Pigments: Chlorophyll, Heme, Carotenoids Flashcards
4 attributes linked to food quality
- which one is the easier to “apply”
- appearance
- flavor (taste, smell, texture)
- Safety
- nutritional value
- APPEARANCE!
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 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!
how to distinguish chlorophyll a and b?
through absorption spectra –> have different peaks
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?
- 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
What happens when enzyme chlorophyllase acts on pheophytin?
- pheophytin –> pheophorbide
- phytol is removed –> pheophorbide is water soluble
- olive brown to olive brown
how can chlorophyll derivatives become colorless products? (2)
- pheophorbide can be oxidized by lipoxygenases (LOX) to form a colorless product
- also, low temperatures cause loss of moisture/dehydration –> activates LOX –> causes bleaching
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 ___________
- pheophytins and pheophorbides
- bleaching by photodegradation (LOX)
- O2 and light
- pheophytins and pheophorbides
- degradation by peroxidation
- how to make chlorophyll derivatives? why?
- uses of chlorophyll derivatives (3)
- 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
why can chlorophyll derivatives act as chelating agents?
- because unsaturated bonds allow to bind metal ions that promote oxidation (ie Cu, Fe and Zn)
how to cook spinach without color loss? (3)
- add baking soda –> alkali
- add lots of water to dilute acid
- keep pot open bc organic acid will evaporate bc they are volatile
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
- 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
- 2 main types of heme pigments?
- of plant or animal origin?
- responsible for ____ colors in ______ foods (4 examples)
- myoglobin (muscle meat) and hemoglobin (blood vessels)
- animal
- red in muscle foods (beef, pork, poultry, fish)
- what are heme pigments generally comprised of? (2)
- forms a single _________ chain with MW of ?
- Mb and Hb are _________ (base structure ish) compounds
- protein part (globin)
- essential non-protein part (heme)
- single polypeptide chain with MW of 16.4 kDa
- tetrapyrole
myoglobin structure:
- single ________ chain
- 4 _________ covalently linked to central __A__ atom through 4 ___B__
- ___A___ atom covalently linked to ___B__ in a __________ in ________
- 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)
Iron: coordination # of ____
- what are the 6 things it coordinates with?
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
why can hemoglobin bind more oxygen than myoglobin? (2 )
- hemoglobin = 4 x myoglobin –> much more capacity
- Cooperative binding! binding of O2 to 1 molecule enhances binding of O2 to other subunits
does myoglobin or hemoglobin reach O2 saturation first? Keyword for both?
myoglobin! (hyperbolic) –> very fast O2 saturation
VS hemoglobin (sigmoidal)
When myoglobin binds O2 = ___________
- binding is reversible/irreversible
- represents what color of fresh meats?
- Fe present as what form?
- oxymyoglobin
- reversible
- bright red color of fresh meat
- Fe 2+
Color + oxidation state of Fe:
- oxymyoglobin
- deoxymyoglobin
- carboxymyoglobin
- metmyoglobin
- oxymyoglobin: bright red, Fe2+
- deoxymyoglobin: purple: Fe2+
- carboxymyoglobin: bright red: Fe2+ (Deoxymyoglobin + CO)
- metmyoglobin: brown ish, Fe3+
what happens to oxymyoglobin when you cook it? (3)
- oxymyoglobin becomes what?
- oxidation of Fe2+ to Fe3+ (ferrous to ferric)
- globin denatures –> easier to digest
- formation of dark brown color (pigment known as hemichrome) ie in barbecued meats
- oxymyoglobin becomes metmyoglobin
what happens when you store meat and it turns brown?
- how can we prevent? + 3 disadvantages ish of this method
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
curing meats:
- primary goal? bonus?
- using what? in what form?
- what does it produce?
- what color?
- 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)
what does cooking of cured meats do? (3)
- denatures protein
- Fe2+ oxidized to Fe 3+
- brown product known as nitroso-hemichrome is produced
are heme pigments stable? can they be used in natural form as food colorant?
no! cannot be explored as food colorant
how to make us of unstable heme pigments?
- 3 benefits
- 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
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)
- 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
carotenoid pigments:
- what colors (3)
- found in (3)
- water soluble or insoluble?
- most carotenoids are in trans or cis form?
- yellow, orange, red-orange
- plants, animals, microorgs
- insoluble! –> soluble in solvent like hexane, acetone and fats/oils
- trans –> when you cook, they become cis
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?
- 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
examples of plant sources of carotenoids (3 big categories + 8 examples ish)
- fruits, vegetables, vegetable oils
- oranges, tomatoes, peaches, papaya, cantaloupe, watermelon, peppers, carrots, pumpkins
- palm oil!!!
animal sources of carotenoid? (5)
milk fat, egg yolk, butter, salmonids, crustacean (lobster, shrimp, crab)
microbial sources of carotenoids (3)
- fungi (mushrooms)
- yeasts (Phaffia rhodozyma)
- all algae (red, rhodophyta)
how to produce carotenoids through microbial fermentation?
- using what microbe?
- 5 key requirements
- 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)
2 types of carotenoids?
- 2 types of structures
- hydrocarbon carotenoids (only hydrocarbon) OR oxy-carotenoids/ oxygenated carotenoids / xanthophylls (contain oxygen)
- cyclic or acyclic/linear
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?
- isoprene! 5C
- terpenes –> terpenoids
- 40C
what are the 3 production methods of carotenoids for commercial applications?
- which one is more used? why? (4)
- 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
examples of hydrocarbon carotenoids (3)
- lycopene
- a-carotene
- b-carotene
similarities and difference between b-carotene and lutein?
- b-carotene –> hydrocarbon carotenoid
- lutein –> oxy-carotenoid –> 2 hydroxyl groups on rings
- BOTH have 40 C and are symmetrical
difference between a-carotene and b-carotene?
- 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
if a carotenoid can yield vit A –> called ?
- if cannot?
- can furnish vit A –> pro-vitamin A carotenoids
- VS non pro-vitamin A carotenoids
lycopene = major pigment in (2)
- symmetrical or asymmetrical?
- has vit A activity? why?
- tomatoes and apricots
- symmetrical but NO ring structures –> acyclic
- NO vitamin A activity
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?
- canthaxanthin and astaxanthin
- pigment deposits in fat of fish
- astaxanthin = more stable VS canthaxanthin loses intense color through storage + through cooking water
2 sources of oxygenated carotenoids?
- green leaves
- egg yolk
what enzyme is used to hydrolyze carotenoids to obtain vit A molecules?
carotenoid oxygenase enzyme
symmetric vs asymmetric synthesis of carotenoids
- symmetric: uses even number of carbons: C16 + C8 + C16 = C40
VS asymmetric: C25 + C15 = C40
how can carotenoids be synthesized from scratch in body? (3 steps ish)
- condensation of acetyl-CoA with acetoacetyl-coA –> forms HMG-CoA (major intermediate)
- HMG-CoA proceeds via mevalonate pathway (using HMG-CoA reductase + other enzymes) to form isopentenyl-5-pyrophosphate (PP)
- PP may undergoe a series of polymerization reactions to form squalene and related compounds like carotenoids and cholesterol
4 industrial applications of carotenoids
- food and feet colorant/additive: candies, bevs, baked goods…
- food fortification to enhance nutritional value: some carotenoids have vit A activity upon hydrolysis (ie milk, butter, margarine, rice)
- biomedicine and pharmaceuticals (antioxidant, anti-cancer, anti-aging properties)
- cosmetics (anti-aging + coloring)
why are carotenoids used as anti-cancer and anti-aging properties?
- 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
- are carotenoids lost to cooking water?
- exposure to (3) causes destruction + extra
- 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
CAROTENOIDS SUMMARY:
- 3 colors
- soluble in what?
- present in (3)
- good food sources include (6)
- some have __________ and ________ activity
- destroyed by (3)
- 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
