Food Chem 2- Pigments
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What are pigments?
Substances that add color to compounds/products
What are some food sources of pigments?
- Chlorophyll (fruits, vegetables)
- Heme (muscle food)
- Carotenoids (eggs, fish, crustaceans, dairy products, fruits and vegetables)
- Anthocyanins (fruits, vegetables, microorganisms)
- Flavanoids (fruits, vegetables, microorganisms)
- Melanins (shellfish, dried fruits and vegetables, microorganisms
What is chlorophyll?
- Green color
- Found in plants, green algae, bacteria
- Methylene bridges to form a tetrapyrol ring structure
- 1 pyrol ring esterified to long chain hydrocarbon alcohol known as phyto
- Another of the rings is esterified to methanol
- Several different chlorophylls, predominant ones are 'a' and 'b'
What is the different between chlorophyll-a and chlorophyll-b?
In chlorophyll-b, the CH3- group at position C-3 of chlorophyll-a is replaced by a formyl group
What causes color loss in chlorophyll and how?
Irradiation of foods form free radicals can cause peroxidation of the unsaturated bonds in chlorophyll and cause color loss
Where is chlorophyll obtained commercially?
Chlorophyll is obtained commercially from afalfa and spirallina for use as colorant for food beverages, cosmetics, drugs, ertc, however it is unstable and the green color is lost readily
How is chlorophyll made more stable as a colorant?
When produced complexed with Ca, chlorophyll becomes more stable for use as a colorant
What are the two forms Ca exits in the blood?
- Complexed with a protein to form ceridoplasmin
- Free Ca++ that binds to albumin- excess free Ca generates free radicals that prouce reactive oxygen species (ROS) such as superoxidase. These species can cause damage to tissues and biomolecules in the body
How does cooking effect chlorophylls?
How does dehydration effect chlorophylls?
Bleaching by photodegredation (lipoxidase)
How dos exposure to O2 effect chlorophylls?
How does blanching effect chlorophylls?
Produces pheophytins and pheophobides
Where are heme pigments found?
Found exclusively in animals- red meats and other muscle foods
What is myoglobin?
Single polypeptide with central atom (Fe)
What is the hemoglobin structure?
4 myoglobins assembled together
What is the function of hemoglobin and myoglobin?
Function as O2 carriers
What is the central atom of heme pigments?
What happens to heme pigments during the storag and cooling of meats?
- Fe2+ gradually oxidizes to Fe3+ and some protein may be denatured
- Oxidation of iron in meats is accompanied by a color change from purplish/bright red to a brownish color
What does iron uptake depend on?
- Iron uptake depends on the oxidation number
- Fe2+ is absorbed more readily than Fe3+
What is the difference in nutrition of well cooked meaasts vs not well cooked meats?
Well cooked meats have more digestible proteins and little or no microbial load; however the Fe3+ is less readily absorbed
What is curing of meats?
- Involves using nitrates or nitrites to preserve meats
- Adds color to meats
- To control growth and proliferation of clostridium
- Nitroso myoglobin (Mb-NO) - red in color
What is the brown colored product formed from cooking meat?
What is oxymyoglobin?
- Bright red color of fresh meats
- Fe pesent as ferrous (Fe2+) form
- Mb + O2 --> MbO2
- Mb (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 is similar between heme pigments and tetrapyrolle?
Both Mb and Hb are tetrapyrolle compounds like chloropyll
Where are carotenoids found?
What color are carotenoids?
Responsibe for bright red, orange and yellow
What is the commercial source for carotenoid pigments?
How are carotenoids derived?
All carotenoids derived from 5 carbon compound known as isoprene
Why do carotenoids act as antioxidants?
They have a high degree of unsaturation which enables them to act nas antioxidants by absorbing free radicals or deactivating reactive oxygen species
What are the 2 different types of carotenoids?
- Oxygenated hydrocarbon
What happens when beta-carotene is hydrolyzed?
Forms 2 molecules of vitamin A
What happens to carotenoids when cooked?
- When it is uncooked, the pigments exist predominantly in the trans-from; when it is cooked, the molecules assume the cis-form predominantly
- Cooking also renders the pigment more absorbable
How does vitamin A help us see?
Vitmain A (aka retinol) can bind to opsin (a protin in the eye) to form zhodopsin which enables us to distinguish light and dark
What happens to carotenoids in high temperature processing?
High temperature processing can cause destruction of the pigment
What happens to carotenoid pigments in dehydration?
Dehydration conditions (such as freezing) enhance the activity of the naturally present enzymes lipoxidases that can cause bleaching of the pigment
What is lycopene?
- A major pigment in tomatoes and apricots
- Lycopene is symmetrical, but unlike alpha- or beta-carotene, the ring structures in lycopene are open
Why does shellfish change color when cooked?
- Carotenoids in crustaceans are complexed with proteins to form carotenoprotein complexes
- The proteins offer protection to the pigments
- During cooking, the protein is either denatured, or disloged from the pigment which results in color change
What is lutein?
- Found in green leaves and egg yolks
- Molecule is similar to alpha-carotene- asymmetrical, but rings are hydroxylated; so has no vitamin A activity
What is canthaxanthin
- Present in microorganisms, plants and animals (mushroom, red pepper, brine shrimp, and flamingos)
- Commercially produced by chemical synthesis
- Used as feed supplement for cultured salmonids and imitation seafood products
- Has no vitamin A activity
What is astaxanthin
- Major carotenoid pigment in salmonids and crustaceans; also 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?
- Major carotenoid pigment in peaches, yellow corn and egg yolk
- Structure similar to alpha-crotene, except for presence of -OH group on one ring
- No vitamin A activity
What is Zeaxanthin?
- Widely distributed in nature
- Major carotenoid in yellow corn and egg yolk
- Cimilar structure to beta-carotene, but has 2-OH goups in addition
- No vitamin A activity
How does handling and processing effect carotenoids?
- O2 and light- major cause of destruction
- Not lost to cookin water
- Destroyed by dehydration
What color are anthocyanins?
Red, blue and violet colors
Are anthocyanins water soluble?
What is the basic structure of anthocyanins?
What is a flavilium ion?
- Basic structure of anthocyanins
- Comprises of a a pyrilium ion linked with 2 benzne rings
What makes an anthocyanin more bluish or reddish?
High -OH content tends to make a molcule more bluish while high methoxy content makes it reddish
How do sugars effect anthocyanins?
- Anthocyanins are sugar esters of anthocyanidins
- Water solubility increases with sugar content
What is a monoside?
Anthocyanidin with 1 sugar
What are biosides?
Anthodcyanidins esterified with 2 sugars (either 1 dissaccharide, or 2 monosaccharides)
What are triosides?
Anthocyanidin esterified with 3 sugars (either 1 disaccharide + 1 monosaccharide, or 2 monosaccharides)
Why are anthocyanins lost in cooking?
High solubility in water
How does high sugar content effect anthocyanins?
High sugar content can cause color changes via glycosylation of the -OH groups on the flavylium ion
How does pH affect anthocyanins?
- pH changes can cause changes in color of the piGment by the influence of pH on -OH and -CH3 groups
- Acidic conditions change pifments to red color
- Alkaline conditions change pigments to shades of blue or colorless
Which additives cause color change in anthocyanins?
Additives such as sulfites, ascorbic acid, H2O2 can cause color loss in anthocyanins
How do anthocyanins effect enzymatic browning?
Because of their phenolyc structure, they can serve as substrates for enzymatic bowning in the presence of O2
Where is cyanidin found?
- Orance-red color
- Found in apples, cherries, oranges, plums, raspberries and cabbage
Where is delphinidin found?
- Blue-red color
- Found in grapes and oranges
Where is malvindin found?
- Blue-red color
- Blue grapes
Where is pelargonidin found?
- Orange color
- Found in strawberries
Where is peonidin found?
- Orange-red color
- Found in cherries and plums
Where is petunidin found?
- Blue-red color
- Found in blueberries
How do metals effect anthocyanins?
Form purple grey colors
How are anthocyanins effected by temperature?
High temperatures cause destruction of anthocyanin pigments (spray drying)
How does sugar effect anthocyanins?
Hgih sugar content and the presence of O2 enhance destruction of anthocyanins
What causes 'pinking' of canned pears?
Colorless forms of anthocyanins may undergo oxidatiom in the presence of O2 to form colored products
How do glucosidases effect anthocyanins?
- Glucosidases or anthocyanases nremove the sugars from anthocyanins, thus destabilizing the molecule and causing loss of color
- Deleteriouis effects of these enzymes curtailed by microwave blanching
What are flavonoids?
- H2O- soluble pigments found in plants and microorganisms
- Most abundant polyphenols in the diet
- aka anthoxanthins (glycosides with a benxopyrone nucleus)
- Most common sugar- rutinose
- Many are antioxidants
What is the general structure of flavonoids?
Glycosides with a benzopyrone ring
What are the 5 classifications of flavonoids?
- Flavones (double bond at 2:3 position)
- Isoflavones (Benzene ring at 3 position)
- Flavonols (Flavonols (-OH group at 3 position; no dbl bond at 2:3)
- Flavonones (no dbl bond at 2:3 position)
- Flavonols (-OH group at 3 position)
What are flavones?
Double bond at 2:3 position
What are Isoflavones?
Benzene ring at 3 position
What are flavonolos?
- -OH group at 3 position
- No double bond at 2:3 position
What are flavonones?
No double bond at 2:3 position
What are flavonols?
-OH group at 3 position
What is quercitin?
- Induces astringency in the mouth and contributes to flavor
- Causes preipitation of proteins in saliva and induces the dry sensation
What is neringenin?
- Bitter taste found a lot in bitter fruits such as citrus - grapefruit in the pith and in the rind
How do flavonoids interact with vitamin C?
Enhance vitamin C by increasing the uptake
Why are flavonoids substrates for enzymatic browning?
Because of their polyphenolic structure
What are betalaines?
- H2O-soluble plant pigments
- Betacyanins (red)
- Betaxanthins (yellow)
- Found mostly in beets
- Degraded by thermal processing
- Some color lost to cooking in water due to high solubility
How are betalaines effected by sulfites?
Additives like sulfites can cause bleaching
What are tannins?
- Complex plant pigments with varying degrees of solubility in H2O, based on different sizes
- Wide range of colors- from colorless to yellow or brown
- Contribute to astringency in foods
- Participate in enzymatic browning reactions
Where are tannis predominantly found?
What are quinones?
- H2O-soluble pigments
- Present in plants and microorganisms
- Range in color from yellw to black
- Extensively used as a natrual dyestuffs and purgatives
What are some common quinones?
What are Xanthones?
- Plant pigments with structureal resemblance to flavonoids and quinones (glycosides)
- H2O-soluble and yellow in color
What is a common xanthone?
What are melanins or malanoids?
- Brown colored pifments found in fruits, vegetables, fundi (mushrooms) and crustacea
- Formed from plymerization of phenolic compounds by PPO and Cu++
- Formation of melanins desirable in certain foods, but undesirable in others
How are melanins formed?
Formed from polymerization of phenolic compounds by PPO and Cu++
What are the 2 types of non-enzymatic browning reactions?
- Maillard reactions
What is caramelization?
- From carbohydrates by heating
- Has a nutty taste/smell
What is maillard browning?
- From interactions of sugars with amino groups from amino acids, proteins, eptides, amines
- Maillard browning is enhanced by heating
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