Abstract: The changes of core browning index, mass loss rate, fruit hardness, respiration intensity, ethylene release rate, phenylalanine ammonian-lyase (PAL) activity and PAL gene expression in late-harvested ‘Yali’ pears under slow and rapid cooling conditions were determined in the present study. And the relationship of PAL gene expression with core browning was studied by qRT-PCR as well. The results showed that the browning index of pears with slow cooling was pronouncedly higher than with rapid cooling, and more significant browning was observed with slow cooling. Moreover, slow cooling showed higher PAL activity than rapid cooling as well as higher relative expression level of PAL gene from the 60th day of storage onwards. The relative expression level of PAL gene was significantly positively correlated with PAL activity and core browning index. In conclusion, slow cooling treatment can accelerate core browning, while rapid cooling can inhibit the relative expression of PAL gene, reduce PAL activity, and maintain higher quality of late-harvested pear fruits during storage.

Key words: late-harvested ‘Yali’ pear, browning, phenylalanine ammonian-lyase (PAL) activity, PAL gene expression, cooling method