Relationship between fresh-packaged spinach leaves exposed to continuous light or dark and bioactive contents: Effects of cultivar, leaf size, and storage duration

Authors: Lester, Gene; Makus, Donald; HODGES, D. MARK - Agriculture And Agri-Food Canada

Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2010
Publication Date: 2/8/2010
Citation: Lester, G.E., Makus, D.J., Hodges, D. 2010. Relationship between fresh-packaged spinach leaves exposed to continuous light or dark and bioactive contents: Effects of cultivar, leaf size, and storage duration. Journal of Agriculture and Food Chemistry. 58(5):2980-2987.

Interpretive Summary: Although simulated retail light conditions were found to be beneficial in maintaining/enhancing essential human-health vitamins C, B9, K1, and E, and the carotenoids lutein, violaxanthin, zeaxanthin, and beta-carotene over time, storage in light contributed to some leaf wilting in ‘Lazio’ flat-leafed type after 3 day storage versus no wilting with ‘Samish’ crinkled-leaf type. ‘Lazio’ baby-leaves had more wilting than ‘Lazio’ older leaves as measured by leaf blade bending. Leaf maturity, regardless of cultivar, was a major determinant in the aforementioned essential human-health compound concentrations, with younger baby-leafed sized leaves generally having higher levels of vitamins C, B9, and K1, and the carotenoids lutein, violaxanthin, zeaxanthin, and beta-carotene. The differences in bioactive compounds measured in this study would not be visually apparent to the consumer, whereas slight wilting may impact consumer acceptance. Focusing on continuous light exposure during retail display combined with specific cultivars (e.g. crinkled-leafed types) and leaf maturity (i.e. baby-leafed size) appears to be the strategy to preserving the concentration of spinach-derived human-health bioactive compounds.

Technical Abstract: Human-health benefits derived from consumption of fruits and vegetables are due to the many bioactive compounds found in produce. The concentrations of these bioactive compounds are heavily influenced by genetics (i.e. cultivar) and environment, especially the many pigments and vitamins that can change during plant maturation, processing, and storage. Current retail marketing conditions allow for produce to receive artificial light 24-hours per day during its displayed shelf-life. Essential human-health vitamins are required, directly or indirectly, for photosynthesis and are activated by light conditions even under chilling temperatures. Spinach leaves, notably abundant in human-health compounds, were harvested from flat-leaf Lazio and crinkled-leafed Samish cultivars at peak whole-plant maturity as baby-leafed (top- and mid-canopy) and larger (lower-canopy) leaves. They were then 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 or dark. Top-canopy spinach leaves generally had higher concentrations of all bioactive compounds, on a dry weight basis, with the exception of carotenoids than bottom canopy leaves. Leaves stored under continuous light generally had higher levels of all bioactive compounds, but lower levels of beta-carotene and violaxanthin, and were more prone to wilting, especially the flat-leafed cultivar. Leaves stored under continuous dark had declining or unchanged levels of bioactive compounds. Findings from this study revealed that spinach leaves exposed to continuous light during storage were, overall more nutritionally dense than leaves exposed to continuous dark.