Mutation Breeding Of Streptomyces Sp.Producing AVG,preparation And Application Of Preservative

Postharvest fruit and vegetables are easy to becoming senescence under the influence of ethylene in the environment,resulting in shortened shelf life and even losses of commodity value.Aminoethoxyvinylglycine（AVG）is an inhibitor of 1-aminocyclopropane-1-carboxylic acid（ACC）,the ethylene precursor.It can block S-Adenosylmethionine（SAM）attacking PLP cofactors and effectively inhibit ethylene biosynthesis,to delay the ripening process of fruit and vegetables.In the previous research,our team isolated and screened a Streptomyces strain and found that its fermentation broth contained AVG.In this study,the preservative containing AVG was prepared through its mutation breeding,optimization of culture conditions and preliminary purification of fermentation filtrate,and its preservative activity on cherry tomato,green pepper and bitter gourd was preliminarily determined.This research provides practical references for developing ethylene synthesis inhibitor products.The main results are as follows:（1）AVG was identified and determined by TLC and elution respectively.N-butanol glacial acetic acid water（4:2:1）was the best development system,and the sample amount was5μL.The AVG standard curve equation is y=468.59 x+2.8414（R~2=0.9974）,and the AVG yield of the initial Streptomyces was 52 mg/L when cultured in YEPEG medium at 28℃for72 hours.（2）The mutation breeding of AVG strain was carried out by diethyl sulfate mutation system.The mutation time was 40 min and the mutation concentration of diethyl sulfate was15μL/m L.Penicillin sensitive strains were screened by spot planting control method,and a strain with a yield of 76 mg/L was selected,which was 31.6%higher than the original strain.The results showed that the high-yield strain was stable after subculture.Different concentrations of AVG preservatives were prepared by removing bacteria,centrifugation,extraction,rotary steaming and sterilization.Their appearance is similar to that of foreign biological preparations containing AVG components,so as to be suitable for postharvest preservation of different kinds of ethylene sensitive fruit and vegetables.（3）The AVG yield（Y）was selected as the response value,and the fermentation temperature（A）,pH value（B）,and fermentation time（C）were selected as the investigation factors to carry out the response surface experiment of three factors and three levels.The regression equation was regressed step by step by using design expert 8.0.6 software.the optimal fermentation parameters were revised as 30℃,pH 7.00 and 85.5 h.Under this condition,the AVG fermentation yield was 86.2 mg/L,which was consistent with the predicted value of the model（87.7529 mg/L）,which verified the reliability of the model.The yield of AVG increased by 39.7%compared with the original strain.（4）AVG preservatives with different concentrations were prepared by removing bacteria,centrifugation,extraction,rotary steaming and sterilization.Under the storage temperature of 25℃,100 mg/L AVG preservative treatment could effectively maintain the shelf quality of cherry tomato and bitter gourd and prolong the shelf life for 3-4 days;50mg/L AVG preservative treatment could effectively maintain the shelf quality of green pepper and prolong the shelf life for 3-4 days.