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Food Chemistry 2 > Pigments: Chlorophyll, Heme, Carotenoids > Flashcards

Pigments: Chlorophyll, Heme, Carotenoids Flashcards

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1
Q

4 attributes linked to food quality
- which one is the easier to “apply”

A
  1. appearance
  2. flavor (taste, smell, texture)
  3. Safety
  4. nutritional value
    - APPEARANCE!
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2
Q

Chlorophyll
- what is it?
- role?
- found in what (4)
- how many types? which are the most abundant?
- structure? difference btw types?
- water or fat soluble?

A
  • a green pigment!
  • carry out photosynthesis!
  • green leafy veg + fruits + bacteria + all algae
  • 6 different types (abcdef) –> a and b most common
  • 4 pyrrole units linked together by methylene bridge (= tetrapyrol) + central Mg atom + esterified to a 20 carbon atom called phytol (much bigger than the rest of the molecule = entire molecule is hydrophobic!)
  • substituent groups on sides of pyrrole units are different
  • fat soluble!
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3
Q

how to distinguish chlorophyll a and b?

A

through absorption spectra –> have different peaks

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4
Q

naturally occurring chlorophyll are highly ___________ due to (what) in (what). During processing, chlorophyll can undergo changes in ___________ and ___________.
1. when phytol group is removed by enzyme ___________, what happens?
2. When chlorophyll is heated, what happens?

A
  • highly unstable due to other constituents in food material.
  • changes in solubility and coloration
    1. chlorphyllase –> residual material is chlorophyllide –> water soluble! (bc no phytol anymore) + imparts greenish color to water
    2. heat treatment combined with organic acids naturally present in plant material –> removes central Mg atom to form brownish color product called pheophytin. Pheophytin still has phytol chain = water insoluble
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5
Q

What happens when enzyme chlorophyllase acts on pheophytin?

A
  • pheophytin –> pheophorbide
  • phytol is removed –> pheophorbide is water soluble
  • olive brown to olive brown
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6
Q

how can chlorophyll derivatives become colorless products? (2)

A
  • pheophorbide can be oxidized by lipoxygenases (LOX) to form a colorless product
  • also, low temperatures cause loss of moisture/dehydration –> activates LOX –> causes bleaching
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7
Q

Effects of processing on chlorophylls:
- cooking produces (2)
- dehydration causes ___________ by ___________ (which enzyme)
- exposure to _____and ______ causes bleaching
- blanching results in formation of (2)
- irradiation leads to ___________ by ___________

A
  • pheophytins and pheophorbides
  • bleaching by photodegradation (LOX)
  • O2 and light
  • pheophytins and pheophorbides
  • degradation by peroxidation
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8
Q
  • how to make chlorophyll derivatives? why?
  • uses of chlorophyll derivatives (3)
A
  • chlorophyll = highly labile and unsuitable for practical uses –> convert it to metal derivatives (ie Cu-chlorophyllin) = more stable + retains green color in finishied product
  • dyes for foods, feeds and textiles + cosmetics/mouthwash + chelating agents
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9
Q

why can chlorophyll derivatives act as chelating agents?

A
  • because unsaturated bonds allow to bind metal ions that promote oxidation (ie Cu, Fe and Zn)
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10
Q

how to cook spinach without color loss? (3)

A
  • add baking soda –> alkali
  • add lots of water to dilute acid
  • keep pot open bc organic acid will evaporate bc they are volatile
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11
Q

SUMMARY:
- chlorophylls are the ______ _________ pigments
- found in (2)
- several forms (how many?), but major ones are (2)
- all are ________
- ____ soluble by virtue of their ______ side chain
- are destroyed by _____ _______ conditions

A
  • green photosynthetic pigments
  • plants and microorganisms
  • a, b, c, d –> major ones are a and c
  • tetrapyrroles
  • fat soluble –> phytol side chain
  • heat acidic conditions
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12
Q
  • 2 main types of heme pigments?
  • of plant or animal origin?
  • responsible for ____ colors in ______ foods (4 examples)
A
  • myoglobin (muscle meat) and hemoglobin (blood vessels)
  • animal
  • red in muscle foods (beef, pork, poultry, fish)
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13
Q
  • what are heme pigments generally comprised of? (2)
  • forms a single _________ chain with MW of ?
  • Mb and Hb are _________ (base structure ish) compounds
A
  • protein part (globin)
  • essential non-protein part (heme)
  • single polypeptide chain with MW of 16.4 kDa
  • tetrapyrole
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14
Q

myoglobin structure:
- single ________ chain
- 4 _________ covalently linked to central __A__ atom through 4 ___B__
- ___A___ atom covalently linked to ___B__ in a __________ in ________

A
  • single polypeptide chain
  • 4 pyrols linked to central iron atom through 4 nitrogens
  • iron also covalently linked to nitrogen in a histidine in a globin (protein)
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15
Q

Iron: coordination # of ____
- what are the 6 things it coordinates with?

A

6 pairs of lone e-!
- 4 from N in pyrol rings
- 5th pair for N from histidine in globin protein
- 6th pair: can bind any electron pair donor (O2, CO, CO2, CN, NO) –> whole basis for fct of O2 as e- transporter –> O2 can bind reversibly to 6th coordination position of the iron

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16
Q

why can hemoglobin bind more oxygen than myoglobin? (2 )

A
  • hemoglobin = 4 x myoglobin –> much more capacity
  • Cooperative binding! binding of O2 to 1 molecule enhances binding of O2 to other subunits
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17
Q

does myoglobin or hemoglobin reach O2 saturation first? Keyword for both?

A

myoglobin! (hyperbolic) –> very fast O2 saturation
VS hemoglobin (sigmoidal)

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18
Q

When myoglobin binds O2 = ___________
- binding is reversible/irreversible
- represents what color of fresh meats?
- Fe present as what form?

A
  • oxymyoglobin
  • reversible
  • bright red color of fresh meat
  • Fe 2+
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19
Q

Color + oxidation state of Fe:
- oxymyoglobin
- deoxymyoglobin
- carboxymyoglobin
- metmyoglobin

A
  • oxymyoglobin: bright red, Fe2+
  • deoxymyoglobin: purple: Fe2+
  • carboxymyoglobin: bright red: Fe2+ (Deoxymyoglobin + CO)
  • metmyoglobin: brown ish, Fe3+
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20
Q

what happens to oxymyoglobin when you cook it? (3)
- oxymyoglobin becomes what?

A
  1. oxidation of Fe2+ to Fe3+ (ferrous to ferric)
  2. globin denatures –> easier to digest
  3. formation of dark brown color (pigment known as hemichrome) ie in barbecued meats
    - oxymyoglobin becomes metmyoglobin
21
Q

what happens when you store meat and it turns brown?
- how can we prevent? + 3 disadvantages ish of this method

A

Fe2+ gradually oxidizes to become Fe3+ (oxymyoglobin becomes metmyoglobin)
- use reducing agent (ie vit C) to convert brown to red again –> not recommended practice bc you’re fooling the consumer + forms greenish tint on side of meat + forms sulfmyoglobin with -SH containing reducing agents

22
Q

curing meats:
- primary goal? bonus?
- using what? in what form?
- what does it produce?
- what color?

A
  • 1° goal = control growth and proliferation of clostridium
  • bonus: added color and flavor changes
  • using nitrites! (ie sausages) in sodium or potassium nitrite
  • first converts to nitrous acid in water (very unstable) –> then forms nitric acid and nitric oxide (NO) which binds to 6th coordinate position of Fe to form nitroso-myoglobin
  • nitroso-myoglobin gives pink color to cured meats (salami, bologna) (Mb-NO)
23
Q

what does cooking of cured meats do? (3)

A
  1. denatures protein
  2. Fe2+ oxidized to Fe 3+
  3. brown product known as nitroso-hemichrome is produced
24
Q

are heme pigments stable? can they be used in natural form as food colorant?

A

no! cannot be explored as food colorant

25
Q

how to make us of unstable heme pigments?
- 3 benefits

A
  • convert to metalloporphyrins (ie Zn protoporphytin)
  • becomes stable to oxidation in storage and processing + used to color imitation meats derived from plants and fish sources + avoids need to use nitrites as colorant
26
Q

summary of heme pigments:
- heme pigments are of ________ origin
- primary function is _____ transport for _______ _______
- 2 major ones?
- one of them is a single ________ linked to (#) ________ rings through a central ______ atom
- the bigger one of them comprises of (#) ___________ sub-units, each subunit equivalent to 1 _______
- thus, molecules have (2 parts)

A
  • animal
  • O2 transport for energy generation
  • Mb and Hb
  • Mb: single polypeptide chain linked to 4 pyrrole rings through a central iron atom
  • Hb –> 4 polypeptide subunits –> each = 1 Mb
  • protein part and essential non-protein part
27
Q

carotenoid pigments:
- what colors (3)
- found in (3)
- water soluble or insoluble?
- most carotenoids are in trans or cis form?

A
  • yellow, orange, red-orange
  • plants, animals, microorgs
  • insoluble! –> soluble in solvent like hexane, acetone and fats/oils
  • trans –> when you cook, they become cis
28
Q

carotenoids are highly ________ = prone to ___A_____
- in nature, they are commonly complexed with ________ –> offer some protection against ______A______
- however, how does being complexed affect the pigment? –> what can fix this?

A
  • highly unsaturated = prone to oxidation
  • with proteins –> protection against oxidation
  • pigment is not readily available –> must be released to be able to exert normal functions (as antioxidant, chelating agents)
  • processing and pretreatment techniques (ie grinding, cooking) disrupts protein complex –> pigment is released to elicit max potential
29
Q

examples of plant sources of carotenoids (3 big categories + 8 examples ish)

A
  • fruits, vegetables, vegetable oils
  • oranges, tomatoes, peaches, papaya, cantaloupe, watermelon, peppers, carrots, pumpkins
  • palm oil!!!
30
Q

animal sources of carotenoid? (5)

A

milk fat, egg yolk, butter, salmonids, crustacean (lobster, shrimp, crab)

31
Q

microbial sources of carotenoids (3)

A
  • fungi (mushrooms)
  • yeasts (Phaffia rhodozyma)
  • all algae (red, rhodophyta)
32
Q

how to produce carotenoids through microbial fermentation?
- using what microbe?
- 5 key requirements

A
  • using phaffia rhodozyma (a type of yeast)
  • key requirements are:
    1. C and N source (usually cheaply furnished by agricultural waste or biomass)
    2. minerals like Fe, Mg, Cu, Co and Zn
    3. light
    4. temp range of 25-29°C
    5. air (O2)
33
Q

2 types of carotenoids?
- 2 types of structures

A
  • hydrocarbon carotenoids (only hydrocarbon) OR oxy-carotenoids/ oxygenated carotenoids / xanthophylls (contain oxygen)
  • cyclic or acyclic/linear
34
Q

what is the base unit of carotenoids? –> how many carbons?
- polymers of this unit are called what? –> so carotenoids are often called _________
- how many carbons are carotenoids generally?

A
  • isoprene! 5C
  • terpenes –> terpenoids
  • 40C
35
Q

what are the 3 production methods of carotenoids for commercial applications?
- which one is more used? why? (4)

A
  • naturally occurring –> obtain by simple extraction using solvents + purify to remove coextracted compounds
  • produced by chemical synthesis (but can lead to harmful waste products/residuals)
  • produced by microbial fermentation (ie yeast) –> cheaper, small space needed, faster/higher yield, less environmental and safety concerns
36
Q

examples of hydrocarbon carotenoids (3)

A
  • lycopene
  • a-carotene
  • b-carotene
37
Q

similarities and difference between b-carotene and lutein?

A
  • b-carotene –> hydrocarbon carotenoid
  • lutein –> oxy-carotenoid –> 2 hydroxyl groups on rings
  • BOTH have 40 C and are symmetrical
38
Q

difference between a-carotene and b-carotene?

A
  • both have same molecular formula
  • a-carotene: asymmetrical (double bond placement in ring)–> only yields 1 vit A molecule upon hydrolysis
  • b-carotene –> splits into 2 vit A molecules
39
Q

if a carotenoid can yield vit A –> called ?
- if cannot?

A
  • can furnish vit A –> pro-vitamin A carotenoids
  • VS non pro-vitamin A carotenoids
40
Q

lycopene = major pigment in (2)
- symmetrical or asymmetrical?
- has vit A activity? why?

A
  • tomatoes and apricots
  • symmetrical but NO ring structures –> acyclic
  • NO vitamin A activity
41
Q

what are the 2 chemically synthesized carotenoid pigments that is added to the feed of salmon and trout?
- how does the color stay in the fish?
- which one is more stable?

A
  • canthaxanthin and astaxanthin
  • pigment deposits in fat of fish
  • astaxanthin = more stable VS canthaxanthin loses intense color through storage + through cooking water
42
Q

2 sources of oxygenated carotenoids?

A
  • green leaves
  • egg yolk
43
Q

what enzyme is used to hydrolyze carotenoids to obtain vit A molecules?

A

carotenoid oxygenase enzyme

44
Q

symmetric vs asymmetric synthesis of carotenoids

A
  • symmetric: uses even number of carbons: C16 + C8 + C16 = C40
    VS asymmetric: C25 + C15 = C40
45
Q

how can carotenoids be synthesized from scratch in body? (3 steps ish)

A
  1. condensation of acetyl-CoA with acetoacetyl-coA –> forms HMG-CoA (major intermediate)
  2. HMG-CoA proceeds via mevalonate pathway (using HMG-CoA reductase + other enzymes) to form isopentenyl-5-pyrophosphate (PP)
  3. PP may undergoe a series of polymerization reactions to form squalene and related compounds like carotenoids and cholesterol
46
Q

4 industrial applications of carotenoids

A
  1. food and feet colorant/additive: candies, bevs, baked goods…
  2. food fortification to enhance nutritional value: some carotenoids have vit A activity upon hydrolysis (ie milk, butter, margarine, rice)
  3. biomedicine and pharmaceuticals (antioxidant, anti-cancer, anti-aging properties)
  4. cosmetics (anti-aging + coloring)
47
Q

why are carotenoids used as anti-cancer and anti-aging properties?

A
  • bc of highly unsaturated nature, carotenoids can act as chelating agents and free radical scavengers –> used in biomedical and foods applications for prevention of certain cancers + slow down aging
48
Q
  • are carotenoids lost to cooking water?
  • exposure to (3) causes destruction + extra
A
  • no! because water insoluble
  • dehydration, air/O2, light –> destruction by oxidation
  • when you freeze and dehydrate –> LOX can be activated –> promotes oxidation and color loss/bleaching
49
Q

CAROTENOIDS SUMMARY:
- 3 colors
- soluble in what?
- present in (3)
- good food sources include (6)
- some have __________ and ________ activity
- destroyed by (3)

A
  • orange, yellow, red-orange
  • soluble in fat, insoluble in water
  • plants, animals and microorgs = ubiquitous
  • crustaceans, milk fat, egg yolk, fruits, vegetables, vegetable oils
  • antioxidant and vit A activity
  • enzymes, light and dehydration

Food Chemistry 2 (7 decks)

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