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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.

Visible/near-infrared (VIS/NIR) spectroscopy is a powerful tool for rapid, nondestructive fruit quality detection. This technology has been widely applied for quality detection of small thin-peel fruit, although less so for large thick-peel fruit because of the low signal-to-noise ratio of the spectral signal, resulting in a reduction of accuracy. More modeling work should be focused on solving this problem. This research explored a method of spectroscopy for the total soluble solid (TSS) content and acidity detection of ‘Shatian’ pomelo, which are two major parameters of fruit internal flavor. VIS/NIR spectral signal detection of 100 pomelo samples during storage was performed. Detection based on raw data, signal jitter, and scattered light noise removal, feature extraction, and deep learning were performed and combined with modeling detection to achieve an accurate step-by-step detection. Our results showed that 600 W is the optimal light intensity for detecting the internal flavor of pomelo. The TSS content of pomelo is optimally detected using Savitzky-Golay (SG) + multiplicative scatter correction (MSC) + genetic algorithm (GA) + principal component analysis (PCA) + convolutional neural network (CNN) + partial least squares regression (PLSR); however, acidity of pomelo is optimally detected using SG + MSC + GA + PLSR. With the optimal detection method, the coefficient of determination and root mean squared error (RMSE) of the validation set for TSS detection are 0.72 and 0.49, respectively; and for acidity detection are 0.55 and 0.10, respectively. Even though the accuracy is not high, the data are still acceptable and helpful in nondestructive quality grading of large quantities postharvest fruit. Therefore, our results demonstrated that VIS/NIR was feasible for detecting the TSS content and acidity of postharvest pomelo, and for providing a possible method for the nondestructive internal quality detection of other large thick-peel fruit.

Rambutan (Nephelium lappaceum L.) (Sapinadeae) fruit, a nutritional staple in Hawaii, exhibits desiccation and physiological browning soon after harvest, and methods to prolong shelf life may be commercially advantageous. In this study, freshly harvested fruit were treated with pectin coatings with or without trans-cinnamaldehyde (TCIN) and stored at 10 °C or 20 °C (room temperature) to evaluate postharvest quality attributes. Control fruit were treated with deionized water only. To find the best formulation of the coatings, three concentrations of TCIN were incorporated into a pectin solution to get 0.05% TCIN, 0.1% TCIN, and 0.2% TCIN coatings. At 0, 2, 4, and 6 days postharvest, fruit stored at 20 °C were evaluated for weight loss, firmness, pericarp browning, sugar, acid, and taste. The results showed that the 0.1% TCIN coating exhibited significantly lower weight loss than both control and the 0.2% TCIN coating through the entire storage time at 20 °C. The 0.1% TCIN coating–treated fruit were significantly firmer than control after 4 days of storage at 20 °C. The 0.1% TCIN coating also significantly reduced the pericarp browning over the control. Therefore, we selected 0.1% TCIN coating for fruit storage at 10 °C for up to 15 days. At 10 °C, the control fruit showed significantly higher pericarp browning than all TCIN-containing coated fruit. The 0.1% TCIN-treated fruit showed a significantly higher overall quality value than control fruit. The results indicate that the 0.1% TCIN coating may extend the commercial shelf life of rambutans and other perishable fruits. By extending shelf life, this coating can reduce postharvest losses and facilitate expanded fruit exports in Hawaii.