In this study, we investigated the effects of ultraviolet (UV)-A light-emitting diodes (LEDs) on the inhibition of fungal spore germination, fruit decay, and accumulation of secondary metabolites, including phytoalexins, in satsuma mandarin. We examined the growth and development of blue (Penicillium italicum) and green (Penicillium digitatum) molds exposed to UV-A LED irradiation in vitro and found that UV-A LEDs with an emission peak of 375 nm and light intensity of 9.4 W m⁻² significantly reduced the growth of both these fungi. In addition, wounded fruits inoculated with P. digitatum were irradiated with UV-A LEDs for 6 days, and we monitored the subsequent changes in green mold symptoms. The results indicated that low-intensity UV-A LED treatment significantly reduced green mold symptoms in fruit, being the effect most pronounced inhibitory on Penicillium sporulation. Furthermore, wounded fruits subjected to UV-A LED treatment were found to have significantly higher contents of the coumarin compound scoparone than fruits maintained in the dark. Contrastingly, scoparone was barely detectable in non-wounded fruits, irrespective of UV-A LED irradiation. The contents of nobiletin, tangeretin, and hesperidin were likewise found to be higher in wounded fruits treated with UV-A LED than in either non-wounded or non-irradiated fruits. These results indicate that treatment with low-intensity UV-A LED irradiation is sufficient to reduce mold symptom development, and accordingly could represent a promising safe approach to the control of post-harvest decay in citrus fruits. On the basis of our observations, we speculate that the biosynthesis of scoparone, polymethoxyflavones, and flavanones could be induced when the peel is injured and irradiated with UV-A contributing to a reduction in fruit decay.

在这项研究中，我们研究了紫外线 (UV)-A 发光二极管 (LED) 对抑制蜜柑中真菌孢子萌发、果实腐烂和次级代谢物（包括植物抗毒素）积累的影响。我们检查了在体外暴露于 UV-A LED 照射的蓝色 ( Penicillium italicum ) 和绿色 ( Penicillium digitatum ) 霉菌的生长和发育，发现 UV-A LED 的发射峰为 375 nm，光强为 9.4 W m ^{- 2}显着降低了这两种真菌的生长。此外，用P. digitatum接种的受伤果实用 UV-A LED 照射了 6 天，我们监测了随后绿色霉菌症状的变化。结果表明，低强度 UV-A LED 处理显着降低了水果中的绿色霉菌症状，对青霉菌的抑制效果最为显着。孢子形成。此外，发现经过 UV-A LED 处理的受伤水果的香豆素化合物东莨菪酮含量明显高于在黑暗中保存的水果。相比之下，在未受伤的水果中几乎检测不到东莨菪碱，无论 UV-A LED 照射如何。同样发现，用 UV-A LED 处理的受伤水果中的 nobiletin、tangeretin 和橙皮苷的含量高于未受伤或未照射过的水果。这些结果表明，用低强度 UV-A LED 照射处理足以减少霉菌症状的发展，因此可以代表一种有前途的安全方法来控制柑橘类水果的采后腐烂。根据我们的观察，我们推测东莨菪酮、聚甲氧基黄酮的生物合成，