Polyphenols and phenolic acids in sweet potato (Ipomoea batatas L.) roots

Sweet potato (Ipomoea batatas L.) is one of the most important food crops in the world. They are rich in polyphenols, proteins, vitamins, minerals and some functional microcomponents. Polyphenols are bioactive compounds, which can protect the human body from the oxidative stress which may cause many diseases including cancer, aging and cardiovascular problems.The polyphenol content is two to three times higher than in some common vegetables. Total polyphenols (determined spectrophotometrically) and phenolic acids (i.e. caffeic acid, chlorogenic acid and isomers - using high performance liquid chromatography) contents were determined in three varieties of sweet potatoes (O´Henry - white, Beauregard-orange and 414-purple). Phenolic compounds contents were determined in raw peeled roots, jackets of raw roots and water steamed sweet potato roots. For all analysis lyophilised samples were used. Total polyphenol content ranged from 1161 (O´Henry, flesh-raw) to 13998 (414, peel-raw) mg.kg-1 dry matter, caffeic acid content from the non-detected values (414, flesh-raw) to 320.7 (Beauregard, peel-raw) mg.kg-1 dry matter and 3-caffeoylquinic acid content from 57.57 (O´Henry, flesh-raw) to 2392 (414, peel-raw) mg.kg-1 dry matter. Statistically significant differences (p ≤0.05) existed between varieties, morphological parts of the root, or raw and heat-treated sweet potato in phenolic compounds contents