Colour, smell and taste – the
beautiful world of plants and
chemistry
Dubrovnik, Croatia, 2012
Alison Foster, University of Oxford Botanic Garden
Plants and Chemistry
• Colour
• Smell
• Taste
Colour
• Main pigment types
– Porphyrins (nitrogen containing)
– Flavonoids (incl. anthocyanins)
– Carotenoids (terpenes)
– Betalains (nitrogen containing)
Colour
cyanidin-3glucoside
β-carotene
betanidin
Colour
Anthocyanins:
• Found in many plant families –
except those in Caryophyllales
• Found in all plant tissues
• 109 tonnes produced per year in
nature
• 2% of all carbon fixed via
photosynthesis is converted to
anthocyanins
Ferns (and Fern allies)
Gymnosperms
Angiosperms
Colour
Functions of anthocyanins:
•Pollinator attractant
•Sunscreen – succulents and autumn
leaf colouration
•Anti-feedants – bitter tasting
Colour
Anthocyanins as pollinator
attractant?
Bromeliaceae
Colour
Anthocyanins as sunscreen or
antifeedant or both?
Colour
Anthocyanins as antifeedant ?
Colour
Metasequoia glyptostroboides
dawn redwood
Rhodoxanthin:
Colour
Daucus carrota
carrot
beta-carotene
Colour
Solanum lycopersicon
tomato
lycopene:
Colour
Betalains:
•Amino-acid derived
•Nitrogen containing – metabolically
more expensive
•Yellow to red pigments (betaxanthins
and betacyanins)
•Only present in plants in order
Caryophyllales
Caryophyllales
Colour
Betalains:
• Caryophyllales:
•Beetroot (Amaranthaceae)
•Bougainvillea (Nyctaginaceae)
•Pokeweed (Phytolaccaceae)
•Carnations (Caryophyllaceae)
Smell
• Nicotiana attenuata from the
SW United States
– Releases benzyl acetone
when flower opens at night
– Attracts hawkmoth
pollinators
• Pollinators are also herbivores
(larval stage)
• Upon herbivore attack, flowers
no longer produce benzyl
acetone nor open at night
• Day opening flowers are then
hummingbird pollinated
Smell
• Lavandula
angustifolia
camphor
cineole
linalyl acetate
linalool
Smell
• Amorphophallus titanum
• Spadix emits smell of
rotting flesh
• Pollinators are attracted
– Carrion-eating beetles
– Flesh flies
• Smell made up of amines
and disulfides
putrescine
cadaverine
Smell
• Cercidiphyllum japonicum
– Senescing and abscising leaves
– Green leaves contain maltol glucosides
– Yellow brown/fallen leaves contain maltol
Taste
• Chilli peppers
(Capsicum
species) contain
capsaicin
• “Hotness”
measured on the
Scoville scale
• Test method
devised in 1912 by
Wilbur Scoville
• Now measured by
HPLC
Taste
• Sweet pepper
0
• Jalapeño pepper
5,000
• Scotch Bonnet
100,000
• Naga jolokia
1,040,000
Chilli pepper
Scoville Heat Units
Taste
•Euphorbia resiniferatoxin
•Resiniferatoxin
16 Billion SHU
Taste
• Ginger – Zingiber
officinalis,
Zingiberaceae
• Active constituent
of fresh ginger is
gingerol
• Cooking ginger
transforms it into
zingerone
Taste
• Ginger – Zingiber
officinalis,
Zingiberaceae
• Dried ginger
contains more of
another molecule,
shogaol
• The Japanese
name for ginger is
shōga
Taste
• Ginger – Zingiber
officinalis,
Zingiberaceae
• Dried ginger
contains more of
another molecule,
shogaol
• The Japanese
name for ginger is
shōga
Taste
• Vanilla– Vanilla
planifolia,
Orchidaceae
Taste
Taste
O
MeN
O
N
Me
O
H
N
HN
N
O
theophylline
N
Me
Me
N
N
theobromine
O
MeN
O
N
Me
Me
N
N
caffeine
Taste
O
MeN
O
N
Me
H
N
N
theophylline
O
HN
O
N
Me
O
Me
N
MeN
N
O
theobromine
N
Me
Me
N
N
caffeine
Conclusions