Relationship between Fresh-Packaged Spinach Leaves Exposed to Continuous Light or Dark and Bioactive Contents: Effects of Cultivar, Leaf Size, and Storage Duration

Current retail marketing conditions allow produce to receive artificial light 24 h per day during its displayed shelf life. Essential human-health vitamins [ascorbic acid (vit C), folate (vit B-9), phylloquinone (vit K-1), (alpha-tocopherol (vit E), and the carotenoids lutein, violaxanthin, zeaxanthin, and beta-carotene (provit A)] also are essential for photosynthesis and are biosynthesized in plants by light conditions even under chilling temperatures. Spinach leaves, notably abundant in the aforementioned human-health compounds, were harvested from flat-leaf 'Lazio' and crinkle-leafed 'Samish' cultivars at peak whole-plant maturity as baby (top- and midcanopy) and larger (lower-canopy) leaves. Leaves were placed as a single layer in commercial, clear-polymer retail boxes and stored at 4 degrees C for up to 9 days under continuous light (26.9 mu mol. m(2) .s) or dark. Top-canopy, baby-leaf spinach generally had higher concentrations of all bioactive compounds, on a dry weight basis, with the exception of carotenoids, than bottom-canopy leaves, All leaves stored under continuous light generally had higher levels of all bioactive compounds, except beta-carotene and violaxanthin, and were more prone to wilting, especially the flat-leafed cultivar. All leaves stored under continuous darkness had declining or unchanged levels of the aforementioned bioactive compounds. Findings from this study revealed that spinach leaves exposed to simulated retail continuous light at 4 degrees C, in clear plastic containers, were overall more nutritionally dense (enriched) than leaves exposed to continuous darkness.