Preparation and antioxidant properties of extracts of Japanese persimmon leaf tea (kakinoha-cha)
Introduction
Epidemiological data, as well as in vitro studies, strongly suggest that foods containing phytochemicals with antioxidant potential have strong protective effects against major disease risks including cancer, diabetes, cardiovascular diseases and Alzheimer's disease (Ames, Shigenga, & Hagen, 1993; Knekt et al., 1997; Willett, 2002). Consumption of fruits, vegetables, and teas has been strongly linked to reduced risk of those diseases (Kanekt, Jarvinen, Reunanen, & Maatela, 1996; Le-Marchand, Murphy, Hankin, Wilkens, & Kolonel, 2000; Xing, Chen, Mitchell, & Young, 2001). The protective action of those foods has been attributed to the presence of antioxidants, especially polyphenolic compounds and antioxidant vitamins, including ascorbic acid, tocopherol and β-carotene (Kalt & Kushad, 2000). Among various foods, green tea has been the most often reported to possess numerous beneficial effects (Mitscher et al., 1997). The pharmacological effects of green tea have been reviewed, including antioxidant activity, antimutagenic activity and anticancer activity. Several studies have conclusively shown that most of antioxidant activity is produced from polyphenolic compounds rather than from ascorbic acid, tocopherol or β-carotene (Eberhardt, Lee, & Liu, 2000; Hanasaki, Ogawa, & Fukui, 1994; Kähkönen et al., 1999; Wang, Cao, & Prior, 1996). In Japan, green tea is drunk almost every day and kakinoha-cha (Japanese persimmon leaf tea) is also a well-known indigenous tea, which has become increasingly popular as a health beverage.
Persimmon (Diospyros kaki) grows in the countries of East Asia, such as Japan, China and Korea. The fruit of persimmon is eaten as fresh or dry fruit and the leaves of this tree are infused with hot (rather than boiling) water and drunk as kakinoha-cha in the same way as green tea. It has traditionally been drunk in localities with many persimmon trees, in the mountainous areas of Japan. The fruits of the persimmon are known to contain persimmon tannin (Matsuo & Ito, 1978), which has been traditionally used for the treatment of hypertensive diseases (Kameda et al., 1987). Two flavonol glucosides, isolated from persimmon, were shown to have a hypotensive action in rats (Funayama & Hikino, 1979). The polyphenols, including condensed tannin of persimmon, are related to the various physiological actions. Leaf of persimmon is also considered to have persimmon tannin, but there are still some unclear points with regard to the content and physiological effects of persimmon leaf tannin.
There are very few studies of reactive oxygen species in relation to water and methanol extracts of persimmon leaf tea against autooxidation and free radicals, such as superoxide anion radical, DPPH radical and hydroxyl radical. In this study, the antioxidant activities of water and methanol extracts of persimmon leaf tea were evaluated by using widely accepted anti-autooxidation and free radical-scavenging model systems.
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Materials and chemicals
Japanese persimmon leaf tea, cut into pieces of about 2 cm in width and dried, was purchased from a local store in Hiroshima Prefecture. Folin–Ciocalteu reagent was obtained from Kanto Chemical Co. (Tokyo, Japan). (+)-Catechin was obtained from Sigma–Aldrich Co. (MO, USA). Gallic acid, sodium carbonate, l-ascorbic acid, 2,4-dinitrophenyl hydrazine, sodium nitrite, aluminium chloride, 2,2′-azobis (2-amidinopropane) dihydrochloride, nitroblue tetrazolium salt, xanthine,
Ascorbic acid, total phenolics and total flavonoid contents of persimmon leaf tea extracts
Water and methanol extracts were prepared from persimmon leaf tea (50 g) and their yields were 10.3 and 9.4 g, respectively. Table 1 shows the contents of ascorbic acid, total phenolics and total flavonoids of persimmon leaf tea extracts. Fresh leaf of persimmon is known to have a relatively high content of ascorbic acid (Matsuura, Asano, Ohba, & Mizuno, 1971), for example the content of ascorbic acid in fresh leaf was 22.1 mg/g in our analytical data, but the water extract in this experiment
Acknowledgements
We thank Mr. R. Ouchi and Mr. K. Yoshimitsu for their technical assistance.
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