Natural Pigments Flashcards
Food quality attributes of natural pigments
- Flavor (taste/smell)
- Texture
- Nutritive value
- Microbial load
- Color / appearance
Natural Food Pigments (8)
- Chlorophyll
- Myoglobin & Hemoglobin
- Carotenoids
- Anthocyanins
- Flavonoids
- Tannins
- Quinones & Xanthones
- Melanins & Betalains
Chlorophyll
• Plant pigment (main sources are green vegetables, root vegetables, fruits) o Mg in the center o Fat soluble o Can be destroyed by heat o Sensitive to acids and alkali o Green color o Plant sources, algae
Chlorophyll structure
tetrapyrrole
Major chlorophylls are ____
‘a’ & ‘b’ (3:1)
The proportion of a and b chlorophylls is
3:1
What colour is alpha chlorophyll
green-bluish colour
What colour is beta chlorophyll
dull green colour
Is chlorophyll water soluble or fat soluble?
fat soluble
Heme pigments are ____ and ____
hemoglobin and myoglobin
Heme pigments general features
- Responsible for red color of muscle foods;
- Complex molecule with a protein part (globin), and an essential non-protein part (heme);
- Both Mb and Hb are tetrapyrrole compounds.
Mb and Hb structure
tetrapyrrole compounds.
Is heme fat or water soluble
water soluble
What are the major food sources that contain heme
meats (beef, pork, chicken, fish)
o The pigment in the muscle is due to myoglobin, and the intensity of the color depends on the myoglobin content
Myoglobin structure
• Single polypeptide chain
• 4 N’s in the 4 pyrole molecules , covalently linked
to central Fe atom
• Fe also covalently linked to N in a histidine residue in globin (protein);
• Fe can bind electron pair donors (e.g., O2, CO, CO2, CN, etc).
Oxymyoglobin
- Bright red color of fresh meats
- Fe present as ferrous (Fe2+) form
- Mb + O2 <==> MbO2
- Mb (purple color; Fe2+)
- MbO2 (bright red; Fe2+)
What is the compound that gives the fresh color to meat?
oxymyoglobin
Metmyoglobin (Met-Mb)
- Brownish color (Fe3+)
- MbO2 <==> Mb ==> Met-Mb
- MbO2 (bright red)
- Mb (purple)
- Met-Mb (brown)
What is the compound that gives the brown color to meat?
metmyoglobin
Chlorophyll a vs. Chlorophyll b
One of the pyrroles have a methyl group = chlorophyll A
Formyl group –CHO = Chlorophyll B
What makes chlorophyll fat soluble molecule?
Fat soluble bc of the presence of the C20 carbon molecule that is attached to the chlorophyll molecule. 20C unit known as PHYTOL (300g/mol)
Phytol side chain is a hydrocarbon and highly hydrophobic, and this accounts to its insolubility in H2O, but highly solubility in lipids. – wax
What happens when the phytol group is removed form chlorophyll?
If we remove the phytol group, the molecule left behind is water soluble
How can we obtain chlorophyllide from chlorophyll and how does the color change?
loss of phytol by chlorophyllase
very bright color
How can we obtain pheophytin from chlorophyll and how does the color change?
expose it to acid and heat
loss of Mg atom
blue color
How can we obtain pheophorbide from chlorophyllide how does the color change?
expose it to acid and heat
loss of Mg atom
red color
How can we obtain pheophorbide from pheophytin how does the color change?
loss of phytol
chlorophyllase
What happens when chlorophyll is exposed to acid?
- removal of the Mg atom from the centre
- if the centre is removed then the molecule is not green anymore (brownish)
- molecule is still water soluble
- PHEOPHYTIN
Alkali/Acid conditions (chlorophyll) cause the removal of the phytol group.
Alkali
True/False
When the phytol group is cleaved, the molecule is still fat soluble.
False
When the phytol group is cleaved, it becomes water soluble.
Pheophytin can go under hydrolysis to remove the phytol group that forms a new molecule that is called __________. This molecule is also water soluble, but the magnesium is lost so this molecule has a brownish color as well.
PHEOPHORBIDE
Moist Cooking vs Dry Heat on chlorophyll
Processes such as moist cooking (blanching) can cause destruction of green color. (chlorophyll). Dry heat (microwave) on the other hand, inactivates enzymes but does not remove Mg so green color is retained
What other effects can cause color loss in chlorophyll
o Fermentation produces acids and can lead to color destruction
o Exposure to light and air can also cause oxidation and lead to color loss.
True/False
Chlorophylls are antioxidants
true
It is highly unsaturated, therefore it can function as antioxidant
Other uses of chlorophyll containing foods
food additives
mouthwash
toothpaste
The magnesium of chlorophyll helps boost the blood volume.
How does cooking affect chlorophyll?
Cooking –> pheophytins
How does dehydration affect chlorophyll?
Dehydration –> bleaching by photodegradation (lipoxidases)
How does exposure to light and 02 affect chlorophyll?
Exposure to O2&light –> bleaching
How does blanching affect chlorophyll?
Blanching –> pheophytins & phophobides
How does irradiation affect chlorophyll?
Irradiation –> degradation by peroxidation
Heme pigments are complex molecules with a protein part (______), and an essential non-protein part (______);
globin
heme
Structure of heme pigment
Both Mb and Hb are tetrapyrrole compounds.
Is Hb bigger than Mb?
o Mb < Hb
♣ 17 < 64 KDA
♣ muscle vs blood vessels
What is the central atom of heme pigments?
Both Mb and Hb are tetrapyrrole compounds. 4 pyrrole rings attached to a central atom Fe
What is the difference between a Mg central atom and a Fe central atom?
Fe, unlike Mg, can accept 6 lone pairs of electrons: 4 from N, 1 from histidine, and 1 donor (O2, CO2, CO, CN, OH)
Fe central atom can accept 6 lone pairs. What types of molecules does it accept?
can accept 6 lone pairs of electrons: 4 from N, 1 from histidine, and 1 donor (O2, CO2, CO, CN, OH)
What color is Mb?
(purple color; Fe2+)
What color is MbO2?
(bright red; Fe2+)
What color is Met-Mb
Met-Mb (brown) (Fe3+)
Phytol:
size
solubility
structure
296 kda, water insoluble, attached directly to tetrapyrrole
Globin:
size
solubility
structure
16.4 kda, water soluble, Fe
4Mb = ? Hb
1
1Hb = ? Mb
4
red meat/poultry/finish color intensity is due to the amount of Mb/Hb present
Mb
Storage of heme pigments
Storage => gradual oxidation, forming dark/brown color
Cooking of heme pigments
- denatures protein;
- oxidation of Fe2+ to Fe3+;
- formation of dark color (as in barbecued meats - pigment formed known as hemichrome)
in barbecued meats - pigment formed known as _______
hemichrome
Curing of meats with nitrites => red colored _______;
nitrosomyoglobin
cooking of cured meats denatures the protein, also Fe2+ is oxidized to Fe3+ - & brown product – ______;
nitrosohemichrome
nitrosomyoglobin
Curing of meats with nitrites => red colored
nitrosohemichrome
cooking of cured meats denatures the protein, also Fe2+ is oxidized to Fe3+ - & brown product
Give an example of a reducing agent that can prevent sulfmyoglobin formation
with –SH containing reducing agent
what do you prevent oxidation by adding reducing agents to meat?
o By adding reducing agents, it is possible to reverse the oxidation.
♣ Fe2+ Fe3+ +e- (by using cysteine cystine / glutamine (GSH) GSSG)
♣ This reverses the brownish color of Met-Mb. However, a yellowish/greenish tinge forms along edges of meat which would indicate that reducing agents have been applied to “old meat” to make it look fresh
♣ The yellowish/greenish tinge is dues to a product known as sulfmyoglobin
what color is sulfmyoglobin
The yellowish/greenish tinge is dues to a product
what does yellowish/greenish tinge along edges of meat indicate?
indicate that reducing agents have been applied to “old meat” to make it look fresh
Fe 3+ on cooked meats______
not readily absorbed through the GIT although there is the advantage of extensive denaturation to facilitate the hydrolysis as well as the destruction of harmful pathogens that may be present in the meat.
Fe2+ on rare/medium cooked meats _______
Fe2+ is rare/medium cooked meats is much more readily absorbed through the intestinal membrane into the cytosol to make more RBCs.
Use of nitrates in foods can form nitroso-amines that are considered to be ______
carcinogenic
When meats are cured with nitroso-amines, what else should be added to decrease the carcinogenic effect?
ascorbic acid/vitamin C is added to the curing brine to reduce nitrosoamines formed back to nitrates to remove the potential harm.
EXAM QUESTION
Compare chlorophyll and myoglobin
o Different sources (plant vs animal)
o Both tetrapyrrole compounds but central atoms are different (Mg vs Fe)
o Different colors (green vs red)
o Relative solubility (fat soluble vs water soluble)
o side groups attached to molecule
o both are heat sensitive
Carotenoid pigments are present in
- Present in plants, animals & microorganism
* Responsible for yellow, orange & red-orange colors in plants & animals
Animal sources of carotenoids
♣ egg yolk,
♣ milk/dairy products,
♣ shellfish
♣ salmons
Plant sources of carotenoids
♣ Fruit
♣ Vegetables
♣ Palm oil
Microbial sources of carotenoids
♣ Yeast
♣ Fungi
Structure of carotenoids
5C compounds – isoprene as repeating unit known as ISOPRENE
Isoprene is cyclic/acyclic
both
Isoprene can be composed of
May be hydrocarbon exclusively (hydrocarbon carotenoids or carotenes), or may contain oxygen (oxy-carotenoids)
Hydrocarbon Carotenoids, a.k.a., Carotenes
β-carotenes,
α-carotene
lycopene
Hydrocarbon carotenoids
carotenes
β-carotenes
gives 2 molecules of vitamin A on hydrolysis - thus described as pro-vitamin A
pro-vitamin A
β-carotenes
the difference between β-carotenes and α-carotene
o α-carotene - same molecular formula as β- carotene, but the α-form is not symmetrical.
o on hydrolysis, the α-carotene yields only one molecule of vitamin A in the body
True/False
B-carotene, a-carotene and lycopene are examples of hydrocarbon carotenoids bc they are comprised of “H” and “C” atoms exclusively
true
β-carotene and α-carotene vs. lycopene
- lycopene is symmetrical, but unlike α- or β- carotenes, the ring structures in lycopene are open
- lycopene has no vitamin A activity
lycopene is cyclic/acyclic
acyclic
hydrolysis of β-carotene gives
2 molecules of vitamin A
α-carotene is symmetrical/nonsymmetrical
nonsymmetrical
Hydrolysis of α-carotene yields to
only one molecule of vitamin A
Lycopene is found in
tomatoes and apricots
Oxy-carotenoids
common ones are: lutein, canthaxanthin, astaxanthin, cryptoxanthin & zeaxanthin
Lutein
Oxy-carotenoid
• Sources:- green leaves and egg yolk
• molecule is similar to β-carotene - asymmetrical; but rings are hydroxylated; so has no vitamin A activity
Sources of lutein
green leaves and egg yolk
Does lutein have vitamin A
NO
Canthaxanthin
Oxy-carotenoid
• present in microorganisms, plants & animals (e.g., mushroom, red pepper, brine shrimp & the flamingo)
• commercially produced by chemical synthesis
• used as feed supplement for cultured
salmonids & imitation seafood products
• has no vitamin A activity
Canthaxanthin sources
• present in microorganisms, plants & animals (e.g., mushroom, red pepper, brine shrimp & the flamingo)
Does Canthaxanthin have vitamin A activity
no
Astaxanthin
Oxy-carotenoids
• major carotenoid pigment in salmonids & crustaceans; also redfish, ocean perch / red snapper
• produced on a commercial scale by chemical synthesis
• more stable than canthaxanthin for use as colorant for
fish flesh
• has no vitamin A activity
Astaxanthin sources
• major carotenoid pigment in salmonids & crustaceans; also redfish, ocean perch / red snapper
True/False
Canthaxanthin is more stable than Astaxanthin
false
Astaxanthin more stable than canthaxanthin for use as colorant for fish flesh
Does Astaxanthin have vitamin A activity
no
Cryptoxanthin
Oxy-carotenoids
• major carotenoid pigment in peaches, yellow corn and egg yolk.
• structure similar to β-carotene, except for presence of -OH group on one ring
• has vitamin A activity.
sources of Cryptoxanthin
• major carotenoid pigment in peaches, yellow corn and egg yolk.
Does Cryptoxanthin have vitamin A activity
yes
Zeaxanthin
• widely distributed in nature
• major carotenoid in yellow corn & egg
yolk
• similar structure to β-carotene, but has an
-OH group substituted to each ring
• has no Vitamin A activity
sources of Zeaxanthin
• major carotenoid in yellow corn & egg
yolk
Does Zeaxanthin have vitamin A activity
no
β-carotene vs Lutein
molecule is similar to β-carotene - asymmetrical; but rings are hydroxylated;
β-carotene vs Cryptoxanthin
structure similar to β-carotene, except for presence of -OH group on one ring
β-carotene vs Zeaxanthin
similar structure to β-carotene, but has an
-OH group substituted to each ring
Effect of Handling & Processing of Carotenoids
- O2 & light major cause of destruction
- not lost to cooking water
- destroyed by dehydration
2 key uses of carotenoids are as
- antioxidants
2. colorants
EXAM QUESTION
True/False
Anthocyanins are present in bacteria
False
they are present in plant sources
EXAM QUESTION (Essay type)
Why is it important to study a particular pigment carotenoid?
o Preserve the color of the food
o Health benefits and they are active compounds
o The color changes
EXAM QUESTION (Essay type)
Suggest 4 ways of controlling the chlorophyll
o Add salt while cooking
o Blanching
o Add sodium bicarbonate to neutralize the acids
—-
Anthocyanins
• Water-soluble plant pigments;
• Impart red, blue and violet colors to
various fruits and vegetables;
• The basic structure is the flavilium ion (a.k.a. anthocyanidin or aglycone).
structure of anthocyanins
flavilium ion (a.k.a. anthocyanidin or aglycone).
Two rings, and several hydroxyl groups attached – polyphenolic compound
They are glycosides or sugar esters of anthocyanidin
Anthocyanins are glycosides or sugar esters of ______
anthocyanidin
Monosides of anthocyanin
one sugar
always a monosaccharide
Biosides of anthocyanin
two sugars
1 disaccharide or 2 monosaccharides
Triosides of anthocyanin
three sugars
1 trisaccharide or 1 disaccharide and 1 monosaccharides
True/False
Anthocyanins can accommodate more than 3 sugars in their structures
false
In nature they can take max 3 sugars
Monosaccharides of anthocyanins can be
D-glucose, D-galactose, L- arabinose, D-xylose L-rhamnose
Disaccharides of anthocyanins can be
gentiobiose,
rutinose,
sophorose,
neohesperidose)*
Trisaccharides of anthocyanins can be
gentiotriose*,
xylosylrutinose,
glucosylrutinose
color and sources of Cynanidin
anthocyanin
(Cy:- orange-red color), in apples, cherries, oranges, plums, raspberries, & cabbage
color and sources of Delphinidin
(Dp:- blue-red color), in grapes & oranges
color and sources of Malvinidin
(Mv:- blue-red color); blue grapes
color and sources of Pelargonidin
(Pg:- orange color) in strawberries
color and sources of Peonidin
(Pn:- orange-red color), in cherries & plums
color and sources of Petunidin
(Pt:- blue-red color) in blueberries
Increasing hydroxy (-OH) content increases _____ color in anthocyanin
blue
Increasing methoxy (-OCH3) content increases ____ color in anthocyanin
red
the effect of ph on anthocyanin
acidic conditions change pigments to red color;
alkaline conditions change pigments to shades of blue or colorless
the effect of cooking on anthocyanin
lost to cooking water
some chemicals that decolorize anthocyanin
sulfites,
ascorbic acid,
H2O2
effect of metals on anthocyanin
Form purple or gray colors with metals
the effect of high temperatures on anthocyanin
High temperatures cause destruction of anthocyanin pigments (e.g., spray drying)
the effect of high sugar content and the presence of oxygen on anthocyanin
High sugar content and the presence of O2 enhance destruction of anthocyanins
Colorless forms of anthocyanins may undergo oxidation in presence of O2 to form colored products (e.g., “_____” of canned pears)
pinking
Glucosidases and anthocyanases effects on anthocyanin
remove the sugars from anthocyanins, thus destabilizing the molecule and causing loss of color
Deleterious effects of these enzymes curtailed by microwave blanching - dry heat
Complexion with metal ions ex. Fe, or Cu can result in _______ color formation which may be undesirable.
blue/green
Uses of anthocyanins in food processing
♣ Antioxidants
♣ Color additive
Flavonoids
• H2O-soluble pigments found in plants and microorganisms
• most abundant polyphenols in the diet
• a.k.a. anthoxanthins – they are glycosides
with a benzopyrone nucleus
• most common sugar – rutinose
• they give certain fruits, vegetables and herbs their dark red, blue and purple colors
• many are antioxidants
what are the most abundant polyphenols in our diets?
flavonoids
anthoxanthins
flavonoids
structure of flavonoids
glycosides with a benzopyrone nucleus
the most common sugar in flavonoids
rutinose
the color of flavonoids
they give certain fruits, vegetables and herbs their dark red, blue and purple colors
classification of flavonoids
flavones isoflavones flavonols flavonones flavononols
True/False
flavonoids are antioxidants
true
flavones
(double bond at 2:3 position)
apigenin
Isoflavones
(benzene ring at 3 position)
Genistein
Flavonols
(-OH group at 3 position)
Quercetin
Flavonones
(no 2x bond at 2:3 position)
Naringenin
Flavanonols
(-OH group at 3 position; no 2x bond at 2:3 position)
Xeractinol
What are the basic differences between flavonoids and anthocyanins
they are both polyphenolic but the basic difference is their structure. They have different parent compounds
♣ anthocyanins with pyrene
♣ flavonoids with benzopyrene
also display a range of colors, but flavonoids tend to be less intensely colored than anthocyanins.
True/False
Flavonoids are more intensely coloured than anthocyanins
false
flavonoids tend to be less intensely colored than anthocyanins.
Polyphenolic nature of flavonoids
o flavonoids can act as substrates for enzymatic browning (and unlike anthocyanins, brown colors formed may manifest because of the low coloring power of flavonoids
True/False
Flavonoids are not antioxidants
False
Also have antioxidant properties by virtue of metal chelation and radical scavenging
Flavonoids more potent antioxidants due to structural differences
Flavonoids suggested to have provitamin ___ activity
C
i.e. enhance vitamin C. activity
Oxidation and further oxidation of Vitamin C
Vitamin C –> dehydroascorbic acid –> (further oxidation) diketogluconic acid
How can you stop and revert vitamin C oxidation?
If the oxidation keeps on going, we lose vitamin C activity but when we have flavonoids, they reduce the dehydroascorbic acid back to vitamin C
How do flavonoids protect/preserve vitamin C?
Flavonoids protect/preserve vitamin C activity by reducing dehydroascorbic acid back to ascorbic acid and prevent further oxidation to the inactive diketogluconic acid form.
Common properties of flavonoids
- Polyphenolic structure, substrates in enzymatic browning reactions;
- May be involved in other discoloration reactions in foods (e.g., may bind Fe in foodstuffs to form blue/green colors);
- Chelating agent;
- Antioxidant / free radical scavenger;
- Pro-Vitamin C activity.
Apigenin sources and common properties
found in fruits, vegetables and leaves.
Common sources are chamomile tea and celery
o Yellow in color with pleasant smell
o Has bitter and astringent taste (the dry sensation we feel in the cheeks-the proteins in saliva are precipitated out by the astringent molecules. Tea, lemon, cider, wine)
o Apart from its antioxidant effect, it is also said to elicit calming effect on consumers (i.e. relieves anxiety)
flavones
Describe Astringent taste
the dry sensation we feel in the cheeks-the proteins in saliva are precipitated out by the astringent molecules. Tea, lemon, cider, wine
Genistein sources and common properties
• is colorless pigment found in plant materials, fruits, vegetables, legumes.
o Ex. Soy, alpha alpha, pea
o Bitter, astringent taste
o Estrogenic effects
o Increase body fat and result in weight gain
o Loss of Zn but retention of Cu
o Utilization of Ca++, thus relieves osteoporosis
o Relieves menopausal symptoms (e.g. hot flashes)
Isoflavones
Quercetin sources and common properties
• is ubiquitous in nature color ranges form shades of yellow to brown.
o Bitter, astringent taste
o Potent antioxidant
Flavonols
Naringenin sources and common properties
o Found in plant material mostly in citrus fruits
o It is colorless and bitter and is what gives grapefruit the bitter taste
Flavonones
Xeractinol sources and common properties
o Found in leaves and is colorless and bitter in taste
o Relatively newly discovered, so not well characterized.
Flavanonols
Betalains
- H2O-soluble plant pigments
- Glycosides (glucose commonly present)
- Two main colors - red & yellow
- Red pigments => betacyanins (e.g., betanin)
- Yellow pigments => betaxanthins (e.g., vulgaxanthin) • Found mostly in beet plants
o Used as food colorants because of color intensity
o Destruction by heating
o Ioss to cooking water
o Ex. Beets, Spanish chard, cactus fruit
betacyanins color
red
e.g., betanin
betaxanthins color
yellow
(e.g., vulgaxanthin) Found mostly in beet plants
Tannins
o Complex plant pigments with a range of color (pale yellow to dark brown) and range of solubility
o The variations of solubility due to size differences
o Found a lot in tree barks and in leaves (tea)
o Cause astringency
o Because they can serve as substrates for enzymatic browning reactions by PPO, even the less intensely colored tannins may undergo enzymatic browning to cause dark discolorations in foods
Quinones
o Are derived from aromatic compounds with even numbered –OH groups
o The –OH groups oxidize to form the corresponding quinone
o So if you were to start with benzene, you would require 2 hydroxylation steps to form dihyroxybenzene which can then oxidize to form a quinone.
o It is water soluble and has intense dark colors that enable it to be used as dyes.
o It is also used as a purgative because of its capacity to induce loose bowels.
Melanins
o Quinone (polymerization) --> melanoidins or Melanins (depending on the sizes) o Depending on the size of Melanins will determine the degree of solubility as well as intensity of the color of the color of the product
Xanthones
- Plant pigments with structural resemblance to flavonoids & quinones, i.e., glycosides;
- H2O-soluble and yellow in color;
- Common e.g., mangiferin.
Caramelization
o When sugars are heated at high temperatures, they oxidize to form various breakdown products that can aggregate to form the colored products caramelans, caramelens, and caramelins. (size increases respectively)
MAILLARD BROWNING
o Non-enzymatic browning due to reaction between sugars and primary amino groups of proteins, peptides, amino acids, amine in foods when they are heated called MAILLARD BROWNING
Gentiobiose
disaccharide
D-glucose
B 1–>6 linkage
It is a product of the caramelization of glucose
Rutinose
disaccharide
is present in some flavonoid glycosides.
Sophorose
disaccharide
It is a product of the caramelization of glucose
Neohesperidose
is the disaccharide which is present in some flavonoids
Rosinidin
red- anthocyanin (-OCH3)
