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Fruits and vegetables

Plant parts we eat (APK)

• See page 247, Lecture Notes.• We eat

– Leaves• Cabbage• Lettuce• Spinach

– Stems• Asparagus• Celery

Plant parts we eat

– Bulbs• Garlic

• Onion

– Roots• Beet

• Carrot

• Radish

• Sweet potato

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Plant parts we eat

– Tubers• Potato

– Flowers• Broccoli• 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 preservep– Color

– Flavor

– Texture

– Nutrient value

Plant tissue types

• Dermal– Outer covering, usually rich in waxes and

lipids (cutin). Protects and waterproofs dj t tiadjacent tissue.

• Vascular – Xylem

• Transports water from roots to leaves

– Phloem• Transports food from leaves to roots for storage

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Plant tissue types

• Ground tissue– Parenchyma

• Most abundant

U diff ti t d• 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)

Parenchyma

Middle lamella is fluorescent due to staining

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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)

Plant cell

Middlelamella

Vacuole

Image courtesy of Beginner’s guide to Molecular Biology (www.res.bbsrc.ac.uk/molbio/guide/cell.html)

Amyloplast

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Plant cell wall polymers

• Cellulose

• Hemicellulose• Hemicellulose

• Lignin

Cellulose

Hemicellulose

• Non-cellulose polymers utilizing the monosaccharides shown below

Image courtesy of www.eng.rpi.Edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/hemicel.htm

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Cell wall xylan

O

O

OH

O

O

OH

O OH

OH

O O

OH

H H

H

A cell wall xylanBeta-1,4-linkage

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.

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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)

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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 towarmed 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• Benzoic– Cranberries--a natural preservative

• Shikimic– Intermediate in secondary metabolism

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Plant acids

O

O

O

O

H

OH

OH

O O

OO

HO

O HH

OO

O O

H HO

Hm a l i c a c i d

H

c itr ic a c idoxalic acid

O

O

O

O

O

O

H

H

H

H

L-tartaric acid

OOH

b e n z o ic a c id

OO

O

O

O

H

H

HH

s h ik im ic a c id

Chlorophyll

Chlorophyll/pheophytin

acid

h t

chlorophyll pheophytin

heat

Mg++

Images courtesy of NYU/ACF Scientific Visualization Laboratory(www.nyu.edu/pages/mathmol)

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Chlorophyll in broccoli

Carotenoids

• These are the most stable class of pigments in fruits and vegetables– Carotene--orangeCarotene orange

• Carrots

– Lycopene--red• Tomato

– Xanthophylls--yellow• Corn

Carotenoids

O

H

v i t a m i n A

b e ta -c a ro te n e

lyc o p e n e

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Carotene in carrots

Flavonoids

O+

B a s ic r in g s t r u c tu r e f o ra n t h o c y a n in p ig m e n t s

Anthocyanin reactions

OO

O

O

OH

H

H

H

-H+

+H+O

OH

OO

O

O

O

OH

flavylium or oxonium ion (red)

Anhydrobase (violet)

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Anthocyanin reactions

OO

O

O

O

H

H

Na

+Na+

-Na+

OH

H

Anhydrobase (violet)OO

O

O

O

OH

HH

Na

Sodium salt of the anhydrobase(blue)

Anthocyanins in red cabbage

Anthoxanthins in onions

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Betalins (beet pigments)

O

O

O

OO

N

O

H

H

O

H+N

O

NO

O

H

H

H

H

O

O

H

O H

b e ta lin

Enzymatic browning

OH

OH

O

Opolyphenoloxidase

+ H 0

Cell wall phenolic

Ortho-quinone

1/2 O2

+ H20

Enzymatic browning

Image courtesy of Robertson and Christiansen (www.orst.edu/instruct/nfm425/phenolic/index.html)

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Browning inhibition

• Remove (or reduce) enzyme activity– Heat

– AcidAcid

• Remove oxygen– Vacuum pack

– Inert gas pack (He, Ar, Carbon dioxide)

Browning inhibition

• Remove substrate– Genetic breeding program

• Use antioxidants• Use antioxidants– Vitamin C is commonly used

• Physical barrier– Cover with heavy syrup, as in freezing

Sulfur compounds -- garlic

SO

N

OOH

H

H2

SO

Sallinase

w ater

Step one

O O

(+)-S-allyl-L-Cysteinesulfoxide (alliin)

Diallyl thiosulfinate(allic in)

O

O

O

H2

pyruvic acid

NH3

+

+

w ater

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Sulfur compounds -- garlic

S

SS

S2

Step two

SO

D ia lly l th io s u lf in a te(a ll ic in )

SO

SO

d ia lly l d is u lfid e(ty p ic a l g a r lic o d o r)

a lly l th io s u lf in a te

+

Sulfur compounds -- onion

SO

OO

N

H

H

H

SH

O

propenylsulfenic acid

enzyme

water

(+)-S-(pro-1-enyl)-L-Cysteinesulfoxide

p p y(lachrymatory factor)

O

O

O

H

pyruvic acid

NH3

+

+

Sulfur compounds -- cabbage

S

O

OO

O

O

H

H

HH

Nmyrosinase

N

S

OS

O

O

O

K

sinigrin

N

Sallyl isothiocyanate(a mustard oil)

C6H12O6

KHSO4

+

+

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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

sweetsweetcorn

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

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Ripening

• To speed ripening– Treat with ethylene (C2H4)

• To slow ripening– Store in modified atmosphere (low in

oxygen, high in carbon dioxide)

Ethylene treatment

Air only Air + lowconcentrationof ethylene

Ethylene treatment

Air only Air + lowconcentrationof ethylene

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Ethylene treatment

Air only Air + lowconcentrationof ethylene

Controlled (modified) atmosphere storage

Nitrogen 78%Oxygen 21%Carbon dioxide

95% Carbon dioxide5% Oxygen

<0.04%

Controlled (modified) atmosphere storage

Nitrogen 78%Oxygen 21%Carbon dioxide

95% Carbon dioxide5% Oxygen

<0.04%

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Controlled (modified) atmosphere storage

Nitrogen 78%Oxygen 21%Carbon dioxide

95% Carbon dioxide5% Oxygen

<0.04%

Controlled (modified) atmosphere storage

Nitrogen 78%Oxygen 21%Carbon dioxide

95% Carbon dioxide5% Oxygen

<0.04%

Controlled (modified) atmosphere storage

Nitrogen 78%Oxygen 21%Carbon dioxide

95% Carbon dioxide5% Oxygen

<0.04%