Abstract: The aroma components of bagged and non-bagged ‘Ruixue’ apples picked on day 165, 180, 195 and 210 after full bloom were analyzed by head-space solid-phase micro extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), and their ethylene contents were determined by gas chromatography (GC). Besides, the expression levels of the genes associated with the synthesis of aroma and ethylene were analyzed by qRT-PCR assay. A total of 68 aroma components were detected in the apples, among which, 46 were found to be present in bagged apples and 62 in non-bagged apples. The aldehyde content in the bagged fruit was significantly higher than that in the un-bagged fruit, while the contents of ester and olefins were significantly lower than those in the un-bagged fruit. The level of ethylene receptor gene expression was significantly down-regulated in the bagged fruit, and the content of ethylene was lower than that in the un-bagged fruit. The expression levels of the genes encoding lipoxygenase (LOX) and alcohol dehydrogenase (ADH) were significantly down-regulated in the bagged fruit. Our results implied that the reduction of ethylene synthesis in the bagged fruit resulted in the down-regulated expression of MdLOX and MdADH genes, affecting the synthesis of aroma components and consequently the flavor quality of apple fruit.

Key words: apple aroma compounds, gas chromatography-mass spectrometry, bagging, gene expression