Quality Detection of Postharvest Litchi Based on Electronic Nose: A Feasible Way for Litchi Fruit Supervision during Circulation Process

Abstract

Susceptibility to mechanical injury and fast decay rates are currently two main problems of litchi fruit after harvesting. To achieve better postharvest management of litchi fruit, this study aimed to find an effective method of litchi fruit supervision during the circulation process that included mechanical injury detection and storage quality detection. For mechanical injury detection, injury-free litchis without any treatment and litchis with mild and severe mechanical injuries were dropped from 80 and 110 cm high, respectively. The electronic nose (E-nose) response, total soluble solid (TSS), and titratable acidity (TA) of samples were tested on days 0, 1, 2, 3, 4, and 5 after injury at room temperature. For storage quality detection, normal litchis were stored in a cold environment. The E-nose response, TSS, and TA of samples were tested on storage days 0, 3, 6, 10, 15, 19, and 24. The experimental results showed that mechanical injury not only accelerated pericarp browning but also accelerated flavor (TA and TSS) loss. The browning index quickly increased during storage, and the TSS and TA of defect-free litchis changed only barely at room temperature and during cold environment storage. After feature extraction, mechanical injury of litchi can be well-detected by E-nose from day 1 to day 4 after injury. The best mechanical injury detection time of litchi fruit is at day 4 after injury under room temperature storage conditions. After singular sensor elimination and comprehensive feature extraction, the storage time and browning degree, but not TSS and TA, of litchi fruit can be detected by E-nose. E-nose data preprocessing should differ according to the litchi variety and detection target.