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Food Chemistry 2 > Pigments > Flashcards

Pigments Flashcards

1
Q

5 important food quality attributes?

A 
flavor
texture
nutritive value
microbial load
color/appearance
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2
Q

describe photosynthesis

A

trapping light energy from sunlight and using it to syntheisze food

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3
Q

what are the major types of chlorophyll?

A

a and b

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4
Q

ratio of a and b chlorophyll in nature?

A

3:1 (a:b)

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5
Q

what colors of chlorophyll a and b?

A

a: bright green bluish color
b: dull green color

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6
Q

solubility of chlorophyll?

A

fat soluble

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7
Q

where are myoglobin and hemoglobin mostly found? what does color intensity depend on?

A

in red meats

intensity depends on myoglobin concentration

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8
Q

difference between heme pigments and chlrophyll?

A

heme has iron instead of Mg

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9
Q

what kind of structure does chlorophyll have?

A

tetrapyrrole structure

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10
Q

how many carbons are in phytol

A

it is a 20 C unit

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11
Q

why is phytol fat soluble and not water soluble?

A

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

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12
Q

describe the structure of a pyrol ring

A

-N-containing 5 membered hytrocyclic ring

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13
Q

what are pyrol rings linked together by?

A

methylene bridges

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14
Q

how many pyrole rings are in one chlorophyll?

A

4

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15
Q

difference between chloro b and a?

A

b has a methyl group with the pyrole ring

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16
Q

what is in the center of chlorophyll?

A

magnesium

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17
Q

molecular weight of chloro?

A

296g/mol

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18
Q

how many absorption optima do chloro a and b have? which are high or low?

A

a: has 2 around the same absorbance
b: has 1 high optima, and one low one

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19
Q

4 forms/structures of chlorophyll?

A
  1. chlorophyll
  2. pheophytin
  3. chlorophyllide
  4. pheophorbide
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20
Q

what is the part of the chlorophyll structure that causes water insolublilty?
what happens when it is removed?

what molecule does it become?

A

the phytol group

removal causes molecule to not be insoluble

chlorophyll becomes chlorophyllide (still has Mg but no phytol)

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21
Q

what happens to chlorophyll during canning?

A

high temp causes removal of Mg

becomes pheophytin

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22
Q

how do you form pheophorbide from chlorophyllide?

from pheophytin?

A

from chlorophyllide: lose Mg

from pheophytin: lose phytol

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23
Q

what enzyme causes loss of phytol?

A

chlorophyllase

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24
Q

what happens to chlorophyll with moist cooking methods?

A
  • destruction of tissues
  • H ions form acids
  • temperature causes breakdown of chlorophyll
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25
Q

what happens to chorophyll during dry cooking?

A

dry heat will destroy enzyme that breaks down phytol (chlorophyllase)

thus, no destruction of color b/c Mg is not removed

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26
Q

what happens to chlorophyll during fermentation?

A

acid production, causes color loss

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27
Q

what happens to chlorophyll with exposure to light and air

A

oxidation

leads to color loss

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28
Q

what is responsible for red color of muscle foods?

A

heme pigments

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29
Q

what is globin and heme?

A

globin: protein part
heme: non-protein part

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30
Q

what kind of structure do myoglobin and hemoglobin have?

A

tetrapyrrole structure

4 pyrol rings attached to a central Fe atom

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31
Q

what is the difference between heme and chlorophyll pigment structures?

A

heme pigments: tetrapyrrole with a central Fe atom

chloro: tetrapyrrole with a central Mg atom

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32
Q

is myoblogin or hemoglobin bigger?

what is their molecular weight?

A

Hemoglobin is bigger

Hb: 64kDa
Mb: 17kDa

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33
Q

what can bind to the Fe in heme structures?

A

electron pair donors (O2, CO2, CN, OH, CO)

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34
Q

in globin, Fe covalently links to ___ in ____

A

Fe covalently links to N in histidine residue

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35
Q

how many N are in heme pigments?

A

4 Ns in the 4 pyrrole molecule

all are linked to the central Fe atom

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36
Q

what is the water solubility of phytol and globin?

A

phytol: water insoluble
globin: water soluble

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37
Q

is phytol of globin bigger??

A

globin: 16.4kD
phytol: 296Da

globin is bigger than phytol

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38
Q

how do myoglobin form hemoglobin?

A

4 Mb comes together to form 1Hb

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39
Q

what does the intensity of color of heme pigments depend on?

A

depends on how much Mb is present

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40
Q

how does oxymyoglobin form?

A

Mb + O2 –> MbO2 (oxymyoglobin)

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41
Q

what is the color of Mb vs MbO2 vs Met-Mb?

A

Mb (myoglobin) is purple
MbO2 (oxymyoglobin) is bright red
Met-Mb (metmyoglobin): brown

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42
Q

what state is Fe in Mb and MBO2?

A

Fe2+ state

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43
Q

what happens to Fe when you leave red meat in storage for too long?

A

Fe2+ of the Mb oxidizes to Fe3+ state (metmyoglobin)

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44
Q

what is metmyoglobin? What is it formed from?

A

formed from oxidation of myoglobin (Fe2+ is oxidized to Fe3+)

brown

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45
Q

what does presence of met-Mb represent?

A

that meat is not fresh

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46
Q

what can be added to meat that is not fresh to turn it red?

what reaction is this?

A

reducing agents, like cysteine or glutathione (reverses action of the oxidation to met-Mb)

Fe3+ –> Fe2+ (reducing reaction)

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47
Q

how is sulfmyoglobin produced? what color is it?

A
  • 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
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48
Q

what happens when meat is cooked?

A

bright red becomes brown b/c:

  1. globin is denatured (makes protein more digestible)
  2. Fe2+ is oxidize to Fe3+ (this forms dark brown hemichrome pigment)
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49
Q

what color is the hemichrome pigment?

A

dark brown

caused by oxidation of Fe2+ to Fe3+

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50
Q

what are the advantages and disadvantages of well done meat?

A

con: Fe3+ is not as readily absorbed in the intestine into the cytosol
pro: already has extensive denaturation of pathogens

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51
Q

what are the pros and cons of rare or medium cooked meat?

A

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)

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52
Q

how are cured meats treated with?

A

Na or K salts of nitrates or nitrites

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53
Q

what is the chemical rxn that occurs in curing meat?

what compound is produced? what color is this compound?

A

Mb + No –> MbNo (bright red nitrosomyoglobin)

No3 or No2 have lone pairs of electrons to donate to Fe in Mb

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54
Q

what are advantages of cured meat?

A

prevents growth of clostridium when cooked meat has a browned color (nitrosohemichrome)

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55
Q

what can form when using nitrates in food?

A

nitroso-amines that canbe carcinogenic

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56
Q

what is used to prevent development of nitroso-amines in cured meats?

what reaction does this cause?

A

ascorbic acid/vit C is added to the curing brine to reduce nitroso-amines back to nitrates

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57
Q

what are differences/similarities between chlorophyll and Mb?

A

different:

  • different sources
  • central atoms are different

same:

  • relative solubilities
  • both are heat sensitive
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58
Q

what colors are caused by carotenoids?

A

responsible for yellow, orange and red-orange plants in plants and animals

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59
Q

what are major plant sources of carotenoids?

A

fruits, veg, veg oils (eg palsm oil)

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60
Q

what are major animal sources of carotenoids?

A

milk fat, egg yolk, butter, salmonoids (eg salmon and trout), crustacean species (eg crab, lobster, shrimp, prawn

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61
Q

what are microbial sources of carotenoids?

A

fungi, yeast, algae

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62
Q

major characteristics of carotenoids?

A
  • ubiquitous (found everywhere)
  • H2O insoluble (hydrophobic)
  • all derived from 5C compound (isoprene)
  • may be cyclic or acyclic
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63
Q

are carotenoids water soluble or insolube?

A

insoluble

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64
Q

what compound are carotenoids derived from?

A

isoprened (5c compound)

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65
Q

example of cyclic carotenoid?

A

beta-carotene

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66
Q

example of acyclic carotenoid?

A

lycopene

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67
Q

difference between hydrocarbon carotenoids (or carotenes) and oxy-carotenoids?

A

hydrocarbon carotenoids (or carotenes): contain only hydrocarbon

oxy-carotenoids: contains O

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68
Q

what are examples of hydrocarbon carotenoids?

A

beta carotene
alpha carotene
lycopene

(contains only H and C)

69
Q

what is the structural difference between beta and alpha carotene with lycopene?

what is the same?

A

difference:
-beta and alpha carotene have ringed structures and lycopene has no ring structures

same

  • both are hydrocarbon carotenoids
  • both are symmetrical
70
Q

why is beta-carotene referred to as provitamin A?

A

the hydrolysis of beta carotene yields 2 identical molecules of Vit A

71
Q

what happens in the hydrolysis of lycopene?

A

yields 2 identical halves, but does not produce vit A

72
Q

does the hydrolysis of beta carotene or lycopene produce vit A?

A

beta carotene

73
Q

lycopene and beta carotene are both ____

A

symmetrical

74
Q

what are sources of oxygenated carotenoids?

A

green leaves and egg yolk

75
Q

how is the structure of oxy-carotenoids different to beta carotenes?

A

oxy carotenoids are asymmetrical and have hydroxylated rings (thus no vitamin A activity)

76
Q

what is the use of canthaxanthin?

A

it is an oxycarotenoid used to feed supplements for cultured salmonoids and imitation seafood products

77
Q

does canthaxanthin have vit A activity?

A

no

78
Q

where are canthaxanthins found?

A

microorganisms, plants, animals

79
Q

what are factors that cause destruction of carotenoids?

A

O2
light
dehydration (b/c it is soluble)

80
Q

what happens when you dehydrate carotenoids

A

they are destroyed b/c carotenoids are water soluble

81
Q

what are 2 key uses of carotenoids?

A

antioxidant

colorant

82
Q

are anthocyanins water soluble? why or why not?

A

yes

soluble because of the OH group

83
Q

what colors are anthocyanins?

A

red
blue
violet

84
Q

what is the basic structure of anthocyanins?

A

flavillium ion

aka anthocyanidin or aglycone

85
Q

what are other names for the flavillium ion

A

anthocyanidin or aglycone

86
Q

how do you form glycosides from anthocyanins?

A

esterifying OH group on parent compound with sugars to form glycosides

87
Q

what are the 3 known sugars of anthocyanins?

A

monosides
biosides
tiosides

88
Q

what is are major functions of anthocyanins?

A
  1. acts as an antioxidant via metal chelation and radical scavenging
    2 act as a substrate for enzymatic browning (b/c of polyphenolic nature)
89
Q

what are the effects of substituent groups on the color of anthocyanins?

A

increasing OH content increases blue color

increasing methoxy content increases red color

90
Q

what are the two major substituent groups on anthocyanins?

A

OH and CH3

91
Q

what color are anthocyanins in acidic and alkaline conditions?

A

acidic: red
alkaline: blue or colorless

92
Q

what pigments of anthocyanins are most stable?

A

red

93
Q

how do additives (sulfites, ascordic acid, H2O2) affect anthocyanins?

A

forms additional compounds with the OH groups of anthocyanins and causes color loss

94
Q

what happens with high sugar content and O2 presence?

A

color loss and destruction of pigments

95
Q

what happens when you add metals to anthocyanins?

A

forms purple or gray colors

96
Q

what happens when you put anthocyanins in high teperatures

A

causes destruction of pigments

pigments can also be lost to water (since they are water soluble)

97
Q

what happens when you oxidize anthocyanins in presence of O2?

what is an example of this?

A

colorless anthocyanins may be oxidize to colored products

example: “pinking” of canned pears

98
Q

what are effects of enzymes on athocyanins?

A

color loss

99
Q

effects of glucosidases or anthocyanases on anthocyanins?

A

removes sugars from athocyanins –> destabilizes molecule –> causes color loss

100
Q

what happens with anthocyanins when you use microwave blanching?

A

dry heat –> deleterious effect of enzymes

101
Q

what happens with anthocyanins when you use moist heat treatment?

A

disintegration of molecule. Results in color loss

102
Q

what happens with anthocyanins when you use complexation with metal ions

A

metals (ie Fe or Ca) can result in blue/green color formation

103
Q

main uses of anthocyanins?

A
  1. antioxidant

2. color additive

104
Q

are flavonoids water soluble or insoluble?

A

water soluble

105
Q

where are flavonoids found?

A

in plants and microorganisms

106
Q

what is the most abundant polyphenol in diet?

A

flavonoids

107
Q

what is an anthoxanthis?

A

glycoside with a penzopyrone nucleus

108
Q

what is a commonly found sugar in flavonoids?

A

rutinose

109
Q

what colors do flavonoids give?

A

dark red, blue and purple

110
Q

flavonoids are _____?

A

antioxidants

111
Q

what is the difference between anthocyanins and flavonoids?

A

different parent compound

anthocyanins have pyran
flavonoids have benzopyrone

flavonoids are less intensely colored than anthocyanins

112
Q

due to polyphenolic nature, flavonoids can…..

A

act as substrates for enzymatic browning

113
Q

brown colors can manifest more in flavonoids than anthocyanins because…?

A

because of the lower coloring power in flavonoids

114
Q

why do flavonoids have antioxidant properties?

A

due to metal chelation ions

115
Q

what are the 5 classifications of flavonoids?

A
  1. Flavones: double bond at 2:3 position
  2. Isoflavones: benzene ring at 3 position
  3. Flavonols OH group at 3 position
  4. Flavonones: no 2x bond at 2:3 position
  5. Flavanonols: OH group at 3 position; no 2x bond at 2:3 position
116
Q

what are common properties of flavonoids?

A
  • 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
117
Q

describe the pro-vitamin C activity of flavonoids

A
  1. vitamin C is oxidized to dehydroascorbic acid

2. diketogluconic acid

118
Q

describe reverse reaction with flavanoids to vitamin C

A

flavonoids can re-oxidize dehydroascorbic acid back to vitamin C

119
Q

what is apigenin

A

a flavonoid found in fruits, veg and leaves

120
Q

what are common sources of apigenin?

A

chamomille tea and celery

121
Q

what are the cahracteristics of apigenin?

A
  • yellow
  • pleasant smell
  • has bitter and astringent taste
122
Q

describe astringent

A

dry sensation in cheeks when certain foods are taken in mouth

caused by precipitation of protein in saliva in cheeks

123
Q

what are uses of apigenin

A

yellow food coloring dye

relieves anxiety and gives a calming effect on consumers

124
Q

color of genistein

A

colorless

125
Q

common sources of genistein?

A

soy
alfalfa
peas

126
Q

taste of genistein?

A

bitter and astringent

127
Q

describe the estrogenic effects of fenistein

A
  • increases body fat and results in weight gain
  • loss of zinc but retains copper ions
  • utilizes Ca2+ (relieves osteoporosis)
  • relieves menopausal symptoms
128
Q

characteristics of quercetin

A
  • ubiquitous in nature
  • color: ranges from yellow to brown
  • taste: bitter and astringent
  • potent antioxidant
129
Q

characteristics of naringenin

A
  • found mostly in citrus fruits
  • colorless and bitter
  • gives grapefruit the bitter taste
130
Q

characteristics of xeractinol

A

found in leaves and is colorless and bitter in taste

-newly discovered

131
Q

are betalains water soluble or insolube?

A

soluble

132
Q

where are betalaines found?

A

in higher fungi

133
Q

what is the parent compound of betalaines

A

indole (C8H7N)

134
Q

describe the structure of betalaines

A
  • polyphenolic groups

- may have sugars in addition to the parent group

135
Q

can betalaines be a substrate for enzymatic browning? why is it not as strong?

A

yes

due to their intense red-yellow colors, browning induced by PPO is not as strong

136
Q

common uses of betalaines

A

antioxidant and food colorant

137
Q

why are betalains good food colorants?

A

because of high color intensity

138
Q

how can betalaines be destructed?

A

-by heating
-loss to cooking water
-thermal processing
-

139
Q

what are common sources of betalaines

A

beets
spanish chard
cactus

140
Q

what are two main colors of betalaines? (

A

red (betacyanins) and yellow (betaxanthins)

141
Q

what are two main colors of betalaines? (

A

red (betacyanins) and yellow (betaxanthins)

142
Q

what is the solubility of tannins?

A

varying degrees of solubility in water based on size

143
Q

color of tannins?

A

ranges from colorless to yellow to brown

144
Q

where are tannins commonly found?

A

in tree bark and leaves (tea)

145
Q

what are common tannin pigments

A

gallic acid

ellagic acid

146
Q

what does tannins contribute in foods?

A

astringency

147
Q

do tannins participate in enzymatic browning reactions? why or why not?

A

yes; can be a substrate for enzymatic browning reactions by PPO

148
Q

do less intensely colored tannins undergo enzymatic browning?

A

yes

149
Q

water solubility in quinones?

A

soluble

150
Q

color of quinones?

A

ranges in color from yellow to black

151
Q

common quinones?

A

emodin and spinulosin

152
Q

what are uses of quinones?

A
  1. natural dye

2/ purgatives

153
Q

what are mechanisms involved with quinones?

A

hydroxylation
hydration
oxidation

154
Q

how are quinones derived?

A

OH groups oxidize aromatic compounds and form quinone

155
Q

describe the formation of quinones from benzene

A
  1. formation of dihydorxylactin
  2. formation of dihydroxybenzene
  3. oxidation to form quinone
156
Q

why are quinones used as purgatives?

A

they are able to induce loose bowels

157
Q

what are xanthones similar to? what is similar?

A

structurally similar to flavonoids and quinones

both have:

  • antioxidant properties
  • OH groups
  • able to remove free radicals and chelate metal ions
158
Q

solubility of xanthones?

A

water soluble

159
Q

color of xanthones

A

yellow

160
Q

common xanthone?

A

mangiferin

161
Q

what are melanins/melanoidins? where are they found?

A

brown colored pigments found in fruits, ve,g fungi and crustacean

162
Q

how are melanins formed?

A

from polymerization of phenolic compounds by PPO and Cu2+

163
Q

why do xanthones have antioxidant properties?

A

due to their aromatic ring structure and OH groups

164
Q

describe carmelization

A

occurs from heating CHO at high temp, causing oxidation to form breakdown products (caramelans, caramelens, caralemins)

165
Q

describe maillard rxn

A

occurs from non-enzymatic brwoning due to interaction of sugars with amino groups from AA during heating

166
Q

what are quinones polymerized to?

A

quinones are polymerized to melanidins or melanins

167
Q

what are the 3 carmelization colored products? what are the smallest and biggest products?

A
  1. caramelans (smallest)
  2. caramelens
  3. caralemins (biggest)
168
Q

what determines the intensity of the browning in the product?

A

depends on the size of product polymerized from quinones

169
Q

what does diacetyl cause in carmelization reactions

A

a volatile compound produced when heating sugar at high temp

responsible for nutty odor and flavor (caramel)

Food Chemistry 2 (4 decks)

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