A simple method for the extraction of tea samples and conditions of HPLC analysis of pheophorbide-a (PB-a) and its related chlorophyll derivatives was developed. Tea samples were extracted with 85% acetone (v/v) with this solution injected directly into the HPLC column. The modified HPLC procedure developed included a gradient solvent system in which solvent A (95% ethanol (v/v) containing 0.005 M sodium chloride) and solvent B (80% ethanol (v/v) containing 0.005 M sodium chloride) were the mobile phase. PB-a, its derivatives and their C-10 epimers could be clearly separated and determined within 35 min. This analytical method could be routinely used to determine low levels of PB-a content (<10 mg/100g) and its related individual chlorophyll derivatives in green teas. Hence, it is applicable to the safety and quality control of green teas.Keywords: pheophorbide-a, chlorophyll derivatives, HPLC analysis, tea leaves Pheophorbide-a (PB-a) is one of the photosensitive derivatives formed after chlorophyll decomposition and is known to cause dermatitis to human and animal skins (Hashimoto & Tsutsumi, 1963; Tamura et al, 1979). In 1981, the standards of the contents of PB-a and total PB-a (PB-a+pB-a produced by chlorophyllase activities after incubation (Kan et al, 1982)) in processed chlorella were established by the notification of the chief of a environment sanitation bureau in the Ministry of Welfare (Kanshoku No. 99).Green tea is thought to contain low levels of PB-a, because the enzyme activity in green tea leaves is inactivated by steaming immediately after plucking; however, very recently we first found the important fact that chlorophyllase activitles still remain in green teas (Kohata et al, 1997). The measurement of PB-a content in green tea was first carried out about 30 years ago by paper chromatography (Saijo, 1970). There has been no recent research on PB-a levels in green tea. We therefore should reinvestigate the accuracy of the PB-a content in green tea. PB-a is not water-soluble; therefore, it is not extracted in tea infusion at all, suggesting that green tea is absolutely safe for drinking. However, the demantd for green tea as an edible tea has recently been increasing. We therefore should also reevaluate the safety of green tea on the basis of PB-a content.The conversion rate of chlorophyll to pheophytin is a very useful indicator of the degree of discoloration of green tea, hence green tea quality. That is because the first step in discoloration during manufacturing or storage is due to the conversion of chlorophyll to pheophytin (Tanaka & Hara, 1972). This conversion rate has been obtained according to the colorimetric method (Tanaka & Hara, 1971) Hashimoto's procedure (Hashimoto, 1985) applied to the deterrnination of PB-a in chlorella is widely used. Whereas this method is a modification of a conventional colorimetric method (Kan et al, 1982) and has much better accuracy than the colorimetric method, there is still room for improving the otherwise tedious sample preparation method for HPLC an...
We investigated the total content of pheophorbide a (PB a), which is sum of the contents of newly produced PB a, including PB a initially present and that converted from chlorophyllide a (Chd a) by the chlorophyllase reaction during incubation, in green tea samples, and found that the total content of PB a markedly increased in both Sencha and Matcha, compared with the initially present PB a content in each. This result demonstrates that chlorophyllase activity still remains in green tea, even after processing fresh green leaves. A comparison of the total contents of PB a produced during the incubation of chlorophyll a (Chl a) with Sencha and fresh green leaf acetone powder indicates that the ratio of chlorophyllase activity in Sencha and in fresh green leaves was about 1:20.
A mold which was isolated from soil produced a large amount of extracellular dextranase in the medium containing dextran. From the comparative taxonomic experiments, the mold was identified as a strain of Aspergillus ustus.When the dextrans produced by various strains of Leuconostoc mesenteroides were used as C-source, they had influence evidently on the productivity of dextranase.Especially, using the dextran produced by Leuconostoc mesenteroides D 12 was isolated from a waste water in our sugar refinery, 330 units of the dextranase per ml of culture broth was produced by the shaking culture at 30°C for 4 days.While the other dextrans gave a lower productivity than the above result, it was appeared that the dextranase productivity was not related to the structure of dextran. When some carbohydrates were separately added to the medium with dextran, the productivity of dextranase was inhibited by fructose, lactose or some sugar alcohols.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.