Short Photoirradiation Induces Flavonoid Synthesis and Increases Its Production in Postharvest Vegetables

Abstract

It is desirable to increase the flavonoid contents of postharvest vegetables since flavonoids play a beneficial role in human health promotion. In the present study, we show that postharvest vegetables increasingly produced flavonoids when irradiated with light near the absorption wavelength of flavonoids in the plant. Three-day exposure to UV-B for 5 min, 98 μmol m⁻² s⁻¹ per day, increased the contents of jaceidin in spinach, kaempherol glycoside in radish sprout, apigenin glycosides in parsley, and isovitexin in Indian spinach after 6 days of storage in a refrigerator, compared to the contents in plants without irradiation. Six days of storage of unripe green strawberry under green light for 5 min, 98 μmol m⁻² s⁻¹ per day, enabled them to mature and turn red, accompanied by 3.5-fold increased contents of pelargonidin. Elucidation of the mechanism in parsley found the stimulating expression of the flavonoid synthesis gene, PAL, C4H, 4CL, CHS, and FNS, 6 h after exposure to single irradiation with UV-B for 5 min, and the higher expression was maintained for 24 h. After 3 days irradiation during 6 days of storage, parsley did not show adverse changes in the contents of ascorbic acid, β-carotene, chlorophyll, and moisture.

Application of Light‐Emitting Diodes in Food Production, Postharvest Preservation, and Microbiological Food Safety

“…Although UV radiation is not part of the visible range of electromagnetic radiation, it is still present in sunlight and in other sources of broad‐spectrum lighting. UV LEDs are reported to stimulate the production of flavonoids and phenylpropanoids as reported by Kanazawa and others (). Watercress and garden pea sprouts were irradiated with a UVA LED (375 nm) for 160 min per day for 3 d at a photon flux of 33 μmol m −2 s −1 , then stored in darkness.…”

“…In contrast, blue LED light (470 nm) was shown to accelerate secondary ripening in strawberries (Table ), evidenced by the increase in respiration, ethylene production, and faster development of red color (Xu and others ,b). Apart from blue light, Kanazawa and others () reported that unripe strawberries exposed to green light from a green lamp (500 to 600 nm) also developed a deep red color faster due to the production of anthocyanins. However, no data were given for the rate of respiration or production rate of the ethylene from the strawberries, and there was no account of the radiant heat from the green lamp received by the strawberries, which might have affected the rate of ripening.…”

“…Several of such studies have even shown a correlation between exposure to LED light and biomolecular responses in terms of gene expression. For example, blue LEDs upregulate the gene expression of certain steps in the phenylpropanoid pathway, hence increasing flavanoid and anthocyanin content (Kanazawa and others , Shi and others ). Red light upregulated carotenoid metabolism‐related genes in Satsuma mandarins (Ma and others ).…”

Influence of Yellow Light-Emitting Diodes at 590 nm on Storage of Apple, Tomato and Bell Pepper Fruit

“…In a previous study, use of a wavelength near the λ max of fl avonoids (i.e. UV-A light at 380-320 nm) increased TFC in radish sprouts, parsley and Indian spinach (42). Also, Harbaum--Piayda et al (43) investigated preharvest UV-B irradiation (at 280-380 nm) of pak choi (Brassica campestris L. ssp.…”

“…There are nevertheless some promising reports that irradiation with light in the range of 500-600 nm results in an increase of ascorbic acid and anthocyanin content (29) and that yellow light with wavelengths in the range of 580-600 nm may infl uence gene expression in plants during growth (30). However, there are no literature data available about the infl uence of irradiation with yellow LED light during storage on secondary metabolites of fruits and vegetables.…”