Studies On Volatiles In Fruit Of Chinese Pear Cultivars And Expression Of Ester Biosynthesis Related Genes

Fruit aroma is one of the most important attributes of fruit quality. In our research, we compared different aromatic constituents of different species and cultivars native to China using SPME and GC/MS. We also studied the expression of some genes which are related to ester biosynthesis including PuLOXs, PuADHs and PuAAT in the fruits of Pyrus ussuriensis during ripening and storage. The main results are as follows:1. We optimized the different parameters of SPME using’Kuerle fragrance’pear as material. Results showed that65μm PDMS/DVB fiber had the best effect of extraction; the optimum factors such as sample volume, extraction time and temperature were10g,45min and40℃respectively.2. In this study, volatile compounds of pear cultivars originating from different species were detected by using an electronic nose. The results revealed that18sensors of the Alpha FOX4000electronic nose responded differently to the volatile compounds of pear cultivars. Likewise, different cultivars resulted in different responses to these sensors. The eight cultivars were clustered into two groups by principal component analysis (PCA). One group with a high concentration of some volatile compounds exhibited higher response values to sensors, and another group with a low concentration of some volatiles showed lower response values to sensors. In addition, these cultivars were clearly differentiated on the basis of their origination and producing area using discrimination factor analysis (DFA). Therefore, the detection of volatile compounds using electronic nose combining with appropriate mathematic analysis could differentiate pear cultivars.3. We compared the different volatile compounds of11pear cultivars belonging to different species. A total of70volatile compounds including three alcohols, six aldehydes, fifty-two esters, three acids, three terpenes and three ketones were identified and quantified. Ester was the dominant chemical class of which a total of52compounds were detected. Hexanal, hexyl acetate, ethyl hexanoate, ethyl2-methylbutanoate and ethyl butanoate were major volatile compounds or character impact odorants. Pyrus ussuriensis Maxim showed a higher concentration of volatiles, especially ester content which was dramatically higher as compared with the other Asian pear species. Cultivars were clearly grouped into four clusters based on the quantity and occurrence of members of different classes. Clusters of different cultivars could be discriminated from each others by the first two PCs (Principal Components). It might be possible to discriminate different Pyrus cultivars by principal component analysis. Volatile profiles of pear aroma were influenced by cultivars qualitatively and quantitatively.4. The volatile compounds of three culitvars of Pyrus ussuriensis Maxim.including’Pingxiangli’,’Xiaoxiangshui’and ’Youhongli’ pear fruit from different ripening stage were extracted by headspace solidphase microextraction and analyzed by gas chromatography-mass spectrometry. More than twenty volatile compounds were detected at different ripening stage. Ester was predominant among the volatile profile and increased dramatically during ripening, while the content of aldehyde decreased. The gene expression of’Pingxiangli’pear fruit showed that it was highly correlated to ethylene and ester biosynthesis. The transcription level of genes including PuACSl, PuACO1, PuACO6, PuLOXl, PuLOX8, PuADH2and PuAAT were on the peak at the third day of ripening in’Pingxiangli’pear fruit. Transcription levels of PuACO2, PuACO5and PuADH3reached to peak on the6th day of ripening. Taking the production of ester during ripening of ’Pingxiangli’pear, we speculated on the condition of enough substrate, ethylene regulated the expression of PuAAT, and then enhanced the production of ester.5. The content of volatile compounds in1-MCP treated fruits was inhibited obviously during storage of’Ruanerli’ pear. As important constituents of fruit aroma, the changes of ester and aldehyde were different during all stroage time. The content of ester increased with the course of ripening, while aldehyde remained a stable content. As compared with untreated fruit, the concentration of ester in1-MCP treated fruit was lower. Nevertheless there wasn’t any difference in the concentration of aldehyde between treated and untreated fruits. The expression of PuLOXs and PuAAT were inhibited in1-MCP treated fruits, while PuADHs weren’t suppressed in treated fruits. These results interpreted that PuLOXs and PuAAT might to be the rate limiting steps for ester biosynthesis, while puADH wasn’t.