VIETNAM NATIONAL UNIVERSITY-HO CHI MINH CITY
UNIVERSITY OF TECHNOLOGY
VO THI KIM NGAN
STUDY ON THE EXTRACTION AND ISOLATION OF
CAFFEINE FROM GREEN TEA Camellia sinensis (L.)
FIELD : ORGANIC CHEMISTRY
MASTERS THESIS
HO CHI MINH CITY, July 2010
CÔNG TRÌNH ĐƯỢC HOÀN THÀNH TẠI
TRƯỜNG ĐẠI HỌC BÁCH KHOA
ĐẠI HỌC QUỐC GIA TP HỒ CHÍ MINH
Cán bộ hướng dẫn khoa học: TS. PHẠM THÀNH QUÂN
Cán bộ chấm nhận xét 1: TS. PHẠM S
Cán bộ chấm nhận xét 2: TS. NGUYỄN THỊ LAN PHI
Luận văn thạc sĩ được bảo vệ tại Trường Đại học Bách Khoa, ĐHQG Tp. HCM ngày
07 tháng 08 năm 2010
Thành phần Hội đồng đánh giá luận văn thạc sĩ gồm:
1. PGS.TS Trần Thi Việt Hoa
2. TS. Phạm Thành Quân
3. TS. Trần Thị Kiều Anh
4. TS. Phạm S
5. TS. Trần Lê Quan
Xác nhận của Chủ tịch Hội đồng đánh giá LV và Bộ môn quản lý chuyên ngành sau
khi luận văn đã được sửa chữa (nếu có).
Chủ tịch Hội đồng đánh giá LV Bộ môn quản lý chuyên ngành
TRƯỜNG ĐẠI HỌC BÁCH KHOA TP. HCM CỘNG HÒA XÃ HỘI CHỦ NGHĨA VIỆT
NAM
PHÒNG ĐÀO TẠO SAU ĐẠI HỌC Độc Lập - Tự Do - Hạnh
Phúc
Tp.HCM, ngày 0 5 tháng 0
QUÂN
CÁN BỘ HƯỚNG DẪN CN BỘ MÔN QL CHUYÊN
NGÀNH
ACKNOWLEDGEMENTS
I would like to acknowledge the following people for their contributions to the project:
My supervisor, Dr. PHAM THANH QUAN for his time, guidance and enthusiasm
throughout the project.
Professors and staffs of the Department of Organic Chemistry and Faculty of Chemical
Engineering for their help and useful advice.
My friends in the Laboratory of Organic Chemistry for their help.
My family for their support and encouragement.
i
ABSTRACT
Caffeine is the world’s most popular drug and consumed everyday by millions of
people in the world. It is also used in many beverages and food. Due to its ability
to relieve headache and stimulate breathing, caffeine has been used in headache
relieving medicine, treatment of cessation of breathing for newborn babies and as
an antidote against the depression of breathing by overdoses of heroin. Caffeine
was found in tea with a content of 3-4 %. Tea has been widely grown in Vietnam
and is a large potential source of caffeine production.
In this project, the extraction and isolation of caffeine from Vietnamese green tea
were intensively studied and several results were obtained as below.
• Green tea was extracted by hot distilled water and the optimal caffeine
extraction was established for 5g of tea: 10 min, 75oC, solid-liquid ratio of
1/20, one-time extraction. The caffeine amount in the tea extract is 3.2
times that of EGCG.
• Caffeine in the tea extracts were adsorbed onto four adsorbent columns
(XAD-4, XAD-7, IR-120H, activated carbon) by passing the extracts
through the columns. XAD-4 was found to have the highest adsorption
-&'(%&4#;'/&3&')&&3 !'&.
*-
-&'(%&4#;'/&3&')&&3'&. *,
-*! &32 )&)'&2 !'&.<%&0=0>.=7?
17&@*6
iii
--! &3'(.&2 !'&.<%&0=0>.=7?7
'@-
-1! &3%&0;0>.<;#@)&&2 !'&.<91&A
7'@-
-,! &3.'4&32 )&)'%&2 !'&.<91&A
7'A=7@
-*!%&0)&45 &0.'%&()&%&()&-9
-*8;- &0.'-9
-*%&()&B5&3!%&4%3& !1*
-**8;9 &0.'1-
-*- )" 4& &0.'1,
-*1;7 &0.'16
C,
,1
40%&3,1
0 .0)&3&'.0%6*
*5( 0;%( 61
iv
LIST OF TABLES
v
LIST OF FIGURES
vi
1. CHAPTER 1: INTRODUCTION
Caffeine is one of the most popular compounds which are taken everyday by millions of
agio Sperimae, variety of agio Sperimae, species of Thea Sinensis L. Camellia
sinensis is a green plant that grows mainly in tropical and sub-tropical climates.
Nevertheless, some varieties can also tolerate marine climates and are cultivated
as far north as Pembrokeshirein the British mainland. Tea plants require at least
127 cm of rainfall a year and prefer acidic soils [1-3].
2
Leaves of Camellia sinensis soon begin to wilt and oxidize, if they are not dried
quickly after picking. The leaves turn progressively darker as their chlorophyll
breaks down and tannins are released. This process, enzymatic oxidation, is called
fermentation in the tea industry, although it is not a true fermentation. It is not
caused by micro-organisms, and is not an anaerobic process. The next step in
processing is to stop oxidation at a predetermined stage by heating, which
deactivates the enzymes responsible. Without careful moisture and temperature
control during manufacture and packaging, the tea will grow fungi. The fungus
causes real fermentation that will contaminate the tea with toxic and sometimes
carcinogenic substances, as well as off-flavors. Tea is traditionally classified
based on the techniques with which it is produced and processed [1-3]:
• White tea: Wilted and unoxidized
• Yellow tea: Unwilted and unoxidized, but allowed to yellow
• Green tea: Unwilted and unoxidized
• Oolong: Wilted, bruised, and partially oxidized
• Black tea: Wilted, sometimes crushed, and fully oxidized
• Post-fermented tea: Green tea that has been allowed to ferment/compost
2.1.2. Green tea’s composition
As mentioned, green tea production does not involve oxidation of young tea
leaves. Therefore, green tea’s chemical composition is very similar to that of fresh
leaf and presented in table 2.1 [1-8].
Green tea contains catechins, a type of antioxidant with EGCG as the main
component, which can compose up to 30 % of the dry weight. Beside catechins,
tea contains caffeine at about 3-4 % of its dry weight. Tea also contains
theophylline, which is a stronger stimulant than caffeine, and theobromine, which
is slightly weaker than caffeine.
The most important sources of caffeine are coffee (Coffea spp.), tea (Camellia
sinensis), guarana (Paullinia cupana), maté (Ilex paraguariensis), cola nuts (Cola
vera), and cocoa (Theobroma cacao). The amount of caffeine found in these
products varies – the highest amounts are found in guarana (4–7%), followed by
tea leaves (3-4%), maté tea leaves (0.89–1.73%), coffee beans (1.1–2.2%), cola
nuts (1.5%), and cocoa beans (0.03%) [11].
Figure 2. 2 Chemical structure of caffeine, theobromin and theophyllin
(from left to right)
6
Some basic information about caffeine is displayed as below:
•
Molecular formula: C
8
H
10
N
4
O
2
•
Molar mass: 194.19 g/mol
•
Appearance: odorless in liquid, white needles or powder.
•
Density: 1.23 g/cm
3
•
Melting point: 227
7
and as a flavoring agent in baked goods, frozen dairy desserts, gelatins, puddings
and soft candy [4].
Caffeine is a substance that can stimulate the central nervous system. It makes
people more alert, less drowsy and improves coordination. Combined with certain
pain relievers or medicines for treating migraine headache, caffeine makes those
drugs work more quickly and effectively. Caffeine alone can also help to relieve
headaches. Antihistamines are sometimes combined with caffeine to weaken the
drowsiness that those drugs cause. Caffeine is also used to treat breathing
problems in newborns and in young babies after surgery [1, 12]. Caffeine content
in some commercial products is shown in table 2.2. In recent years, various
manufacturers have begun putting caffeine into shower products such as shampoo
and soap, claiming that caffeine can be absorbed through the skin. However, the
effectiveness of such products has not been proven, and they are likely to have
little stimulatory effect on the central nervous system because caffeine is not
readily absorbed through the skin.
Table 2. 2 Caffeine in some commercial products
Product
Serving size Caffeine per serving
(mg)
Caffeine tablet (regular-strength) 1 tablet 100
Caffeine tablet (extra-strength) 1 tablet 200
Excedrin tablet 1 tablet 65
Excedrin 1 tablet 65
Bayer Select Maximum Strength
1 tablet
65.4
Midol Menstrual Maximum
Strength
1 tablet
intact in the tea-making process. Other green tea ingredients include 6% to 8% of
9
minerals such as aluminium, fluoride and manganese. Green tea also contains
organic acids such as gallic and quinic acids, and 10% to 15% of carbohydrate
and small amount of volatiles [3].
10
2.1.4. Tea production in the world
Figure 2. 3 Tea distribution in the world
Tea is produced in many countries. China is the largest tea producing country that
produces green tea, oolong tea and black tea. Other than China, tea is also
produced in India, Kenya, Russia, Sri Lanka, Indonesia, Thailand, Vietnam,
Japan, Turkey, etc. The annual production of tea is about 2.9-3.9 million tons.
Table 2.3 shows the tea production data in the world in 2000-2007 [13].
11
Table 2. 3 Tea production in the world (tons)
2.1.5. Tea in Vietnam
Vietnam has a strong tea culture dating back thousands of years. Tea has been produced
commercially since the beginning of the 20
th
century. Tea plantations are most plentiful in
the north but are also found in central Vietnam. Vietnam has traditionally been an
exporter of black tea – most of which ends up in blends. The Vietnamese people,
however, have a long tradition of drinking green tea, and this green tea is gaining a
reputation as some of the finest green tea available.
There are many different types of Vietnam tea. Black tea is the leader in exports, but it
has a reputation as being a “cheap tea” that can only be used for blending. Vietnam also
produces oolong tea and white tea. The best Vietnam tea, however, is green tea. Vietnam
has been producing green tea for thousands of years and this long history shows in the
quality of the tea. The climate and soil are ideal for growing tea, and there are many
regional variations and methods of production. Since 1995 tea production in Vietnam has
Liquid or solid
stationary phase
Partitioning or adsorption
Leaching solid liquid Partitioning
Soxhlet extraction solid liquid Partitioning (with applied heat)
Sonication solid liquid
Partitioning (with applied
ultrasound energy)
Accelerated solvent
extraction
solid liquid Partitioning (with applied heat)
Microwave-assisted
extraction
solid liquid
Partitioning (with applied
microwave irradiation)
Supercritical fluid
extraction
Solid, liquid Supercritical fluid Partitioning (with applied heat)
Purge-and-trap solid, liquid gas Partitioning
Thermal desorption solid liquid gas Partitioning (with applied heat)
2.2.1.1. Requirements for extraction
Chemical samples requiring extraction are composed of the compound of interest and the
sample matrix, which may contain interfering species. Prior to choosing an extraction
method, knowledge must be gained about the structure (including functional group
arrangement), molecular mass, polarity, solubility, pKa, and other physical properties of
both the species of interest and potential interfering compounds [15, 16].
Some requirements of a suitable extraction solvent [15, 16]:
• Selectivity, i.e. the ability to extract the material of interest in preference to other,
interfering material.
Copyright: Tài liệu đại học ©