Química de Alimentos

Pigmentos

Dr. Enrique Palou

Departamento de Ingeniería Química y Alimentos
COLOR
 Important from a food standpoint
 Review of light
– Electromagnetic radiation
• wavelength = l
• frequency = n = cycles / s
• n=c/l c = speed of light
• E=hn
• visible range: l (nm)
450 800
Violet Indigo Blue Green Yellow Orange Red
Electromagnetic Radiation
 Interaction of light with matter
– Transmitted
– Reflected
– Absorbed

 Certain compounds (pigments)

selectively absorb part of the visible
light and transmit the rest which we see
An example
CLASIFICATIONS OF FOOD COLOR

A. Opaque light will not pass

through
B. Transparent clear image of a light
source can be seen
through
C. Translucent diffuse image of light
can be seen through
 COLOR
OF
TRANSPARENT / TRANSLUCENT
FOODS
A. Develops as white light enters the
product and is modified by pigments
(absorb specific l)

B. Color of translucent foods also

influenced by scattering of light by the
backing (container)
 HUMAN EYE

 Two types of sensitive cells

a. Rods Lightness - darkness
b. Cones Red, green, blue color sensitive

RGB
system
RedGreenBlue
 COLOR MIXING

A. Additive Mixing light

– combined l Þ white
– primary colors Þ red, green, blue
– secondary colors Þ purple, turquoise, yellow
B. Subtractive Mixing pigments (reflected)
– combined l Þ black
– primary colors Þ purple, turquoise, yellow
– secondary colors Þ. red, green, blue
Color mixing
Color mixing
 COMPLEMENTARY COLORS

 Opposite colors that will give black

for pigments
 COLOR MEASUREMENT

 Hue Hue
red - green (± a)

yellow - blue (± b)

 Lightness-darkness Value
L (0 to 100)

 Saturation/purity Chroma
 CHEMICAL STRUCTURE
&
COLOR

 Only organic pigments will be

discussed
 Extended conjugated system of
unsaturated bonds
 ≥ 9 conjugated bonded carbons
PIGMENTS
 Three general classes of natural
compounds
– Porphyrins
• Chlorophyll green
• Hemoglobin red
– Carotenoids
• Carotenes orange - red
• Xanthophylls yellow - orange
– Phenolics
• Anthocyanins blue - red
• Flavonoids yellow
 CHLOROPHYLL (CHL)

 Conjugated tetrapyrrole
 CHLa and CHLb most important of the
many CHL in nature
 Important photosynthesis
 Always present with b-carotene
 Not approved for food use as a colorant
– USA
 PHYSICAL PROPERTIES

 Chlorophyll / pheophytin
– insoluble water (phytol group)

 Chlorophyllides / Pheophorbides
– soluble water (loss of phytol)
 REACTIONS

1. Acid
– loss of Mg
– replaced by 2H
a) chlorophyll ! pheophytin (olive green - brown)
canned vegetables

b) methylchlorophyllide ! methylpheophorbide

c) chlorophyllin ! phorbide
2. Alkali
– saponification of ester linkages

a) Chlorophyll ! chlorophylin + phytol + methanol

(water soluble pigments loss in brines)
b) Pheophytin ! phorbide + phytol + methanol
olive green
c) formation of pheophytin from chlorophyll does
not readily occur
 BLAIR PROCESS
– add alkali to reduce color loss
• canned peas

– alkaline pH ! poor flavor quality

vitamin C
losses
thiamin

– Mg in center

Mg(OH)2, MgCO2
pH increase
3. Enzymes

– Chlorophyllase hydrolysis of phytol

a) Chlorophyll ! clorophyllide + phytol
b) Pheophytin ! pheophorbide + phytol

– Lipoxygenase (LOX)
• chlorophyll sensitive to hydroperoxides formed
by the oxidation of fa by LOX
 - Mg
Chlorophyll Pheopytin
- phytol - phytol

- Mg
Chlorophyllide Pheophorbide

Chlorophylin Phorbide

Methyl Methyl
Chlorophyllide Pheophorbide
 CAROTENOIDS

 Higher plants
– spinach, tomato, orange
 Animals
– shrimp, salmon, flamingo
 Some bacteria
 STRUCTURE
 C40 components
3
 isopentyl groups unsaturated
5
• base unit 1 2
4

 Rings
• monocycle g- carotene
• bicyclic b - carotene
• acyclic lycopene
 Nomenclature
• carotenes: hydrocarbons (enes)
• xanthophylls: oxygenated derivatives
IMPORTANCE

 Humans
• “eye appeal”
• vitamin A

 Plants
• Photosynthesis
• Photoxidation
 PROPERTIES
1. Solubility
– Insoluble in water
– Soluble in non-polar solvents
• hexane, acetone, methanol
– Commercial preparations prepared as
suspensions
• emulsions
• many foods are water based
2. Color of commercial preparations
– Color due to conjugated double bonds
– Extent of conjugation affects color
• less  yellow
• more  red
– Stereochemistry cis vs trans
• trans  more yellow
– Addition of functional groups
• addition of C = O group ! increase color
affect l max
b-carotene

11
max l !
E x 10-4

all trans
15 cis

300 380 460 540 nm

3. Stability
a) oxigen
• similar problems as unsaturated fats
• can produce aldehydes & ketones
– off-flavors, loss of color
• Metals / Enzymes catalyze oxidation
– autoxidation possible
• package food in an inert atmosphere (N2 gas)
• use antioxidants (absorbic acid, SO2 )
b) light
• accelerates oxidation
• loss of a single double bond ! color loss
c) heat
• no major effect up to 60 °C color
• can get cis isomers ! changes lower lmax
vitamin A value

• @ 150 - 200 °C ! poor stability

– antioxidants can help
d) pH
• color not affected @ pH 2 - 7
• exception: carotenoids with acid groups
e) flavor
• tasteless
– unless breakdown products
f) nutrition
• need ring group b without any substitutions for
pro vitamin A activity ! b-carotene

(2 b rings)

better vitamin A source than

a - carotene (1 b ring)

• involves splitting carotenoid

• vitamin A is 1/2 a carotenoid
 BETALAINS
 Structure if R or R’
– Beta Xanthin yellow does not
– Beta Cyanin red does
 Properties extend resonance
1. Water Soluble
2. Color fairly uniform over wide pH range
pH < 3: violet pH (3-7): reasonably stable
pH >7: blue @ pH 5: most stable
3. O2 and light
increase rate of breakdown
4. Degradation by thermal processing
→ usually sufficient pigment remains
→ food is colored
→ canned red beets
Amaranto
 FLAVONOIDS

 Diverse class of pigments (3000 known)

– include anthocyanins
 Share common biosynthetic origin
 Divided into 12 classes
– based on oxidation level of central pyran
ring
 PROPERTIES
– Water soluble
– Colorless to yellow
– Anthocyanins
• red (orange) to blue
 STRUCTURE
– 3 rings

ACN
structure
 ANTHOCYANINS (ACN)

 Group of reddish water soluble pigments

 Present in many fruits & vegetables
• flowers

 ACN
– ≈ 140 known
– are derivatives of the flavylium cation
Å
7

3
5
 – additional substitution possible
– sugar molecules can be esterified to acids
• ferullic, caffeic, ...

 CLASSES OF ACN
1. Monosides One sugar attached @ 3 position
D-glucose > D-galactose > D-xylose > D-rahmnose > L-arabinose

2. Biosides Two sugar molecules @ 3, 3 & 5, 3 & 7

disaccharide rarely
3. Triosides Three sugars
 COLOR
– Very sensitive to pH:

quinoidal base red flavylium base

A AH+
(blue) (red)

C B
(colorless) (colorless)
chalcone carbinol pseudobase
 100
AH+

% B
of
total
pigment C
A
1 2 3 4 5 pH

pH of red wine: 3.3 to 4.0  Color differences

 CHEMICAL REACTIONS
1. Acid / Base ! see pH graph
2. Bisulfite (bleaches color)

Example:
ACN + SO2 ! ACN - SO3H (colorless) very stable
(@ position 2 or 4)

Strong Acid
+
boiling

Jam with regenerated ACN

Bisulfito
 ACN Degradation
A) high T
B) pH
greater destruction @ higher pH
C) Ascorbic Acid
• mechanism not fully understood
– destruction of ACN due to H2O2 ?
» H2O2 formed during oxidation of AAcid
– condensation ACN - AAcid ?
» brownish red color
D) Other constituents
• High sugar
• Amino Acids
• Enzymes : glycosidases, phenolases
• Complexes with ions:
Al, K, Fe, Cu, Ca, Sn, aa’s, proteins,pectin,
carbohydrates, polyphenols

lined cans

Tin cans ! Red cherries ! violet

due to metal
 TANNINS

 Loose term used for a long time

 tannic acid gallotannic acid

 astringent flavor
 GENERAL DESCRIPTION
1. Polyphenolic compounds (mixture)
Enzymatic Browning
2. Colorless to yellow / brown
3. Precipitate proteins ! wine without astringent flavor
4. MW 500 to 3000
• commercial
C75 H56 O46
9 molecules of gallic acid
1 molecule of glucose
 TWO GROUPS

1. Hydrolyzable tannins
• gallotannin (polymer of gallic acid)
• ellagitannin (polymer of gallic & ellagic acid)

2. Condensed tannins
• dimers
– Phenolic ! cathechin
– other molecules
 SUMARY OF PLANT PIGMENTS
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 COLOR ADDITIVES
A. Legislation
Food, Drug & Cosmetic Act (1938)
• color additive amendment (1960)
– 21 CFR parts 70-82

B. Interest on Synthetic colorants

1) toxicity
2) poor quality ! sell (deaths)
C. Definition
• “Any dye, pigment, or other substance made or
obtained from a vegetable, animal, mineral, or other
source, capable of coloring a food, drug, or
cosmetic on any part of the human body”
TYPES OF COLOR ADDITIVES

A. Certified color additives

– known structure, high purity
• chemical synthesis
– certified & batch tested by FDA
• specification compliance
– FD&C color prefixes and numbers
• Erythrosine ! FD&C Red No.3 (1938)
… TYPES OF COLOR ADDITIVES

B. Exempt color additives

– “natural” colors
• safety assumed
• NATURAL not recognized by FDA
– not pure
– specifications are broad
• not certified
CERTIFIED COLORS

Dyes Lakes

 water soluble  water soluble dye

absorbed to Al or Ca
 color by dissolving substrate ! insoluble
pigments

 color by dispersion
DYES

A. Uses:
soft-drinks, confections, pet foods, baked
goods, dairy
B. Market Forms
1. Powder
• least expensive
• easy dissolving in water
• poor flow characteristics & dusting problems
… Market Forms
2. Liquid
• No dusting
– color must be dissolved prior to use
• higher cost
• increased storage space
3. Granules
• reduced dusting & good flow characteristics
• too large particle size for use in dry mixes and
extruded products
4. Others
• pastes
• dispersions
LAKES

A. Uses
solid fat & waxes, food can linings, films,
icings
B. Market forms
Various carriers: vegetable oil, sugar syrup,
propylene glycol
M&M’s label: Red 40 lake, Blue 2 lake, Yellow 5,
Yellow 6, Blue 1 lake, Red 40, Blue 1
Dyes vs. Lakes

Dyes : foods with sufficient

 A. Where used moisture to hydrate
color
Lakes: oil based or dry
products

 B. Rate of use Dyes : 0.01 to 0.03 %

Lakes : 0.1 to 0.3 %
… Dyes vs. Lakes

 C. Light stability ! better Lakes (Dyes : good)

 D. Heat stability ! better Lakes (Dyes : good)
Dyes : high degree
 E. Clarity of foods
Lakes : opaque
CERTIFIED FD & C COLORS

 lots of rings
 resonance
 different substitution groups
“NATURAL” COLORS

 A. Legal
– exempt from certification
 B. Problems
– stability
– no blue or green
– can not predict behavior
• not true hues but mixtures
 … “NATURAL” COLORS

C. Types
1. Annatto (orange - yellow)
• carotenoids
• extracted from tree seeds
• sensitive to light, O2
• dairy products
– margarine
– ice creams
2. Beet Juice (deep red - red purple)
• betalains (water soluble, insoluble in oil)
• sensitive to heat, µo, O2, light
– dairy products
– sauces
– products with short distribution life
3. Paprika (red - orange)
• carotenoids
• sensitive to light, O2
– meat products
– salad dressings
4. Caramel
• heating sugar solutions
• water soluble
• charged ! isoelectric point ! functionality & stability
– beverages (soda) Ü Acid proof form (IP = 2)
– baked goods Ü Baker’s form
• brown in Microwave products
5. Cochineal / Carmine (bright red-purple red)
• Insects
• Insoluble cold water and oil
• carminic acid
• soluble in alkaline solutions
Puuuffff……...