aroma-producing Yeasts And Preparation Of Active Dry Yeast By Freeze-drying Method

China is one of the oldest birthplaces of wine with a large amount of wine production per year. The origin and development of brewing culture has become a single show in the river of China’s traditional culture, witnessed the history of five thousand years of Chinese civilization. Wine is traditional distilled liquor in China and one of the world’s oldest species. Wheat, sorghum and maize etal. were subjected to saccharification and fermentation with koji, yeasts and other agents to produce all kinds of liquor production in both ancient and modern China. The main processes include cooking, saccharifying, fermenting, distilling, aging and blending. There is a great variety of microorganisms, such as yeasts, mycetes and bacteria etal. in the distiller’s yeast of wine, which constitutes a biotic community. Performing their roles and interaction of the various microorganisms shapes the mellow flavor and intense perfume of the wine. There are a large number of flavor components dissolving in the wine, mainly containing ethanol, higher alcohols, esters, aromatic alcohol and so on. Flavor-producing yeast is a general name for yeasts that can produce plentiful flavor components. In the liquor brewing, the flavor components will increase observably by adding the right amount of flavor-producing yeasts. However, there are so far a few studies on the flavor-producing yeasts which mainly depend on imported up to now.Active dry yeast (ADY), which its manufacture depends on the development of various drying technology, is a high-tech product with a capability of keeping yeast vitality and performance for a long time. Study on the technologies for drying process of yeas and preparing ADY using the living yeast will be better for the conservation and utilization of yeast. In this study, a strain of yeast that is capable of producing expressive fruit flavors with a high production of ethyl acetate was screened and its species was identified to determine the properties of the strain. Subsequently, based on shaking flask and the premise of increasing the biomass of tested microorganism, the optimal growth conditions, the centrifugal conditions and the process of freeze-drying technology were investigated by using the method of combination of single factor, PB and BBD. The ADY was prepared with vacuum freeze-drying technology after a kind of composite protective agents for the freeze-drying process were screened and optimized. The results we obtained are summarized as follows:Firstly, a flavor-producing yeast strain, named C42, being good at producing aroma formers was screened and isolated from the sample of high-quality jujubes. This yeast strain can produce ethyl acetate up to0.154g/L in the primary fermentation. It was identified as Wickerhamomyces anomalus (W. anomalus) by18s rDNA assay and the physiological and biochemical tests.Secondly, the growth conditions of C42were investigated. The results were as follows: The optimal sugar concentration is4%, the optimum nitrogen source was peptone, the inoculum size was6%and the cultivation temperature was32℃.Thirdly, in order to prepare high active dry yeast using strain C42, we also examined the technological parameters for fermentation, collection and freezing-drying. The results show that the best harvest time was that the culture was shaked at200rpm for18-20h after inoculation. The best condition for collecting the yeast cells with the highest rate of collection up to95%was centrifugation at4500rpm for20min. Most suitable protection agents of lyophilization was that10.00%skim milk,2.90%glycerin,10.33%raffinose and9.63%sodium glutamate, The survival rate is (80.56±1.19)%, which was optimized with the Box-Benhnken design.