Contrary to Red, Blue Monochromatic Light Improves the Bioactive Compound Content in Broccoli Sprouts

Abstract

Broccoli sprouts are rich in health-promoting bioactive compounds. Their content depends on both cultivation light quality and temperature. However, these effects have been previously addressed in isolation. Here, the dual inputs of cultivation light quality [blue (B), red (R), mixture of R and B (R+B), mixture of R and UVA (R+UVA)] and air temperature (15, 19, and 23 °C) on determining growth, external quality, and the cotyledon and hypocotyl content of five major bioactive compounds were investigated. The carbohydrate status at harvest and postharvest ratio of variable to maximum fluorescence (Fv/Fm) were also assessed. Hypocotyl length was generally enhanced under monochromatic light (R or B) and elevated temperature. Total phenolic, total flavonoid, and glucoraphanin contents were generally higher in cotyledon as compared to hypocotyl. Hypocotyl anthocyanin, total phenolic, total flavonoid, and ascorbic acid contents were generally enhanced by R+B, and were decreased by R. Cotyledon content in these metabolites was generally stimulated by B, and reduced under R or R+UVA. Temperature affected metabolite content depending on the metabolite, organ, and light quality. Lower temperatures, R (23 °C) or R+UVA (15, 19, and 23 °C) were associated with decreased postharvest Fv/Fm. In conclusion, low cultivation temperature (<23 °C), as well as R or R+UVA ought to be avoided. Instead, B and R+B are suitable, with B being preferable, owing to better external quality and enhanced metabolite content in cotyledon which generally holds higher content than hypocotyl.

Keywords

• anthocyanins
• ascorbic acid
• <i>Brassica oleracea</i>
• flavonoids
• glucoraphanin
• polyphenols