Pigments Flashcards
5 important food quality attributes?
flavor texture nutritive value microbial load color/appearance
describe photosynthesis
trapping light energy from sunlight and using it to syntheisze food
what are the major types of chlorophyll?
a and b
ratio of a and b chlorophyll in nature?
3:1 (a:b)
what colors of chlorophyll a and b?
a: bright green bluish color
b: dull green color
solubility of chlorophyll?
fat soluble
where are myoglobin and hemoglobin mostly found? what does color intensity depend on?
in red meats
intensity depends on myoglobin concentration
difference between heme pigments and chlrophyll?
heme has iron instead of Mg
what kind of structure does chlorophyll have?
tetrapyrrole structure
how many carbons are in phytol
it is a 20 C unit
why is phytol fat soluble and not water soluble?
it is a 20 C unit structure, making it mostly hydrocarbon (hydrophobic). Thus it is unable to dissolve in water and highly soluble in fats
describe the structure of a pyrol ring
-N-containing 5 membered hytrocyclic ring
what are pyrol rings linked together by?
methylene bridges
how many pyrole rings are in one chlorophyll?
4
difference between chloro b and a?
b has a methyl group with the pyrole ring
what is in the center of chlorophyll?
magnesium
molecular weight of chloro?
296g/mol
how many absorption optima do chloro a and b have? which are high or low?
a: has 2 around the same absorbance
b: has 1 high optima, and one low one
4 forms/structures of chlorophyll?
- chlorophyll
- pheophytin
- chlorophyllide
- pheophorbide
what is the part of the chlorophyll structure that causes water insolublilty?
what happens when it is removed?
what molecule does it become?
the phytol group
removal causes molecule to not be insoluble
chlorophyll becomes chlorophyllide (still has Mg but no phytol)
what happens to chlorophyll during canning?
high temp causes removal of Mg
becomes pheophytin
how do you form pheophorbide from chlorophyllide?
from pheophytin?
from chlorophyllide: lose Mg
from pheophytin: lose phytol
what enzyme causes loss of phytol?
chlorophyllase
what happens to chlorophyll with moist cooking methods?
- destruction of tissues
- H ions form acids
- temperature causes breakdown of chlorophyll
what happens to chorophyll during dry cooking?
dry heat will destroy enzyme that breaks down phytol (chlorophyllase)
thus, no destruction of color b/c Mg is not removed
what happens to chlorophyll during fermentation?
acid production, causes color loss
what happens to chlorophyll with exposure to light and air
oxidation
leads to color loss
what is responsible for red color of muscle foods?
heme pigments
what is globin and heme?
globin: protein part
heme: non-protein part
what kind of structure do myoglobin and hemoglobin have?
tetrapyrrole structure
4 pyrol rings attached to a central Fe atom
what is the difference between heme and chlorophyll pigment structures?
heme pigments: tetrapyrrole with a central Fe atom
chloro: tetrapyrrole with a central Mg atom
is myoblogin or hemoglobin bigger?
what is their molecular weight?
Hemoglobin is bigger
Hb: 64kDa
Mb: 17kDa
what can bind to the Fe in heme structures?
electron pair donors (O2, CO2, CN, OH, CO)
in globin, Fe covalently links to ___ in ____
Fe covalently links to N in histidine residue
how many N are in heme pigments?
4 Ns in the 4 pyrrole molecule
all are linked to the central Fe atom
what is the water solubility of phytol and globin?
phytol: water insoluble
globin: water soluble
is phytol of globin bigger??
globin: 16.4kD
phytol: 296Da
globin is bigger than phytol
how do myoglobin form hemoglobin?
4 Mb comes together to form 1Hb
what does the intensity of color of heme pigments depend on?
depends on how much Mb is present
how does oxymyoglobin form?
Mb + O2 –> MbO2 (oxymyoglobin)
what is the color of Mb vs MbO2 vs Met-Mb?
Mb (myoglobin) is purple
MbO2 (oxymyoglobin) is bright red
Met-Mb (metmyoglobin): brown
what state is Fe in Mb and MBO2?
Fe2+ state
what happens to Fe when you leave red meat in storage for too long?
Fe2+ of the Mb oxidizes to Fe3+ state (metmyoglobin)
what is metmyoglobin? What is it formed from?
formed from oxidation of myoglobin (Fe2+ is oxidized to Fe3+)
brown
what does presence of met-Mb represent?
that meat is not fresh
what can be added to meat that is not fresh to turn it red?
what reaction is this?
reducing agents, like cysteine or glutathione (reverses action of the oxidation to met-Mb)
Fe3+ –> Fe2+ (reducing reaction)
how is sulfmyoglobin produced? what color is it?
- produced after a longer period of time after reducing agents (ie cysteine or glutathione) were added to try to make old meat look fresh
- yellow/green color
what happens when meat is cooked?
bright red becomes brown b/c:
- globin is denatured (makes protein more digestible)
- Fe2+ is oxidize to Fe3+ (this forms dark brown hemichrome pigment)
what color is the hemichrome pigment?
dark brown
caused by oxidation of Fe2+ to Fe3+
what are the advantages and disadvantages of well done meat?
con: Fe3+ is not as readily absorbed in the intestine into the cytosol
pro: already has extensive denaturation of pathogens
what are the pros and cons of rare or medium cooked meat?
pros: Fe2+ is ore easily absorbed in intestine into cytosol to make more RBCs. Thus, more dietary iron will be absorbed
con: protein is not as denatured as well done meat (still may have harmful pathogens)
how are cured meats treated with?
Na or K salts of nitrates or nitrites
what is the chemical rxn that occurs in curing meat?
what compound is produced? what color is this compound?
Mb + No –> MbNo (bright red nitrosomyoglobin)
No3 or No2 have lone pairs of electrons to donate to Fe in Mb
what are advantages of cured meat?
prevents growth of clostridium when cooked meat has a browned color (nitrosohemichrome)
what can form when using nitrates in food?
nitroso-amines that canbe carcinogenic
what is used to prevent development of nitroso-amines in cured meats?
what reaction does this cause?
ascorbic acid/vit C is added to the curing brine to reduce nitroso-amines back to nitrates
what are differences/similarities between chlorophyll and Mb?
different:
- different sources
- central atoms are different
same:
- relative solubilities
- both are heat sensitive
what colors are caused by carotenoids?
responsible for yellow, orange and red-orange plants in plants and animals
what are major plant sources of carotenoids?
fruits, veg, veg oils (eg palsm oil)
what are major animal sources of carotenoids?
milk fat, egg yolk, butter, salmonoids (eg salmon and trout), crustacean species (eg crab, lobster, shrimp, prawn
what are microbial sources of carotenoids?
fungi, yeast, algae
major characteristics of carotenoids?
- ubiquitous (found everywhere)
- H2O insoluble (hydrophobic)
- all derived from 5C compound (isoprene)
- may be cyclic or acyclic
are carotenoids water soluble or insolube?
insoluble
what compound are carotenoids derived from?
isoprened (5c compound)
example of cyclic carotenoid?
beta-carotene
example of acyclic carotenoid?
lycopene
difference between hydrocarbon carotenoids (or carotenes) and oxy-carotenoids?
hydrocarbon carotenoids (or carotenes): contain only hydrocarbon
oxy-carotenoids: contains O
what are examples of hydrocarbon carotenoids?
beta carotene
alpha carotene
lycopene
(contains only H and C)
what is the structural difference between beta and alpha carotene with lycopene?
what is the same?
difference:
-beta and alpha carotene have ringed structures and lycopene has no ring structures
same
- both are hydrocarbon carotenoids
- both are symmetrical
why is beta-carotene referred to as provitamin A?
the hydrolysis of beta carotene yields 2 identical molecules of Vit A
what happens in the hydrolysis of lycopene?
yields 2 identical halves, but does not produce vit A
does the hydrolysis of beta carotene or lycopene produce vit A?
beta carotene
lycopene and beta carotene are both ____
symmetrical
what are sources of oxygenated carotenoids?
green leaves and egg yolk
how is the structure of oxy-carotenoids different to beta carotenes?
oxy carotenoids are asymmetrical and have hydroxylated rings (thus no vitamin A activity)
what is the use of canthaxanthin?
it is an oxycarotenoid used to feed supplements for cultured salmonoids and imitation seafood products
does canthaxanthin have vit A activity?
no
where are canthaxanthins found?
microorganisms, plants, animals
what are factors that cause destruction of carotenoids?
O2
light
dehydration (b/c it is soluble)
what happens when you dehydrate carotenoids
they are destroyed b/c carotenoids are water soluble
what are 2 key uses of carotenoids?
antioxidant
colorant
are anthocyanins water soluble? why or why not?
yes
soluble because of the OH group
what colors are anthocyanins?
red
blue
violet
what is the basic structure of anthocyanins?
flavillium ion
aka anthocyanidin or aglycone
what are other names for the flavillium ion
anthocyanidin or aglycone
how do you form glycosides from anthocyanins?
esterifying OH group on parent compound with sugars to form glycosides
what are the 3 known sugars of anthocyanins?
monosides
biosides
tiosides
what is are major functions of anthocyanins?
- acts as an antioxidant via metal chelation and radical scavenging
2 act as a substrate for enzymatic browning (b/c of polyphenolic nature)
what are the effects of substituent groups on the color of anthocyanins?
increasing OH content increases blue color
increasing methoxy content increases red color
what are the two major substituent groups on anthocyanins?
OH and CH3
what color are anthocyanins in acidic and alkaline conditions?
acidic: red
alkaline: blue or colorless
what pigments of anthocyanins are most stable?
red
how do additives (sulfites, ascordic acid, H2O2) affect anthocyanins?
forms additional compounds with the OH groups of anthocyanins and causes color loss
what happens with high sugar content and O2 presence?
color loss and destruction of pigments
what happens when you add metals to anthocyanins?
forms purple or gray colors
what happens when you put anthocyanins in high teperatures
causes destruction of pigments
pigments can also be lost to water (since they are water soluble)
what happens when you oxidize anthocyanins in presence of O2?
what is an example of this?
colorless anthocyanins may be oxidize to colored products
example: “pinking” of canned pears
what are effects of enzymes on athocyanins?
color loss
effects of glucosidases or anthocyanases on anthocyanins?
removes sugars from athocyanins –> destabilizes molecule –> causes color loss
what happens with anthocyanins when you use microwave blanching?
dry heat –> deleterious effect of enzymes
what happens with anthocyanins when you use moist heat treatment?
disintegration of molecule. Results in color loss
what happens with anthocyanins when you use complexation with metal ions
metals (ie Fe or Ca) can result in blue/green color formation
main uses of anthocyanins?
- antioxidant
2. color additive
are flavonoids water soluble or insoluble?
water soluble
where are flavonoids found?
in plants and microorganisms
what is the most abundant polyphenol in diet?
flavonoids
what is an anthoxanthis?
glycoside with a penzopyrone nucleus
what is a commonly found sugar in flavonoids?
rutinose
what colors do flavonoids give?
dark red, blue and purple
flavonoids are _____?
antioxidants
what is the difference between anthocyanins and flavonoids?
different parent compound
anthocyanins have pyran
flavonoids have benzopyrone
flavonoids are less intensely colored than anthocyanins
due to polyphenolic nature, flavonoids can…..
act as substrates for enzymatic browning
brown colors can manifest more in flavonoids than anthocyanins because…?
because of the lower coloring power in flavonoids
why do flavonoids have antioxidant properties?
due to metal chelation ions
what are the 5 classifications of flavonoids?
- Flavones: double bond at 2:3 position
- Isoflavones: benzene ring at 3 position
- Flavonols OH group at 3 position
- Flavonones: no 2x bond at 2:3 position
- Flavanonols: OH group at 3 position; no 2x bond at 2:3 position
what are common properties of flavonoids?
- polyphenolic structure (allows for enzymatic browning reactions)
- involved in discoloration reactions in foods (eg. can bind Fe in food to form blue/gree color)
- chelating agent
- antioidant and free radical scavenger
- pro vit C activity
describe the pro-vitamin C activity of flavonoids
- vitamin C is oxidized to dehydroascorbic acid
2. diketogluconic acid
describe reverse reaction with flavanoids to vitamin C
flavonoids can re-oxidize dehydroascorbic acid back to vitamin C
what is apigenin
a flavonoid found in fruits, veg and leaves
what are common sources of apigenin?
chamomille tea and celery
what are the cahracteristics of apigenin?
- yellow
- pleasant smell
- has bitter and astringent taste
describe astringent
dry sensation in cheeks when certain foods are taken in mouth
caused by precipitation of protein in saliva in cheeks
what are uses of apigenin
yellow food coloring dye
relieves anxiety and gives a calming effect on consumers
color of genistein
colorless
common sources of genistein?
soy
alfalfa
peas
taste of genistein?
bitter and astringent
describe the estrogenic effects of fenistein
- increases body fat and results in weight gain
- loss of zinc but retains copper ions
- utilizes Ca2+ (relieves osteoporosis)
- relieves menopausal symptoms
characteristics of quercetin
- ubiquitous in nature
- color: ranges from yellow to brown
- taste: bitter and astringent
- potent antioxidant
characteristics of naringenin
- found mostly in citrus fruits
- colorless and bitter
- gives grapefruit the bitter taste
characteristics of xeractinol
found in leaves and is colorless and bitter in taste
-newly discovered
are betalains water soluble or insolube?
soluble
where are betalaines found?
in higher fungi
what is the parent compound of betalaines
indole (C8H7N)
describe the structure of betalaines
- polyphenolic groups
- may have sugars in addition to the parent group
can betalaines be a substrate for enzymatic browning? why is it not as strong?
yes
due to their intense red-yellow colors, browning induced by PPO is not as strong
common uses of betalaines
antioxidant and food colorant
why are betalains good food colorants?
because of high color intensity
how can betalaines be destructed?
-by heating
-loss to cooking water
-thermal processing
-
what are common sources of betalaines
beets
spanish chard
cactus
what are two main colors of betalaines? (
red (betacyanins) and yellow (betaxanthins)
what are two main colors of betalaines? (
red (betacyanins) and yellow (betaxanthins)
what is the solubility of tannins?
varying degrees of solubility in water based on size
color of tannins?
ranges from colorless to yellow to brown
where are tannins commonly found?
in tree bark and leaves (tea)
what are common tannin pigments
gallic acid
ellagic acid
what does tannins contribute in foods?
astringency
do tannins participate in enzymatic browning reactions? why or why not?
yes; can be a substrate for enzymatic browning reactions by PPO
do less intensely colored tannins undergo enzymatic browning?
yes
water solubility in quinones?
soluble
color of quinones?
ranges in color from yellow to black
common quinones?
emodin and spinulosin
what are uses of quinones?
- natural dye
2/ purgatives
what are mechanisms involved with quinones?
hydroxylation
hydration
oxidation
how are quinones derived?
OH groups oxidize aromatic compounds and form quinone
describe the formation of quinones from benzene
- formation of dihydorxylactin
- formation of dihydroxybenzene
- oxidation to form quinone
why are quinones used as purgatives?
they are able to induce loose bowels
what are xanthones similar to? what is similar?
structurally similar to flavonoids and quinones
both have:
- antioxidant properties
- OH groups
- able to remove free radicals and chelate metal ions
solubility of xanthones?
water soluble
color of xanthones
yellow
common xanthone?
mangiferin
what are melanins/melanoidins? where are they found?
brown colored pigments found in fruits, ve,g fungi and crustacean
how are melanins formed?
from polymerization of phenolic compounds by PPO and Cu2+
why do xanthones have antioxidant properties?
due to their aromatic ring structure and OH groups
describe carmelization
occurs from heating CHO at high temp, causing oxidation to form breakdown products (caramelans, caramelens, caralemins)
describe maillard rxn
occurs from non-enzymatic brwoning due to interaction of sugars with amino groups from AA during heating
what are quinones polymerized to?
quinones are polymerized to melanidins or melanins
what are the 3 carmelization colored products? what are the smallest and biggest products?
- caramelans (smallest)
- caramelens
- caralemins (biggest)
what determines the intensity of the browning in the product?
depends on the size of product polymerized from quinones
what does diacetyl cause in carmelization reactions
a volatile compound produced when heating sugar at high temp
responsible for nutty odor and flavor (caramel)
