Experiment 1 - pigments Flashcards
what is a colorant
a generic term that describes any substance that colors something
pigments
natural constituents of cells and tissues of plants or animals that imparts color
classification of pigments
solubility and chemical structure
what are the classifications of pigments acc to structure
isoprenoid derivatives
tetrapyrrole derivatives
benzopyran derivatives
betalamic acid derivatives
chlorophyll
green pigment in plants tissues that allow plants to absorb light energy through photosynthesis
main components of chlorophyll
phytol tail
porphyrin ring
what is the ion present in the porphyrin ring?
magnesium
what is the R group in chlorophyll a?
Ch3 or methyl group
what is the R group in chlorophyll b?
CHO or carbohydrates
what is the hydrophobic part of a chlorophyll molecule
phytol tail
what is a porphyrin ring
a fully unsaturated macrocyclic structure containing four pyrrole rings linked through methine bridges
what is the nucleus of all chlorophylls?
phorbin
what are the derivatives formed and thejr color when chlorophyll is exposed to heat and acid?
Mg-free: olive brown, Mg-containing: green
exposure of chlorophyll to severe heat or acid generates what pigments
pheophytin
pyropheophytin
the formation of chlorophyllides results from what activity
chlorophyllase activity
true or false: chlorophyllides are less heat stable and more likely to degrade to Mg-free derivatives liek pheophorbide
true
at what pH is chlorophyll more heat stable?
in basic pH or around pH 9
at what pH is chlorophyll unstable?
around pH 3
pyrochlorophylls are formed when
chlorophylls lose the C-10 carbomethoxy group prior to displacement of the magnesium from the porphyrin ring
formed from the enzymatic cleavage of phytol from pheophytin
pheophorbides
true or false:
chlorophylls are susceptible to photodegradation
true
tdue or false: complete color loss/bleaching happens when chlorophyll is exposed to light and oxygen
true
reaction which leads to destruction of porphyrins (total loss of color)
hydroxy radicals/singlet oxygen reacts with tetrapyrroles forming peroxide free radicals leading to distruction of porphyrins
what are carotenoids
are fat-soluble compounds having yellow, orange, or red shades
classes of carotenoids
hydrocarbon carotenes
oxygenated xanthophylls
carotenoids are formed with what polymerization?
head-to-tail polymerization of isoprene units
carotenoids require at leasr how mang conjugated double bonds before the appearance of yello color?
at least 9
as the number of conjugate bonds in caretoneoids increases, what happens to the color?
color gets darker or wavelength shifts to a redder color
trans bond in carotenoids:
cis bonds in carotenoids:
what color
trans: deeper color
cis: color fading
are all carotenoids precursors of vitamin a?
no
vit a precursor have the presence of unsubstituted beta ionine ring
carotenoids are easily oxidized because?
of their large number of conjugated double bonds
oxidatibe destruction of beta carotene is intensified in the presence of
sulfite and metal ions
what enzyme hastens oxidative degradation of carotenoid pigments
lipoxygenase
are carotenoids moderately heat stable
yes
what process destroys enzymes that bleach carotenoids
blanching
Carotenoids are more stable in what pH?
basic
anthocyanin colors
blue, pink, or violet
term used to describe anthocyanin because of its pH dependency
amphoteric molecule
building block of anthocyanin
flavylium cation
true or false: more OH groups in anthocyanin decreases its stability
true
true or false: higher -Ome substituents in anthocyanin increases its stability
true
this can either accelerate or retard degradation in anthocyanin
copigmentation
color of anthocyanin in acidic environment pH 2
red
at which pH condition is anthocyanin more stable
acidic pH
heating anthocyanjn shifts the equilibria to toward what form?
chalcone form/yellow/colorless
formation of unstable anthocyanidins happen because of
anthocyanin hydrolysis which is favored by heat
are anthocyanins susceptible to oxidation?
yes because of their unsaturated nature
stability of anthocyanin is good at what range of water activity range
0.63 to 0.79
