Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2007
Publication Date: 8/8/2007
Citation: Truong, V., McFeeters, R.F., Thompson, R.L., Dean, L.L., Shofran, B. 2007. Phenolic acid content and composition in leaves and roots of common commercial sweetpotato (Ipomea batatas L.) cultivars in the United States. Journal of Food Science. 72(6):C343-C349. Interpretive Summary: Fruits and vegetables including sweetpotatoes are a rich source of polyphenolic compounds. Recent studies indicated that these phytochemicals have high antioxidant activity that can exert several health-promoting functions such as reducing the risks of cancer, heart and neurodegenerative diseases. However, limited information is available on the phenolic content and composition of sweetpotato cultivars grown in the United States. Therefore, the objective of this study was to develop a high-performance liquid chromatography method for rapid, routine analysis of the phenolics in the leaves and root tissues of sweetpotatoes. With a quick method developed in this study, five major phenolic acids were well separated in less than 25 min compared to about 120 min with the common methods. Identification of the isolated phenolic compounds was confirmed by tandem mass spectrometry. Quantitative analysis of these phenolic compounds showed significant variation among the cultivars and tissues. Chlorogenic acid was highest in root tissues while di-caffeoylquinic acid isomers were predominant in sweetpotato leaves. Steam cooking resulted in increases in the concentration of total phenolics and most of the individual phenolic acids identified. Sweetpotato leaves had the highest phenolic acid content followed by the peel, whole root and flesh tissues. However, there was no significant difference in the total phenolic content and antioxidant activity between purees made from the whole and peeled sweetpotatoes. The findings on the phenolic composition and antioxidant activity in the U. S. sweetpotato cultivars and the analytical method developed in this study would enhance the development of sweetpotatoes for functional foods.
Technical Abstract: Phenolic acids in commercially important sweetpotato cultivars grown in the United States were analyzed using the reversed phase HPLC. Caffeic acid, chlorogenic acid, 4,5-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, and 3,4-di-O-caffeoylquinic acid were well separated with an isocratic elution in less than 25 min compared to about 120 min for analyzing and re-equilibrating the column with a gradient method. The isocratic elution order of these caffeoylquinic acid derivatives was confirmed by LC-MS/MS. Chlorogenic acid was highest in root tissues while 3,5-di-O-caffeoylquinic acid and/or 4,5-di-O-caffeoylquinic acid were predominant in the leaves. Steam cooking resulted in slight increases in the concentration of total phenolics and all the individual phenolic acids identified, except for 3,5-diCQA. Sweetpotato leaves had the highest phenolic acid content followed by the peel, whole root and flesh tissues. However, there was no significant difference in the total phenolic content and antioxidant activity between purees made from the whole and peeled sweetpotatoes.