A consideration on afterripening management of kiwifruits based on relation between fruit density and sugar content

A high precision non-destructive measurement technique for early kiwifruit sugar content estimation was proposed. Sugar contents of matured kiwifruits were estimated at harvest when the fruits were still immature. By estimating density of the immature fruit, starch content can be determined that was found closely related to sugar content of the fruit when it is fully matured. The fruit density was calculated from weight and volume information of the fruit. Considering the fact that the range of densities of kiwifruit is very narrow (about 1.02~1.06g/cm3), the measurement of volume requires high accuracy. In this study, the volume of about 2000 kiwifruits at harvest was measured with a Helmholtz acoustic resonance method that offered good correlation with a reference method with R2=0.9254, SEP=0.0019g/cm3. The fruit weight was measured with an electronic scale. The relationship between the fruit density at harvest and sugar content following ethylene treatment was also verified. The proposed system can be used for precision grading of kiwifruit quality based on prediction of sugar contents.