ARS | Publication request: Distribution of Phenolic Compounds and Antioxidative Activities in Parts of Sweet Potato (Ipomoea batata L.) plants and in home processed roots

Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 22, 2010
Publication Date: September 1, 2010
Citation: http://dx.doi.org/10.1016/j.jfca.2010.1003.1025

Interpretive Summary: The sweet potato (Ipomoea batata L.; Lam.) is a dicotyledonous vegetable plant belonging to the family Convolvulaceae. China produces about 90% of the world production of ~117 million tons of sweet potatoes. Approximately 50% of the crop is used for animal feed. Sweet potatoes are the 7th most important crop worldwide and the 5th most important crop in developing nations. The plants are adaptable to a wide variety of growing conditions and are often grown by small farmers as a back-up crop to insure against other crop failures. Published studies reported that sweet potato phenolics were found to inhibit the growth of human colon, leukemia, and stomach cancer cells, to ameliorate diabetes in humans, and to inhibit growth in vitro of viruses and fungi. The main objectives of this collaborative study were (a) to determine the phenolic acid content in sweet potato roots, stems, leaves, and flowers from several plants grown in Korea; (b) to compare radical scavenging and antioxidative activities of extracts of the sweet potato plant by three different methods; and (c) to evaluate the stability of phenolics in roots subjected to six home-cooking methods. We found that leaves of sweet potato plants contained significantly higher amounts of total caffeoylquinic compounds than other plant parts. Petioles contained lower amounts than did the other parts, but the amounts were not significantly lower than in the stems. The data suggest that different parts of the sweet potato plant may provide a source for potential antimicrobial and antitoxin food ingredients, and that high-phenolic sweet potato leaves, widely consumed in Asian countries as a vegetable, merit inclusion in diets of other countries.

Technical Abstract: We measured six phenolic compounds by HPLC, the total phenolic content by Folin-Ciocalteu, and antioxidative activities by three methods in the sweet potato plant and in home processed roots. Total phenolic content was highest in the leaves. Eight root varieties were partitioned and analyzed for phenolics. The stem end of the root had significantly more phenolics. In all samples the predominant chlorogenic acids were 5-CQA(caffeoylquinic acid) and 3,5-diCQA. 3,4-diCQA was present in significant amounts in the leaves and the flower, and 4,5-diCQA in the leaves. Six home-processing/cooking techniques reduced phenolic content from 7% (baking) to ~40% (deep-frying/boiling). High correlations were observed between phenolic compounds determined by HPLC and Folin Ciocalteu, radical scavenging activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH), and oxidative activity by ferric thiocyanate (FTC) and thiobarbituric acid (TBA) methods. The results show that there is a large variation in phenolics among sweet potato varieties and different parts of the plant and that high-phenolic sweet potato leaves, widely consumed in Asian countries as a vegetable, merit inclusion in diets of other countries.