36th International Carrot Conference Abstract

Influence of pigmentation and management practices on the antioxidant content of carrots.

Mary Ruth McDonald¹, Chanli Hu^1,2 Rong Cao², and Al Sullivan¹

¹Department of Plant Agriculture, University of Guelph, Guelph, On, N1G 2W1 Canada

²Agriculture and Agri-Food Canada, Guelph, ON, Canada

Carrots (Daucus carota L.) provide important nutrients in the human diet including carotenoids, such as β-carotene, lycopene, lutein and zeaxanthin and contain phenolic compounds including chlorogenic, caffeic, and p-hydroxybenzoic acids along with numerous cinnamic acid derivatives. These compounds have high antioxidant activity. Carrots were grown on organic soil in 2008 (pH 6.3, organic matter 48%) and 2009 (pH 7.0, organic matter 74%) to determine the effect of pigment and cultivar on antioxidant activity. The carrots that were evaluated both years were breeding lines from the USDA Univ. of Wisconsin carrot breeding program: purple 106-6, red 104-3, dark orange 101-23, yellow 102-1 and white 105-7, and cultivars Atomic Red, Mello Yello, and Eny. Trials on mineral soil (pH 7.9, organic matter 4.5%) were conducted to determine if nitrogen fertilizer and fungicide application could affect antioxidant levels in orange carrot Enterprise. This was a factorial design with nitrogen applied as ammonium nitrate at 0, 110 and 220 kg/ha in combination with zero or five fungicide sprays: two each of Cabrio (pyracolstrobin 20%), Bravo 500 (chlorothalonil 50% ) and one application of Lance (boscalid 70%). Carrots were harvested in October, placed in cold storage and samples were freeze dried in February. Total antioxidant activity (TAA) of the carrot extracts was determined using two methods, DPPH (2,2-diphenyl-1-picrylhydrazyl radical) and ferric reducing antioxidant power (FRAP). Purple-fleshed carrots tended to have the highest total antioxidant activity, but differences were much greater in 2009 than in 2008. Fungicide application did not affect TAA, but TAA decreased as N rate increased, based on the FRAP assessment (TAA=4.68-0.0021N, R²=0.9778). The TAA of the hydrophilic fraction was highest, and of the lipophilic fraction was lowest, at the high rate of N. There was a negative correlation between the TAA of the hydrophilic fraction and the lipophilic fraction in the DPPH assay (R =-0.71, P<0.05).There were no differences in yield in response to the different rates of applied N (65-67 tonnes/ha), which suggests that N was not deficient in this trial and there was no dilution effect. The total antioxidant content of the carrots and the antioxidant activity of the hydrophilic fraction were higher in 2008, a warmer and slightly drier growing season compared to 2009.

Last updated Thursday, 25-Jul-2013 11:54:12 CDT