Collard, mustard and turnip greens: Effects of genotypes and leaf position on concentrations of ascorbic acid, folate, β-carotene, lutein and phylloquinone

Abstract

Leaf green Brassica crops: collard (Brassica oleracea L.), mustard (Brassica juncea L.) and turnip (Brassica rapa L.) greens are important commercial and culinary vegetables, especially in the southern United States. However, almost no information on essential human-health vitamins [ascorbic acid (vitamin C), folate (vitamin B9), phylloquinone (vitamin K1) and the carotenoids lutein and β-carotene (provitamin A)] is available. Leafy green Brassicas (15 collard, 2 mustard and 2 turnip greens) were harvested at peak whole-plant maturity, separated into younger (top-canopy) or older (bottom-canopy) leaves and assayed for the aforementioned vitamins and carotenoids. On a 100g fresh mass basis, percent dry mass (14.7g versus 13.2g), total (132.7mg versus 109.1mg) and free (58.7mg versus 52.8mg) ascorbic acid, folate (183μg versus 112μg) and lutein (9790μg versus 8950μg) concentrations were significantly higher in younger versus older leaves. Phylloquinone (435μg versus 459μg) and β-carotene (11,130μg versus 11,619μg) were equally concentrated in younger and older leaves. On a fresh mass basis, all vitamins were found to be highly concentrated in all nineteen leafy green Brassica genotypes, with particular genotypes within each Brassica species having exceptionally high concentrations. Findings from this study revealed that leafy green Brassica genotypes are nutritionally dense in essential human-health vitamins C, B9, K, provitamin A (β-carotene) and lutein. Concentration differences in the examined nutritional components among the genotypes (e.g. significant differences in lutein concentrations from 5120 to 15,360μg/100gfm) reveal potential differences that might be exploited in genetic improvement through plant selection and breeding.