EFFECT OF COOKING METHOD ON XANTHOPHYLL CONTENT OF YELLOW-FLESHED POTATO

Authors: Clevidence, Beverly; Haynes, Kathleen; Rao, David; Novotny, Janet

Submitted to: United States Japan Natural Resources Protein Panel
Publication Type: Proceedings
Publication Acceptance Date: 9/20/2005
Publication Date: 10/20/2005
Citation: Clevidence, B.A., Haynes, K.G., Rao, D.D., Novotny Dura, J. 2005. Effect of cooking method on xanthophyll content of yellow-fleshed potato. United States Japan Natural Resources Protein Panel. 34:280-284.

Interpretive Summary: Xanthophylls are yellow pigments. They provide color to potatoes that have yellow flesh. Such potatoes are commonly consumed in Europe, but not in the U.S. However, the yellow-fleshed ‘Yukon Gold’ potato has been gaining popularity in the U.S. Both nutritionists and plant scientists are interested in these potatoes. This is because yellow-fleshed potatoes have appealing color, and because they provide lutein and zeaxanthin, xanthophylls that may protect against degenerative diseases including macular eye degeneration. The purpose of this study was to determine the effects of cooking on content of lutein, zeaxanthin and other xanthophylls in Yukon Gold potatoes. Potatoes were quartered and one quarter of each potato was assigned to each treatment: raw (control), steamed (20 minutes), microwaved (4 minutes) or cut in strips and fried (4 minutes). The process was repeated to obtain 5 replicates. Frying produced the lowest xanthophyll levels. Lutein values were highest following steaming and microwave cooking; zeaxanthin values were highest after steaming. Lutein and zeaxanthin values were lower from raw potato than from steamed or microwaved potatoes suggesting that these cooking methods altered the plant cell structure and liberated these compounds. This information will be useful to plant scientists because the common practice of analyzing raw potato for xanthophyll content appears to yield falsely low values. The information is useful to nutritionists because it identifies effects of cooking on content of bioactive compounds.

Technical Abstract: The xanthophylls lutein and zeaxanthin are of interest as phytochemicals because they are well-absorbed by humans and have been linked to protection of human health. However, lutein intake in the U.S. is typically low because the major dietary sources, dark-green leafy vegetables, are not popular. Yellow-fleshed potatoes, while containing modest levels of lutein, have gained wide acceptance and are a potential vehicle for increasing lutein consumption. Although yellow-fleshed potato cultivars have been analyzed for xanthophylls, most have been analyzed from raw potato. The purpose of this study was to assess the effect of cooking on xanthophyll content of the ‘Yukon Gold’ potato. Four potatoes were quartered and one quarter of each was assigned to each treatment: raw (control), steamed (20 min), microwaved (4 min), or fried (4 min). The process was repeated to obtain 5 replicates. Xanthophylls were repeatedly extracted from potato and analyzed by HPLC using a reverse phase C30 analytical column and a diode array detector at 450 nm. Frying produced the lowest xanthophyll levels. Lutein values were highest following steaming and microwave cooking; zeaxanthin values were highest after steaming. Lutein and zeaxanthin values were lower from raw potato than from steamed or microwaved potatoes suggesting that these cooking methods altered the plant matrix and liberated these compounds. This indicates that the common practice of analyzing raw potato for xanthophyll content of yellow-fleshed potato yields falsely low values. It was concluded that cooking alters xanthophyll content of yellow-fleshed potato. Some xanthophylls become more easily liberated from the plant matrix following cooking; others appear to be reduced or lost. Steaming produces the best outcome for lutein and zeaxanthin.