Fruits and vegetables

Plant parts we eat (APK)

• See page 250, Lecture Notes.• We eat

– Leaves• Cabbage• Lettuce• Spinach

– Stems• Asparagus• Celery

Plant parts we eat

– Bulbs• Garlic• Onion

– Roots• Beet• Carrot• Radish• Sweet potato

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)

Parenchyma

Middle lamella is fluorescent due to staining

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

Plant cell wall polymers

• Cellulose

• 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

Cell wall xylan

O

O

OHO

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.

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

Chlorophyll/pheophytin

pheophytin

acid

heat

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

Chlorophyll in broccoli

Carotenoids

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

• Carrots

– Lycopene--red• Tomato

– Xanthophylls--yellow• Corn

Carotenoids

OH

v i t a m i n A

b e ta -c a ro te n e

ly co p en e

Carotene in carrots

Flavonoids

O+

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

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+

Anthocyanins in red cabbage

Anthocyanin extracts from red cabbage at different pH

pH 1 pH 10

Anthoxanthins in onions

Betalins (beet pigments)

O

O

O

OO

NO

O

NO

O

H

H

H

H

H

OH

O

O

H

+O H

b e ta lin

Enzymatic browningOH

OH

O

Opolyphenoloxidase

Cell wall phenolic

Ortho-quinone

1/2 O2

+ H20

Formation of melanin from dopamine (bananas)

Formation of melanin from tyrosine (lettuce, shrimp and mushrooms)

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)

Ethylene treatment

Air only Air + lowconcentrationof ethylene

Ethylene treatment

Air only Air + lowconcentrationof ethylene

Ethylene treatment

Air only Air + lowconcentrationof ethylene

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

Controlled (modified) atmosphere storage

Nitrogen 78%Oxygen 21%Carbon dioxide<0.04%

95% Carbon dioxide5% Oxygen