Recently, colder weather has been occurring frequently in winter due to climate change, and this has a negative effect on the production of late maturing citrus cultivar such as Shiranuhi mandarin. Therefore, we investigated how freezing at a low temperature affects cold tolerance, fruit characteristics, amino acid content, volatile compounds, and antioxidant activity of Shiranuhi mandarin. A tree in a non-heated plastic greenhouse was surrounded on five sides by a self-assembly expanded polystyrene panel; the temperature was controlled using an air conditioner at –5°C, and –7°C for 6 h. An untreated tree was used as the control. In the –5°C treatment, there was no difference among organs according to the number of days after treatment (DAT), but –7°C-treated leaves showed high damage compared to the branches. The total soluble solid (TSS) content was no difference among treatments at 7 DAT, but low-temperature treatments reduced the TSS content at 14 DAT compared with the control, showing a significant difference between the treatments. The color space values and firmness were significantly lower in the –7°C treatment than in the other treatment. Furthermore, the freezing low-temperature treatment affected the sucrose, citric acid, and malic acid contents. The leucine content significantly increased by approximately six-fold compared with the control levels, depending on temperature and DAT. Low -temperature treatments elevated amino acid combinations associated with bitterness. Among volatile compounds, the monoterpenes contents increased under the treatments, whereas the sesquiterpenes and other compounds content decreased. The total phenol and flavonoid content increased with DAT, but differed with tissue and temperature. Therefore, it seems necessary to improve heating facilities or develop new varieties with strong low-temperature tolerance to prepare for cold winter conditions in plastic greenhouses.

近期，由于气候变化，冬季频繁出现寒冷天气，这对不知火蜜柑等晚熟柑橘品种的生产产生了负面影响。因此，我们研究了低温冷冻如何影响不知火蜜桔的耐寒性、​​果实特性、氨基酸含量、挥发性化合物和抗氧化活性。非加热塑料温室中的一棵树被自组装发泡聚苯乙烯板的五面包围；使用空调将温度控制在 –5°C 和 –7°C 下 6 小时。使用未经处理的树作为对照。在 –5°C 处理中，根据处理后天数 (DAT)，器官之间没有差异，但与枝条相比，–7°C 处理的叶子显示出更高的损伤。总可溶性固形物 (TSS) 含量在 7 DAT 处理之间没有差异，但与对照相比，低温处理在 14 DAT 降低了 TSS 含量，显示处理之间存在显着差异。–7°C 处理的色彩空间值和牢固度显着低于其他处理。此外，冷冻低温处理影响了蔗糖、柠檬酸和苹果酸的含量。与对照水平相比，亮氨酸含量显着增加了大约六倍，这取决于温度和 DAT。低温处理提高了与苦味相关的氨基酸组合。在挥发性化合物中，处理下单萜含量增加，而倍半萜和其他化合物含量降低。总酚和类黄酮含量随 DAT 增加，但随组织和温度而异。因此，似乎有必要改善供暖设施或开发耐低温性强的新品种，为塑料大棚的寒冷冬季条件做好准备。