Detection of pear freezing injury by non-destructive X-ray scanning technology

During storage and long-distance refrigerated transport, low temperatures may lead to invisible freezing injury, which lowers the overall fruit quality and shortens storage time. As a result, nondestructive evaluation of freezing injury is necessary to evaluate the quality of fruit. The freezing injury of pear Xinli No.7 was experimentally investigated using X-ray technology and scanning electron microscope (SEM). It was found that the gray value of the freezing region in the X-ray image of pear was higher than that of the healthy region, based on which the freezing injury could be distinguished nondestructively. Besides, the area of the freezing region increased linearly with the decrease of the freezing temperature and the gray value increased monotonically when the freezing time increases. Based on the observation of the micro-structure of the freezing pear using an electron microscope, the variation of the gray value is due to the changes of the cavities formed by ice crystals, increasing with the degree of freezing injury. This study explored the X-ray images to determine the severity of pear freezing injury and revealed the mechanism of X-ray variation caused by freezing injury, which is conducive to determining the freezing time and temperature for the purpose of preservation, reducing storage cost and optimizing long-distance refrigerated transportation.