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
