Far-red radiation during indoor cultivation reduces lettuce nutraceutical quality and shortens the shelf-life when stored at supra optimal temperatures

To improve yield in lettuce during indoor cultivation, far-red radiation (FR, 700–800 nm) is often added to the photosynthetic active radiation (PAR, 400–700 nm). Different scenarios was applied in this study: in one scenario FR is applied throughout the 16 h photoperiod (FR-Day); in another scenario FR is applied for a short duration (1 h) at the end of the day (FR-EOD). We have shown that FR-Day is optimal for improving yield, whereas FR-EOD is optimal for production efficiency (Zou et al., 2019). Here, we evaluated the impact of both scenarios on the postharvest quality of lettuce. Shelf-life of excised packaged (polyethylene film) leaves was monitored during dark storage at 4 and 16 ℃, respectively. FR during cultivation decreased the content of major health-promoting metabolites at harvest, especially under FR-Day. At 4 ℃, shelf-life was not affected by the cultivation regime. At 16 ℃, instead, FR was associated with increased postharvest deterioration rate and reduced overall visual quality throughout storage. The reduced shelf-life following FR during cultivation was related to elevated O2•− content along with decreased activity of enzymatic (superoxide dismutase) and reduced levels of non-enzymatic (carotenoids, total phenolics, and flavonoids) antioxidants. We conclude that FR during cultivation especially under FR-Day is associated with reduced nutraceutical quality at harvest, and potentially shorter shelf-life. Notably, the latter was only observed under inappropriate postharvest temperature management.