Regulation of the Photon Spectrum on Growth and Nutritional Attributes of Baby-Leaf Lettuce at Harvest and during Postharvest Storage

Abstract

The photon flux density (PFD) and spectrum regulate the growth, quality attributes, and postharvest physiology of leafy vegetables grown indoors. However, limited information is available on how a photon spectrum enriched with a broad range of different wavebands regulates these factors. To determine this, we grew baby-leaf lettuce ‘Rouxai’ under a PFD of 200 µmol m−2 s−1 provided by warm-white (WW; control) light-emitting diodes (LEDs) supplemented with either 30 µmol m−2 s−1 of ultraviolet-A (+UV30) or 50 µmol m−2 s−1 of blue (+B50), green (+G50), red (+R50), or WW (+WW50) light. We then quantified growth attributes and accumulated secondary metabolites at harvest and during storage in darkness at 5 °C. Additional +G50 light increased shoot fresh and dry weight by 53% and 59% compared to the control. Relative chlorophyll concentration increased under +UV30, +G50, and especially +B50. At harvest, +B50 increased total phenolic content (TPC) by 25% and anthocyanin content (TAC) by 2.0-fold. Additionally, +G50 increased antiradical activity (DPPH) by 29%. After each day of storage, TPC decreased by 2.9 to 7.1% and DPPH by 3.0 to 6.2%, while TAC degradation was less pronounced. Principal component analysis indicated a distinct effect of +G50 on the lettuce at harvest. However, concentrations of metabolites before and during storage were usually greatest under the +B50 and +R50 treatments.

The Combination of Monochromatic LEDs and Elicitation with Stressors Enhances the Accumulation of Glucosinolates in Mustard Sprouts with Species-Dependency

“…Previous works have reported that the use of either monochromatic blue or red LEDs may affect several growth parameters in broccoli sprouts, but did not produce a biomass increase [ 24 , 25 ]. Neither the supplementation of warm-white light with blue or red LEDs (50 µmol m −2 s −1 ) was effective for increasing the biomass in baby-leaf lettuce [ 26 ]. Furthermore, even the combination of red/blue light may require supplemental broad-spectral energy of 500–600 nm (red–blue–white lighting) to increase the biomass in leafy crops, as the works of Lin et al and Piovene et al [ 27 , 28 ] suggest.…”

Controlled Environment Agriculture and Its Ability to Mitigate Food Insecurity

“…CEAs offer many advantages for urbanized food systems. CEAs can increase plant production by environmentally controlling conditions regardless of the season [86]. One of the opportunities that indoor farming offers is optimal environmental settings by eliminating exposure to extremes in temperature, wind, and water, which can positively influence plant growth [87].…”

UV and Visible Spectrum LED Lighting as Abiotic Elicitors of Bioactive Compounds in Sprouts, Microgreens, and Baby Leaves—A Comprehensive Review including Their Mode of Action

“…This nitrate assimilation is directly related to the optimum growth parameters and chlorophyll content of both varieties. Vaštakaitè-Kairienè et al [78] studied the characteristics of babyleaf lettuce growth under 200 µmol m −2 s −1 of warm white lights and supplemented with 30 µmol m −2 s −1 UV-A or 50 µmol m −2 s −1 blue, 50 µmol m −2 s −1 green, 50 µmol m −2 s −1 red, or 50 µmol m −2 s −1 warm white LEDs. The obtained results showed that the different supplementations did not affect the physiological development, whereas green LEDs increased the total antioxidant activity (measured by DPPH), blue LEDs increased the accumulation of secondary metabolites at harvest, and red LEDs preserved the phytochemicals during a short postharvest storage.…”