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PUrvlS 99: 1 UNIVERSITI MALAYSIA S.A..BAH
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rnen gaku membenarkan tesis (LPS/ Sarjana/ Doktor Falsafah) ini di simpan di Perpustakaan Universiti Malaysia Sabah dengan syarat-syarat kegunaan seperti berikut:
1. Tesis adalah hakmilik Universiti Malaysia Sabah. 2. PeIlJustakaan Universiti Malaysia Sabah dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. PeIlJustakaan dibenarkan membuat sa1inan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. ** Si1a tandakan ( / )
SULIT
(Mengandungi maldumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang terrnaktub di dalam AKT A RlillSlA RASMI 1972)
TERHAD (Mengandungi maklumat TERHAD yang te1ah ditentukakan oleh organisasilbadan di mana penyelidikan dija1ankan)
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:1\. TATAN: * Potong yang tidak berkenaan. * Jika tesis ini SULrr atau TERHAD, si1a lampiran surat daripada pihak berkuasa/organsasi
berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SUUT
* *;s~Ed~:~ldkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelii~an, atau disertasl bagl pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (LPSM).
,
. u u it m
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DECLARATION
I hereby declare that the material in this thesis is my own except for quotations, excerpts, equations, summaries and references, which have been duly acknowledged.
20th April 2009
.P -PUN SIT WAN HN200S-4768
TITTLE
DEGREE
VIVA DATE
SIGNATURE
1. SUPERVISOR
: DETERMINATION OF FLAVONOIDS, TOTAL CAROTENOmS CONTENT AND VITAMIN C OF CUcurblta moschata, Limnocharis f/ava AND !asia spinosa
: BACHELOR OF SCIENCE
: 2009
VERIFIED BY
(DR. PATRICIA MATANJUN )
2. EXAMINER 1 (ASSOC. PROF. DR. CHVE FOOK VEE)
3. EXAMINER 2 (DR. MUHAMMAD IQBAL HASHIMI)
4. DEAN (ASSOC. PROF. DR. MOHD ISMAIL ABDULlAH)
11
ACKNOWLEDGEMENTS
First and foremost, I would like to acknowledge to my supervisor, Dr. Patricia
Matanjun for the support and advices that she had given to me on research. Dr.
Patricia also provided financial assistance for buying standards and other chemical
substances.
Appreciation is also gratefully extended to laboratory assistants from School
of Food Science Nutrition for the provision of solvents and apparatus and and School
of Science Technology for the privilege in the use of HPLC. They are pretty kind and
willing to give training on machine functioning.
Furthermore, i m grateful to my parents for the support they have been
giving to me during my study. Besides, they also provided financial support on
buying samples, transportation expenses and other expenses.
At last, appreciation is extended to master students, coursemates and fellow
friends for giving advice, helpful discussion and co-operation when using laboratory
equipments.
iii
ABSTRACT
The study was conducted to determine flavonoids (quercetin, kaempferol and catechins), total carotenoids content and vitamin C in leaves and stems of selected edible plants, Cucurbita moschata, Limnocharis flava, Lasia spinosa and was compared to cultivated plant. Selected edible plants were collected from local market in Kota Kinabalu. Flavonoids content were extracted by using methanol solvent and determined by HPLC analysis. Total carotenoid content were extracted by using acetone solvent whereas 5% meta-phosphoric acid used to extract vitamin C. Both compounds were analyzed by using spectrophotometer. The highest flavonols content was in Cucurbita moschata (17.73 mg/100g quercetin and 7.49 mg/100 g kaempferol) whereas the Lasia spinosa was detected with the most catechins levels (114.29 mg/100g ECG, 523.17 mg/100 9 CA, 793.36 mg/100g EC, 383.63 mg/100 g EGCG, and 103.34 mg/100 9 ECG) and followed by Cucurbita moschata with catechins range from 4.36 to 205. 67 mg/100 g. Then, level of total carotenoids content was ranged from 168.74 mg/100 9 (Limnocharis flava) to 1304.73 mg/100 9 (Brassica chinensis var parachinensis). Lasia spinosa recorded highest concentration (103.74 mg/100 g) of vitamin C and followed by Cucurbita moshata (55.25 mg/100 g). In conclusion, edible plants Cucurbita moschata and Lasia spinosa can be potential sources of natural antioxidants for human nutrition.
IV
ABSTRAK
PENENTUAN KANDUNGAN FLAVANOID, JUMLAH KANDUNGAN KAROTENOID DAN VITAMIN C DALAM DAUN DAN TANGKAI TUMBUHAN TERPILIH UNTUK DIMAKAN,
Cucurbita moschata, Limnocharis flava DAN Lasia spinosa.
Kajian telah dijalankan untuk menentukan flavonoid (quercetin, kaempferol dan catechins), jumlah kandungan karotenoid dan vitamin C dalam daun serta tangkai tumbuhan terpilih untuk dimakan, Cucurbita moschata, Limnocharis flava, Lasia spinosa dan berbanding dengan tumbuhan tanaman. Tumbuhan terpilih untuk dimakan telah dikumpul dari pasar tempatan di Kota Kinabalu. Kandungan flavonoid telah diesktrak dengan menggunakan methanol dan ditentukan oleh anal isis HPLC. Jumlah kandungan karotenoid telah diesktrak dengan acetone manakala 5% asid meta-fosforik telah digunakan untuk mengesktrakan vitamin C. Kedua-dua komponen telah dianalisis dengan menggunakan spectrophotometer. Kandungan flavonol yang tertinggi dicatatkan pada Cucurbita moschata (17.73 mgj100g quercetin dan 7.49 mgj100 9 kaempferol) manakala Lasia spinosa dicatat dengan kandungan catechins yang terbanyak (114.29 mgj100g ECG, 523.17 mgj100 9 CA, 793.36 mg/100g EC, 383.63 mg/100 9 EGCG, and 103.34 mg/100 9 ECG) dan ini diikuti dengan Cucurbita moschata mempunyai linkungan catechins dari 4.36 hingga 205.67 mg/100 g. Setelah itu, linkungan bagi jumalah kandungan karotenoid adalah dari 168.74 mg/100 9 (Limnocharis flava) hingga 1304.73 mg/100 9 (Brassica chinensis var parachinensis). Lasia spinosa mencatatkan kepekatan vitamin C (103.74 mg/100 g) yang tertinggi dan diikuti dengan Cucurbita moshata (55.25 mg/100 g). Kesimpulannya, tumbuhan untuk dimakan, Cucurbita moschata dan Lasia spinosa adalah sumber yang berpotensi dalam antioksidan untuk pemakanan manusia.
v
TABLE OF CONTENT Pages
TITLE
DECLARATION ii
VERIFIED BY EXAMINERS iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENT vii
LIST OF TABLES vii
LIST OF FIGURES x
LIST OF SYMBOLS xi
LIST OF APPENDIX xii
CHAPTER 1 INTRODUCTION 1
1.1 OBJECTIVE 3
CHAPTER 2 LITERATURE REVIEW
2.1 OVERVIEW OF LEAFY VEGETABLES 4
2.2 Cucurbita moschata 5
2.2.1 NUTRmON AND USAGE 6
2.3 Limnocharis flava 6
2.3.1 NUTRmON AND USAGE 7
2.4 Lasia spinosa 8
2.4.1 NUTRmON AND USAGE
2.5 FLA VONOIDS 9
2.5.1 MECHANISMS 12
vi
2.5.2 BIOLOGIC FUNCTIONS 14
2.6 CAROTENOIDS 14
2.6.1 MECHANISM 15
2.6.2 COMPOSmON OF CAROTENOIDS 16 IN FOOD
2.6.3 BIOLOGIC FUNCTIONS 18
2.7 VITAMIN C 19
2.7.1 MECHANISMS 20
2.7.2 BIOMARKER OF PROTEIN OXIDATION 21
2.7.3 DIETARY AVAILABILITY 22
2.7.4 BIOLOGIC FUNCTIONS 22
CHAPTER 3 MATERIALS AND METHODS
3.1 MATERIALS 24
3.1.1 CHEMICALS
3.1.2 APPARATUS
3.1.3 EQUIPMENTS
3.2 METHODS 25
3.2.1 SAMPLE COLLECTION
3.2.2 SAMPLE PREPARATION
3.2.3 DETERMINATION OF FLAVONOIDS 26
3.2.3.1 QUERCETIN AND KAEMPFEROL 3.2.3.2 CATECHINS
3.2.4 DETERMINATION OF TOTAL CAROTENOIDS 27 CONTENT
3.2.5 DETERMINATION OF ASCORBIC ACID 28
3.3 STATISCAL ANALYSIS 29
vii
CHAPTER 4 RESULT AND DISCUSSION
4.1 FLA VONOIDS
4.2 TOTAL CAROTENOID CONTENT
4.3 ASCORBIC ACID
CHAPTER 5 CONCLUSION AND DISCUSSION
5.1 CONCLUSION
5.2 SUGGESTION
REFERENCES
30
38
41
44
45
46
Vlll
LIST OF TABLES
PAGES
Table 2.1 Main groups of flavonoids, compounds and 12 food sources
Table 3.1 Gradient elution of mobile phase 27
Table 4.1 Flavonoid content in selected edible plants 31
Table 4.2 Total carotenoids content in selected edible plants 38
Table 4.3 Vitamin C content in selected edible plants 41
ix
LIST OF FIGURES
PAGES
Figure 2.1 Leaves and stems of Cucurbita moschata 6 (Pucuk labu merah)
Figure 2.2 Leaves and stems of Limnocharis flava (Tayaan) 8
Figure 2.3 Leaves and stems of Lasia spinosa (8ugor) 9
Figure 2.4 Major classes of flavonoids 10
Figure 2.5 Structure of common flavonoids compounds 11
Figure 2.6 Structure of common dietary carotenoids 17
Figure 2.7 Structure of oxidative ascorbic acid 21
Figure 4.1 Chromatogram profiles of flavonols in three
selected edible plants and a cultivated vegetables 34
Figure 4.2 Chromatogram profiles of catechins in three selected edible plants and a cultivated vegetables 35
x
LIST OF SYMBOLS
% Percentage
g Gram
kg Kilogram
mg Milligram
ml Mililiter
> More than
< Less than
+ Plus minus
mg/ml Concentration of mg per ml
Xl
LIST OF APPENDIX
PAGES
Appendix A One way ANOVA of Quercetin 58
Appendix B One way ANOVA of Kaempferol 59
Appendix C One way ANOVA of Catechins 60
Appendix D Chromatograms of Standard 64
Appendix E Calibration Curves of Standards 66
Appendix F Chromatogram of flavonols in 69 Cucurbita moschata
Appendix G Chromatogram of flavonols in 70 Limnocharis flava
Appendix H Chromatogram of flavonols in 71 Lasia spinosa
Appendix I Chromatogram of flavonols in 72 Brassica chinensis var parachinensis
Appendix] Chromatogram of catechins in 73 Brassica chinensis var parachinensis
Appendix K Chromatogram of catechins in 74 Cucurbita moschata
Appendix L Chromatogram of flavonols in 75 Limnocharis flava
Appendix M Chromatogram of flavonols in 77 Lasia spinosa
xii
Chapter 1
Introduction
An edible plant is a plant or plant part that is served either raw or cooked as part of
the main course of a meal like vegetable. Variety of vegetable can be based upon
edible plant parts such as a leaf, shoot, root, tuber, flower, or stem. For instances,
leaf part of a plant is lettuce, seed part of the plant is peas, root is carrot, tuber is
potato and flower is broccoli. People usually select vegetable is based on their
preference or taste of the vegetable. Nowadays, due to awareness of health related
disease, people will consume vegetable according to it nutritive values and health
related content.
Edible plants are potential sources of natural antioxidants for human diet.
There is an epidemiology found that a diet rich in vegetables (more than 5 serving
per day) is recommended along with whole grains and fruits showed a negative
association of health risk (Tee et al., 1997). Foods of plant origin not only provide
diet with certain antioxidant vitamins like vitamin C (ascorbic acid), vitamin E (0-
tocopherol) and pro-vitamin A (~-carotene), but also a complex mixture of other
natural substances with antioxidant capacity (Arnao et al., 2000). Besides vitamins A,
C, and E, the most important naturally occurring plant substances showing
antioxidant activity are carotenoids, flavonoids and other simple phenolic compounds
which, in differing proportions and quantities, are to be found in cereals, fruits and
vegetables (Duell, 1996; Mackerras, 1995). According to the Nutrient Composition of
Malaysian Foods, these green vegetables have been found to contain about 1825 -
4760 I-Ig of ~ -carotene /100 g edible portion, 27.6 - 107 mg of vitamin C/I00 g
edible portion and 0.15 - 0.55 mg of riboflavin/100 g edible portion (Tee et al.,
1997).
1
Recently there has been increasing interest in the protective biochemical
function of these phytochemicals in the prevention of oxidative damage to an
organism. In the past few years, an increasing number of epidemiological studies
have shown an inverse correlation between the consumption of fruit and vegetables
and the incidence of degenerative diseases (Ames et al., 1993; Riceevans & Miller,
1995). This correlation is based on a presence of difference phytochemicals in
vegetables with the potential effect on human health. Phytochemical like flavonoids
have been showed a wide range of biochemical and pharmacological effects
including anti-oxidation, anti-inflamation, anti-platelet, anti-thrombotic action, and
anti-allergic effects (Havsteen, 1983; Gryglewski et al., 1987; Middleton et al., 1992;
Cooks et al., 1996). Other phytochemicals like carotenoids, vitamin C and vitamin E
which play an important role as antioxidant where these phytochemicals can reduce
risk of cancer and cardio-vascular (Kris-Etherton et al., 2001). Apart from this,
vegetables can act as medicinal herbs which will contribute nutritive values and
therapeutic values to health. Gelang pasir is one kind of vegetable and also use as
herb. It can eat raw or boil it and by drinking the water can reduce pain and prevent
rheumatism.
Local markets have offered variety types of edible plants or vegetables
ranging from leafy to tubers consumption. People from Peninsular Malaysia prefer to
consume green vegetable such as Chinese mustard, Chinese kale, lettuce, and
swamp cabbage; whereas market in Sabah mostly can find vegetables like ulam raja,
rebung manis, tayaan, tuhau, pucuk labu merah, pucuk kacang dan keladi liar. Life
quality of some places in Sabah still need to be improved. Majority of the people are
still relying on planting vegetables or selling vegetables as their major income.
People from suburban places usually sell vegetables that are rare or planted by
themselves. Therefore, majority of these vegetables are not commercially planted,
they may grow wildly in the forest, grow rarely besides the lake, rivers or even after
harvested paddy field. Some of these edible plants are seasonal grown where it is
quite difficult to get the same edible plants frequently.
Therefore, in this study several edible plants that can be found in Sabah
market will be chosen. These selected plants are Cucurbita moschata, Limnocharis
flava and Lasia spinosa. Fruit of Cucurbita moschata, labu merah is a cultivated plant,
but the leaf part is less common vegetables consumed by local people. In the same
2
way, Limnocharis flava and Lasia spinosa are less commonly consumed by local
people as well. These vegetables are less frequently to get in the market owing to
they are not cultivated for commercial purpose. Although there are some studies on
antioxidant activity in vegetables or tropical plants (Miean et al., 2001; Ching et al.,
2001; Lakshminarayana et al., 2005), there is a lack of studies or chemical analysis
concerning these phytochemicals in these selected edible plant, Cucurbita moschata,
Limnocharis flava and Lasia spinosa in Sabah.
1.1 Objective
1. To determine f1avonoids compounds, total carotenoids content and vitamin C
in selected edible leave and stem of Cucurbita moschata, Limnocharis flava
and Lasia spinosa.
2. To compare the amount of antioxidant compounds of selected edible leave
and stem of Cucurbita moschata, Limnocharis flava and Lasia spinosa with
Brassica chinensis var. parachinensis.
3
Chapter 2
Literature Review
2.1 Overview of leafy vegetables
Leafy or salad vegetables or salad greens are vegetables whose leaves and petioles
only are eaten. They are mainly eaten in fresh forms and hence called leafy or salad
greens (Engle and Altoveros, 2000). More than eighty species of leafy vegetables are
popularly grown in the world. Among these leafy brassicas, lettuce and spinach are
universally popular. Leafy vegetables are fast growing and are short duration crops.
They particularly thrive in the tropics and subtropics. Many leafy vegetables mature
in 30-40 days after sowing and therefore are favourable crops for inclusion into
various types of vegetable production systems such as field vegetable cultivation,
protected cropping, home gardening and market gardening. Hence they are grown
under diverse agro-climatic conditions and management practices. Leafy vegetables
are excellent sources of vitamins A and C, minerals and fibres (Larkcom, 1991).
Leafy vegetables are high in water and moderate to high in vitamin and
minerals. They are considered as excellent nutritional sources of vitamins A, B, C and
E, Ca, Fe, P and K. High water and dietary fibre contents of leafy vegetables attribute
for greater digestive properties. The US National Cancer institute reports that foods
rich in Vitamins A and C have been associated with reduced risk of certain cancers.
Leafyvegetables are very low in calories and sodium, and are free of fat and
cholesterol. Hence, the need for vegetable green food is being greatly emphasised.
However, the composition of oxalates, nitrates, heavy metals and pesticide residues
make them inferior due to antinutritional or toxic effects. Since leafy vegetables are
4
grown under numerous agro-climatic conditions and management practices, pre
harvest factors highly influence on the nutritional properties. Therefore, pre-harvest
crop management to obtain quality fresh produce appeared to be is very much
important for ensuring nutritional quality and functional properties in food chains.
External qualities and some internal qualities of vegetables are conventional price
determinants of fresh leafy vegetables. However the present trend of high popularity
for health food has created a substantial demand for internal qualities, especially
which are related to the nutritional and functional values. Therefore studies on the
factors affecting nutritional value will be highly prospective for the future
improvements of fresh market leafy vegetables.
2.2 Cucurbita moschata
Cucurbita moschata, pumpkin also known as labu merah in Malaysia. It is
categorized in the Cucurbitaceae family where in this family of Cucurbitaceae,
including about 90 genera and more than 700 species of monoecious or dioecious
herbs and erect shrubs which widely distributed over the warm parts of the world.
The genus Cucurbita is native to America, and includes about 25 species of
monoecious, prostrate, trailing, vine-like plants with rough, prickly, angled stems
which tend to root at the nodes (Cobley, 1976). The tendrils of Cucurbita spp. are
branded and the large alternate leaves may be more or less entire or deeply lobed.
Large, bright-yellow unisexual flowers occur singly in the leafaxils, the males often
produced before the females. Several species that widespread throughout the tropics
are C maxima, C moschata, C pepo and C mixta. They all produce fruits which are
variously called pumpkins, summer or winter squashes or marrows. Summer squash
are those that have tender skins and soft, moist flesh and are eaten while immature.
Those that are round, orange and strong flavoured are called pumpkin. Within the
four species which have mild flavoured, fine-grained flesh, hard skin is called winter
squash (Cobley, 1976).
Cucurbita moschata was widely distributed throughout the North and South
America before Columbus. Of the four commonly cultivated species of Cucurbita,
Cucurbita moschata grows best in the wet tropics, and will thrive not only in humid
climates, but also in very hot ones. It can be concluded that it is more widespread in
5
the tropics than other species (Tsuchiya & Gupta, 1991). Cucurbita moschata has
soft stem without prickly hairs, and palmately divided leaves with rounded lobes. The
calyx-lobes of the flowers are broader and leaf-like. The large, variable fruits are
borne on stiff, angular peduncles which are markedly expanded where they join the
fruit.
2.2.1 Usage and Nutrition
Cucurbita moschata is a common vegetable for Malay tradisional meal. Flesh of
Cucurbita moschata usually cook with oil, boil and other reCipes which are favoured
by local people. Apart from cooking, it can be made as cake and bakery biscuits.
Leaves of Cucurbita moschata also favourite tradisional meal for local people. It often
cook with prawn, anchovy, and samba!.
Cucurbita moschata contains high nutritional values especially in vitamin A. In
every 100g of edible portion of Cucurbita moschata contains about 84.4 9 of water,
0.9 9 of protein, 0.1 9 of fat, 13.9 9 of carbohydrate, 21 mg of calCium, 39 mg of
phosphorus, 50 mg of sodium and 0.7 mg of iron whereas leaves contain high
amount of vitamin A and vitamin C.
Figure 2.1 Leaves and stems Cucurbita moshata (pucuk labu merah)
2.3 Limnocharis flava
Limnocharis flava, known as tayaan by local people, is an aquatic weed that could
invade wetlands, rivers and dams in northern Australia. Native to tropical America, it
has become a pest of rice and a serious environmental weed from India throughout
Southeast Asia to Indonesia, and the USA. The Greek words "Limno" and "charis"
mean "pond" and "grace", respectively. Limnocharis flava also known as sawah
lettuce, velvetleaf or yellow bur-head in English whereas local people may call this
plant as tayaan, jinjir or paku rawan. Limnocharis flava mostly occurs in agricultural
area, ruderal or wetlands. It inhabits in shallow swamps, ditches, pools and wet rice
fields or in stagnant fresh water (Saidin, 2000).
Limnocharis flava is an erect, clump-forming herb to c. 1m tall that grows
rooted in the mud. Where moisture is present year-round it is perennial, but annual
in ephemeral water-bodies and sites with pronounced dry seasons. Limnocharis flava
has rounded leaf blades and triangular leaf and inflorescence stalks. Inflorescences
are 'octopus-like' and comprise up to15, 3-lobed yellow flowers. Limnocharis flava
reproduces by seed and vegetatively. Spherical capsules develop after flowering and
eventually split into crescent-shaped segments, each containing numerous tiny
brown seeds. Mature fruit and individual segments float for several days, scattering
seeds as they float downstream. Vegetative plantlets develop from the central
inflorescence bud and either root in the mud below or break off and float away to
form new infestations (Saidin, 2000).
2.3.1 Usage and Nutrition
Limnocharis flava is valued as an ornamental plant in some countries and cultivated
in botanic gardens or private homes. This ornamental use has been documented in
the USA, Singapore, Sri Lanka and Indonesia. In some South-East Asian countries
Limnocharis flava is used as a source of food. For example, in Java the plant is a
much-esteemed vegetable, which is cultivated in rice fields and sold in markets for
its young leaves, stems and flower clusters. In Vietnam, Limnocharis flava occurs
naturally in many bodies of water and is used as a vegetable in dishes; it is
particularly popular in the Mekong Delta. Known as keo neo or cu neo, it is
frequently gathered by ethnic Vietnamese (Kinh) women and sold in local markets
and by boat vegetable vendors. The young leaves and tops of the plant are boiled or
cooked in mixed soups. The leaves of Limnocharis flava are also collected for
household consumption in Bangladesh by women (Saidin, 2000).
The vegetable contains relatively high levels of Ca, Fe and B-carotene, which
are minerals that are frequently insufficient in the diets of women in low-income
countries (Ogle et al., 2001). In every 100 g edible portion of Limnocharis flava
contain about 93.5 % of water, 23.1 g of protein, 0.4 g of fat, 2.7 g of carbohydrate,
1.0 g of fibre, 63 mg of phosphorus, 252 mg of potassium and 23 mg of calcium
(Maisuthisakul et aI., 2008).
Figure 2.2 Leaves and stems of Limnocharis flava (Tayaan)
2.4 !asia spinosa
Lasia spinosa, known as 'bugor' by local people, is categorized into Araceae family
where it is native to Vietnam and widespread in southeastern Asian, including China,
Thailand and Malaysia (Li, 1979). Lasia spinosa is a perennial evergreen plant
growing on wet, nutrient-rich soils near or in ditches, brooks, ponds or grass-clusters,
commonly characterized by seasonally changing water levels. The plants can reach
about 0.5-1.0 meter height. They have round, prickly stems, and roughly long leaves
with approximately 32-60cm length and 1S-S0cm width when it matured.
These valuable swamp species can be used as an ornamental, mediCine and
vegetable. Shoot and petiole of the young plant can be pickled after peeled off the
prick. Pickled shoot and petiole can be cooked with curry or own traditional recipe. L.
spinosa is toxic especially inside the flesh and it cannot eat raw. It is better to cook
the plant before eating, at least by blanching or pickling. Nevertheless, there are only
little information about genus Lasia and this plant information available (Li, 1979).
Figure 2.3 Leaves and stems of Lasia spinosa (Bugor)
2.5 Flavonoids
Flavonoids are generally found in fruits, vegetables, tea and wine where belong to
the natural substances with variable phenolic structure (Middleton, 1998). Thus
flavanoids are remarkably reported as highly efficient antioxidants. Flavonoids are a
group of natural benzo-y-pyran derivaties and are ubiquitous in photosynthesizing
cells (Havsteen, 1983). More than 4000 varieties of flavonoids have been identified,
many of which are responsible for their attractive colors of flowers, fruits and leaves.
Flavonoids exist as aglycones, glycosides and methylated derivatives. The flavonoid
aglycone consists of a benzene ring that condensed with a six membered ring, which
in the 2-position carries a phenyl ring as a substituent (Figure 2.2) (Narayaan et a/.,
2001).
Flavonoids can be found many different chemical groups in substances which
it depends on the basis of molecular structure and degree of oxidation of the central
pyran ring. These groups include f1avonols, dihydroflavonols, flavones, isoflavones,
flavanones, anthocyanins, and anthocyanidins. Six-member ring that condensed with
the benzene ring can be formed either a-pyrone (flavonols and flavonones) or its
dihydroderivative (flavanols and flavanones) (Havsteen, 1983). Flavonoid class can
divide into flavonoids (2-position) and isoflavonoids (3- position) due to the position
of the benzenoid substituent. Flavonols differ from flavonones by hydroxyl group the
3-position and C2-C3 double bonds (Havsteen, 1983). Flavonoids are often
hydroxylated in position 3, 5, 7, 2', 3', 4', 5'. Methylethers and acetylesters of the
alcohol group are known to occur in nature. When glycosides are formed, the
9
glycosidic linkage is normally located in positions 3 or 7 and the carbohydrate can be
L-rhamnose, D-glucose, glucor-hamnose, galactose or arabinose (Middleton, 1984).
The pyran ring can be opened (chalcones) and recyclized into a furan ring (aurones)
(Brunetone, 1999). The most widespread polyphenolic, bioflavonoids (condensed
tannins), named proanthocyanidins, are polyepicathechins, polyepigallocathechins
and polyepiafzeiecnin (Bruneton, 1999). Within each of these groups falls hundreds,
and sometimes thousands of different f1avonoids. For example, in f1avonols group,
there have compounds like quercetin. kaempherol, myricetin, isorhamnetin and
querctagetin.
( Isoflavone (eg: daidzein, genistein)
(------Fla-vono-----.,id 1 ~ ~
[ Anthocyanin (eg: cyanidin, malvidin) ) [ Flavonol (eg: quercetin, kaempferol) ) [ Pro anthocyanin (eg: polymeric flavanols) 1 [ Flavanol (eg: siliinin, taxifolin) )
( Flavone (eg: tangeretin, apegenin) )
( Flavanone (eg: Hesperetin, Naringenin) )
Figure 2.4 Major classes of flavonoids.
10
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