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Flavonoids from two tropical Zingiberaceae plants : extraction, isolation, chemical characterization and antioxidant studies
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Type
Thesis
Author
Chang, Yong Qin
Supervisor
Tan, Swee Ngin
Chia, Lian Sai
Abstract
Zingiberaceae, a family of tropical plants, is widely used for culinary and medicinal purposes. Chemical investigations, pharmacological studies and clinical practice on Zingiberaceae plants have demonstrated that flavonoids could be one of the groups of beneficial compounds responsible for their bioactivities. One of the medicinal uses of flavonoids is for the treatment of diseases related to an imbalance between oxidative attack and antioxidant defenses. Therefore, this dissertation focused mainly on investigating the flavonoids with high antioxidant ability from two Zingiberaceae plants.
This dissertation can be broadly divided into three sections. The first section provided the relevant literature review on flavonoids in Zingiberaceae and different phytochemical techniques (Chapters 1~2); the second section presented the various experimental results (Chapters 3~6); and the final section, i.e. Chapter 7, was devoted to giving the general conclusions and the discussion of the extension for future work.
The first section gave an introduction to chemistry, biosynthesis of flavonoids and their medicinal functions. The overall survey of flavonoids in Zingiberaceae is listed in the first chapter. The second chapter summaries the phytochemical techniques used for sample preparation, extraction procedure, and structural elucidation of flavonoids.
The second section involved the numerous results of experimental works. The third chapter examined antioxidant activity of crude extracts from eight medicinal ginger plants measured by TEAC method. It was observed that the antioxidant activity had a close relationship with the total phenolic contents and total flavonoid contents. Based on the antioxidant activity results, Costus speciosus (Keong) Smith and Etlingera elatior (Jack) Smith with high antioxidant ability were selected for further investigation.
The fourth chapter focused on the extraction, isolation, purification and structural elucidation of flavonoids present in leaves and flowers of C. speciosus and E. elatior. Flavonoids in fractions with high antioxidant activity were systematically investigated. It was interesting to note that most of the isolated compounds were identified as flavon-3-ol with high antioxidant abilities. In addition, the identities of flavonoids would shed insights into the high antioxidant activity of C. speciosus and E. elatior. The compounds which were separated from samples are as follows: three flavonoids (quercetin, quercitrin and rutin) were obtained from both flowers and leaves of C. speciosus. Meanwhile, three compounds (kaempferol-3-O-glycoside, kaempferol and quercetin) were obtained from flowers of E. elatior. Furthermore, nine compounds (quercetin, kaempferol, quercetin-3-O-rhamnoside, 7-methyl-quercetin-3-O-glacoside, quercitrin, rutin, quercetin-7-O-glucoside, 5-O-caffeoylquinic acid, 5-O-caffeoylquinic acid methyl ester and anthraquinone) were obtained from leaves of E. elatior.
Subsequently, the fifth chapter reported on the quantitative analyses of key flavonoids in the two Zingiberaceae species. A new and relatively simple LC-MS method was developed for the simultaneous determination of 16 flavonoids including many isomers. Furthermore, the developed LC-MS method was successfully applied to analyze flavonoids in different parts of C. speciosus and E. elatior obtained from different sources. Besides, the identities of the flavonoids present in C. speciosus and E. elatior were further confirmed using independent LC-MS/MS analysis. The results showed that the contents of the flavonoids varied greatly in different parts, sources or the season of harvest of C. speciosus and E. elatior. For C. speciosus, quercitrin was the flavonoid present in the highest concentration among the three flavonoids, namely, rutin, quercitrin and quercetin. The concentration of quercitrin in flowers was higher than its concentration in rhizomes and leaves.
The sixth chapter was devoted to develop a simple and effective green approach for the rapid extraction and analysis of bioactive flavonoids in C. speciosus flowers using surfactant assisted PLE and MEKC. Surfactant assisted PLE proved to be comparable to Soxhlet extraction in terms of quantitative analysis of bioactive flavonoids. The results showed that it was possible to carry out the surfactant assisted PLE at room temperature with relatively shorter extraction time. This green approach is of significance, as it provided a totally organic solvent free system for sample extraction and analysis, which had not been achieved by earlier studies.
The present study provided the following valuable knowledge of C. speciosus and E. elatior: Firstly, the antioxidant activities, types of endogenous flavonoids and contents of the major flavonoids were studied systematically for these two plants. Secondly, different extraction and analytical methods were developed and compared for identifying and quantifying flavonoids in the plants materials. Thirdly, the different extraction and analytical methods could aid in chemical standardization for quality control of various botanicals. Results obtained from this research could provide useful information for further investigation on the use of the two medicinal plants as commercial health promoting products.
The final section presented the general conclusions based on the research achievements of the dissertation. Future works including isolating and identifying bioactive flavonoids from rhizomes of C. speciosus and E. elatior, and applying the green extraction and analytical approach to E. elatior were also discussed.
This dissertation can be broadly divided into three sections. The first section provided the relevant literature review on flavonoids in Zingiberaceae and different phytochemical techniques (Chapters 1~2); the second section presented the various experimental results (Chapters 3~6); and the final section, i.e. Chapter 7, was devoted to giving the general conclusions and the discussion of the extension for future work.
The first section gave an introduction to chemistry, biosynthesis of flavonoids and their medicinal functions. The overall survey of flavonoids in Zingiberaceae is listed in the first chapter. The second chapter summaries the phytochemical techniques used for sample preparation, extraction procedure, and structural elucidation of flavonoids.
The second section involved the numerous results of experimental works. The third chapter examined antioxidant activity of crude extracts from eight medicinal ginger plants measured by TEAC method. It was observed that the antioxidant activity had a close relationship with the total phenolic contents and total flavonoid contents. Based on the antioxidant activity results, Costus speciosus (Keong) Smith and Etlingera elatior (Jack) Smith with high antioxidant ability were selected for further investigation.
The fourth chapter focused on the extraction, isolation, purification and structural elucidation of flavonoids present in leaves and flowers of C. speciosus and E. elatior. Flavonoids in fractions with high antioxidant activity were systematically investigated. It was interesting to note that most of the isolated compounds were identified as flavon-3-ol with high antioxidant abilities. In addition, the identities of flavonoids would shed insights into the high antioxidant activity of C. speciosus and E. elatior. The compounds which were separated from samples are as follows: three flavonoids (quercetin, quercitrin and rutin) were obtained from both flowers and leaves of C. speciosus. Meanwhile, three compounds (kaempferol-3-O-glycoside, kaempferol and quercetin) were obtained from flowers of E. elatior. Furthermore, nine compounds (quercetin, kaempferol, quercetin-3-O-rhamnoside, 7-methyl-quercetin-3-O-glacoside, quercitrin, rutin, quercetin-7-O-glucoside, 5-O-caffeoylquinic acid, 5-O-caffeoylquinic acid methyl ester and anthraquinone) were obtained from leaves of E. elatior.
Subsequently, the fifth chapter reported on the quantitative analyses of key flavonoids in the two Zingiberaceae species. A new and relatively simple LC-MS method was developed for the simultaneous determination of 16 flavonoids including many isomers. Furthermore, the developed LC-MS method was successfully applied to analyze flavonoids in different parts of C. speciosus and E. elatior obtained from different sources. Besides, the identities of the flavonoids present in C. speciosus and E. elatior were further confirmed using independent LC-MS/MS analysis. The results showed that the contents of the flavonoids varied greatly in different parts, sources or the season of harvest of C. speciosus and E. elatior. For C. speciosus, quercitrin was the flavonoid present in the highest concentration among the three flavonoids, namely, rutin, quercitrin and quercetin. The concentration of quercitrin in flowers was higher than its concentration in rhizomes and leaves.
The sixth chapter was devoted to develop a simple and effective green approach for the rapid extraction and analysis of bioactive flavonoids in C. speciosus flowers using surfactant assisted PLE and MEKC. Surfactant assisted PLE proved to be comparable to Soxhlet extraction in terms of quantitative analysis of bioactive flavonoids. The results showed that it was possible to carry out the surfactant assisted PLE at room temperature with relatively shorter extraction time. This green approach is of significance, as it provided a totally organic solvent free system for sample extraction and analysis, which had not been achieved by earlier studies.
The present study provided the following valuable knowledge of C. speciosus and E. elatior: Firstly, the antioxidant activities, types of endogenous flavonoids and contents of the major flavonoids were studied systematically for these two plants. Secondly, different extraction and analytical methods were developed and compared for identifying and quantifying flavonoids in the plants materials. Thirdly, the different extraction and analytical methods could aid in chemical standardization for quality control of various botanicals. Results obtained from this research could provide useful information for further investigation on the use of the two medicinal plants as commercial health promoting products.
The final section presented the general conclusions based on the research achievements of the dissertation. Future works including isolating and identifying bioactive flavonoids from rhizomes of C. speciosus and E. elatior, and applying the green extraction and analytical approach to E. elatior were also discussed.
Date Issued
2012
Call Number
QK898.F5 Cha
Date Submitted
2012