The antibacterial activity of artificially grown sweetpotato [Ipomoea batatas (L.) Lam.] leaves was investigated against both gram positive and gram negative bacteria namely Escherichia coli (O157:H7), Bacillus and Ecolai using three different cultivars, which are developed to use as a leafy vegetables namely Simon-1, Kyushu-119 and Elegant Summer. The sweetpotato leaves were grown under different temperatures (20 °C, 25 °C, and 30 °C) and artificial shading (O%, 40% and 80%) conditions. There were some cultivar differences but the lyophilized leaf powder (100 mg) from all the cultivars in the Trypto Soya Broth cultivation medium (10 mL) strongly suppressed the growth of all the bacteria studied and its effect was detectable even after autoclave treatment. But the antibacterial extract of the leaves had no effect on the growth of five types of bifidobacterium useful for human health. The water extracted antibacterial fractions from all the cultivars were viscous and the color was brown. Furthermore, the leaves grown under moderate low temperature (20 °C) with 0% shading treatments strongly suppressed the bacterial growth as comported to other treatments, which was accompanied by significantly high accumulation of sugar and polyphenol contents in the leaves. The results also suggest that there were a strong relationship among bacterial growth and antioxidatative compounds in the sweetpotato leaves. Therefore, the antibacterial action of sweetpotato leaves may depend on their antioxidative compounds or/and pectin like materials. Thus, the practical use of sweetpotato leaves is expected to prevent bacteria caused food poisoning.
Sweetpotato leaves contain biologically active anthocyanins that have significant medicinal value for certain human diseases and may also be used as natural food colorants. Foliar anthocyanins and their relative abundance were investigated in leaves of sweetpotato cultivars `Shimon-1', `Kyushu-119', and `Elegant Summer' grown under artificial shading and different temperature conditions. High-performance liquid chromatography profiles of the cultivars tested showed similar peaks but with peak areas differing with cultivar, temperature and shading. The relative quantity of individual anthocyanin was YGM (Yamagawamurashaki)-1a> YGM-4b> YGM-1b> YGM-5a> YGM-0d> YGM-0a> YGM-2> YGM-0c> YGM-3> YGM-6> YGM-5b> YGM-0b> YGM-0f> YGM-0e> YGM-0g. Seven were peonidin and eight cyanidin derivatives. The highest anthocyanin contents were found in plants grown at a moderate temperature (20 °C) with lower levels at 25 and 30 °C. The leaves of plants grown in full sun accumulated significantly more total as well as the major individual anthocyanins than plants grown in 40% and 80% shade. The results indicate that growing sweetpotatoes at moderate temperatures and without shading facilitates the accumulation of anthocyanins in the leaves. The anthocyanin composition of the leaves is discussed relative to their physiological function in human health.