The browning of the fruit pericarp is one of the most significant quality deterioration characteristics of litchi during storage, transportation, and circulation after harvest, which seriously affects its commercial value. In this study, three stress treatments were applied to litchi, mild dehydration treatment (DT), heat shock treatment (HT), and cold shock treatment (CT). We analyzed the changes in appearance quality, browning index, physiological indices, and the activities of polyphenol oxidase (PPO), peroxidase (POD), and superoxide dismutase (SOD) after treatment to explore a new approach to delay pericarp browning by inducing resistance in litchi. The results indicated that after the three stress treatments, the browning of the litchi pericarp was exacerbated, accompanied by a decrease in pericarp brightness, water content, and increased membrane permeability at room temperature. The browning in the DT group was the most rapid, reaching a browning index of 4.99 on the 6th day. In contrast, HT and CT significantly delayed the browning of the litchi pericarp. The completely browned pericarp in the DT group was dry, yellow, and brittle, with the lowest water content (27.76%), which was significantly lower than that in the HT and CT groups (45.20% and 42.99%, respectively). The order of respiration rates was CT>HT>DT, and the relative electrical conductivity was DT>HT>CT. The activity of PPO and POD in the HT and CT groups was inhibited during the early part of storage, while the activity of SOD significantly increased at the later stage. Transmission electron microscopy results showed that the cell structure of the brown peel was destroyed and the contents were largely degraded in the DT and CT groups, whereas the brown pericarp cells in the HT group remained structurally intact and contained a large amount of coalesced sediments. Correlation analysis results showed that the browning index of the litchi pericarp under the three stress treatments was positively correlated with relative conductivity and negatively correlated with L* (brightness), water content in the pericarp, and anthocyanin content (P<0.05). In conclusion, mild dehydration treatment led to rapid browning of litchi, while heat shock and cold shock stress treatments maintained higher water content in the pericarp and respiratory intensity of the litchi fruit. The treatments inhibited the increase of relative electrical conductivity and the activities of PPO and POD enzymes and increased the activity of SOD in the later storage period by stimulating the litchi’s self-resistance, thereby inhibiting the browning of litchi fruits and delaying the decline in fruit quality.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |