Preharvest Far-Red Light Affects Respiration Rate and Carbohydrate Status in Lettuce Grown in a Vertical Farm and Stored Under Modified Atmosphere Conditions

Vertical farming allows for precise control of environmental conditions, including light quality, enabling the optimization of plant growth and the synthesis of specific phytochemicals. However, the effects of such conditions on postharvest quality remain underexplored. In this study, butterhead lettuce (Lactuca sativa cv. ‘Alyssa’) was grown for three weeks under light-emitting diode (LED) lighting (190 µmol m−2 s−1; 89% red, 11% blue), with or without supplemental far-red light (ca. 50 µmol m−2 s−1). Growth and quality parameters were assessed at harvest, followed by postharvest evaluation of fresh-cut lettuce stored under equilibrium modified atmosphere packaging (EMAP: 3% O2, balance N2) at 7 °C in darkness for 13 days. The respiration rate of the produce was also determined. Far-red light supplementation increased dry weight (+17%) and elevated glucose (+57%) and fructose (+64%) levels at harvest, without affecting fresh weight, pigment content, vitamin C, or sucrose levels. Although respiration rates during storage were about 54% higher for lettuce grown under far-red light, visual quality seemed slightly better preserved. Total aerobic psychrotrophic counts showed no significant differences between treatments at harvest or during storage. These findings suggest that far-red light can enhance certain quality traits of lettuce, particularly carbohydrate accumulation and dry weight, but the associated rise in respiration may limit these benefits postharvest. Further research is needed to clarify its long-term impact in vertical farming systems.