Study On Quality Deterioration And Flavor Of Pitaya During Storage

Pitaya is a typical tropical fruit.It is loved by consumers because of its unique shape and unique flavor.Among them,red pitaya is very popular because of its unique variety and bright color.The output within the scope is growing rapidly over the world.The flavor quality of pitaya during storage is mainly affected by volatile substances and non-volatile substances.In this thesis,two varieties of red pitayas,'Meiguixiang' and 'Dahongyihao',were used as experimental materials to study the physiological and biochemical,volatile flavor and non-volatile flavor changes during storage at 25 °C.Mainly from the two aspects of "taste" and "flavor" to explore the mechanism of the deterioration of the flavor quality of red pitaya during storage,and provide scientific basis for further research on the influence of flavor characteristics of red pitaya during post-harvest storage.The main findings are as follows:1.During storage at room temperature,the storage quality of the two red pitaya such as skin hardness,pulp hardness,total phenols,ascorbic acid and titratable acid decreased significantly;but the soluble solids and soluble sugar content did not change significantly.The correlation analysis of sugar-acid ratio and solid-acid ratio shows that the titratable acid content is significantly related to the sugar-acid ratio and the solid-acid ratio.It is inferred that the decrease of the titratable acid content causes the imbalance of red pitaya sugar-acid ratio.The main reason for the bad taste and quality of red pitaya after harvest.2.The changes of non-volatile substances in red pitaya under normal temperature storage were studied.The results showed that the red pitaya is a malic acid type fruit,and the decrease of the malic acid content dominates the decrease of the organic acid content,the acid-sweet ratio is imbalanced,and the taste deteriorates.The content of malic acid was significantly positively correlated with the enzyme activities of NAD-MDH and PEPC related to synthesis,and the enzyme activities of NADP-ME related to degradation were both significantly negatively correlated.NAD-MDH,NADP-ME and PEPC were all positively correlated with their gene expression;Among the flavored amino acids,the content of sweet amino acids is reduced,and the content of bitter amino acids is increased.However,since the total free amino acids in red pitaya had a very low content,the contribution to the taste is limited.3.A total of 62 volatile compounds were detected from the red pitaya of ‘Meiguixiang'and ‘Dahongyihao' variety,and the overall content increased first and then decreased during storage.The unique rose fragrance of ‘Meiguixiang' is derived from geraniol and nerol.In the early stage of storage,the main aroma contributing substances of the two varieties of red pitaya are n-hexanal.In the later stage of storage,the ‘Meiguixiang' variety is converted to geraniol,and the ‘Dahongyihao' is converted to 2,6-nonadienal.The content of the main aroma-contributing substances decreased significantly during storage,causing flavor deterioration.