EFFECTS OF MANUFACTURING PROCESS ON ASCORBIC ACID, POLYPHENOLS, AND RADICAL SCAVENGING ACTIVITY OF PERSIMMON LEAF TEA

Persimmon (Diospyros kaki Thunb.) leaves, calyxes, and branches have been used in Chinese medicine to treat hiccups and coughing. Because of the high levels of ascorbic acid and polyphenols in persimmon leaves, its consumption as a tea and in health foods is increasing in Japan. The manufacturing process has significant effects on ascorbic acid and polyphenol contents in persimmon leaf tea. We developed a manufacturing process for persimmon leaf tea that retains high levels of ascorbic acid, polyphenols, and radical scavenging activity. We used persimmon leaves collected during May from 14-year-old trees in a 'Saijo' Japanese persimmon orchard. The raw persimmon leaves were washed with tap water and spin-dried to remove surface water. The leaves were divided into approximately 300 g lots and then steamed for 0, 1, 5, 10, or 20 min. After steam treatment, persimmon leaves were air-dried for 12 h at 60°C in a spontaneous convection oven. We measured ascorbic acid, polyphenols, and 1,1-diphenyl1-2-picrylhydrazyl (DPPH) radical scavenging activity in persimmon leaf tea immediately after manufacturing and after storage for one year at room temperature. Immediately after manufacturing, the levels of ascorbic acid, polyphenols, and DPPH radical scavenging activity in non-steamed tea were 3,300 mg/100 g DW, 8,500 mg catechin eq./100 g DW and 510 μmol Trolox eq./g DW respectively; after storage for one year they were 0 mg/100 g DW, 5,250 mg catechin eq./100 g DW and 370 μmol Trolox eq./g DW, respectively. Immediately after manufacturing, the levels in leaves that were steamed for 5 min were 4,700 mg/100 g DW, 9,300 mg catechin eq./100 g DW and 530 μmol Trolox eq. /g DW, respectively; after storage for one year, these levels were 3,000 mg/100 g DW, 6,560 mg catechin eq./100 g DW, and 450 μpmol Trolox eq./g DW, respectively. Our results show that a 5 min steam treatment during the manufacturing process produces persimmon leaf tea that retains high levels of ascorbic acid, polyphenols, and DPPH radical scavenging activity, even after storage for one year.