**3. Mechanism of LED irradiation on horticultural crops**

As mentioned above, due to their peculiar, distinctive properties, LEDs have gained popularity in the postharvest handling of horticultural crops. Even though the effect of various wavelengths, irradiation intensity, and exposure time of these LEDs on fresh fruit and vegetables has proved to be beneficial in enhancing color, bioactive compounds, antioxidants, shelf life, and overall quality [7, 11, 18–21], the mechanism(s) involved in LED irradiation technology is (are) still not clear. It is, however, known that the photosynthesis period of postharvest horticultural produce may be extended by illumination with LEDs. This can result in the long-term preservation of these commodities. The expression of genes and signaling of phytochrome may be inhibited or enhanced by irradiation with LED lights; this potentially affects fruit and vegetable senescence [22]. LEDs can reduce the breakdown of storage phytochemicals in the fruit/vegetable by delaying the emergence of ethylene and the respiratory peak [23]. Further, LED exposure can also cause a fluctuation in enzyme activity due to a change in the secondary structure of proteins. Other aspects involved in the mechanism of action of LED irradiation on fruit and vegetables require further investigations.
