| Fruit aroma is one of the most important attributes of fruit quality.In this study,HS-SPME and GC-MS were used to detect aromatic components of fruit at development stages,mature and after-ripening stages for five representative pear cultivars:’Bartlett’,’Hongnanguo’,’Korla Xiangli’,’Dangshansuli’ and’Housui’.Furthermore,aromatic components of matured fruit of 12 Occidental pear cultivars were investigated and compared.In addition,we compared the aroma components of Yuluxiang’ matured fruits which were treated with different fruit bags.Expression patterns of genes involved in aroma formation including PbrLOXs,PbrADHs and PbrAATs were studied during development and storage peirods of five representative pear cultivars.The main results are as follows:1.There fruits of five cultivars have higher aroma concentration at early development stages than fruit at middle development stages,then,the aroma concentration rising constantly from fruit middle development period to mature period.After stored 60 days at 4℃ and after-ripning to reach optimum taste period(OTP),the aroma content change of five cultivars showed different patterns.They were divided into 2 groups,group Ⅰ includes’Bartlett’(2212.1 μg/kg),’Hongnanguo’(2206 μg/kg)and ’Korla Xiangli’(171.4 μg/kg)with aroma amount rose after storage;group Ⅱ includes ’Dangshansuli’(41.7 μg/kg)and’Housui’(49.1 μg/kg)with aroma amount decreased after storage.Aldehydes are primary components in early and middle development periods in five cultivars,and the primary aldehydes including hexanal,(E)-2-hexenal and phenyl acetaldehyde.Esters are the primary components in pears in mature period and OTP in ’Bartlett’,’Hongnanguo’ and ’Korla Xiangli’.The results of gene expression analysis revealed that PbrAAT1,PbrLOX3 and PbrLOX5 are closly realated to aroma formation,while PbrAAT2,PbrADH1,PbrADH1,PbrEEBl and PbrPDC are not working in pear fruits during development and ripening.2.A total of 335 volatile organic compounds were identified,including esters,alcohols,alkanes,acids,ketones,terpenes and aldehydes.The highest concentration of total aroma was found in ’Alexandrine Douillard’(18730 μg/kg),whereas the lowest total concentration was in ’Bartlett-Max Red’(330μg/kg).Based on the ABC’s of Perfumery System,the 12 pear cultivars were divided into two groups,in which‘La france’,’ Abate Fetel’,’Bartlett’,’Beurre Bosc’,’Alexandrine Douillard’,’Doctor Jules Guyot’ and ’Yubileen Dar’ were classifiled into the fruit scent type(Group one);and ’Butirra Rosata Morettini’,’beurre Hardy’,’Bartlett-Max Red’,’Clapp Favorite’ and ’Red Clapp Favorite’ were classifiled into the aliphatic scent type(Group two).3.The main aroma components in ’Yuluxiang’ with bagging treatment and untreated fruit are volatile esters,however,contents of aldehydes are the highest in fruits with white paper bag.Results indicated that the ’ Yuluxiang’ fruits with plastic bag and white paper bag have an enhanced aroma,and aroma content is highest in fruit with plastic bag(43.22μg/kg).Whereas the double layer bags make the ’Yuluxiang fruit’ fruit have a weakened aroma,aroma content is lowest in fruit with yellow white bag(26.69 μg/kg).Morever,bagging treatment makes the aorma components number increased,and fruit with yellow white bag has most kind of chemicals(46).At the same time,11 chemicals were detected in each of the five treatments.Ester was the scent type in ’ Yuluxiang’ fruit with plastic bag,white bag and yellow black bag,fruit and green grass was the scent type in ’ Yuluxiang’ with yellow white bag,and phenol was the scent type in ’ Yuluxiang’ with CK. |
