Changes Of Flavor Compounds And Establishment Shelf-life Model In Post-harvest Apple

The quality and flavor of apple constant change during post-harvest storage.In this thesis,the differences on quality and flavor of eight common fresh apple varieties in western Liaoning province were studied,and the cluster analysis was also carried out.Then,the two different types of apple,‘Golden Delicious'and‘Huafu',were chosen as the raw materials to investigate the changes of quality and flavor under different temperature storage conditions(4°C and 20°C),and the shelf life prediction model was constructed.This study revealed the changes of flavor substances in apple during storage,and analyzed the correlation between apple flavor index and quality index.In addition,apple shelf life prediction model was built based on electronic nose.This study could enrich post-harvest preservation mechanism of apple,and provided a theoretical reference for the rapid detection on post-harvest shelf life of apples.The main results were as follows:1.The differences in quality and flavor of eight common fresh apple varieties,including‘Wangshanhong',‘Hanfu',‘Huafu',‘Ralls',‘Jonagold',‘Golden Delicious',‘Orin'and‘Indo',were analyzed.Studies have shown that the color difference of peel and flesh of 8 kinds of apples were significant.The peel and flesh of‘Huafu'and‘Ralls'were relatively hard.The moisture content of‘Ralls'fruit was higher,followed by‘Huafu'and‘Jonagold'.The different forms of sugar,titratable acid and sugar-acid ratio in the fruit had a better correlation with the acidity,umami and salty taste measured by the electronic tongue,and had a significant effect on the evaluation of the taste of the fruit.The radar chart analysis of the electronic nose sensor showed that the electronic nose was sensitive to the aroma components of the apple fruit,and can quickly and non-destructively detect the aroma components of the fruit.PCA and LDA can distinguish 8 apple flavors well,the fruit flavor of‘Wangshanhong'and‘Orin'was quite different from other varieties.The analysis of electronic tongue showed that there were significant differences in the sour,umami and salty tastes of the eight apple fruits.The difference analysis of the contents of 8 kinds of apple volatile flavors by SPME/GC-MS showed that the contents of aroma components of 8 kinds of fruits were significantly different.Aroma threshold analysis showed that 2-methylbutyl acetate,hexyl acetate,hexanal and(E)-2-hexenal had an important effect on the aroma of eight apples;ethyl butyrate only contributes to the aroma components of‘Orin'.Principal component analysis based on flavor materials showed that dipentene,nonanal,geranyl acetone,phytane,m-xylene,hexyl acetate,(E)-2-hexenal,?-farnesene and toluene were the main characteristic volatile substance in apples.Systematic cluster analysis based on flavor materials divided eight apples into two categories,one was‘Wangshanhong',‘Huafu',‘Ralls',‘Orin'and‘Hanfu',and the other was‘Jonagold',‘Golden Delicious'and‘Indo'.2.Taking two typical flavors of apple varieties,‘Golden Delicious'and‘Huafu',as research objects,the changes of flavor substances during normal temperature and low temperature storage were investigated.According to the electronic nose analysis,the aroma components of‘Golden Delicious'and‘Huafu'apples were significantly changed at 4°C and 20°C,and the aroma components of‘Huafu'fruits at 4°C and 20°C end of storage were significantly different.As far as the sensor was concerned,the sensors with a higher contribution rate stored at 4°C were R2 and R6,while the sensors with a higher contribution rate stored at 20°C were R2,R6 and R8;there were many types of aroma components stored at 20°C.The analysis of electronic tongue showed that the taste change of‘Huafu'during storage was more significant.During storage at 4°C,the acidity,bitterness,astringency and salty taste changed significantly,and the sourness,bitterness and astringency changed significantly during storage at 20°C.According to SPME/GC-MS analysis,esters,alcohols and aldehydes were the main aroma components of‘Golden Delicious'and Huafu apples during storage.The main components of the‘Golden Delicious'during storage at 4°C were butyl acetate,2-methylbutyl acetate,butyl butyrate,hexyl acetate,2-methylbutyl butyrate,hexyl butyrate,Hexyl isovalerate,1-butanol and hexanal,the main aroma components stored at 20°C were hexyl acetate,propyl hexanoate,hexyl propionate,hexyl isobutyrate,hexyl butyrate,hexyl isovalerate,hexyl hexanoate,1-hexanol,?-farnesene,and the like.The main aroma components of‘Huafu'stored at4°C werehexyl acetate,hexylbutyrate,2-methyl-1-butanol and?-farnesene,the main aroma components stored at20°C were butyl butyrate,amyl butyrate,hexyl isobutyrate,hexyl butyrate,1-heptanol,(E)-2-hexenal and the like.On the whole,the main aroma components detected by‘Golden Delicious'and‘Huafu'apples during storage at 4°C were less,and more aroma components were detected during storage at20°C.3.The shelf life prediction model based on electronic nose was established by partial least squares regressions(PLS)to predict the shelf life of‘Golden Delicious'and‘Huafu'apples.First,the correlation between the electronic nose sensor and the sensory quality of two apples was analyzed to select the suitable sensor to build the shelf life model.The results of PLS prediction model showed that the shelf life prediction model of‘Golden Delicious'stored at 4°C was R~2=0.86,RMSEC=3.94;the shelf life prediction model established stored at 20°C had R~2=0.83 and RMSEC=2.98.The shelf life was predicted using this model,the predicted and measured values of R~2stored at 4°C and 20°C were 0.98 and 0.92,respectively.This showed that the model was relatively accurate.The shelf life prediction model established by6 sensors related to sensory qualities for‘Huafu'stored at 4°C had R~2=0.80,RMSEC=3.08,and the shelf life prediction model established by 10 sensors had R~2=0.65,RMSEC=4.01.The shelf life using two model stored at 4°C was predicted,and R~2 were 0.92 and 0.84,respectively;the shelf life prediction model established by 4 sensors related to sensory qualities for‘Huafu'stored at 20°C had R~2=0.83,RMSEC=3.78,and the shelf life prediction model established by 10 sensors had R~2=0.74,RMSEC=4.33.The shelf life was predicted using two model,R~2‘Huafu'stored at 4°C and 20°C were 0.92 and0.90,respectively.Overall,the shelf life prediction model based on electronic nose response sensor,which had strong correlation with sensory quality,was better than that of all sensors.