Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 30, 2012
Publication Date: July 15, 2012
Citation: Farnham, M.W., Lester, G.E., Hassell, R. 2012. Collard, mustard and turnip greens: Effects of varieties and leaf position on concentrations of ascorbic acid, folate, B-carotene, lutein and phylloquinone. Journal of Food Composition and Analysis. 27:1-7. Interpretive Summary: Collard, turnip, and mustard greens are economically important vegetables grown throughout the United States, and that are especially important in southern states. These leafy-green vegetables are known to be rich sources of numerous vitamins and other important nutritional components, but formal reports describing leaf concentrations of such components in field-grown plants are lacking. With this in mind, scientists with the USDA-ARS at Charleston, SC, and Beltsville, MD, in cooperation with a scientist at Clemson University, SC, conducted field and laboratory studies to determine the general makeup of important vitamins and other nutritional components including vitamin C, vitamin K, folic acid, proVitamin A, and lutein, in field-harvested leaves. They also ran tests to discern the relative effects played by the vegetable variety and the leaf age when sampling plants. The results showed that leaf age effects concentration, with younger leaves generally exhibiting higher concentrations of vitamins than lower leaves, and also that varieties differ in concentration from one another. Most importantly, results indicate that collards and the other leafy green vegetables tested are exceptionally rich sources of all the vitamins assayed. Information from this work will be very useful to plant breeders working to modify vitamin concentration in collard, turnip, and mustard greens. This research also provides a more accurate estimation than previously available of the amount of particular vitamins that consumers derive in their diet when eating these nutritious vegetables.
Technical Abstract: Leafy Brassica crops: collard (Brassica oleracea L.), mustard (B. juncea L.) and turnip (B. rapa) greens are important commercial and culinary vegetables; especially in the southern United States. However, almost no information on essential human-health vitamins [ascorbic acid (vit C), folate (vit B9), phylloquinone (vit K1), and the carotenoids lutein and B-carotene (provit A)] is available. Nineteen cultivars or varieties of leafy green Brasicas (15 collard, 2 mustard, and 2 turnip) were harvested at peak whole-plant maturity. Leaves were separated as younger (top-canopy) or older (bottom-canopy) and assayed for the aforementioned human-health vitamins and carotenoids. Percent dry mass, total and free ascorbic acid, folate and lutein concentrations were significantly higher in younger versus older leaves. Phylloquinone and B-carotene were equally concentrated in younger and older leaves. On a fresh mass basis all assayed human-health vitamins were found to be highly concentrated in all 19 leafy green Brassisca cultivars and varieties with particular cultivars within each Brassica species having exceptionally high concentrations. Findings from this study revealed that leafy green Brassica cultivars and varieties are nutritionally dense in essential human-health vitamins C, B9, K, provitamin A (B-carotene) and lutein. Concentration differences in the examined nutritional components among the cultivars reveal potential differences that might be exploited in genetic improvement through plant selection and breeding.