Aroma volatile characterisation and gene expression analysis during fruit development and ripening of five pear (Pyrus L.) species

Bartlett, Hongnanguo, Korla Xiangli, Dangshansuli and Housui are representative cultivars from the five cultivated pear species that were chosen to identify aromatic compounds in fruit during developmental, mature and storage periods. We explored the expression levels of aroma formation-related genes during developmental and storage periods. The concentrations of the aromatic compounds first decreased, then increased in all five cultivars. For the climacteric pears, Bartlett and Hongnanguo, the increase continued to optimal sensory quality (OSQ), whereas those for the non-climacteric pears, Korla Xiangli, Dangshansuli and Housui decreased. Aldehydes contributing the 'green' odour and 1,4-benzoquinone were the primary components during early and middle developmental periods. Esters contributing the 'fruity' and 'sweet' odour, were the primary components in Bartlett, Hongnanguo and Korla Xiangli fruits during storage and at OSQ. Methyl- and ethyl-(E, Z)-2,4-decadienoate (pear-like odour), ethyl caproate (liquor odour), and hexyl acetate (fruity odour) were the key characteristic odorants in mature pear fruits of Bartlett, Hongnanguo and Korla Xiangli, respectively. Alcohol dehydrogenase (PbrADH-1 and PbrADH-2) and lipoxygenase (PbrLOX3) might participate in the formation of C-6 and C-9 volatile aldehydes and alcohols. The aroma content and volatiles of pear fruits during development and storage probably revealed a common pattern.