Lettuce (Lactuca sativa) is cultivated in controlled environment agriculture via vertical production or hydroponic well systems. To extend shelf-life, growers harvest “living lettuce” by keeping roots intact, but there is limited data supporting this harvesting technique. The objective of this study was to assess the use of clamshell and root treatments on the shelf-life and nutritional quality of lettuce. Treatments included storage either inside or outside of plastic clamshells and with roots removed or intact. Lettuce was stored for 28 days at 4 oC, 85% relative humidity. Percent weight loss (%weight loss), visual ratings (1 to 5 scale, 1 = poor and 5 = excellent), and colorimeter analysis (L*, a*, b*, c*, hue angle) were measured every 3 days. Total assays of chlorophyll, carotenoids, anthocyanins, flavonoids and phenolic activity were analyzed via UV VIS spectrophotometry every 7 days throughout storage. Few differences were seen in root treatment. As days in storage progressed, %weight loss progressed to 16.9%. Closed clamshells decreased %weight loss (5.5%) compared to open (18.1%). Visual ratings of yellowing/nutrient deficiency, relative greenness, wilt/head looseness, and salability decreased through storage. Lettuce stored in closed clamshells decreased %weight loss by 12% and delayed wilt/head looseness by 11 days. Similarly, lettuce stored in closed clamshells with roots were salable until 18 days in storage, while open clamshells were no longer salable after 7 days. Short root length (~4 cm) may be the dominant factor for the lack of significance as previous research suggested harvesting “living lettuce” with 9 cm roots increased storage and quality. Color data differed, and lettuce stored in closed clamshells with roots had more intense red color a* (-3.7 vs. -2.7), blue color b* (12.6 vs 10.1), and were purer in color c* (13.3 vs. 10.5) compared to open clamshells with roots. No differences were seen in total anthocyanin (mg/L), total chlorophyll (g/g) or total carotenoid (g/g) content in clamshell or root treatment (p > 0.05). Through 14 days of storage, total anthocyanins degraded by 7.55 mg/L (Day 0 = 10.78 vs. Day 14 = 3.22), while no loss of total chlorophyll (9204.84 g/g) or total carotenoids (1947.25 g/g) were seen. Anthocyanins are water soluble pigments and with increased weight/water loss, anthocyanins solubilize leading to degradation. Chlorophylls and carotenoids were not lost, potentially due to low enzyme activity of chlorophyllase. This experiment indicates consumers should eat lettuce within 7-10 days of harvest for highest nutritional and postharvest quality.
