Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/12/2008
Publication Date: 6/3/2008
Citation: Im, H., Suh, B., Lee, S., Kozukue, N., Ohnisi-Kameyama, M., Levin, C.E., Friedman, M. 2008. Analysis of Phenolic Compounds by HPLC and LC/MS in Potato Plants, Flowers, Leaves, Stems, and Tubers and in Home Processed Potatoes. Journal of Agriculture and Food Chemistry. 56, 3341-3349 Interpretive Summary: The potato plant produces phenolic compounds, secondary metabolites that are involved in the defense of plant against invading pathogens including insects, bacteria, fungi, and viruses. These phenolic compounds also possess health-promoting properties including the ability to inactivate foodborne pathogenic bacteria and fungi. As part of an effort to discover new and effective plant antimicrobials, we determined with the aid of a validated HPLC method (in a collaborative study with Korean and Japanese scientists) the content and distribution of phenolic compounds in flowers, leaves, and stems of blooming potato plants, in the peel, pulp (flesh) of Korean potatoes and in a large number of commercial potato varieties sold in the United States as well as in home processed Superior Korean potatoes. The flowers of a Superior Korean potato plant and colored potatoes such as the Peruvian Purple variety (available at Berkeley Bowl, Berkeley, California) contained exceptionally large amounts of the phenolic compounds. Compared to six other processing methods evaluated, steam cooking of potatoes was the least damaging to the phenolic compounds. Our studies facilitate defining the roles of antioxidative potato phenolic compounds in plant physiology, food microbiology, and the diet.
Technical Abstract: Potato plants synthesize phenolic compounds as protection against bruising and injury from bacteria, fungi, viruses, and insects. Because antioxidative phenolic compounds are also reported to participate in enzymatic browning reactions and to exhibit health-promoting effects in humans, a need exists for accurate methods to measure their content in fresh and processed potatoes. To contribute to our knowledge about the levels of phenolic compounds in potatoes, we validated and used HPLC and LC/MS to measure levels of chlorogenic acid, a chlorogenic isomer, and caffeic acid in flowers, leaves, stems, and tubers of the potato plant, and in home-processed potatoes. Total phenolic content of flowers (626 mg/100 g fresh wt) was 21 and 59 times greater than that of leaves and stems, respectively. For all samples, chlorogenic acid and its isomer contributed 96 to 98% to the total. Total phenolic levels (in g/100 g fresh wt) of peels of five potato varieties grown in Korea ranged from 6.5 to 42.1 and of the flesh (pulp) from 0.5 to 16.5, with peel/pulp ratios ranging from 2.5 to 21.1. Total phenolic content for 25 American potatoes ranged from 1.0 to 172. The highest amounts were present in red and purple potatoes. Home processing of pulp with various forms of heat induced reductions in the phenolic content. The described methodology should facilitate future studies on the role of potato phenolic compounds in the plant and the diet.