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what attracts us to food?
- appearance : texture and color
- flavour: smell/odor and taste
- microbial load
- nutritive value
what are some natural food pigments?
- myoglobin & hemoglobin
- quinones and xanthones
- melanins and betalains
what are different food sources of natural food pigments?
- chlorophyll : fruits, vegetables
- heme : muscle foods
- carotenoids : eggs, fish, crustaceans, dairy products, fruits and vegetables
what is chlorophyll?
- green pigment found mainly in plants : fruits, vegetables, algae, seaweed
- has a blue-green color
- these organisms = photosynthetic + can use light energy to produce chemical energy (food)
- 5 membered ring
what are 2 types of chlorophyll?
- 1. Chlorophyll abright green
- CH3- methyl group in 1 of pyrole rings in "a"
- 2. Chlorophyll bdark green
- is replaced by a formyl group in "b" (CHO)
what do both types of chlorophyll have?
both chlorophylls have side chain 20-C alcohol (phytol) esterified to one of the pyrole rings
what is the molecular weight of chlorophyll?
what is the molecular weight of phytol?
300 (1/3 of chlorophyll)
what is phytol?
- phytol = fat soluble, H2O insoluble
- it is the portion of the molecule that makes chlorophyll fat soluble
- (dissolved in the fat of plastrols** in the plants)
what is the effect of the phytol group?
the molecules listed above are toxic to humans thus chlorophyll can act as a detoxicant antioxidant
- ↑ degree of unsaturation impacts free radical binding capacity to chlorophylls
- enable them to behave as antioxidants
- the hydrophilic nature of the phytol side chain enables chlorophyll to bind tightly (via non-covalent bonds) with other hydrophobic molecules
- polycyclic aromatic hydrocarbons
- heterocyclic amines
what are some pigments related to chlorophyll?
= dark green + H2
= bright green and H2
O insoluble but dull brown in color
O soluble but brown in color
what are some uses of chlorphyll?
- food colorant
- added to cosmetics and other personal hygiene products ex. mouth wash
- heat : cooking + blanking = formation of brown coloured products
- dehydration = color loss
whats the effect of processing on chlorophyll?
- cooking → pheophytins
- dehydration → blanching by photodegredation (lipoxidases)
- exposure to O2 + light → bleaching
- blanching → pheophytins and pheophobides
- irradiation → degradation by peroxydation
summary - chlorophyll
- chlorophyll is a plant pigment
- it is a tetrapyrolle compound
- it is green in color and fat soluble
- it is destroyed by heating under acidic conditions
- it is degraded by various enzymes such as chlorophyllase and lipoxidase
what is an enzyme treatment?
its a change in functional properties from fat soluble → H20 soluble
What are heme pigments?
- ex. myoglobin and hemoglobin
- responsible for red color of muscle
- complex molecules with protein part (global) and an essential non protein part (heme)
- both Mb and Hb are tetrapyrolle compounds
what the main differences between the myobglobin and hemoglobin?
- found in muscle
- about 1/4 smaller than hemoglobin
- Hemoglobinfound in blood vessels
- bigger than myoglobin
what are some similarities between myoglobin and hemoglobin?
- both hemoglobin and myoglobin are found in animals and are both H2O soluble
- both tetrapyrole compounds are similar to chlorophyll
what are some major food sources of myoglobin nd hemoglobin?
- meats: beef, pork, chicken
- single polypeptide chain
- 4 N's in the 4 pyrole molecule, covalently linked to central Fe atoms
- Fe also covalently linked to N in a histidine residue global (protein)
- Fe can bind electron pair donors (ex. O2, CO, CO2, CN)
what is oxymyoglobin?
- bright red color of fresh meats
- Fe present as ferrous (Fe2+) form
- Mb + O2 ↔ MbO2Mb (purple color; Fe2+)
- MbO2 (bright red; Fe2+)
what is metmyoglobin (Met-Mb)?
- brownish color (Fe3+)
- MbO2 ↔ Mb → Met-Mb
- MbO2 (bright red)Mb (purple)
- Met-Mb (brown)
what are the effects of handling and processing of meats?
- gradual oxidation, forming dark/brown color
- denature proteins: also oxidation of Fe2+ to Fe3+
- formation of dark color (as in barbecued meats - pigment formed knowns as hemichrome)
- Curing of meats
- with nitrites → red coloured nitrosomyoglobin
- cooking cured meats denatures the protein
- Fe2+ → Fe3+ (by oxidation)
- froms a brown product called nitrosohemichrome
- reducing agents may be used to reverse oxidation in meats
- (unacceptable ex. formation of sulfmyoglobin with SH- containing reducing agents)
Curing of meats
- a form of meat conservation by treatment with nitrites
- the nitrates have a lone pair of electrons to donate to Fe2+ in Mb to from a complex as nitrosomyoglobin
) + :NO ⇌ MbNO (Fe2+
/ nitrosomyoglobin /reddish color)
- addition of nitrites/nitrates to meats in primarily to curtail (stop/control) growth of harmful pathogen like clostridium
- the red color formation we associate that with cured meat products like salami, sausages, hot dogs, ham etc.
- when cured meats are cor lead**, there is also denaturation of the protein global and oxidation of Fe2+ → Fe3+
this is also accompanied by color change and the reddish brown to brownide and the product is known as nitrosohemichrome
summary of heme pigments
- heme pigments are of animal origin
- there are 2 types - Mb and Hb
- Mb = single polypeptide linked to 4 pyrole rings through a central Fe atoms
- Hb = 4 sub units and each subunit is equivalent to 1 Mb
- both Mb and Hb are tetrapyrolle compounds like chlorophylls
what are carotenoids pigments?
- present in plants, animals microorganisms
- responsible for yellow, orange and red orange in plants and animals
what are the major sources of carotenoids
- plants: fruits, vegetables, vegetable oils
- ex. tomatoes, carrots, peaches, papaya, canteloupe, water melon . peppers, oranges, palm oil
milk fat, egg yolk, butter, salmonids (ex. salmon, trout), crustacean species (ex. crab, lobster, shrimp, prawn)
fungi (mushrooms), yeasts (ex. Phaffia rhodozyma), algae
what are the structure of carotenoids?
- 5C compound - isoprene repeating unit
- may be cyclic of acyclic
- may be hydrocarbon exclusively (hydrocarbon carotenoids or carotenes) or may contain oxygen (oxy-carotenoids)
what are different hydrocarbon carotenoids a.k.a carotenes?
what is the most common hydrocarbon carotenoid?
- it gives 2 molecules of vitamin A on hydrolysis
- thus described as pro-vitamin A
what is α carotene?
- has the same molecular formula as β carotene
- but the α form is NOT symmetrical
- by hydrolysis = yields only 1 molecule of vitamin A in the body
what is lycopene?
- a major pigment in tomatoes and apricots
- lycopene is symmetrical
- unlike in α and β carotenes, the ring structures in lycopene are open → acyclic
- lycopene has no vitamin A activity
what are oxy-carotenoids?
- oxygen containing carotenoids
- common ones : lutein, canthaxanthin, astaxanthin, cryptoxanthin and zeaxanthin
what is lutein?
- and oxy-carotenoid
- found in : green leaves and yolk
- molecule is similar to β-carotene : its asymmetrical but rings are hydroxylated
- so has no vitamin A activity
what is canthaxanthin?
- an oxy-carotenoid
- present in microorganisms, plants and animals
- ex. mushroom, red pepper, brine shrimp and the flamingo
- commercially produced by chemical synthesis
- used as feed supplement for cultured salmonids and imitation seafood products
- has no Vitamin A activity
what are astaxanthin?
- an oxy-carotenoid
- major carotenoid pigment in salmonides and crustaceans, redfish, ocean perch/red snapper
- produced on a commercial scale by chemical synthesis
- more stable than canthaxanthin for use as colorant for fish flesh
- has no vitamin A activity
what is cryptoxanthin?
- an oxy-carotenoid
- major carotenoid pigment in peaches, yellow corn and egg yolk
- structure similar to β-carotene, except for presence of -OH group on 1 ring
- HAS vitamin A activity
what is zeaxanthin?
- an oxy-carotenoid
- widely distributed in nature
- major carotenoid in yellow corn and egg yolk
- similar structure to β-carotene, but has 2-OH groups in addition
- has no vitamin A activity
what are the effects of handling and processing?
- O2 and light = major cause of destruction
- not lost to cooking water
- destroyed by dehydration
summary - carotenoids
- yellow, orange, red-orange in color
- fat soluble and water insoluble
- present in plants, animals and microorganisms
- good food sources include crustacea, egg yolk, milk fat, fruits, vegetables and vegetable oils
- some have antioxidant and vitamin activity
- destroyed by exposure to light and dehydration and by lipoxygenases
what are anthocyanins?
- water soluble plant pigments
- impart red, blue and violet colors to various fruits and vegetables
- the basic structure is the flavilium ion (a.k.a anthocyanidin or aglycone)are glycosides (or sugar esters) of anthocyanidin
- can be monoxides (1 sugar), biosides (2 sugars) and triosides (3 sugars)
what are different sugars of anthocyanin?
what are common athocyanins and their distribution in fruits and vegetables
- Cy: orange-red color
- found in: apples, cherries, oranges, plus, raspberries and cabbage
- Dp: blue-red color
- found in: grapes and oranges
- Mv: blue red color
- found in: blue grapes
- Pg: orange color
- found in : strawberries
- Pn: orange-red color
- found in: cherries and plums
- Pt: blue red color
- found in: blueberries
what is the effect of substituent groups of color on anthocyanin?
- ↑ hydroxyl (-OH) content = ↑ in blue color
- ↑ methoxy (-OCH3) content = ↑ in redness
what are the effects of handling and processing of anthocyanins?
- acidic conditions change pigments to red color
- alkaline conditions change pigments to shades of blue or colorless
- Effect of cooking
- loss to cooking water
- Decolonized by additives
- sulphites, SO2, ascorbic acid, H2O2
- form purple or gray colors with metals
- High temperatures
- cause destruction of anthocyanin pigments
- ex. spray drying
- High sugar content + presence of O2
- enhance destruction of anthocyanins
- Colorless forms of anthocyanins may undergo oxidation in the presence of O2 to form coloured products
- ex. "pinking" of canned pears
what are the effects of enzymes on anthocyanins?
- Glucosidases or anthocyanases
- remove sugars from the anthocyanin
- thus destabilizing the molecule
- causing loss of color
deleterious effects of these enzymes curtailed by microwave blanching***
what are flavanoids?
- H2O soluble pigments found in plants and microorganisms
- most absurd polyphenols in the diet
- a.k.a antioxidants - they are glycosides with a benzopyrone nucleus
- most common sugar - rutinose
- they give certain fruits, vegetables and herbs their dark red, blue and purple colors
- many are antioxidants
how are flavonoids classified?
- double bond at 2:3 positions
- benzene ring at 3 position
- -OH group at 3 position
- no 2x bond at 2:3 position
- -OH group at 3 position; no 2x bond at 2:3
what are some common properties of flavonoids?
- polyphenolic structure
- substrates browning reactions
- may be involved in other discoloration reactions in foods
- ex. may bind Fe in foodstuffs to form blue/green colors
- chelating agent
- antioxidant/free radical scavenger
- pro-vitamin C activity
what are betalaines?
- H2O soluble plant pigments
- synthesized by the aa tyrosine + dihydroxyphenylalanine (DOPA) as intermediate
- glycosides (glucose commonly present)
how are betalaines classified?
into 2 groups based on color differences:
- betacyanins (ex. betanin) → reddish violet
- betaxanthins (ex. vulgaxanthin) → yellow + orange
where are betalaines mostly found?
found mostly in beet plants
what are betalaines used for?
- extensively used as a food colorant because of its intense color
- also used in beverage and powdered mixes
what are the effects of handling and processing of betalaines?
- degraded by thermal processing (affected by light and heat/temeprature)
- some color lost to cooking water due to ↑ solubility in H2O
what are tannins?***
- complex plant pigments
- with varying degrees of solubility in H2O based on size differences
- small ones = more H2O soluble
- wide range of colors - from colourless to yellow or brown
- common ones: gallic acid and ellargic acid
what are 2 types of tannins?*****
- 1. Hydrolysable tannins
- undergo hydrolysis when heated in H2O to form sugars and phenolic compounds
- 2. Condensed or non-hydrolysable tannins
- imp. in teas
- cause proteins in cheeks to precipitate
- not hydrolyzed
- remain to cause astringency to products such as tea
what are tannins used for?
- tannins contribute to astringency in foods
- participate in enzymatic browning reactions
what are quinones?
- H2O soluble pigments
- present in plants and microorganisms
- range in color = from yellow → black
- common ones : emodin and spinulosin
what are quinones used for?
- extensively used as natural dyes for textile because of their intense dark colors
- can also cause irritation in the gut to make us "run" if consumed in ↑ quantities and thus is used as a purgative
what are xanthones?
- plant pigments with structural resemblance to flavonoids and quinones
- ex. glycosides
- H2O soluble and yellow in color
- common one: mangiferin
- because of their phenolic nature, the can serve as substances for enzymatic browning
what are phytocyanins?
- blue coloured pigments
- found mainly in microorganisms
- have ↑ antioxidant potency because of their free radical scavenging capacity
- ex. in blue green algae and cyanobacteria
what are phytoerythrins?
- red coloured pigments
- found in microorganisms
- ex. in red algae
what are melanins or melanoidins?
- brown coloured pigments
- found in fruits and vegetables, fungi (mushrooms) and crustacea
- formed from oxidation of phenolic compounds (tyrosine) by PPO
- O2 is a co-reactant in the reaction
- Cu++ is required as a cofactor for PPO
- formation of melanins desirable in certain foods, but undesirable in others
- protect against oxidation**
- they absorb free radicals**
- ↓ (PPO)
- ↓ (PPO)
- ↓ (polymerisation)
what are 2 types of non-enzymatic browning?
Caramelization and Maillard reaction
what is caramelization?
- oxidation of sugars @ ↑ temperature
- reaction leads to brown coloured products + volatile compounds (ex. diacetyl)
- responsible for nutty falcons in caramelized products
what is the maillard reaction?
- series of chemical events
- take place when amino groups from aa, proteins, peptides and amines are reacted with carbohydrates (sugars) @ ↑ temperature
- reaction leads to brown coloured products + formation of flavor compounds
- some Maillard reactions have antioxidant properties while others are suspected to be potential toxicants