L20 - Pigments Flashcards
Pigments: Role
- Pigments act as visible signals to attract insects, birds and animals for pollination and seed dispersal
- They protect plants from damage caused by UV and visible light
- Important quality features… for commodities
- Can be a Harvest index
- Connection of visible pigments to health-related features
Types of pigments
- Chlorophyll
- Carotenoids
- Flavonoids
- Betalains
Chlorophylls
- Primary photosynthetic pigments in plants
- Capture light to drive photosynthesis
- Fresh fruits and green vegetables are rich in Chl
- Food additive (green colorant) used in a variety of foods and beverages
- Generally, Chl comprises 0.6% -1.6% on a dry weight basis
Ripening and Chlorophyll breakdown
• During ripening of tomato, change in colour through degradation of
chlorophyll and accumulation of carotenoids
• Mutants in this breakdown: green flesh (gf)
• Chlorophyl and carotenoids (lycopene): brownish
Chlorophylls
• Cyclic tetrapyrrole ring
• Chl a blue-green Chl b yellow-green
• Both highly susceptible to degradation during processing: food color changes
•
Breakdown is enzymatic process, 2 main pathways:
- Removal of phytate, Mg, and oxidative cleavage
- Oxidative degradation of Chl through hydroperoxide and radical formation by oxidation of lipids
Carotenoids
• Yellow, orange and red pigments – Lipid soluble • Synthesized in plants, algae and some photosynthetic bacteria • 1000 - 750 found in nature
Carotenoids role
Plants:
- Photosynthetic system
- Prevent photo oxidative damage
- Plant grow and development (ABA & strigolactones)
- Role in defense mechanisms
Carotenoids biosynthesis
- Branches from the plastidialterpenoid pathway
- Biosynthesis in the plastid
- Biosynthesis divided in 2 parts:
1. early lycopene yielding
2. α, and β-carotene and xanthophylls
Carotenoids regulation
Seems to be connected more to development than to specific regulators for carotenoid biosynthesis
• RIN, NAC1, MYB68, RCP1 (MYB)
Carotenoids examples
• Carotenes: Provitamin A function (α-and β-carotene)
Eye and Brain development
• Lycopene: Antioxidant activity
• Lutein, Zeaxanthin: Blue light filtering
• Tocopherol: Vitamin E
Carotenoids examples
• Carotenes: Provitamin A function (α-and β-carotene)
Eye and Brain development
• Lycopene: Antioxidant activity
• Lutein, Zeaxanthin: Blue light filtering
• Tocopherol: Vitamin E
Flavonoids
- Wide colour range: pale yellow to blue
- Water soluble pigments,
- Stored in the vacuole
- Widely distributed in seed plants
Flavonoids
Anthocyanins, Proanthocyanins, Flavonols, Flavones, Chalcones, Aurones
Over 6000 flav. compounds
Flavonoids role
Plants:
- Attraction of pollinators and seeds dispersers
- Signalling between plants and soil borne symbiont bacteria
- Defence against microorganisms
Humans:
- Antioxidant, quality and appreciation
- pH indicator: Litmus test
Widely used as natural food colorants
Flavonoid structure
Basic structure C6-C3-C6
Anthocyanin biosynthesis:
Pigments
- Cyanidin
- Pelargonidin
- Delphinidin
Betalains
- Yellow-to-red colors
- Nitrogen-containing
- Water soluble
- Derived from Tyr (Tyrosine)
Betalains role
- Plants:
• Attraction of animal pollinators and dispersers
• Photoprotection, tolerance to droughts and salinity stress
• High antioxidant and free radical scavenging activities - Human:
• Commercial food colorants and additives
• Health connection: preventative to several forms of cancer and intermediates are important pharmaceuticals for treatment of Parkinson’s disease (L-DOPA)
• Substate substrates for other pharmaceutical agents (e.g.dopamine and isoquinolinealkaloids such as morphine)
Classes of betalains
- Betaxanthins:
Derived from betalamic acid conjuction with amines/amino acids - Betacyanins:
From condensation of
Betalamic acid with cyclo-DOPA
Caryophyllales
Only found in limited number of plants
Does not coincide with anthocyanins in nature
Substitutes ubiquitous anthocyanin pigmentation in those species
Pattern of mutual exclusion between the two pigments types
GMOs can have both
