Plant Secondary Metabolism
(aka, natural products chemistry)
Definition of secondary (2o) products/metabolism:
-not essential & not found in all plants
-primary functions of 2o products-
-defense against herbivores & pathogens
-attraction of pollinator & seed/fruit dispersers
(through scent, sight, and taste)
-important to humans in medicine, industry, food & agriculture
-most crop plants have been selected to make low levels of 2o
-three major categories of 2o cmpds
1) Isoprenoids (or terpenes)
3) Nitrogen-containing compounds
(1) terpenes (aka, isoprenoids):
-built from 2C (acetyl CoA) & 5C (isoprene) compounds
-isoprene subunits used to build larger molecules
-some terpenes are primary metabolites (e.g., pigments, hormones)
-2o cmpds often localized to trichomes or resin ducts
-monoterpenes (10C)- pyrethroids & oils (e.g., pine oil, lemon
-sesquiterpenes (15C)- gossypol
-diterpenes (20C)- resins (e.g., in pines and euphorbs)
-triterpenes (30C)- phytoecdysones (insect molting hormones),
limonoids (in citrus rind), cardenolides (glycosidic
triterpenes; e.g., digitalis & those in milkweeds)
-polyterpenes (>40C)- natural rubber & latex
-produced via shikimic acid pathway in plants, fungi, & bacteria, but not in animals
(which is why animals can't make tryptophan, phenylalanine, & tyrosine)
-lignin (complex polymer built mostly from 3 kinds of phenolic-alchohol
-flavonols (eg, UV-absorbing cmpds found in flowers, UV-screening
cmpds found in epidermal cells; these cmpds don't absorb 400-to-
-isoflavonoids (e.g., phytoalexins...anti-microbial cmpds)
-tannins (several different categories...big and small; general toxins)
-others (e.g., salicylic acid & coumarins)
-others (e.g., salicyclic acid, coumarins)
(3) N-containing cmpds:
-many different kinds
-alkaloids (N-containing ring, often basic)
-non-protein amino acids & oligopeptides
(e.g., defensins, thionins)
-proteins; e.g., proteinase inhibitors, lectins ((CH2O)n-binding
proteins, a.k.a. agglutinins), cytochrome P450
Coffee, tea, cocoa
History of coffee
• Native to E. Africa; used first in Ethiopia.
• Arabs were first to brew coffee (ca. 1300 AD)
and use spread from Arabia to Egypt and then to
Europe (ca. 1600).
– Arabic origin: mocha, kava, coffee
• Coffee was particularly popular in England.
• Arabs monopolized trade by boiling seeds to kill
them, but Dutch and French were able to obtain
seeds and grow the trees themselves.
• Brazil and Columbia currently lead the world in
• Second to oil, coffee is the most widely traded
Rust epidemic in coffee
• In 1868, Ceylon was the leading coffee producer (export
of 100 million lbs); by 1890, no coffee could be exported
• leaf disease caused by a fungus, Hemileia vastatrix
• Java 1876; East Africa 1894; Brazil 1970
• made worse by limited diversity; highly variable
• controlled by fungicides --> uneconomical in many
regions, except where optimal climate
• genetic resistance: C. canephora (Robusta); lower
quality used in cheap blends and instant coffee
• replace by other crops: e.g., tea
Views of coffee change through
• hailed as a medicinal cure-all
• others condemned it as the devil's brew
– usually for political or religious reasons
• mid 1900‟s: research discovered caffeine
& its relation to human health
– in moderation, coffee consumption is usually
not a health risk
– can indeed confer some health benefits
• Small evergreen tree or shrub
with shiny, simple leaves.
• Traditionally a „shade‟ tree.
• Fruit = berry (“cherry”).
• Each fruit contains 2 seeds =
beans, mostly endosperm.
• Coffee is best grown in tropical
and subtropical high-land cool
climates, with fertile soils and
60-100" rainfall, but requires
dry season for flower
development. Frost sensitive.
• Trees begin producing at 3
years and produce for 40
(of ca. 60 in genus)
• Coffea arabica - 90% of world's production
– Only kind grown in Latin America, ca. 1% caffeine (on
DW basis), milder than other species
• C. canephora -9% - Robusta coffee
– Grown in Africa & Asia
• C. liberica - 1% - Liberian coffee
– Grown in Africa
• The last two are hardier plants than C. arabica,
and C. canephora produces more fruits, but C.
arabica still predominates.
• C. arabica is a self-compatible polyploid, other
are self-incompatibile diploids with a more bitter
• Seeds are separated
from fruit, fermented and
• Light roast-to-Dark
Roasts (stronger flavor
due to roasting at higher
temperature; beans are
high temperature brings
oils to surface).
Most coffees sold in U.S.
are light- and medium-
Famous coffee types
• Light roast
– Pronounced nut-like flavor, high coffee acidity
• Medium roast
– Pronounced caramel like flavor, full coffee flavor, with some loss
• Full roast
– Full coffee flavor, good balance of acidity and sugar
– Dark roast flavor
• French Roast
– Bitter, smoky taste and pungent aroma
• Espresso Dark
– Burnt flavor that is strong and sweet
• Kona Coffee
– the only coffee found in the Hawaiian Islands
– Full coffee flavor, balance of acidity and sugar
– Pressurized hot water quickly forced through finely,
ground & densely packed, dark roasted arabica
– Expresso with steamed milk
– Latte with less steamed milk, but with chocolate syrup
– Expresso with less steamed milk than a latte, but with
large cap of foamed milk
• Instant coffee
– ground beans brewed under pressure, dehydrate
brew by freezing or spraying
– before roasting, when beans are still 'green',
– removing about 97-98%
– Solvent - methylene chloride or ethyl acetate is used
to remove caffeine, solvent is removed (hopefully)
during roasting. Caffeine is removed from solvent with
water and crystallized.
– Water - green beans are percolated with water that
contains all water-soluble compounds found in coffee
with exception of caffeine, which diffuses out; more
expensive than solvent extraction.
• Chemical name, 1,3,7-trimethylxanthine; an
• dimethylxanthine derivatives, theophylline and
theobromine, are also found in a variety of
• occurs naturally in the leaves, seeds, or fruit of
more than 60 plant species; coffee beans are ca.
1-2% caffeine by weight
• discourages grazing animals
• 75% of purified caffeine (2 million pounds) is
used in soft drinks, rest in headache and cold
• readily absorbed into the blood and body
• half-life of approximately four hours (1-10)
• rapidly metabolized and excreted
• smokers break down caffeine more quickly
• contraceptive pill & pregnancy slow the
rate of caffeine metabolism
• Effects range from mild alertness to
heightened anxiety and body tension.
• Medically, caffeine is useful as a cardiac
stimulant, and also as a mild diuretic.
• Recreationally, it is used to provide a "boost of
energy" or a feeling of heightened alertness.
• Temporary increase in the metabolic rate and
the rate of fat breakdown (lipolysis).
• minor diuretic under normal consumption
• beverages containing caffeine should not
be used to promote fluid replacement
during prolonged exercise
• Caffeine's effects are more mild than
amphetamines, cocaine, and heroin, but it
is manipulating many of the same
• Some regular users who stop consuming
caffeine may experience withdrawal
symptoms, including: drowsiness,
headaches, irritability, nausea and
vomiting, and depression.
Amounts of caffeine per item (mg) Typical
Coffee (150ml cup)
Brewed, drip method 115
Brewed, percolator 80
Espresso (30ml cup) 40
Teas (150ml cup)
Brewed, major brands 40
Iced (240ml glass) 45
Some soft drinks e.g. cola (180ml) 18
Chocolate milk beverage (240ml) 5
Milk Chocolate (30g) 6
Dark chocolate, semi-sweet (30g) 20
Cooking chocolate (30g) 26
Caffeine & related stimulants
Compound Source effect
Caffeine Coffee, Stimulant of central
tea, cola nervous system, cardiac
nuts muscle, and respiratory
Theophylline Tea Cardiac stimulant,
smooth muscle relaxant,
Theobromine cocoa Diuretic, smooth muscle
bean, cola relaxant, cardiac
nuts & tea stimulant, vasodilator
printed labels from a
Japanese Tea Box
(antique mall in Grand Island, Nebraska)
The Cup of Tea. Mary Cassatt,
1880, oil on canvas.
The Tea Cup. Jackson Pollock, 1946, oil on
canvas. American. Abstract Expressionist
• World‟s most popular beverage, next to water
– Every day, 800 million cups or glasses of tea are consumed
• Camellia sinensis - native to China/India/Tibet/Burma
area; cultivation and use of tea originated in Asia (China
or India, probably 4-5000 years ago).
• Portuguese & Dutch introduced tea to Europe inca.
1600; tea was important trade item in Europe by 1700.
• Colonial Americans were fond of tea and were angered
by tea tax imposed by British, which resulted in the
Boston Tea Party.
• Cultivation: has not been grown very
successfully in New World, except Argentina:
most tea is grown in Asia.
• Plants are small evergreen trees, which prefer
abundant rainfall and warm-to-cool temperatures
(but no frost).
• Trees are pruned to force bush-like growth.
• Picking is by hand, youngest leaves and terminal
bud only are picked; plants can be picked once
a week. Tips are orange pekoe; larger leaves
are souchong and pekoe.
• Tea bags were initially used as samples.
Fermentation & additives affects
color, flavor and aroma
• Non-fermented: e.g., Green Tea,
Lungching (Dragonwell), Pilochun,
• Semi-fermented: Oolong
• Light: Chinchua, White tea
• + Flowers: Jasmine tea
• + Bergamot oil: Earl Gray
• Fully-fermented: Black or „red‟ tea
– 95% of tea consumed in US
Essential oils and tannins
• Essential oil: theol
– Discourage herbivores
– Used as stains, dyes, inks, tanning agents
Benefits of drinking tea?
• Improving immune system and preventing
• Slowing down aging process
• Preventing loss of bone calcium
• Alleviating blood lipoid, cholesterol, blood
pressure, and arteriosclerosis
• Helping sterilization and reinforcing teeth
• Reducing urine hyperacidity and gout
• Eliminate body fat
• Preventing sunburn and resisting UV
Charleston, SC Tea Plantation
Some other plants used for “tea”
• Sassafras albidum - aromatic bark used to
make medicinal tea; may be carcinogenic.
• Herb teas - made from a huge variety of
fragrant plants (chamomile, chicory, etc.)
• Ginseng - Panax quinquefolium - use roots
roots to make tea, straight tea does not
taste very good so is usually used with
honey or herb tea. Thought to have many
positive affects, especially by Asians.
• Ephedra species – “Mormon” tea
The “Food of the Gods”?
• Theobroma cacao - chocolate and cacao
• New World origin in eastern Andes, "Food of
the Gods" to Mayans, Mayan drink included
cacao, red pepper, vanilla and other spices.
• Sweet hot chocolate became very popular in
Europe by 1650 (introduced ca. 1500).
Spanish, then Dutch, then Germans, became
involved in establishment of cacao plantations.
• W. Africa and Brazil are now world's largest
• Cacoa plants are small trees grown in shade, in warm
wet tropical climates.
• The pods contain 20-50 seeds, are broken open and
cleaned by hand.
• Seeds are fermented, which changes their white color to
purple. Seeds are very bitter at this point. Seeds are
then roasted, cracked to remove seed coats to yield nibs
(cotyledons), nibs are ground, making enough heat to
melt fat and produce chocolate liquor which can be
molded into baking chocolate.
• Cocoa is made by pressing out fat (cocoa
butter), dry powder is treated with alkali to
produce Dutch cocoa.
Milk chocolate is produced by continuous
stirring of a mixture of chocolate liquor +
cocoa butter + sugar + condensed milk.
Processing of Chocolate
• Growth • Crack, fan, winnow
• Harvest • Grind
• Ferment • Mix
• Dry • Refine
• Ship • Conch
• Roast • Temper
What chemicals does
• Caffeine and theobromine are both
considered alkaloids (or methylxanthines).
• Phenylethylamine is an anti-depressive
and anti-stress agent.
• Serotonin is a hormone which is also
produced naturally by the brain.
• Various flavonoids
different types of chocolate
• Unsweetened or Baking :
– chocolate liquor that has been cooled and hardened.
• Dark or Bittersweet Chocolate:
– must contain a minimum of 34 percent cacao solids.
• Semi-sweet Chocolate
– chocolate with extra cocoa butter and sugar added.
• German Chocolate:
– sweeter and richer than semi-sweet chocolate, and is
a special blend of chocolate, sugar and cocoa butter.
– creamy sweet chocolate that has extra cocoa butter,
sugar, milk, and vanilla.
– chocolate liquor with the cocoa butter having been
removed, creating a fine bitter tasting powder.
• Dutch Process Cocoa
– special process used to neutralize the natural acids in
• White chocolate:
– cocoa butter without the cocoa, and is therefore not
– cheap imitations that substitute vegetable oil for
• Decorator’s or Confectioner’s Chocolate
– a chocolate flavored candy.
Chocolate factory tours
• Kola tree- Cola nitida - relative of cacao; native
to W. Africa.
• original Coca Cola had seeds cleaned and
allowed to ferment, then dried and pulverized to
• seeds contain caffeine and kolanin (heart
stimulant) and appetite suppressant.
• Since 1903, the cocaine has been removed
before the coca extracts are added.
Other beverages, cont.
• Root beer - carbonated, sweetened
beverage flavored by extracts (caramel,
• Teas (e.g., mate) made from various
species with caffeine (e.g., Ilex species)
are common in S. & C. America.