Screening And Characterization Of The Yeast Degrading Ethyl Carbamate

In recent years,the domestic wine industry and other brewing industries have developed rapidly and have formed certain regional characteristics.However,most of the selection of strains depends on imports,causing a very serious homogenization of products.Ethyl carbamate(also known as urethane)is a class 2A carcinogen that can be used as a neuroanesthetic in medicine.Studies have shown that microbial fermentation in the production of fermented foods and alcoholic beverages will produce a certain dose of ethyl carbamate,making the fermented foods have a certain safety hazard.In this study,a large number of yeasts were isolated from the grape of Xinjiang,and yeast species were identified based on the ITS sequences.Five strains of urethane-degrading yeasts were obtained by screening and acclimation with carbamic acid as sole carbon source or nitrogen source.The degradation characteristics of five strains of urethane-degrading yeasts were studied.The specific studies were as follows:1.Separation and Identification of High-quality YeastIn order to obtain safe and high-quality yeast strains,88 strains of yeast were isolated from the skin of grapes and pears using YEPD medium.The yeast strains were identified based on ITS sequence analysis.The results showed that: The 88 strains of yeast belonged to Metschnikowia biscuspidata,Hanseniaspora uvarum,Yarrowia lipolytica,Candida xylopsoci,Pichia fermentans,Pichia kudriavzevii.2.Screening of Degradation of Ethyl Carbamate88 yeast strains were screened using two different kinds of defective culture medium to obtain 15 strains of urethane-degrading yeast strains,which were domesticated to obtain 5 strains that could tolerate a wide range of urethanes.Using a modified SPE-GC-MS to determine the degradation ability of the strain,a yeast strain YX36 with the highest ability to degrade was obtained.The yeast belongs to Metschnikowia biscuspidata and the degradation rate of ethyl carbamate is reached54.4%.3.Related characteristics researchThe tolerance test showed that Metschnikowia biscuspidata YX36 had a maximum tolerance of 14% for sugar,a tolerance of p H 3.5,a tolerance of 12% for ethanol,and a tolerance of 2% for SO2.The urethane degrading enzyme production condition test showed that the optimal enzyme production temperature was 28?,and the optimum enzyme production p H was 7.When the inoculum size was 2.3%,the initial p H was 7 and the reaction temperature was 30?,the strain produced the best degradation activity of urethane.However,the thermal stability of this enzymewas poor,and the enzyme activity was reduced by more than 50% at 50? for 100 min,while Fe2+ had a significant activation effect on enzyme activity.Single factor and response surface tests showed that the inoculum size was 3.5% and fermentation was carried out at 30? for 5.5 d.The urethane degradation was greatest at this time.