Effects Of Drying,Storage And Packaging Materials On Chinese Jujube Aroma

Chinese jujube has a strong characteristic aroma.Currently,there have been a mass of studies on the aroma components of Chinese jujube,but there are few studies on the formation of dried Chinese jujube aroma and its changes during storage.In this study,Ziziphus jujuba was taken as the research object,headspace solid-phase microextraction/gas chromatography-mass spectrometry(HS-SPME-GC-MS)and electronic nose analysis technology were adopted,the characteristic aroma components of Ziziphus jujuba were found out,the influence rules of drying and storage on the aroma of Ziziphus jujuba were mastered,and the influence of packaging materials and storage temperature on the aroma of dried Ziziphus jujuba was clarified,so as to provide theoretical reference for the processing and storage quality improvement of Chinese jujube.The main results are as follows:(1)With volatile substance content as the indexes,the effects of extraction temperature(30,40,50,60,70 and 80?),extraction time(10,15,20,25 and 30 min)and desorption time(1,2,3,4 and 5 min)on the extraction of volatile compounds from Chinese jujube were explored,and its extraction process was optimized.The optimum extraction conditions were obtained as follows: extraction temperature for 60?,extraction time for 25 min,resolution time for 3 min.(2)58 volatile components were identified by HS-SPME-GC-MS,including 21 esters,10 acids,5ketones,2 aldehydes,4 terpenes,2 alcohols,8 furans,2 pyrazines and 4 others.The main volatile components in fresh Chinese jujube were esters and aldehydes,and benzaldehyde,ethyl caproate and ethyl benzoate accounted for the largest proportion,thus showing fruity aroma in Chinese jujube.The main volatile components in dried Chinese jujube were pyrazines and furans,furfural,5-ethyldihydro-2(3H)-furanone,5-methylfurfural and 2-ethyl-6-methylpyrazine accounted for the largest proportion,which mainly show baking aroma and sweet aroma;terpenes,esters and acids were the main volatile components of dried Chinese jujube stored at room temperature for 6 months and 12 months,and D-limonene,benzoic acid,acetic acid and caprylic acid accounted for the largest proportion.In order to understand the effects of drying and storage on volatile components of Ziziphus jujuba,discriminant factor analysis and principal component analysis were carried out on samples by electronic nose.As the drying time increased,the content of volatile components tended to be stable.However,with the increase of storage time,volatile components declined or disappeared.Discriminant factor analysis showed that the cumulative contribution rate of the first two DFs was 94.60%,indicating that these two discriminant factors contain most of the information of electronic nose response value,Discriminant factor analysis could effectively distinguish the differences between samples,with the good discrimination effect.Principal component analysis divided X variable and Y variable into four zone groups,and 99% of the variability in the dataset could be explained by two principal components.The results of electronic nose analysis were basically consistent with those of temperament analysis.(3)Dried Ziziphus jujuba was packed in polyethylene bag,polyethylene and polyethylene terephthalate composite bag,food grade yin-yang vacuum bag and aluminum foil bag,and then stored at room temperature and 4? respectively,and sampled and analyzed at intervals of 2 months.The results showed that with the prolongation of storage time,the total amount of aroma components of Chinese jujube decreased.Except for the increase of acids,the esters and aldehydes with the highest content in aroma components decreased,and furans and pyrazines with great contribution rate to Chinese jujube aroma decreased or disappeared.After storage for 6 months at room temperature,ethyl phenylacetate,ethyl myristate,ethyl palmitate,ethyl hexadec-9-enoate and pyrazines disappeared,the content of aroma components with small molecular weight decreased,and the characteristic aroma of Chinese jujube became weak.The loss rate of volatile components in Ziziphus jujuba stored at 4? was lower than that stored at room temperature,which was better than that stored at room temperature.According to the data change analysis of volatile component content of Ziziphus jujuba in 4 packages,Chinese jujube packed in aluminum foil bags had the best stability,aroma components were well maintained and shelf life was long,followed by yin-yang vacuum bag as well as polyethylene and polyethylene terephthalate composite bag.Valeric acid,4-oxoethyl ester,myrcene,?-terpenene,guaiacol,2,6-bis(1,1-dimethylethyl)-4-(1-oxopropyl)phenol and other volatile components was determined in Ziziphus jujuba packed with polyethylene bag,indicating there is the possibility of isoprene,o-aminoanisole,phenol and olefins in polyethylene materials,which is inferior to the other three packaging materials in storability and quality of Chinese jujube.In conclusion,the results show that the longer the storage time is,the higher the oxidation deterioration rate of Chinese jujube aroma is,the better the storability of Chinese jujube packed with aluminum foil is,and the low temperature storage is beneficial to the preservation of volatile components in Chinese jujube.