Determinaton of physiological ripening time based on change in physicochemical characteristics during fruit development of ‘Hanareum’ pear (P. pyrifolia Nakai)

This study was conducted to determine the optimal physiological ripening time and suggest a reasonable harvest time indicator by analyzing the relationship between change in physicochemical characteristics and the sugar composition change patterns during development of 'Hanareum' fruit from 54 days after full bloom (DAFB) to 130 DAFB. The weight of fruits from 96 to 115 DAFB rapidly increased and then became gentle showing a typical sigmoidal curve. Flesh hardness decreased steadily after 96 DAFB; there was no significant difference in flesh hardness for 115, 125 and 130 DAFB fruits. The starch content began to reduce around the core for 119 DAFB. Moreover, sucrose and fructose contents started to increase with fruit development; however, the sucrose content continuously increased, whereas the fructose content started to decrease for 110 DAFB. Fruits of 125 and 130 DAFB did not show coloration according to the iodine test. Based on these results, it was estimated that the optimal physiological ripening time of 'Hanareum' was between 119 and 125 DAFB. The results of correlation analysis between fruit development change and sugar composition change patterns of fruits of 'Hanareum' showed that there was a strong linear relationship. Correlation coefficient between the sucrose/fructose (S/F) ratio and flesh hardness is -0.57, between S/F ratio and iodine test results is 0.80. Namely, S/F ratio is possible to use for harvest time determination indicator and the point of S/F ratio of 0.9–1.1 was considered to be ideal for the determination of the optimal physiological ripening time at which starch completely degrades.