Term
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Definition
-- Chlorophyll
• 2 types – chlorophyll a and chlorophyll b
--Carotenoids
--Flavanoids
• Anthocyanins
-• Betalins
• Anthoxanthins |
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Term
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Definition
green pigments, found in chloroplasts in the
protoplasm of the plant cell.
Predominate form of pigments in plants – color seen by the eye is
influenced by other pigments especially in under ripe fruits and
vegetables.
Chlorophyll content decreases during ripening.
Fat soluble.
Most common forms:
Chlorophyll a (most abundant form) – a methyl group in the R
position - contributes blue-green coloring
Cholorophyll b – an aldehyde group in the R position – contributes
yellow-green coloring
Ratio of the two forms varies between plants and within plants
Color – due to resonance around the tetrapyrole ring structure and
influenced by the R groups |
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Term
Chlorophyll -
Reactions affecting color--- TEMPERATURE |
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Definition
Temperature – expels air from the interstitial spaces
within the plant cells resulting in gradual color changes
First – color intensifies
As heating continues – central Mg+ ion is replaced by
H+ and pheophytin is formed – color changes to
greenish-gray for pheophytin a and to olive green for
pheophytin b (especially above 5 minutes)
Prolonged heating can also result in the loss of the
both the phytyl group and the Mg+ ion resulting in
pheophorbide – yielding an olive-green color (seen in
canned green beans and pickles)
Can reduce the effects of by adding the
vegetables/fruits to boiling water, stir-frying, steaming,
or blanching (all quick cooking methods) |
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Term
Chlorophyll -
Reactions affecting color---ACID |
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Definition
added to the food during
cooking/processing or naturally occurring in
the plant
Acid makes the conversion of chlorophyll to
pheophytin occur more rapidly
Can reduce the effects by allowing some of
the steam to escape (releases volatile
acids), by leaving the lid off the pot, or by
diluting with additional water |
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Term
Chlorophyll -
Reactions affecting color- ALKALI |
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Definition
adding baking soda to the
cooking medium can intensify the
chlorophyll colorations
pH above 7.0 results in unpleasant
textures and the formation of
chlorophyllin (phytyll and methyl
groups removed from the chlorophyll
molecule but Mg+ ion retained) |
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Term
Chlorophyll -
Reactions affecting color- CHLOROPHYLLIN |
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Definition
results in unrealistic
bright green color (undesirable)
Color change can be avoided by
controlling the pH to below 7.0
Textural changes can be minimized by
adding calcium salts or calcium
acetate which blocks hemicellulose
from breaking down |
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Term
Chlorophyll -
Reactions affecting color-- ENZYMES |
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Definition
action of enzymes can
dramatically affect color
Chlorophyllase – cleaves the phytyl
group from the chlorophyll molecule
yielding chlorophyllide
• Turns the cooking liquid green – |
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Term
Plant Pigments -
Carotenoids |
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Definition
– plant pigments (over 300) ranging in
color from yellow to orange to red. Formed in the
chromoplasts in the protoplasm of the parenchyma
cell. Also found in crystalline form in the vacuole and
associated with lipids in the vacoule. All are fat
soluble. Carotenoid colors may be masked by
chlorophyll in some F/V’s
-- Two categories:
-Carotenes – only carbon and hydrogen
-Xanthophylls – carbon, hydrogen and at least one
oxygen molecule
-- Color results from resonance of the isoprene
polymers
--Most carotenoids in trans-form at the double bonds –
contributes to the bright color
--Beta carotene (orange)– classic
example – 40 carbon isoprenoid
polymer chain with closed-ring at each
end
-- α-carotene (yellow-orange) – a
closed-ring structure at only one end
--Lycopene (red) – acyclic isoprenoid
polymer. 95% of lycopene in foods is
in the all-trans form.
-Food sources – tomatoes, grapefruits,
apricots, papaya |
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Term
Carotenoids -
Reactions affecting color |
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Definition
--Heat and acid stable under normal cooking
conditions
--High heat (thermal processing, etc.) – can
cause conversion of the trans to cis double
bonds
-Results in lighter, less intense color
-Exception – rutabagas – which start in the
cis-form and convert to the trans-form going
from lighter to brighter with thermal
processing
--Oxidation – responsible for some
loss of color in F/V’s containing
carotenoids particularly in dried fruits
-Can be minimized by blanching prior
to drying |
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Term
| Plant Pigments - Flavonoids |
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Definition
Related group of pigments consisting of 2
phenyl rings joined by a 5 or 6 membered
ring
--2 categories
Anthocyanins – oxygen in the center ring is
charged (+). Highly colored and water
soluble – red to purple to blue
Anthoxanthins – oxygen itn eh center ring is
uncharged. Colorless or white (acid) or
cream (neutral), color may change to yellow
(basic) |
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Term
| Flavanoids - Anthocyanins |
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Definition
As the number of –OH groups
substituted on right ring increases, color
goes from red (1 –OH group) to purple
(2 –OH groups) to blue (3 –OH groups)
•Complex frequently with simple sugars
•Sensitive to changes in pH – due to
shift in charge on oxygen – most
common form (red). As pH increases
towards neutral color, oxygen loses
positive charge and color changes to
violet. In basic pH, salt forms and color
shifts to blue.
•Severity of color shifts due to changes
in pH increases as number of –OH
groups increases. |
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Term
Anthocyanins -
Reactions affecting color |
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Definition
Oxidation – can readily undergo oxidation
in the presence of oxygen and/or heat –
color vibrancy decreases
Contact with metallic ions – iron, copper,
aluminum, tin can complex with the
pigments and form weird off-colors
Enzymes – anthocyanase – can destroy
color or cause oxidative reactions
Mild heat treatment sufficient to inactivate
most of these enzymes |
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Term
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Definition
--Betalin – closely related to anthocyanins
--2 groups:
-Betacyanins – red
• Includes betanin and betanidin which are watersoluble
and leach into cooking liquid, are sensitive
to pH changes (red at acid, bluish at basic)
• Betanin (derived form beets) is used commercially
as a coloring agent
-Betaxanthins - yellow |
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Term
| Flavanoids - Anthoxanthins |
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Definition
Anthoxanthins (tannins) – subtle in color
but sensitive to changes in pH. Also
responsible for taste (astringency)
-White at acid / yellow at basic conditions
-More O2 in the structure than anthocyanins
-Prone to complexing with metal ions –
complex with aluminum is yellow and with
iron is dark |
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Term
| Flavanoids - Anthoxanthins |
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Definition
Anthoxanthins, con’t
Some can be converted to anthocyanins – proanthocyanin
to cyanidin conversion results in pink tinge of canned pears
which are heated for too long)
Enzymatic Browning - can brown or blacken due to enzyme
(polyphenyloxidase) and can occur in many F/V’s when they
are bruised, cut, or exposed to air
• Caused by polyphenoloxidases which catalyzes the oxidation
of polyphenolic compounds
• Tyrosine and catechins serve as substrates and undergo
numerous reactions to yield melanin (brown pigment)
• Can be prevented by:
• eliminating oxygen or using antioxidants
• Can be retarded through refrigeration, adding acid (citric or
ascorbic), adding sulfur or adding sodium chloride |
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Term
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Definition
Can be prevented by:
Cold temperature storage
Addition of acid to cut surfaces (inhibits
enzyme)
Sulfur dioxide or bisulfite
Elimination of O2 (inhibits enzyme) –
submerging the F/V in water accomplishes
this
Addition of ascorbic or citric acid (reduces
substrate) |
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Term
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Definition
Interest in using “natural” colorings
increasing
FDA – “natural coloring” not allowed on
labels
Have to use “color added with_______” or
“________color”
Certified colors (approved by the FDA):
Dyes – water-soluble coloring agents
Lakes – water-insoluble coloring agents
used with fats or oils |
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Term
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Definition
Plant Flavors include:
--Sweetness – sugars
• Main one is glucose but also contain sucrose,
fructose, galactose, ribose, arabinose, and xylose
--Sourness – organic acids
• In fruits (mostly) and vegetables:
• Malic – apples
• Citric – citurs
• Tartaric – grapes
• Oxalic – spinach
--Bitterness – flavanones in citrus peels can
be extremely bitter
--Astringency – due to presence of flavanols
and other polyphenols (unripe bananas,
peaches, persimmons)
--Aromas – esters, aldehydes, acids,
alcohols, ketones, ehters
--Sulferous compounds – allium and
cruciferae |
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Term
| Plant Flavors--Sulferous compounds |
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Definition
Allium family – onions, garlic, chives,
leeks
Cruciferae family – cabbage, broccoli,
cauliflower, mustard, horseradish |
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Term
Plant Flavors – Sulferous
compounds---- ALLIUM |
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Definition
--Diallyl disulfide - When activated by the
enzyme allinase, alliin is converted to diallyl
thiosulfinate which is then converted to
diallyl disulfide – this is the strong and
pungent aroma associated with garlic
Other important compunds – hydrogen
sulfidem di- and tri-sulfides, porpanethiol
-- Porpenylsulfenic acid – the eye irritant found
in raw onions. Extremely volatile, escapes
during cooking |
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Term
Plant Flavors – Sulferous
compounds-- CRUCIFERAE |
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Definition
Isothiocyanates
• One such is sinigrin which is converted
enzymatically to allyl isothocyanate
(pungetn, hot!) found in cabbage,
mustard, and horseradish
-• Goes away/mellows out after cooking
• Hydrogen sulfide and dimethyl sulfide in
cooked vegetables
-• Do not go away with cooking – stay strong
-• Cooked cabbage smell |
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Term
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Definition
Includes legumes and peanuts
Soy beans are important as ingredients in
commercial products
Cooking beans:
Have to consider hard outer covering – need
to soak in unsalted water before simmering:
• Can soak overnight
• Boil 2 minutes, then soak one hour, then simmer
• Baking soda (0.5 g per 623 ml water) can be
added and reduces softening time by 1/3 |
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Term
Plant Proteins – Soy
Proteins |
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Definition
Soy Protein
Dried soybeans contain 34% protein, do not contain
appreciable starch so they do not soften when cooked
Products include:
• Soy flour – beans dehulled, defatted and ground
• Soy protein concentrate – acid treated flour with 70% protein
content
• Soy protein isolate – oligosaccharides removed from defatted
soy flour – 95% protein
• Textured soy protein (TSP) – made from ISP which is spun
and coagulated into fibers, used for fabrication of imitation
meat products
• Textured Vegetable Proteins (TVP) – made form soy flour or
isolate, dough has flavors and colors added, then extruded and
dried. Used as a meat extender in school lunch programs
(should be less used at 20% or less ) |
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Term
| Plant Proteins – Soy milk |
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Definition
Soy beans are ground and filtered and
mixed with water to desired consistency
Tofu – soy milk is coagulated to make a curd
• Types – firm, soft, silken
Tofutti – soybean tofu ice cream
Tempeh – cooked soybeans fermented and
molded to form cakes
Natto – fermented soybean product used as
a spread or in soups |
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