fruits and vegetables - purdue university · • transports food from leaves to roots for storage....
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Plant parts we eat (APK)
• See page 250, Lecture Notes.• We eat
– Leaves• Cabbage• Lettuce• Spinach
– Stems• Asparagus• Celery
Plant parts we eat
– Tubers• Potato
– Flowers• Broccoli• Cauliflower
– Fruits• Tomato• Pepper• Cucumber
– Seeds -- beans, corn, peas, soybeans
Fruit and vegetable characteristics to preserve• In preparation, processing, or
preservation of fruit and vegetables we want to preserve– Color– Flavor– Texture– Nutrient value
Plant tissue types
• Dermal– Outer covering, usually rich in waxes and
lipids (cutin). Protects and waterproofs adjacent tissue.
• Vascular – Xylem
• Transports water from roots to leaves– Phloem
• Transports food from leaves to roots for storage
Plant tissue types
• Ground tissue– Parenchyma
• Most abundant• Undifferentiated
– Collenchyma• Strength cells• Strings on green beans and celery
– Sclerenchyma• Even stronger than collenchyma• Strings in green beans, grittiness in pears
Parenchyma
Image courtesy of Plants and Society, Levitin and McMahon(www.life.umd.edu/pbio100/contact1.html)
Collenchyma
Image courtesy of Plants and Society, Levitin and McMahon(www.life.umd.edu/pbio100/contact1.html)
Sclerenchyma
Image courtesy of Plants and Society, Levitin and McMahon(www.life.umd.edu/pbio100/contact1.html)
Image courtesy of Beginner’s guide to Molecular Biology (www.res.bbsrc.ac.uk/molbio/guide/cell.html)
Plant cell
Middlelamella
Amyloplast
Vacuole
Hemicellulose
• Non-cellulose polymers utilizing the monosaccharides shown below
Image courtesy of www.eng.rpi.Edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/hemicel.htm
LigninA polymer comprised of phenylpropane molecules such as those shown below. Provides strength and woodiness toplant materials when it occurs in large concentration.
Lignin monomers
Image courtesy of www.eng.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/lignin.html.
Proposed lignin sub-structure
Image courtesy of www.eng.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/lignin.html.
Vacuole
• Contains the cell sap. Basically a drop of water contained in the cell in which various substances are dissolved.– Tannins– Sugars– Salts– Organic acids– Flavanoids
Plant acids
• Malic acid– Found in apples and many other fruits and
vegetables• Citric acid
– Main acid in citrus fruits, many berries, pineapple
• Oxalic– Spinach, rhubarb (especially the leaves)
Silly stuff
• Dr. James van Meeter, speaking in 1830 to a crowd in Salem, Massachusetts, about Colonel Robert Gibbon Johnson, who was going to publicly eat a tomato…
Silly stuff• "The foolish colonel will foam and froth at the
mouth and double over with appendicitis. All that oxalic acid, in one dose, and you're dead. If the Wolf Peach (tomato) is too ripe and warmed by the sun, he'll be exposing himself to brain fever. Should he, by some unlikely chance, survive, I must warn him that the skin ... will stick to his stomach and cause cancer."
Plant acids
• L-tartaric– Grapes
• Benzoic– Cranberries--a natural preservative
• Shikimic– Intermediate in secondary metabolism
Plant acids
O
O
O
O
H
H
OH
m a l i c a c i d
OH
O O
OO
HO
O HH
c itr ic a c id
OO
O O
H H
oxalic acid
O
OO
O
OO
H
H
H
H
L-tartaric acid
OOH
b e n z o ic a c id
OO
OO
O
H
H
HH
s h ik im ic a c id
chlorophyll
Chlorophyll/pheophytin
pheophytin
acid
heat
Mg++Images courtesy of NYU/ACF Scientific Visualization Laboratory(www.nyu.edu/pages/mathmol)
Carotenoids
• These are the most stable class of pigments in fruits and vegetables– Carotene--orange
• Carrots
– Lycopene--red• Tomato
– Xanthophylls--yellow• Corn
Anthocyanin reactions
OO
O
OO
H
H
H
H
OH
OO
O
OO
OH
-H+
+H+
flavylium or oxonium ion (red)
Anhydrobase (violet)
Anthocyanin reactions
OO
OO
OO
H
HH
H
Anhydrobase (violet)OO
OO
OO
H
HH
Na
Sodium salt of the anhydrobase(blue)
+Na+
-Na+
Enzymatic browning
Image courtesy of Robertson and Christiansen (www.orst.edu/instruct/nfm425/phenolic/index.html)
Browning inhibition
• Remove (or reduce) enzyme activity– Heat– Acid
• Remove oxygen– Vacuum pack– Inert gas pack (He, Ar, Carbon dioxide)
Browning inhibition
• Remove substrate– Genetic breeding program
• Use antioxidants– Vitamin C is commonly used
• Physical barrier– Cover with heavy syrup, as in freezing
• Enzymatic browning
Sulfur compounds -- garlic
SO
N
OOHH
H2
SO
S
(+)-S-allyl-L-Cysteinesulfoxide (alliin)
Diallyl thiosulfinate(allicin)
OO
OH2
pyruvic acid
NH3
+
+
allinase
water
Step one
Sulfur compounds -- garlic
SO
S
D ia lly l th io s u lf in a te(a llic in )
SS
SO
SO
2
d ia lly l d is u lf id e(ty p ic a l g a r lic o d o r)
a lly l th io s u lfin a te
+
Step two
Sulfur compounds -- onion
SO
OO
NH
HH
(+)-S-(pro-1-enyl)-L-Cysteinesulfoxide
SH
O
propenylsulfenic acid(lachrymatory factor)
OO
OH
pyruvic acid
NH3
+
+
enzyme
water
Sulfur compounds -- cabbage
N
S
OSO
O
O
K
O
OO
O
O
HH
HH
sinigrin
NS
allyl isothiocyanate(a mustard oil)
C6H12O6
KHSO4
+
+
myrosinase
Changes in fruits and vegetables on ripening• Color
– Green of chlorophyll may give way to other colors
• Texture– Goes from hard to tender-crisp to mushy.
Principally a function of changes in the middle lamellar pectic substances.
Changes in fruits and vegetables on ripening• Flavor
Starch Sugarbanana
sweetcorn
Tannins decrease on ripening
Acids generally decrease on ripening(except for citrus fruits)
Pectic substances
Protopectin Pectinicacid
Pectic acid
Underripe Ripe OverripeInsoluble Colloidal Soluble
No gel Gel No gelLots ofmethyl
Less methyl Almost nomethyl
Hard Optimum Mushy
Stone walls and plant tissue texture
Stones held together by mortar between stones. Strength (texture)of the wall largely determinedby mortar.
Cells held together by pecticsubstances in middlelamella. Texture of plant tissue largely determined bypectic substances
What happens over time?
In both cases the texture changesdue to a change in what isgluing the stones/cells
together.
Ripening
• To speed ripening– Treat with ethylene (C2H4)
• To slow ripening– Store in modified atmosphere (low in
oxygen, high in carbon dioxide)
Controlled (modified) atmosphere storage
Nitrogen 78%Oxygen 21%Carbon dioxide<0.04%
95% Carbon dioxide5% Oxygen
Controlled (modified) atmosphere storage
Nitrogen 78%Oxygen 21%Carbon dioxide<0.04%
95% Carbon dioxide5% Oxygen
Controlled (modified) atmosphere storage
Nitrogen 78%Oxygen 21%Carbon dioxide<0.04%
95% Carbon dioxide5% Oxygen
Controlled (modified) atmosphere storage
Nitrogen 78%Oxygen 21%Carbon dioxide<0.04%
95% Carbon dioxide5% Oxygen