**3. Light emitting diode (LED)**

#### **3.1 LEDs induce phytonutrients in fresh produces**

Light is an important environmental factor that influences plant growth and development, as it offers both the source of energy for photosynthesis and the signal for a wide range of physiological and biochemical processes. LED technology can produce monochromatic light within a narrow wavelength between 400 nm and 700 nm, where LEDs of different wavelengths (such as red, blue, green, and white light) can trigger different responses in plants. The blue and red LED lights are the most effective wavelengths for plant photosynthesis, while yellow and green light have a negligible effect because the absorption spectra of the photosynthetic pigments mainly target blue (400–500nm) and red (600–700nm) light spectra [30]. While LEDs are used widely in protected cropping, LED lights are becoming widely studied for their postharvest applications to extend the shelf life and maintain the postharvest quality of fresh produce due to their wavelength specificity, long lifespan, low thermal energy, and non-toxicity [31]. The quality of light has been shown to affect the accumulation of phytonutrients and enhance the levels of phytonutrients in plants


#### **Table 1.**

*Effect of LEDs in inducing the levels of phytonutrients on fresh produces.*

[32]. Ambient light supplemented with blue, red, green, or blue: red LEDs enhanced the total phenolics, flavonoids, anthocyanins, lycopene, α-tocopherol, and other compounds in several fruits and vegetables (**Table 1**).

LEDs' role in the induction of bioactive compound production in plants seems to be associated with phenylalanine ammonia-lyase (PAL) enzyme, which is engaged in the initial step of the phenylpropanoid pathway [45]. It has previously been reported that LED increased accumulation of primary metabolites in plants and induced the suppression of the translocation of photosynthetic products. LEDs also affect the signal transduction pathways by inducing the production of secondary metabolites in plants [46]. LED lights have a significant effect on the accumulation of phytonutrients and therefore could be used as an alternative technique for enhancing the quantity and quality of the phytonutrient profiles linked to nutrition and human health. However, the use of single- or combination-spectral light ratios may vary effect depending on the plant species or cultivars [47]. Therefore, more investigation is required to establish the spectrum qualities that make the best choice for enhancing the phytonutrient properties of fresh produce.
