Characteristics of folic acid and polyphenol in okinawan sweet potato (Ipomoea batatas L.) foliage

Abstract

To utilize foliage of sweet potato (Ipomoea batatas L.) as a food material, the functional components of folic acid and polyphenol in foliage (leaf, petiole and stem) of 16 species of Okinawan sweet potato were determined, The amounts of folic acid and polyphenol in eligible parts (leaf and petiole), except in Okinawa 100 species, contained higher amounts than stems and were similar to amounts of spinach. Miyanou 36 had the highest amounts of folic acid. Folic acid in Bise harvested in summer was higher than that of the spring sample. Harukogane contained the highest amounts of polyphenol, while Okihikari and Ayamurasaki had comparatively less polyphenol than other species. Polyphenol content of Bise and Okiyumemurasaki harvested in summer increased 2-3 times compared to spring. The sweet potatoes were cultivated on main Okinawan soils (Jaagaru, shimajiri maaji and kunigami maaji) ; cultivation on shimajiri maaji soil tends to increase the amounts of folic acid and polyphenol in sweet potato foliage in all but a few species. In Okinawa, vegetable shortages occur during summer ; thus, foliage of sweet potatoes such as Bise and Okiyumemurasaki could be used as summer vegetables or processed food materials. These basic data also would provide useful information for the selection and cultivation of suitable sweet potato species.