11 Colorants Flashcards
Part of colouring substances responsible for colour
chromophores
Any chemical, natural or synthetic, that imparts color
colorant
Natural substances in cell and tissues of plants that impart color
Pigments
Any substance that lend color refereing to colorant used in the textule industry OR “certified colors” that have been approved by the FDA as food-grade water soluble colorant
dye
Dyes extended on substratum and are oil dispersible
Lakes
Pigments found in animal and plant tissue
- Hemes (myoglobin/haemoglobin)
- Chlorophyll
- Carotenoids
- Flavonoids and other phenolic compounds (anthocyanins
- Betalaines
Protein portion of myoglobin
globin
Chromophore in myoglobin
Porphyrrin ring with Fe in the center, complexed with four tetrapyrole N (known as heme)
Meat colour is determined by
- Chemistry of myoglobins
- Ligands bound to heme
- Oxidation state
- State of globin protein
Oxygenation of myoglobin yields…
explain the changes in colour
Oxymyoglobin (MbO2-Fe2+)
Purple-red to bright red
Oxidation of myoglobin yields…
explain the changes in colour
Metmyoglobin (MetMb-Fe3+)
Purple-red to brownish-red
Oxidation of oxymyoglobin yields…
explain the changes in colour
Metmyoglobin (MetMb-Fe3+)
Bright red to brownish-red
Two sources of green discoloration
- Choleglobins
- Sulphomyoglobin
Mechanism of choleglobin synthesis
Reaction of hydrogen peroxide (H2O2) with ferrous/ferric site of heme
Mechanism of sulphomyoglobin synthesis
Presence of H2S and O2
Mechanism to stable pink colour in cured meat
Steps:
1. Myoglobin + Nitric oxide (NO) yields Nitrosylmyoglobin (bright red; unstable)
2. Heating of nitrosylmyoglobin denatues globin, forming nitric oxide myochemochromogen (nitrosylhemochrome), which is pink in colour
Formation of brown color from pink in cured meat
Exposure of nitrosohemachrome(Fe2+) to air and light, forming nitrosohemachrome(Fe3+)
Explain nitrite burn
Reaction of metmyoglobin and excess nitrite, yielding nitrimyoglobin (NMb), followed by heating in a reducing environment yielding nitrohemin, a green pigment
Structure of chlorophyll
Magnesium complexes derived from porphin, a fully unsaturated micro -cyclic structure containig four pyrrol rings linked by single bridging carbons
Substituted porphins are called porphyrin
The nucleus of chlorophylls are called PHORBIN and is formed by the addition of a fifth isocyclic ring to porphin
Also contains PHYTOL, a 20C monounsaturated isoprenoid alcohol
Difference between chrolorphyll a and chlorophyll b
Substituent in C1 ring A is CH3 for chlorophyll a and CHO for chlorophyll b
chlorophyll derivatives containing Mg
Phyllin
Magnesium free derivatives of chlorophyll
Pheophytin
Colour: olive green
(formed during reactions with head + acid)
Products of reactions of chlorophyll resulting in hydrolysis of phytyl ester (phytol tail)
Chlorophyllides
Colour: bright green
(formed during blanching, which accelerates action of endogenous enzyme chlorophyllase)
Products of reactions of chlorophyll resulting in the removal of Mg and hydrolysis of phytyl ester (phytol tail)
Pheophorbides
Colour: brown
(formed during treatment of chlorophyllide with heat + acid)
Methods of preserving chlorophyll colour
- HTST
- Base addition
- Commercial application of metallocomplex
Mechanism of chlorophyllin manufacture to retain chlorophyll colour
Addition of NaOH and CuSO4, in which the Cu oil replaces Mg and phytol tail is removed
Mechanism of regreening in chlorophyll
Addition of Zn2+ with head and acid ro replace central Mg with Zn
Basic structure of carotenoids
Backbone consists of isoprene units linked head-to-tail to create a symmetrical molecule
Comprised of two structural groups
1. hydrogen carbon carotenes
2. oxygenated carotenoids (xantophylls)
Six types of carotenoids
- lutein
- crocetin
- alpha carotene
- beta carotene
- lycopene
- zeaxanthin
Chromophore in carotenes
Conjugated double bonds
How is the red colour in cooked shrimp brought about
red ASTAXANTHIN in shrimp exoskeleton is blue when complexed with proteins, which denature during cooking
Carotenoids are susceptible to what chemical reaction?
Oxidation due to the large number of double bonds, causing colour loss and forming epoxides and carbonyl compounds
Oxidative destruction of beta carotene is intensified in the presence of what
sulfite, metal ion and lipoxygenase enzyme
Antioxidative properties of carotenoids
- easily oxidised
- quenchs singlet oxygen
- photochemical protectos
- isomerization from all trans to cis (decreasing activity to 13-53%)
Characteristics of oxidation products of carotenoids
polymer, volatile, short chain, low Mr, water soluble compounds
Difference between oxidation products of beta carotene due to chemical oxidation and light
Chemical: beta carotene-5,6-epoxide
Chemical: beta carotene-5,8-epoxide
Effect of cooking and canning on beta carotene
forms neo beta carotene (38% vit C activity)
Degradation products of beta carotene due to high temperature
toluene, ionine, 4-methyl-acetophenone
Structure of anthocyanin
FLAVONOIDS comprise the skeleton of anthocyanins (C3-C6-C6) (A, C, B respectively)
substituents on ring A and B determine the colour
Water soluble form of anthocyanins
Anthocyanin glycoside (anthocyanidin +sugar)
Less water soluble form of anthocyanin
Anthocyanidin (rare in nature)
Changes in anthocyanin forms and their respective colours
(A)
quinonoid: blue
(AH+)
flavylium: red
(B)
carbinol base: colorless
(C)
chalcone: colorless
How to increase stability of anthocyanins
- acidic conditions
- decreased hydroxylation as aglycone substituent
- increased methylation as aglycone substituent
- less paelargonidin, cyanidin, or delphinidin aglycones
- more petunidin or malvidin aglycones (blocks reactive hydroxyl groups)
- increased glucosylation (as in monoglucosides and diglucosides)
- high concentrations of sugars due to lower water activity
- metal complex Ca, Fe, Al, Sn
effect of SO2 on anthocyanins
Bleaching effect
Reversible: when preserved in 500-2000ppm SO2; can be restored by desulfuring (through washing) before further processing
Irreversible: attachment of SO2 at C4, formation of colorless complex
Colour of quinones
Darker colours
fungi and lichens: yellow, orange, brown
sea lilies and coccid: red, blue, purplr
Colour of xanthones
Yellow (e.g. in mangoes)
Betalaines betacyanin are similar to what pigments?
Flavonoids (yellow) and anthocyanins (red)
Types of betalaines
- Betacyanin (violet-red): betanin, betanidin
- Betaxanthins (yellow): vulgaxanthin
Pigment found in sappan wood
brazillin (isoflavonoid)
physical properties of brazillin
yellow crystal
becomes brownish-red when oxidised (brazilein, water soluble)
becomes red when exposed to sunlight
changes in colour due to pH of brazilein
pH 2-5: yellow
pH 6-7: red
pH > 8: red-purple
Degradation of brazilein affected by what factors
temperature, UV light, oxidator, reductor. metal
Permitted natural colorants
caramel
beta carotene
chlorophyll
curcumin
Permitted synthetic colorants
Brilliant blue
Tartrazine
Indogotine
Sunset yellow
Erythrosine
Allura red
Orange B
Citrus red no.2
