Abstract
The effect of light intensity applied shortly before harvest on the nutritional quality, postharvest performance, and shelf life of loose-leaf lettuce (Lactuca sativa L. cv. Expertise RZ Salanova®) was investigated. Lettuce was grown either in a greenhouse with supplemental high-pressure sodium light (Experiment 1, EXP 1) or in a climate room under white LED light (Experiment 2, EXP 2). In both experiments full grown plants were transferred to a climate room for the End of Production (EoP) light treatments during the last week of cultivation. During EoP lighting plants were exposed to different intensities (0, 110, and 270 μmol m–2 s–1 in EXP 1; 50, 210, and 470 μmol m–2 s–1 in EXP 2) from white-red LEDs for 6 (EXP 2) or 7 days (EXP 1). Mature leaves were then harvested and stored in darkness at 10°C to study the postharvest performance. Changes in dry matter content, total ascorbic acid, and carbohydrates (including glucose, fructose sucrose, and starch) levels were determined during EoP lighting and during the subsequent shelf life as indicators of lettuce nutritional quality. Quality aspects (appearance, texture, and odor) were accessed during the shelf life as indicators of postharvest performance. In both experiments, high light intensities applied in EoP lighting increased dry matter percentage and contents of ascorbic acid (AsA) and carbohydrates at harvest and these increased levels were maintained during the shelf life. Increased light intensity in EoP treatment also extended the shelf life. The levels of AsA and carbohydrates at harvest correlated positively with the subsequent shelf life, indicating that the prolonged shelf life relies on the improved energy and antioxidant status of the crop at harvest.
Highlights
Leafy vegetables generally have a short postharvest life due to mechanical damage and the lack of light during storage and transportation
Vitamin C is defined as the total ascorbic acid (TAsA), which is the sum of ascorbic acid (AsA), and dehydroascorbic acid (DHA)
In Experiment 1 (EXP 1), TAsA concentration decreased over time of 7 days End of Production (EoP) light treatment at all light intensities compared to its start level at day 0
Summary
Leafy vegetables generally have a short postharvest life due to mechanical damage and the lack of light during storage and transportation. Postharvest performance is related to both nutritional quality (measured as the levels of health and flavor related compounds) and sensorial quality (accessed as visual quality scores, texture, and odor). Improving nutritional and visual quality is important for achieving a good postharvest performance. Important nutritional elements and quality markers include the levels of carbohydrates (sucrose, fructose, glucose, and starch) and vitamin C. Carbohydrates may relate to the sensorial quality of leafy vegetables by providing sweeter or less bitter taste and delaying crop texture deterioration (shape and crispness) and discoloration (Lin et al, 2013; Hasperué et al, 2015). High levels of carbohydrates and TAsA are potentially beneficial for postharvest performance
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