vegetables and vegetable products

17 Vegetables and Vegetable Products

17.1 Vegetables

17.1.1 Foreword

Vegetables are defined as the fresh parts of plantswhich, either raw, cooked, canned or processedin some other way, provide suitable human nutri-tion. Fruits of perennial trees are not consideredto be vegetables. Ripe seeds are also excluded(peas, beans, cereal grains, etc.). From a botanicalpoint of view, vegetables can be divided into al-gae (seaweed), mushrooms, root vegetables (car-rots), tubers (potatoes, yams), bulbs and stem orstalk (kohlrabi, parsley), leafy (spinach), inflo-rescence (broccoli), seed (green peas) and fruit(tomato) vegetables. The most important vegeta-bles, with data relating to their botanical classi-fication and use, are presented in Table 17.1. In-formation about vegetable production follows inTables 17.2 and 17.3.

17.1.2 Composition

The composition of vegetables can vary signif-icantly depending upon the cultivar and origin.Table 17.4 shows that the amount of dry matterin most vegetables is between 10 and 20%. Thenitrogen content is in the range of 1–5%, car-bohydrates 3–20%, lipids 0.1–0.3%, crude fiberabout 1%, and minerals close to 1%. Some tu-ber and seed vegetables have a high starch contentand therefore a high dry matter content. Vitamins,minerals, flavor substances and dietary fibers areimportant secondary constituents.

17.1.2.1 Nitrogen Compounds

Vegetables contain an average of 1–3% nitrogencompounds. Of this, 35–80% is protein, the restis amino acids, peptides and other compounds.

17.1.2.1.1 Proteins

The protein fraction consists to a great extentof enzymes which may have either a beneficialor a detrimental effect on processing. They maycontribute to the typical flavor or to formationof undesirable flavors, tissue softening and dis-coloration. Enzymes of all the main groups arepresent in vegetables:

• Oxidoreductases such as lipoxygenases, phe-noloxidases, peroxidases;

• Hydrolases such as glycosidases, esterases,proteinases;

• Transferases such as transaminases;• Lyases such as glutamic acid decarboxylase,

alliinase, hydroperoxide lyase.• Ligases such as glutamine synthetase.

Enzyme inhibitors are also present, e. g., potatoescontain proteins which have an inhibitory effecton serine proteinases, while proteins from beansand cucumbers inhibit pectolytic enzymes. Pro-tein and enzyme patterns, as obtained by elec-trophoretic separation, are often characteristic ofspecies or cultivars and can be used for analyti-cal differentiation. Figure 17.1 shows typical pro-tein and proteinase inhibitor patterns for severalpotato cultivars.

17.1.2.1.2 Free Amino Acids

In addition to protein-building amino acids, non-protein amino acids occur in vegetables as well asin other plants. Tables 17.5 and 17.6 present dataon the occurrence and structure of these aminoacids. Information about their biosynthetic path-ways is given below.The higher homologues of amino acids, such ashomoserine, homomethionine and aminoadipicacid, are generally derived from a reaction se-quence which corresponds to that of oxalacetate

H.-D. Belitz · W. Grosch · P. Schieberle, Food Chemistry 770© Springer 2009

17.1 Vegetables 771

Tab

le17

.1.L

isto

fso

me

impo

rtan

tveg

etab

les

Num

ber

Com

mon

nam

eL

atin

nam

eC

lass

,ord

er,f

amil

yC

onsu

med

as

Mus

hroo

ms

(cul

tiva

ted

orw

ildl

ygr

own

edib

lesp

ecie

s)1

Rin

ged

bole

tus

Suil

lus

lute

usB

asid

iom

ycet

es/B

olet

ales

2Sa

ffro

nm

ilk

cap

Lac

tari

usde

lici

osus

Bas

idio

myc

etes

/Aga

rica

les

3Fi

eld

cham

pign

onA

gari

cus

cam

pest

erB

asid

iom

ycet

es/A

gari

cale

s4

Gar

den

cham

pign

onA

gari

cus

hort

ensi

sB

asid

iom

ycet

es/A

gari

cale

s5

Cep

Xer

ocom

usba

dius

Bas

idio

myc

etes

/Bol

etal

es6

Tru

ffle

Tube

rm

elan

ospo

rum

Asc

omyc

etes

/Tub

eral

esSt

eam

ed,f

ried

,dri

ed,

7C

hant

erel

leC

anth

arel

lus

ciba

rius

Bas

idio

myc

etes

/Aph

yllo

phor

ales

pick

led

orsa

lted

8X

eroc

omus

chry

sent

eron

Bas

idio

myc

etes

/Bol

etal

es9

Mor

elM

orch

ella

escu

lent

aA

scom

ycet

es/P

eziz

ales

10E

dibl

ebo

letu

sB

olet

used

ulis

Bas

idio

myc

etes

/Bol

etal

es11

Goa

t’sli

pX

eroc

omus

subt

omen

tosu

sB

asid

iom

ycet

es/B

olet

ales

Alg

ae(s

eaw

eed)

12Se

ale

ttuc

eU

lva

lact

uca

Eat

enra

was

asa

lad,

cook

edin

soup

s(C

hile

,Sco

tlan

d,W

estI

ndie

s)13

Swee

ttan

gle

Lam

inar

iasa

ccha

rina

Eat

enra

wor

cook

ed(S

cotl

and)

14L

amin

aria

sp.

Eat

endr

ied

(“co

mbu

”)or

asa

vege

tabl

e(J

apan

)15

Porp

hyra

laci

niat

aE

aten

raw

insa

lads

,coo

ked

asa

vege

tabl

e(E

ngla

nd,A

mer

ica)

16Po

rphy

rasp

.D

ried

orco

oked

(“na

ri”

prod

ucts

,Ja

pan

and

Kor

ea)

17U

ndar

iapi

nnat

ifida

Eat

endr

ied

(“w

akam

i”)

and

asa

vege

tabl

e(J

apan

)

Roo

tyve

geta

bles

18C

arro

tD

aucu

sca

rota

Api

acea

eE

aten

raw

orco

oked

19R

adis

h(w

hite

elon

g-R

apha

nus

sati

vus

var.

nige

rB

rass

icac

eae

The

pung

entfl

eshy

root

eate

nra

w,

ated

flesh

yro

ot)

salt

ed20

Vip

er’s

gras

s,sc

orzo

nera

Scor

zone

rahi

span

ica

Ast

erac

eae

Coo

ked

asa

vege

tabl

e21

Pars

ley

Petr

osel

inum

cris

pum

Api

acea

eL

ong

tape

red

root

sco

oked

asss

p.tu

bero

sum

ave

geta

ble,

orus

edfo

rse

ason

ing

Tube

rous

vege

tabl

es(s

prou

ting

tube

rs)

22A

rrow

root

Tacc

ale

onto

peta

loid

esTa

ccac

eae

Coo

ked

orm

ille

din

toflo

urfo

rbr

eadm

akin

g

772 17 Vegetables and Vegetable Products

Tab

le17

.1.(

Con

tinu

ed)

Num

ber

Com

mon

nam

eL

atin

nam

eC

lass

,ord

er,f

amil

yC

onsu

med

as

23W

hite

(Iri

sh)

pota

toSo

lanu

mtu

bero

sum

Sola

nace

aeC

ooke

d,fr

ied

orde

epfr

ied

inm

any

form

s,or

unpe

eled

bake

d,al

sofo

rst

arch

and

alco

holp

rodu

ctio

n24

Cel

ery

tube

rA

pium

grav

eole

ns,

Api

acea

eC

ooke

das

sala

d,an

dco

oked

and

var.

rapa

ceum

frie

das

ave

geta

ble

25K

ohlr

abi,

Bra

ssic

aol

erac

eaco

nvar

.B

rass

icac

eae

Eat

enra

wor

cook

edas

ave

geta

ble

turn

ipca

bbag

eac

epha

lava

r.go

ngyl

odes

26R

utab

aga

Bra

ssic

ana

pus

var.

napr

obra

ssic

aB

rass

icac

eae

Coo

ked

asa

vege

tabl

e27

Rad

ish

(red

dish

roun

dro

ot)

Rap

hanu

ssa

tivu

sva

r.B

rass

icac

eae

The

pung

entfl

eshy

root

isea

ten

raw

,sa

tivu

s/va

r.ni

ger

usua

lly

salt

ed28

Red

beet

,bee

troo

tB

eta

vulg

aris

spp.

Che

nopo

diac

eae

Coo

ked

asa

sala

dvu

lgar

isva

r.co

ndit

iva

Tube

rous

(rhi

zom

atic

)ve

geta

bles

29Sw

eetp

otat

oes

Ipom

oea

bata

tas

Con

volv

ulac

eae

Coo

ked,

frie

dor

bake

d30

Cas

sava

(man

ioc)

Man

ihot

escu

lent

aE

upho

rbia

ceae

Coo

ked

orro

aste

d31

Yam

Dio

scor

eaD

iosc

orea

ceae

Coo

ked

orro

aste

d

Bul

bous

root

yve

geta

bles

32V

eget

able

fenn

elFo

enic

ulum

vulg

are

Api

acea

eE

aten

raw

assa

lad,

cook

edas

ave

geta

ble

var.

azor

icum

33G

arli

cA

lliu

msa

tivu

mL

ilia

ceae

Raw

,coo

ked

asse

ason

ing

34O

nion

All

ium

cepa

Lil

iace

aeE

aten

raw

,fri

edas

seas

onin

g,co

oked

asa

vege

tabl

e34

aL

eek

All

ium

porr

umL

ilia

ceae

The

pung

ents

uccu

lent

leav

esan

dth

ick

cyli

ndri

cals

talk

are

cook

edas

ave

geta

ble

Stem

(sho

ot)

vege

tabl

es35

Bam

boo

root

sB

ambu

savu

lgar

isPo

acea

eC

ooke

dfo

rsa

lads

36A

spar

agus

Asp

arag

usof

ficin

alis

Lil

iace

aeY

oung

shoo

tsco

oked

asa

vege

tabl

eor

eate

nas

sala

d

Lea

fy(s

talk

)ve

geta

bles

37C

eler

yA

pium

grav

eole

nsva

r.du

lce

Api

acea

eL

eafy

cris

pyst

alks

eate

nra

was

sala

d,or

are

cook

edas

vege

tabl

e38

Rhu

barb

Rhe

umrh

abar

baru

m,

Poly

gona

ceae

Lar

geth

ick

and

succ

ulen

tpet

iole

sar

eco

oked

Rhe

umrh

apon

ticu

mas

pres

erve

sor

bake

d;us

edas

api

efil

ling

17.1 Vegetables 773

Tab

le17

.1.(

Con

tinu

ed)

Num

ber

Com

mon

nam

eL

atin

nam

eC

lass

,ord

er,f

amil

yC

onsu

med

as

Lea

fyve

geta

bles

39W

ater

cres

sN

astu

rtiu

mof

ficin

ale

Bra

ssic

acea

eM

oder

atel

ypu

ngen

tlea

ves

are

eate

nra

win

sala

dsor

used

asga

rnis

h40

End

ive

(esc

arol

e,ch

icor

y)C

icho

rium

inty

bus

L.v

ar.

Cic

hori

acea

eE

aten

raw

asa

sala

d,or

isco

oked

asa

vege

tabl

efo

lios

um41

Chi

nese

cabb

age

Bra

ssic

ach

inen

sis

Bra

ssic

acea

eE

aten

raw

insa

lads

,or

isco

oked

asa

vege

tabl

e42

Lam

b’s

sala

d(l

ettu

ceVa

leri

anel

lalo

cust

aV

aler

iana

ceae

Eat

enra

win

sala

dsor

corn

sala

d)43

Gar

den

cres

sL

epid

ium

sati

vum

Bra

ssic

acea

eE

aten

raw

insa

lads

44K

ale

(bor

ecol

e)B

rass

ica

oler

acea

conv

ar.

Bra

ssic

acea

eC

ooke

das

ave

geta

ble

acep

hala

var.

sabe

llic

a45

Hea

dle

ttuc

eL

actu

caca

pita

tava

r.ca

pita

taC

icho

riac

eae

Juic

ysu

ccul

entl

eave

sar

eea

ten

raw

insa

lads

46M

ango

ld(m

ange

l-B

eta

vulg

aris

spp.

Che

nopi

diac

eae

Coo

ked

asa

vege

tabl

ew

urze

l,be

etro

ot)

vulg

aris

var.

vulg

aris

47C

hine

se(P

ekin

g)B

rass

ica

peki

nens

isB

rass

icac

eae

Coo

ked

asa

vege

tabl

eca

bbag

e48

Bru

ssel

ssp

rout

sB

rass

ica

oler

acea

conv

ar.

Bra

ssic

acea

eC

ooke

das

ave

geta

ble

oler

acea

var.

gem

mif

era

49R

edca

bbag

eB

rass

ica

oler

acea

conv

ar.

Bra

ssic

acea

eE

aten

raw

insa

lads

oris

cook

edas

ave

geta

ble

capi

tata

var.

capi

tata

f.ru

bra

50R

omai

nele

ttuc

eL

actu

caca

pita

tava

r.cr

ispa

Cic

hori

acea

eE

aten

raw

asa

sala

d51

Spin

ach

Spin

acia

oler

acea

Che

nopo

diac

eae

Coo

ked

asa

vege

tabl

eor

isea

ten

raw

asa

sala

d52

Whi

te(c

omm

on)

Bra

ssic

aol

erac

eaco

nvar

.B

rass

icac

eae

Juic

ysu

ccul

entl

eave

sar

eea

ten

raw

inca

bbag

eca

pita

tava

r.ca

pita

tasa

lads

,or

are

ferm

ente

d(s

auer

krau

t),

f.alb

ast

eam

edor

cook

edas

ave

geta

ble

53W

inte

ren

dive

Cic

hori

cum

endi

via

Cic

hori

acea

eE

aten

raw

asa

sala

d54

Savo

yca

bbag

eB

rass

ica

oler

acea

conv

ar.

Bra

ssic

acea

eC

ooke

das

ave

geta

ble

capi

tata

,var

.sab

auda

Flo

wer

head

(cal

ix)

vege

tabl

es55

Art

icho

keC

ynar

asc

olym

usA

ster

acea

eFl

ower

head

isco

oked

asa

vege

tabl

e56

Cau

liflo

wer

Bra

ssic

aol

erac

eaco

nvar

.B

rass

icac

eae

Coo

ked

asa

vege

tabl

eor

used

insa

lads

botr

ytis

var

botr

ytis

.(r

awor

pick

led)

57B

rocc

oli

Bra

ssic

aol

erac

eaB

rass

icac

eae

The

tigh

tgre

enflo

rets

are

cook

edco

nvar

.bot

ryti

sva

r.it

alic

aas

ave

geta

ble


Tab

le17

.1.(

Con

tinu

ed)

Num

ber

Com

mon

nam

eL

atin

nam

eC

lass

,ord

er,f

amil

yC

onsu

med

as

Seed

vege

tabl

es58

Che

stnu

tC

asta

nea

sati

vaFa

gace

aeC

ooke

das

ave

geta

ble,

roas

ted,

orm

illed

into

aflo

uran

dus

edin

soup

san

dbr

ead

doug

hs59

Gre

enbe

ans

Pha

seol

usvu

lgar

isFa

bace

aeT

heim

mat

ure

pod

isco

oked

asa

vege

tabl

eor

isst

eam

edor

pick

led

for

sala

ds60

Gre

enpe

asP

isum

sati

vum

ssp.

sati

vum

Faba

ceae

The

roun

ded

smoo

thor

(wri

nkle

d)G

reen

seed

sar

eco

oked

asa

vege

tabl

eor

are

stea

med

/coo

ked

for

sala

ds

Fru

ity

vege

tabl

es61

Egg

plan

tSo

lanu

mm

elon

gena

Sola

nace

aeSt

eam

edas

ave

geta

ble

62G

arde

nsq

uash

Cuc

urbi

tape

poC

ucur

bita

ceae

Coo

ked

asa

com

pote

oras

ave

geta

ble

63G

reen

bell

pepp

erC

apsi

cum

annu

umSo

lana

ceae

Eat

enra

win

sala

ds,o

ris

cook

ed,

stea

med

orba

ked

64C

ucum

ber

Cuc

umis

sati

vus

Cuc

urbi

tace

aeE

aten

raw

insa

lads

,coo

ked

asa

vege

tabl

eor

pick

led

65O

kra

Abe

lmos

chus

escu

lent

usM

alva

ceae

Its

muc

ilag

inou

sgr

een

pods

are

cook

edas

ave

geta

ble

inso

ups

orst

ewed

,or

eate

nas

asa

lad

66To

mat

oLy

cope

rsic

only

cope

rsic

umSo

lana

ceae

The

redd

ish

pulp

ybe

rry

isea

ten

raw

,in

sala

ds,c

ooke

das

ave

geta

ble,

used

asa

past

eor

seas

oned

pure

e;im

mat

ure

gree

nto

mat

oes

are

pick

led

and

then

eate

nas

sala

d67

Zuc

chin

iC

ucur

bita

pepo

conv

ar.g

irom

onti

ina

Cuc

urbi

tace

aeT

hecy

lind

rica

ldar

kgr

een

frui

tsar

epe

eled

and

cook

edas

ave

geta

ble

17.1 Vegetables 775

Table 17.2. Production of vegetables in 2006 (1000 t)

Continent Vegetables Cabbages Artichokes Tomatoes+ melons, grand total

World 903,405 68,991 1270 125,543

Africa 56,498 2038 167 14,336America, Central 14,192 441 1 3331America, North 39,296 1262 38 11,829America, South

and Caribbean 39,220 1023 190 10,559Asia 667,827 52,200 122 66,990Europe 97,200 12,426 752 21,326Oceania 3365 42 – 503

Continent Cauliflower Pumpkin, squash Cucumbers and Eggplants (aubergines)and gourds gherkins

World 18,141 21,003 43,887 31,930

Africa 299 1669 1163 1497America, Central 365 89 582 50America, North 1324 924 1173 75America, South

and Caribbean 452 1335 859 88Asia 13,544 13,168 35,405 29,364Europe 2325 3672 5271 900Oceania 196 235 17 4

Continent Chiliesa and peppers, Onions, air dried Garlic Green beansgreen

World 25,924 61,637 15,184 6424


and Caribbean 2252 5140 386 141Asia 17,056 38,842 13,396 4574Europe 3154 8383 823 976Oceania 54 256 1 39

Continent Green peas Carrots and turnips Watermelons Cantaloupes and othermelons (muskmelons)

World 7666 26,830 100,602 27,977


and Caribbean 271 1536 3704 2070Asia 4599 12,799 85,735 20,827Europe 1193 8992 4905 2340Oceania 90 381 119 86


Table 17.2. (Continued)

Country Vegetables Country Cabbages Country Artichokes+ melonsgrand total

China 448,446 China 34,826 Italy 469India 81,947 India 6148 Spain 200USA 37,052 Russian Fed. 4073 Argentina 89Turkey 25,723 Korea Rep. 3068 Egypt 70Egypt 16,165 Japan 2287 Peru 68Russian Fed. 15,930 Ukraine 1465 China 60Iran 15,760 Indonesia 1293 Morocco 55Italy 15,133 Poland 1249 France 54Spain 12,513 Romania 1113 USA 38Japan 11,624 USA 1100 Turkey 35

∑ (%)b 75 ∑ (%)b 82 ∑ (%)b 90

Country Tomatoes Country Cauliflower Country Pumpkin, squashand gourds

China 32,540 China 8083 China 6060USA 11,250 India 4508 India 3678Turkey 9855 USA 1288 Russian Fed. 1185India 8638 Spain 460 Ukraine 1064Egypt 7600 Italy 438 USA 862Italy 6351 France 362 Egypt 690Iran 4781 Mexico 305 Iran 591Spain 3679 Poland 250 Italy 512Brazil 3278 UK 219 Cuba 447Mexico 2878 Pakistan 209 Philippines 371Russian Fed. 2415 ∑ (%)b 89 Turkey 365Greece 1712 ∑ (%)b 75∑ (%)b 76

Country Cucumbers and Country Eggplants Country Chiliesa and peppers,gherkins (aubergines) green

China 27,357 China 17,530 China 13,031Turkey 1800 India 8704 Turkey 1842Iran 1721 Egypt 1000 Mexico 1681Russian Fed. 1423 Turkey 924 Spain 1074USA 982 Japan 372 USA 894Ukraine 685 Italy 338 Indonesia 871Japan 628 Sudan 272 Nigeria 722Egypt 600 Indonesia 252 Egypt 460Indonesia 553 Philippines 192 Korea, Rep. 395Spain 500 Spain 175 Italy 345

∑ (%)b 83 ∑ (%)b 93 ∑ (%)b 82

17.1 Vegetables 777


Country Onions, air dried Country Garlic Country Green beans

China 19,600 China 11,587 China 2431India 6435 India 647 Indonesia 830USA 3346 Korea, Rep. 331 Turkey 564Pakistan 2056 Russian Fed. 256 India 420Russian Fed. 1789 USA 211 Egypt 215Turkey 1765 Egypt 162 Spain 215Iran 1685 Spain 148 Italy 191Egypt 1302 Ukraine 145 Morocco 142Brazil 1175 Argentina 116 Belgium 110Japan 1158 Myanmar 104 USA 97Mexico 1151 ∑ (%)b 90 ∑ (%)b 81Spain 1151Netherlands 983Korea, Rep. 890Morocco 882Indonesia 809

∑ (%)b 76

Country Green peas Country Carrots and Country Watermelonsturnips

China 2408 China 8700 China 71,220India 1918 Russian Fed. 1918 Turkey 3805USA 859 USA 1588 Iran 3259France 354 Poland 833 USA 1719Egypt 290 UK 833 Brazil 1505Morocco 147 Japan 762 Egypt 1500UK 133 Uzbekistan 745 Russian Fed. 986Turkey 90 France 693 Mexico 969Italy 88 Ukraine 640 Algeria 785Hungary 85 Italy 615 Korea, Rep. 778

∑ (%)b 83 Spain 600 ∑ (%)b 86Germany 504Netherlands 487Indonesia 440Turkey 402Mexico 383

∑ (%)b 75

Country Cantaloupes andother melons

China 15,525Turkey 1766USA 1208Iran 1126Spain 1042India 653Morocco 648Italy 625Mexico 570Egypt 565

∑ (%)b 85a Data including other Capsicum species.b World production = 100 %.


Table 17.3. Production of starch containing roots, rhizomes and tubers in 2006 (1000 t)

Continent Roots and tubers Potato Sweet potato Cassavagrand total (manioc)

World 736,748 315,100 123,510 226,337

Africa 216,059 16,446 12,904 122,088America, Central 2759 1951 63 508America, North 25,447 24,709 737 –America, South and Caribbean 57,276 16,015 1846 37,042Asia 307,396 129,624 107,320 67,011Europe 126,869 126,515 77 –Oceania 3700 1792 626 196

Country Roots and Country Potato Country Sweettubers potatogrand total

China 176,433 China 70,338 China 100,222Nigeria 92,214 Russian Fed. 38,573 Nigeria 3462Russian Fed. 38,573 India 23,910 Uganda 2628India 32,485 USA 19,713 Indonesia 1852Brazil 30,602 Ukraine 19,467 Vietnam 1455Indonesia 23,139 Germany 10,031 Tanzania 1056Thailand 22,842 Poland 8982 Japan 989USA 20,451 Belarus 8329 India 955Ukraine 19,467 Netherlands 6500 Burundi 835Congo 15,523 France 6354 Kenya 809Ghana 14,988 UK 5684 ∑ (%)a 93Mozambique 11,615 Canada 4995Angola 10,088 Iran 4830Germany 10,031 Turkey 4397Vietnam 9539 Bangladesh 4161Poland 8982 ∑ (%)a 75Belarus 8329Uganda 8182

∑ (%)a 75

Country Cassava (manioc)

Nigeria 45,721Brazil 26,713Thailand 22,584Indonesia 19,928Congo 14,974Mozambique 11,458Ghana 9638Angola 8810Vietnam 7714India 7620

∑ (%)a 77a World production = 100%.

17.1 Vegetables 779

Table 17.4. Average composition of vegetables (as % of fresh edible portion)

Vegetable Dry N-Com- Available Lipids Dietary Ashmatter pounds carbo- fiber

(N ×6.25) hydrates

MushroomsChampignon (cultivated

Agaricus arvensis, campestris) 9.0 4.1 0.6 0.3 2.0 1.0Chanterelle 8.5 2.6 0.2 0.5 3.3 1.6Edible boletus (Boletus edulis) 11.4 5.4 0.5 0.4 6.0 0.9

Rooty vegetablesCarrots 11.8 1.1 4.8 0.2 3.6 0.8Radish (Raphanus sativus,

elongated white fleshy root) 7.0 1.0 2.4 0.2 2.5 0.8Viper’s grass, scorzonera 23.2 1.4 2.2 0.4 18.3 1.0Parsley 16.1 2.9 6.1 0.6 1.6

Tuberous vegetables (sprouting tubers)White (Irish) potato 22.2 2.0 14.8a 0.1 2.1 1.1Celery (root) 11.6 1.6 2.3 0.3 4.2 1.0Kohlrabi 8.4 2.0 3.7 0.2 1.4 1.0Rutabaga 10.7 1.1 5.7 0.2 2.9 0.8Radish (Raphanus sativus,

reddish fleshy root) 5.6 1.1 2.1 0.1 1.6 0.9Red beet, beetroot 13.8 1.6 8.4 0.1 2.5 1.1

Tuberous root vegetablesSweet potato 30.8 1.6 24.1b 0.6 3.1 1.1Cassava (manioc) 36.9 0.9 32.0 0.2 2.9 0.7Yam 31.1 2.0 22.4 0.1 5.6 1.0

Bulbous root vegetablesOnion 11.4 1.2 4.9 0.3 1.8 0.6Leek 12.1 2.2 3.3 0.3 2.3 0.9Vegetable fennel 7.6 1.4 3.0 0.2 2.0 1.0

Stem (shoot) vegetablesAsparagus 6.5 1.9 2.0 0.2 1.3 0.6

Leafy (stalk) vegetablesRhubarb 7.3 0.6 1.4 0.1 3.2 0.6

Leafy vegetablesEndive (escarole) 5.6 1.3 2.3 0.2 1.3 0.8Kale (curly cabbage) 14.1 4.3 2.5 0.9 4.2 1.5Head lettuce 5.1 1.2 1.1 0.2 1.4 0.9Brussels sprouts 15.0 4.5 3.3 0.3 4.4 1.2Red cabbage 9.0 1.5 3.5 0.2 2.5 0.7Spinach 8.5 2.6 0.6 0.3 2.6 1.5Common (white) cabbage 9.6 1.3 4.2 0.2 3.0 0.7

Flowerhead (calix) vegetablesArtichoke 17.5 2.4 2.6 0.1 10.8 1.3Cauliflower 9.0 2.5 2.3 0.3 2.9 0.9Broccoli 10.9 3.6 2.7 0.2 3.0 1.1a Starch content 14.1%. b Starch and saccharose contents 19.6 and 2.8%, respectively.



Vegetable Dry N-Com- Available Lipids Dietary Ashmatter pounds carbo- fiber

(N ×6.25) hydrates

Seed vegetablesChestnut 55.1 2.4 41.2 1.9 8.4 1.2Green beans 10.5 2.4 5.1 0.2 1.9 0.7Green peas 24.8 6.6 12.4 0.5 4.3 0.9

Fruity vegetablesEggplant 7.4 1.2 2.5 0.2 2.8 0.6Squash 9.0 1.1 4.6 0.1 2.2 0.8Green bell pepper 7.7 1.1 2.9 0.2 3.6 0.4Cucumber 4.0 0.6 1.8 0.2 0.5 0.5Tomato 5.8 1.0 2.6 0.2 1.0 0.5

Fig. 17.1. Protein patterns of different potato cultivars obtained by isoelectric focussing on polyacrylamide gelpH 3–10. a Protein bands stained with Coomassie Blue; b Staining of trypsin and chymotrypsin inhibitors (TI,CTI): Incubation with trypsin or chymotrypsin, N-acetylphenylalanine-β-naphthyl ester and diazo blue B: in-hibitor zones appear white on a red-violet background. (according to Kaiser, Bruhn and Belitz, 1974)

17.1 Vegetables 781

to ketoglutarate in the Krebs cycle:

(17.1)

4-Methyleneglutamic acid (Table 17.5: XXXI) isformed from pyruvic acid:

(17.2)

The important precursors of onion flavor, theS-alkylcysteine sulfoxides, are formed as follows:

(17.3)

2,4-Diaminobutyric acid and some othercompounds are derived from cysteine (cf. Reac-tion 17.4).The aspartic acid semi-nitrile formed initiallycan be decarboxylated to β-amino propionitrilewhich, just as its γ-glutamyl derivative, isresponsible for osteolathyrism in animals.Hydrolysis of the semi-nitrile yields aspartic acid,hydrolysis and reduction yield 2,4- diaminobu-tyric acid, the oxalyl derivative of which, likeoxalyldiaminopropionic acid, is a human neu-rotoxin. The main symptoms of neurolathyrismare paralysis of the limbs and muscular rigidity.2,4-Diaminobutyric acid can be converted via theaspartic acid semialdehyde into 2-azetidine car-boxylic acid (XXI), which occurs, for example,in sugar beets (Table 17.5).

(17.4)


Table 17.5. Occurrence of nonprotein amino acids in plants (the Roman numerals refer to Table 17.6)

Amino acid Plant Family

Neutral aliphatic amino acidsI 2-(Methylenecyclopropyl)-glycine litchi Litchi chinensis Sapidaceae

II 3-(Methylenecyclopropyl)-L-alanine akee Bligia sapida Sapidaceae(Hypoglycine A)

III 3-Cyano-L-alanine common vetch Vicia sativa FabaceaeIV L-2-Aminobutyric acid garden sage Salvia officinalis LamiaceaeV L-Homoserine garden pea Pisum sativum Fabaceae

VI O-Acetyl-L-homoserine garden peaVII O-Oxalyl-L-homoserine vetchling Lathyrus sativum Fabaceae

VIII 5-Hydroxy-L-norvaline jackbean Canavalia ensiformis FabaceaeIX 4-Hydroxy-L-isoleucine fenugreek Trigonella Fabaceae

foenum-graecumX 1-Amino-cyclopropane- apple Malus sylvestris Rosaceae

1-carboxylic acid pear Pyrus communis Rosaceae

Sulfurcontaining amino acidsXI S-Methyl-L-cysteine garden bean Phaseolus vulgaris Fabaceae

XII S-Methyl-L-cysteinesulfoxide radish, cabbage Brassica oleracea Brassicaceaecauliflower,broccoli

XIII S-(Prop-l-enyl)cysteine garlic Allium sativum LiliaceaeXIV S-(Prop-1-enyl)cysteinesulfoxide onion Allium cepa LiliaceaeXV γ-Glutamyl-S-(prop-1-enyl)cysteine chive Allium schoenoprasum Liliaceae

XVI S-(Carboxymethyl)cysteine radish Raphanus sativus BrassicaceaeXVII 3,3′-(Methylenedithio)dialanine djenkol bean Pithecolobium lobatum Fabaceae

(Djenkolic acid)XVIII 3,3′(-2-Methylethenyl-1,2-dithio)- chive Allium schoenoprasum Liliaceae

dialanine (as γ-Glutamyl derivative)XIX S-Methylmethionine jackbean Canavalia ensiformis Fabaceae

white cabbage Brassica oleracea Brassicaceaeasparagus Asparagus officinalis Liliaceae

XX Homomethionine white cabbage Brassica oleracea Brassicaceae

Imino acidsXXI Azetidine-2-carboxylic acid sugar beet Beta vulgaris ssp. Chenopodiaceae

XXII tr-4-Methyl-L-proline apple Malus sylvestris RosaceaeXXIII cis-4-Hydroxymethyl-L-proline apple peel Malus sylvestris RosaceaeXXIV trans-4-Hydroxymethyl-L-proline loquat Eriobotrya japonica RosaceaeXXV trans-4-Hydroxymethyl-D-proline loquat Eriobotrya japonica Rosaceae

XXVI 4-Methylene-D,L-proline loquat Eriobotrya japonica RosaceaeXXVII cis-3-Amino-L-proline morel Morchella esculenta Ascomycetes

XXVIII Pipecolic acid many plantsXXIX 3-Carboxy-6,7-dihydroxy-1,2,3,4- cowage Mucuna sp. Fabaceae

tetrahydroisoquinolineXXX 1-Methyl-3-carboxy-6,7-dihydroxy- cowage Mucuna sp. Fabaceae

1,2,3,4-tetrahydroisoquinoline

Acidic amino acids and related compoundsXXXI 4-Methyleneglutamic acid peanut Arachis hypogaea Fabaceae

XXXII 4-Methyleneglutamine peanut Arachis hypogaea FabaceaeXXXIII N5-Ethyl-L-glutamine (L-Theanine) tea Thea sinensis TheaceaeXXXIV L-threo-4-Hydroxyglutamic acid

17.1 Vegetables 783

Table 17.5. (continued)

Amino acid Plant Family

XXXV 3,4-Dihydroxyglutamic acid garden cress Lepidium sativum Brassicaceaerhubarb Rheum rhabarbarum Polygonaceaecarrot Daucus carota Apiaceaecurrant Ribis rubrum Saxifragaceaespinach Spinacia oleracea Chenopodiaceaelongwort Angelica archangelica Apiaceae

XXXVI L-2-Aminoadipic acid many plants

Basic amino acids and related compoundsXXXVII N2-Oxalyl-diaminopropionic acid vetchling Lathyrus sativus Fabaceae

XXXVIII N3-Oxalyl-diaminopropionic acid vetchling Lathyrus sativus FabaceaeXXXIX 2,4-Diaminobutyric acid sugar beet Beta vulgaris ssp. Chenopodiaceae

(as N4-Lactyl compound)XL 2-Amino-4-(guanidinooxy)butyric jackbean Canavalia ensiformis Fabaceae

acid (Canavanine) soybean Glycine max FabaceaeXLI 4-Hydroxyornithine common Vicia sativa Fabaceae

vetchXLII L-Citrulline watermelon Citrullus lanatus Cucurbitaceae

XLIII Homocitrulline horse bean Vicia faba FabaceaeXLIV 4-Hydroxyhomocitrulline horse bean Vicia faba FabaceaeXLV 4-Hydroxyarginine common Vicia sativa Fabaceae

vetchXLVI 4-Hydroxylysine garden sage Salvia officinalis Lamiaceae

XLVII 5-Hydroxylysine lucern Medicago sativa FabaceaeXLVIII N6-Acetyl-L-lysine sugar beet Beta vulgaris Chenopodiaceae

XLIX N6-Acetyl-allo-5-hydroxy-L-lysine sugar beet Beta vulgaris Chenopodiaceae

Heterocyclic amino acidsL 3-(2-Furoyl)-L-alanine buck wheat Fagopyrum esculentum Polygonaceae

LI 3-Pyrazol-l-ylalanine watermelon Citrullus lanatus CucurbitaceaeLII 1-Alanyluracil (Willardin) cucumber Cicumis sativus Cucurbitaceae

garden pea Pisum sativum FabaceaeLIII 3-Alanyluracil (Isowillardin) garden pea Pisum sativum FabaceaeLIV 3-Amino-3-carboxypyrrolidine musk melon Cucurbita monlata CucurbitaceaeLV 3-(2,6-Dihydroxypyrimidine-5-yl)- garden pea Pisum sativum Fabaceae

alanineLVI 3-(Isoxazoline-5-one-2-yl)alanine garden pea Pisum sativum Fabaceae

LVII 3-(2-β-D-Glucopyranosyl- garden pea Pisum sativum Fabaceaeisoxazoline-5-one-4-yl)alanine

Aromatic amino acidsLVIII N-Carbamoyl-4-hydroxy- horse bean Vicia faba Fabaceae

phenylglycineLIX L-3,4-Dihydroxyphenylalanine horse bean Vicia fabea Fabaceae

cowage Mucuna sp. FabaceaeOther amino acids

LX γ-Glutamyl-L-β-phenyl-β-alaninie adzuki bean Phaseolus angularis FabaceaeLXI Saccharopine yeast Saccharomyces Saccharomy-

cerevisiae cetaceae

Freshly harvested mushrooms contain aprox.0.1% agaritin, β-N-(γ-L(+)-glutamyl)-4 hy-droxymethylphenylhydrazine. Enzymes present

can hydrolyze agaritin and oxidize the re-leased 4-hydroxymethyl-phenylhydrazine to thediazonium salt.


Table 17.6. Structures of nonprotein amino acids in plants (structures and Roman numerals refer to Table 17.5)

17.1 Vegetables 785




17.1.2.1.3 Amines

The presence of amines has been confirmed invarious vegetables; e. g., histamine, N-acetylhist-amine and N,N-dimethylhistamine in spinach;and tryptamine, serotonin, melatonin and tyra-mine in tomatoes and eggplant (cf. 18.1.2.1.3).

17.1.2.2 Carbohydrates

17.1.2.2.1 Mono- and Oligosaccharides,Sugar Alcohols

The predominant sugars in vegetables areglucose and fructose (0.3–4%) as well as su-crose (0.1–12%). Other sugars occur in smallamounts; e. g. glycosidically bound apiose inUmbelliferae (celery and parsley); 1F-β- and6G-β-fructosylsaccharose in the allium group(onions, leeks); raffinose, stachyose and verbas-cose in Fabaceae; and mannitol in Brassicaceaeand Cucurbitaceae.

17.1.2.2.2 Polysaccharides

Starch occurs widely as a storage carbohydrateand is present in large amounts in some root andtuber vegetables. In Compositae (e. g., artichoke,viper’s grass, bot. Scorzonera), inulin, rather thanstarch, is the storge carbohydrate.Other polysaccharides are cellulose, hemicel-luloses and pectins. The pectin fraction hasa distinct role in the tissue firmness of vege-tables. Tomatoes become firmer as the totalpectin content and the content of some minerals(Ca, Mg) increases, and as the degree of ester-ification of the pectin decreases. In processingcauliflower (cf. 17.2.3), 70 ◦C is favorable forpreserving tissue firmness. The reason for thiseffect is the presence of pectinmethylesterasewhich, in vegetables, is fully inactivated onlyat temperatures above 88 ◦C, while at 70 ◦C itis active and provides a build-up of insolublepectates. For the conversion of protopectin topectin during plant tissue maturation or ripeningsee 18.1.3.3.1.

17.1 Vegetables 787

Table 17.7. Carotenoidsa in vegetablesb

Green bell Red pepper Tomato Watermelonpepper (paprika)

Total 0.9–3.0 12.7–28.4 5.1–8.5 5.5carotenoidsb

Phytoene (I) − 0.03 1.3 −Phytofluene (II) 0.01 0.56 0.7α-Carotene (VI) 0.01 0.1 − −β-Carotene (VII) 0.54 2.7 0.59 0.23γ-Carotene (V) − − − 0.09ζ -Carotene (III) 0.01 0.45 0.84 −Lycopene (IV) 4.7 4.5α-Cryptoxanthinβ-Cryptoxanthin

}0.7 1.3 0.5 0.46

Lutein (IX) 0.6 − 0.12 0.01Zeaxanthin (VIII) 0.02 3.9 − −Violaxanthin (XIII) 0.6 2.4 − −Capsanthin (X) 9.4 − −Neoxanthin (XX) 0.23 0.16 − −a Roman numerals refer to structural formula presented in Chapter 3.8.4.1.b Values in mg carotene/100 g fresh weight.

17.1.2.3 Lipids

The lipid content of vegetables is generallylow (0.1–0.9%). In addition to triacylglyce-rides, glyco- and phospholipids are present.Carotenoids are occasionally found in largeamounts (cf. 18.1.2.3.2). Table 17.7 providesdata on carotenoid compounds in green belland paprika peppers, tomato and watermelon.For the occurrence of bitter cucurbitacins inCucurbitaceae, see 18.1.2.3.3.

17.1.2.4 Organic Acids

The organic acids present in the highest concen-tration in vegetables are malic and citric acids(Table 17.8). The content of free titratable acidsis 0.2–0.4 g/100 g fresh tissue, an amount whichis low in comparison to fruits. Accordingly, thepH, with several exceptions such as tomato orrhubarb, is relatively high (5.5–6.5). Other acidsof the citric acid cycle are present in negligibleamounts. Oxalic acid occurs in larger amounts insome vegetables (Table 17.8).

Table 17.8. Organic acids in vegetables (mg/100 gfresh weight)

Vegetable Malic Citric Oxalicacid acid acid

Artichoke 170 100 8.8Eggplant 170 10 9.5Cauliflower 201 20 –Green beans 177 23 20–45Broccoli 120 210 –Green peas 139 142 –Kale 215 220 7.5Carrot 240 12 0–60Leek – 59 0–89Rhubarb 910 137 230–500Brussels sprouts 200 350 6.1Red beet 37 195 181Sorrel – – 360White common cabbage 159 73 –Onion 170 20 5.5Potato 92 520 –Tomato 51 328 –Spinach 42 24 442


17.1.2.5 Phenolic Compounds

The phenolic compounds in plant material aredealt with in detail in 18.1.2.5. Hydroxyben-zoic and hydroxycinnamic acids, flavones andflavonols also occur in vegetables. Table 17.9provides data on the occurrence of anthocyaninsin some vegetables.

17.1.2.6 Aroma Substances

Characteristic aroma compounds of severalvegetables will be dealt with in more detail. Thenumber following each vegetable corresponds tothat given in Table 17.1. For aroma biosynthesissee 5.3.2.

17.1.2.6.1 Mushrooms (4)

The aroma in champignons originates from(R)-l-octen-3-ol derived from enzymatic oxida-tive degradation of linoleic acid (cf. 3.7.2.3).A small part of the alcohol is oxidized to 1-octen-3-one in fresh champignons. This compoundhas a mushroom-like odor when highly dilutedand a metallic odor in higher concentrations.It contributes to the mushroom odor becauseits threshold value is lower by two powersof ten. Heating of champignons results inthe complete oxidation of the alcohol to theketone. Dried morels are a seasoning agent.The following compounds were identified as

Table 17.9. Anthocyanins in vegetables

Vegetable Anthocyanin

Eggplant Delphinidin-3-(p-coumaroyl-L-rhamnosyl-D-glucosyl)-5-D-glucoside

Radish Pelargonidin-3-[glucosyl(1 → 2)-6-(p-coumaroyl)-β-D-glucosido]-5-glucosidePelargonidin-3-[glucosyl(1 → 2)-6-(feruloyl)-β-D-glucosido]-5-glucoside

Red cabbage Cyanidin-3-sophorosido-5-glucoside(sugar moiety esterified with sinapicacid, 1–3 moles)

Onion Cyanidin glycoside(red shell) Peonidin-3-arabinoside

typical taste-compounds: (S)-morelid, (mixtureof (S)-malic acid 1-O-α- and (S)-malic acid1-O-β-D-glucopyranoside), L-glutamic acid,L-aspartic acid, γ-aminobutyric acid, malic acid,citric acid, acetic acid. (S)-Morelid intensifiesthe taste of L-glutamic acid and of NaCl. Themushroom Lentium ediodes, which is widelyconsumed in China and Japan, has a very intensearoma. The presence of 1,2,3,5,6-pentathiepane(lenthionine) has been confirmed, and it isa typical impact compound:

(17.5)

Its threshold values are 0.27–0.53 ppm (in water)or 12.5–25 ppm (in edible oil) It is derivedbiosynthetically from an S-alkyl cysteine sulfox-ide, lentinic acid. Truffles, edible potato-shapedfungi, contain approx. 50 ng/g 5α-androst-16-ene-3 α-ol, which has a musky odor thatcontributes to the typical aroma (cf. 3.8.2.2.1).

17.1.2.6.2 Potatoes (23)

3-Isobutyl-2-methoxypyrazine and 2,3-diethyl-5-methylpyrazine belong to the key aroma sub-stances in raw potatoes. These two pyrazines arealso essential for the aroma of boiled potatoes.The substances responsible for the aroma ofboiled potatoes are shown in Table 17.10.The potato aroma note can be reproduced withan aqueous solution (pH 6) of methanethiol,dimethylsulfide, 2,3-diethyl-5-methylpyrazine,3-isobutyl-2-methoxypyrazine and methional inthe concentrations given in Table 17.10. Al-though it smells of boiled potatoes, methionalonly rounds off this aroma quality. In the dryingof blanched potatoes to give a granulate, theconcentrations of the two pyrazines decrease and,therefore, the intensity of the potato note alsodecreases.

17.1.2.6.3 Celery Tubers (24)

Celery aroma is due to the occurrence ofphthalides in leaves, root, tuber and seeds. The

17.1 Vegetables 789

Table 17.10. Odorants in boiled potatoesa

Odorants Concentrationb

(µg/kg)

Methylpropanal 4.42-Methylbutanal 5.73-Methylbutanal 2.6Hexanal 102.0(E,E)-2,4-Decadienal 7.3trans-4,5-Epoxy-(E)-2-decenal 58.0Methional 65.0Dimethyltrisulfide 1.0Methanethiol 15.4Dimethylsulfide 8.82,3-Diethyl-5-methylpyrazine 0.173-Isobutyl-2-methoxypyrazine 0.074-Hydroxy-2,5-dimethyl-3(2H)- 67.0

furanone (HD3F)3-Hydroxy-4,5-dimethyl-2(5H)- 2.2

furanone (HD2F)Vanillin 1000aPotatoes, boiled in water for 40 min, then peeled.bReference: fresh weight; water content: 78%.

main compound 3-butyl-4,5-dihydrophthalide(sedanolide: I, Formula 17.6) occurs in amountsof 3–20 mg/kg. In addition, 3-butylphthalide-(II, 0.6–1.6 mg/kg), 3-butyl-3a,4,5,6-tetrahydro-phthalide (III, 1.0–4.4 mg/kg), 3-butylhexa-hydrophthalide (IV) and (Z)-3-butyliden-4,5-dihydrophthalide (Z-ligustilide: V, 0.6–2 mg/kg)have been identified. The (S)-enantiomer of IIplays a big part in the aroma and it not onlypredominates, but also has a much lower odorthreshold when compared with the (R)-enantio-mer (S: 0.01 µg/kg; R: 10 µg/kg, water). Of the

Table 17.11. Glucosinolates in different types of cabbage (mg/kg fresh weight)

Compounda Broccoli Red Brussels Cauliflower Savoy Whitecabbage sprouts cabbage cabbage

Glucobrassicin (Ia) 20 16 31 21 46 224-Hydroxy-glucobrassicin (Ib) 54-Methoxy-glucobrassicin (Ic) 4Glucoiberin (II) 4 11 24 16 52 23Gluconapin (III) n.d. 8 5 0.1 0.3 2Glucoraphanin (IV) 21 21 4 0.7 1 4Progoitrin (R-V) n.d. 18 11 3 2 8Sinigrin (VI) n.d. 14 44 17 46 30a The chemical structures are shown in Formula 17.7 und 17.10.n.d.: not detected.

eight possible stereoisomers of the phthalide IV,the enantiomers 3R,3aR,7aS and 3S,3aR,7aSdominate in celery. But their contribution tothe aroma must be low because of the highodor threshold (>125 µg/kg). Apart from thephthalides, the participation of (E,Z)-1,3,5-undecatriene in the aroma is under discussion.

(17.6)

17.1.2.6.4 Radishes (27)

The sharp taste of the radish is due to 4-me-thylthio-trans-3-butenyl-isothiocyanate, which isreleased from the corresponding glucosinolate af-ter the radish is sliced. Glucosinolates are widelydistributed among Brassicaceae and some otherplant families. Their occurrence in some types ofcabbage is presented in Table 17.11.


Glucosinolates are hydrolyzed by myrosinase,a thioglucosidase enzyme, to the correspondingisothiocyanates (mustard oils) on disintegrationof the tissue (Formula 17.7). The residue R forthe glucosinolates presented in Table 17.11 isshown in Formula 17.8.

(17.7)

(17.8)

The decomposition corresponds to a Lossen’s re-arrangement of a hydroxamic acid. In additionto isothiocyanates, rhodanides and nitriles havebeen observed among the reaction products.The isothiocyanates can react further, e. g., withhydroxy compounds or thiols, to form thio-urethanes or dithiourethanes. In the presence ofamines, thioureas result; while hydrolysis yieldsthe corresponding amines and releases CO2 andH2S:

(17.9)

Biosynthesis of glucosinolates (reaction 17.10)starts from the corresponding amino acids, andproceeds via an oxime (I) and thiohydroximicacid (III). The intermediate reactions between

steps I and III are not yet clarified. Tests with14C- and 35S-labelled compounds suggestthat the aci-form of the corresponding nitro-compound (II) functions as a thiol acceptor.Cysteine may be involved as a thiol donor. Thesulfation is achieved by 3′-phosphoadenosine-5′ -phosphosulfate (PAPS). The biosynthetic path-way for cyanogenic glycosides branches at thealdoxime (I) intermediate (cf. 16.2.6).

(17.10)

17.1.2.6.5 Red Beets (28)

Geosmin (structure cf. 5.1.5) is the character im-pact compound of the red beet.

17.1.2.6.6 Garlic (33) and Onions (34)

The compound which causes tears (the lachry-matory factor) is (Z)-propanethial-S-oxide (II)which, once the onion bulb is sliced, is de-rived from trans-(+)-S-(1-propenyl)-L-cysteinesulfoxide (I) by the action of the enzyme al-liinase. Alliinase has pyridoxalphosphate asits coenzyme (cf. reaction sequence 17.11).Chopping of onions releases 3-mercapto-2-methylpentan-1-ol, which, with its very lowthreshold of 0.0016 µg/l (water), smells ofmeat broth and onions. Raw onions contain8–32 µg/kg, and onions which have been cut,stored for 30 minutes and then cooked contain

17.1 Vegetables 791

34–246 µg/kg. The formation involves theattachment of H2S to the aldol condensationproduct of propanal and enzymatic reduction ofthe carbonyl group.

(17.11)

Alkylthiosulfonates (III) are also respon-sible for the aroma of raw onions, whilepropyl- and propenyl disulfides (IV) andtrisulfides are also supposed to play a rolein the aroma of cooked onions. The aromaof fried onions is derived from dimethyl-thiophenes.Precursors of importance for the aroma ofonions, other than compound I, are S-methyl andS-propyl-L-cysteine sulfoxide. Precursor I isbiosynthesized from valine and cysteine (cf. re-action sequence 17.12).

(17.12)

The key precursor for garlic aroma is S-allyl-L-cysteine sulfoxide (alliin) which, as in onions,occurs in garlic bulbs together with S-methyl-and S-propyl-compounds. The allyl and propyl-compounds are assumed to be synthesized fromserine and corresponding thiols:

(17.13)

Diallylthiosulfinate (allicin) and diallyldisulfideare formed from the main component by meansof the enzyme alliinase. Both are character impactcompounds of garlic.

17.1.2.6.7 Watercress (39)

Phenylethylisothiocyanate is responsible forthe aroma of this plant of the mustard fam-


ily (Brassicaceae). Decomposition of thecorresponding glucosinolate gives phenylpropi-onitrile, the main component, and some othernitriles, e. g., 8-methylthiooctanonitrile and9-methylthiononanonitrile.

17.1.2.6.8 White Cabbage, Red Cabageand Brussels Sprouts (52, 49, 48)

Mustard oil is more than 6% of the total volatilefraction of cooked white and red cabbages. Thereis such a high proportion of allylisothiocyanate(I, Formula 17.14) present that it participates inthe aroma of boiled white cabbage in spite of itshigh odor threshold of 375 µg/kg (water). In ad-dition, 2-phenylethylthiocyanate (II, odor thres-hold 6 µg/kg, water), 3-methylthiopropylisothio-cyanate (III, 5 µg/kg) and 2-phenylethylcyanide(IV, 15 µg/kg) could be involved in the aroma.Dimethylsulfide is another important odorantformed during the cooking of cabbage andother vegetables. It also appears that 3-alkyl-2-methoxypyrazine plays a role in cabbage aroma.

(17.14)

The total impact of the aroma in cooked frozenBrussels sprouts is less satisfactory than incooked fresh material. In the former case,analysis has revealed comparatively little allylmustard oil and more allylnitrile. Isothiocyanatesin low concentrations are pleasant and appetite-stimulating, while nitriles are reminiscent ofgarlic odor. The shift in the concentration ratioof the two compounds is attributed to myrosinaseenzyme inactivation during blanching prior tofreezing. As a consequence of this, allylglucosi-nolate in frozen Brussels sprouts is thermallydegraded only on subsequent cooking, preferen-tially forming nitriles. Goitrin is responsible for

the bitter taste that can occur in Brussels sprouts(cf. 17.1.2.9.3).

17.1.2.6.9 Spinach (51)

The compounds (Z)-3-hexenal, methanethiol,(Z)-1,5-octadien-3-one, dimethyltrisulfide, 3-iso-propyl-2-methoxypyrazine and 3-sec-butyl-2-methoxypyrazine contribute to the aroma of thefresh vegetable. In cooked spinach, (Z)-3-hexenaldecreases and dimethylsulfide, methanethiol,methional and 2-acetyl-1-pyrroline are dominant.

17.1.2.6.10 Artichoke (55)

1-Octen-3-one, the herbaceous smelling 1-hexen-3-one (odor threshold 0.02 µg/kg, water) andphenylacetaldehyde contribute to the aroma ofboiled artichokes with high aroma values.

17.1.2.6.11 Cauliflower (56), Broccoli (57)

In cooked cauliflower and broccoli, the aromacompounds of importance are the sulfur com-pounds mentioned for white cabbage. 3-Methyl-thiopropylisothiocyanate, 3-methylthiopropyl-cyanide (odor threshold 82 µg/kg, water) andnonanal contribute to the typical aroma ofcauliflower and 4-methylthiobutylisothiocyanate(V, cf. Formula 17.14), 4-methylthiobutylcyanideas well as II and IV to the aroma of broccoli.During blanching of these vegetables, cystathionine-β-lyase (EC 4.4.1.8, cystine lyase) mustbe inactivated because this enzyme, whichcatalyzes the reaction shown in formula 17.15,produces an aroma defect. The undesirable aromasubstances are formed by the degradation of thehomocysteine released.

(17.15)

17.1 Vegetables 793

17.1.2.6.12 Green Peas (60)

The aroma of green peas is derived from aldehy-des and pyrazines (3-isopropyl-, 3-sec-butyl- and3-isobutyl-2-methoxypyrazine).

17.1.2.6.13 Cucumbers (64)

The following aldehydes play an important role incucumber aroma: (E,Z)-2,6-nonadienal and (E)-2-nonenal. Linoleic and linolenic acids, as shownin Fig. 3.31, are the precursors for these andother aldehydes (Z)-3-hexenal, (E)-2-hexenal,(E)-2-nonenal.

17.1.2.6.14 Tomatoes (66)

Among a large number of volatile compounds,(Z)-3-hexenal, β-ionone, hexanal, β-damasce-none, 1-penten-3-one, and 3-methylbutanal areof special importance for the aroma of tomatoes(cf. Table 17.12).

Table 17.12. Odorants in tomatoes and tomato paste

Compound Aroma valuea

Tomato Tomato-paste

(Z)-3-Hexenal 5×104 <30β-Ionone 6.3×102 –b

Hexanal 6.2×102 –(E)-β-Damascenone 5×102 5.7×103

1-Penten-3-one 5×102 –3-Methylbutanal 130 152(E)-2-Hexenal 16 –2-Isobutylthiazole 10 –Dimethylsulfide – 1.4×103

Methional – 6503-Hydroxy-4,5-dimethyl- – 213

5(2H)-furanone (HD2F)4-Hydroxy-2,5-dimethyl- – 138

3(2H)-furanone (HD3F)Eugenol – 95Methylpropanal – 40a The aroma values were calculated on the basis of theodor threshold in water.b The compound does not contribute to the aroma here.

In tomato paste, for example (cf. Table 17.12),it was found that the changes in aroma causedby heating are primarily due to the formation ofdimethylsulfide, methional, the furanones HD2Fand HD3F and the increase in β-damascenone,and a substantial decrease in (Z)-3-hexenal andhexanal.

17.1.2.7 Vitamins

Table 17.13 provides data on the vitamin contentof some vegetables. The values given mayvary significantly with vegetable cultivar andclimate. In spinach, for example, the ascorbicacid content varies from 40–155 mg/100g freshweight. Freshly harvested potatoes contain15–20 mg/100 g of vitamin C. The content dropsby 50% on storage (4 ◦C) for 6–8 months and by40–60% on peeling and cooking.

17.1.2.8 Minerals

Table 17.14 reviews the mineral content of somevegetables. Potassium is by far the most abun-dant constituent, followed by calcium, sodiumand magnesium. The major anions are phosphate,chloride and carbonate. All other elements arepresent in much lower amounts. For nitrate con-tent see 9.8.

17.1.2.9 Other Constituents

Plant pigments other than carotenoids and antho-cyanins, e. g., chlorophyll and betalains, are alsoof great importance in vegetables and are coveredin this section together with goitrogenic com-pounds occurring in Brassicaceae.

17.1.2.9.1 Chlorophyll

The green color of leaves and unripe fruits is dueto the pigments chlorophyll a (blue-green) andchlorophyll b (yellow-green), occurring togetherin a ratio shown in Table 17.15 (see Formula17.16). Figure 17.2 shows the absorption spectraof chlorophylls a and b. Removal of magnesium


Table 17.13. Vitamin content in vegetables (mg/100g fresh weight)

Vegetable Ascorbic acid Thiamine Riboflavin Nicotinicacid Folacid α-Tocopherol β-Carotene

Artichoke 8 0.14 0.01 1.0 – 0.19 0.10Eggplant 5 0.05 0.05 0.6 0.03 0.03 0.04Cauliflower 78 0.09 0.10 0.7 0.09 0.07 0.01Broccoli 100 0.10 0.18 0.9 0.11 0.61 0.9Kale 105 0.10 0.26 2.1 0.19 1.7 5.2Cucumber 8 0.02 0.03 0.2 0.02 0.06 0.4Head lettuce 10 0.06 0.09 0.3 0.06 0.6 1.1Carrot 8 0.06 0.05 0.6 0.03 0.4 7.6Green bell pepper 138 0.05 0.04 0.3 0.06 2.5 0.5Leek 26 0.09 0.06 0.5 0.10 0.5 0.7Radish 26 0.03 0.03 0.4 0.02 – 0.01Brussels sprouts 102 0.10 0.16 0.7 0.10 0.6 0.5Red beet 10 0.03 0.05 0.2 0.08 0.04 0.01Red cabbage 61 0.06 0.04 0.4 0.04 1.7 0.02Celery 8 0.05 0.06 0.7 0.01 – 2.9Asparagus 20 0.11 0.10 1.0 0.11 2.0 0.5Spinach 51 0.10 0.20 0.6 0.15 1.3 4.8Tomato 23 0.06 0.04 0.5 0.02 0.8 0.6

Table 17.14. Minerals in vegetables (mg/100g fresh weight)

Vegetable K Na Ca Mg Fe Mn Co Cu Zn P Cl F I

Potato 418 2.7 6.4 21 0.4 0.15 0.001 0.09 0.3 50 50 0.01 0.003Spinach 554 69 60 117 3.8 0.6 0.002 0.1 0.6 46 54 0.08 0.012Carrot 321 61 37 13 0.4 0.2 0.001 0.05 0.3 35 59 0.02 0.002Cauliflower 328 16 20 17 0.6 0.2 – 0.05 0.2 54 19 0.01 0.006Green beans 256 1.7 51 26 0.8 0.2 – 0.1 0.3 37 13 0.01 0.003Green peas 296 2 26 33 1.9 0.4 0.003 0.2 0.9 119 40 0.02 0.004Cucumber 141 8.5 15 8 0.5 0.1 – 0.04 0.2 17 37 0.01 0.003Red beet 336 86 29 1.4 0.9 0.2 0.01 0.08 0.4 45 0.2 0.01 0.005Tomato 297 6.3 14 20 0.5 0.1 0.01 0.06 0.2 26 30 0.02 0.002White common 227 13 46 23 0.5 0.2 0.01 0.03 0.2 36 37 0.01 0.005cabbage

Table 17.15. Chlorophylls a and b in vegetables andfruit

Food Chlorophyll a Chlorophyll b(mg/kg)a

Green beans 118 35Kale 1898 406White cabbage 8 2Cucumber 64 24Parsley 890 288Green bell pepper 98 33Green peas 106 22Spinach 946 202Kiwi 17 8Gooseberry 5 1a Refers to fresh weight.

from the chlorophylls gives pheophytins a and b,both of which are olive-brown. Replacing mag-nesium by metal ions such as Sn2+ or Fe3+ like-wise yields greyish-brown compounds. If, how-ever, Mg2⊕ is replaced by Zn2⊕ and Cu2⊕ (weightratio 10:1), a green colored complex is formed,which is very stable at pH 5.5. Upon removal ofthe phytol group, for example by the action ofthe chlorophyllase enzyme, the chlorophylls areconverted into chlorophyllides a and b, while thehydrolysis of pheophytins yields pheophorbidesa and b.Chlorophylls and pheophytins are lipophilic dueto the presence of the phytol group, while chloro-phyllides and pheophorbides, without phytol,

17.1 Vegetables 795

(17.16)

are hydrophilic. Conversion of chlorophylls topheophytins, which is accompanied by a colorchange, occurs readily upon heating plant ma-terial in weakly acidic solutions and, less read-ily, at pH 7. Color changes are encountered mostvisibly in processing of green peas, green beans,kale, Brussels sprouts and spinach. Table 17.16shows that higher temperatures and shorter heat-ing times provide better color retention than pro-longed heating at lower temperatures.Chlorophyllase is mostly inactivated when vege-tables are blanched, hence chlorophyllides and

Fig. 17.2. Absorption spectra of chlorophylls a (I) andb (II). Solvent: diethyl ether (I) or diethyl ether +1%CCI4 (II)

pheophorbides are rarely detected. However, inthe fermentation of cucumbers, chlorophyllase isactive. The result is a color change from dark-green to olive-green, caused by large amounts ofpheophorbides.On stronger heating (sterilization, drying), a partof the pheophytins undergoes hydrolysis, re-leasing carbonic acid monomethylester whichdecomposes into CO2 and methanol:

(17.17)

The corresponding pyropheophytins are formedwhich can be determined next to the pheophytinsby using HPLC (Fig. 17.3). For example,Table 17.17 shows the changes in the chloro-pigments of spinach as a function of the durationof heat sterilization.A change in color occurs during storage of driedvegetables, its extent increases with increasingwater content. The conversion of chlorophyllsto pheophytins continues in blanched vegeta-

Fig. 17.3. HPLC of chloro-pigments from sterilizedcans. Green beans (a), spinach (b) (according toSchwartz and von Elbe, 1983). 1 Pheophytin b, 2 py-ropheophytin b, 3 pheophytin a, 4 pyropheophytin a


Table 17.16. Changes in the chlorophyll fraction during processing (values in % of the total pigment content ofunprocessed vegetables)

Vegetable Process Chlorophylls Chlorophyllides Pheophytins Pheophorbides

a b a b a b a b

Green beans Untreated 49 25 0 0 18 8 0 0Blanched, 37 24 0 0 19 10 0 04 min/100 ◦C

Cucumbers Untreated 51 30 0 0 15 5 0 0Blanched, 34 24 6 3 22 1 5 74 min/100 ◦C

Cucumbers Untreated 67 33 0 0 0 0 0 0Fermented (pickled), 6 days 4 7 3 5 10 3 47 15Fermented (pickled), 24 days 0 0 0 0 16 7 57 28

Table 17.17. Effects of the heat sterilization of spinachon the composition of chloropigments (mg/g solids)

Chlorophyll Pheophytin Pyropheophytin

Heatingto 121 ◦C(min) a b a b a b

Control 6.98 2.49 0 0 0 02 5.72 2.46 1.36 0.13 0 04 4.59 2.21 2.20 0.29 0.12 07 2.81 1.75 3.12 0.57 0.35 0

15 0.59 0.89 3.32 0.78 1.09 0.2730 0 0.24 2.45 0.66 1.74 0.5760 1.01 0.32 3.62 1.24

bles even during frozen storage. In beans andBrussels sprouts, immediately after blanching(2 min at 100 ◦C), the pheophytin contentamounts to 8–9%, while after storage for12 months at −18 ◦C it increases to 68–83%.Pheophytin content rises from 0% to only 4–6%in paprika peppers and peas under the sameconditions.

17.1.2.9.2 Betalains

Pigments known as betalains occur in centrosper-mae, e. g., in red beet and also in some mush-rooms (the red cap of fly amanita). They con-sist of red-violet betacyanins (λmax ∼540 nm) andyellow betaxanthins (λmax ∼480 nm). They havethe general structure:

(17.18)

About 50 betalains have been identified. The ma-jority have an acylated sugar moiety. The acids in-volved are sulfuric, malonic, caffeic, sinapic, cit-ric and p-coumaric acids. All betacyanins are de-rived from two aglycones: betanidin (I) and iso-betanidin (II), the latter being the C-15 epimer ofbetanidin:

(17.19)

17.1 Vegetables 797

(17.20)

Betanin is the main pigment of red beet. It is a be-tanidin 5-0-β-glucoside. The betaxanthins haveonly the dihydropyridine ring in common. Theother structural features are more variable thanin betacyanins. Examples of betaxanthins are nat-ural vulgaxanthins I and II, also from red beet(Beta vulgaris):

(17.21)

Betalain biosynthesis starts with dopa by openingof its benzene ring, followed by cyclizationto a dihydropyridine. The (S)-betalamic acidwhich is formed undergoes condensation with(S)-cyclodopa to betacyanins or with someother amino acids to betaxanthins (cf. reactionsequence 17.21).Red betanin is water soluble and is used to colorfood. Its application is, however, limited becauseit hydrolytically decomposes into the colorlesscyclodopa-5-0-β-glucoside and the yellow (S)-betalamic acid. This reaction is reversible. Sincethe activation energy of the forward reaction(72 kJ ×mol−1), greatly exceeds that of the backreaction (2.7 kJ × mol−1), a part of the betaninis regenerated at higher temperatures. Betanin isalso sensitive to oxygen.


17.1.2.9.3 Goitrogenic Substances

Brassicaceae contain glucosinolates whichdecompose enzymatically, e. g., into rhodanides.For example, in savoy cabbage the rhodanidecontent is 30 mg/100g fresh weight, while incauliflower it is 10 mg and in kohlrabi 2 mg.Since rhodanide interferes with iodine uptakeby the thyroid gland, large amounts of cabbagetogether with low amounts of iodine in the dietmay cause goiter.Oxazolidine-2-thiones are also goitrogenic. Theyoccur as secondary products in the enzymatichydrolysate of glucosinolates when the initiallyformed mustard oils contain a hydroxy group inposition 2:

(17.22)

The levels of the corresponding glucosinolatesare up to 0.02% in yellow and white beets andup to 0.8% in seeds of Brassicaceae (all mem-bers of the cabbage family; kohlrabi, turnip; rape-seed). The leaves contain only negligible amountsof these compounds.There are 3–15 mg/kg of 5-vinyloxazolidine-2-thione in sliced turnips. Direct intake ofthiooxazolidones by humans is unlikely sincethe vegetable is generally consumed in cookedform. Consequently, the myrosinase enzyme isinactivated and there is no release of goitrogeniccompounds. However, brussels sprouts are excep-tions, as higher amounts (70–110 mg/kg) ofbitter tasting goitrin is formed from progoitrin

(17.23)

during cooking. An indirect intake is possiblethrough milk when such plants are used as an-imal feed, resulting in a goitrogenic compoundcontent of 50–100 µg/l of milk. The oxazolidine-2-thiones inhibit the iodination of tyrosine, an ef-fect unlike that of rhodanides, which may be off-set not by intake of iodine but only by intake ofthyroxine.

17.1.2.9.4 Steroid Alkaloids

Steroid alkaloids are plant constituents havinga C27 steroid skeleton and nitrogen content.Solanaceae contain these compounds, theiroccurrence in potatoes being the most interestingfrom a food chemistry point of view.The main compounds in the potato tuber areα-solanine (Formula 17.23) and α-chaconine,which differs from the former compound only inthe structure of the trisaccharide (substitution ofgalactose and glucose with glucose and rham-nose). α-Solanine and α-chaconine and theiraglycone solanidine have a bitter/burning taste(Table 17.18) and these sensations last long. Thetaste thresholds have to be determined in thepresence of lactic acid due to a lack of water

Table 17.18. Taste of the steroid alkaloids occurring inpotatoes

Compounda Taste threshold (mg/kg)

Bitter Burning

α-Solanine 3.1 6.25α-Chaconine 0.78 3.13Solanidine 3.1 –Caffeine 12.5 –a Dissolved in 0.02% lactic acid.

17.2 Vegetable Products 799

solubility. Caffeine was used as a comparison. Inpotatoes, the bitter taste appears if the concentra-tion of the steroid alkaloids exceeds 73 mg/kg.Stress during growth and the exposure of thepotatoes to light after harvesting stimulate theformation of these bitter substances.

17.1.3 Storage

The storability of vegetables varies greatly anddepends mostly on type, but also on vegetablequality. While some leafy vegetables, such aslettuce and spinach as well as beans, peas,cauliflower, cucumbers, asparagus and tomatoeshave limited storage time, root and tuber vegeta-bles, such as carrots, potatoes, kohlrabi, turnips,red table beets, celery, onions and late cabbagecultivars, can be stored for months. Cold storageat high air humidity is the most appropriate. Ta-ble 17.19 lists some common storage conditions.The relative air humidity has to be 80–95%. Theweight loss experienced in these storage timesis 2–10%. Ascorbic acid and carotene contentsgenerally decrease with storage. Starch andprotein degradation also occurs and there can bea rise in the free acid content of vegetables suchas cauliflower, lettuce and spinach.

Table 17.19. Effect of cold storage temperature onvegetable shelf life

Vegetable Temperature Shelf liferange (◦C) (weeks)

Cauliflower −1/0 4–6Green beans +3/+4 1–2Green peasa −1/0 4–6Kale −2/−1 12Cucumber +1/+2 2–3Head lettuce +0.5/+1 2–4Carrot −0.5/+0.5 8–10Green bell pepper −1/0 4Leek −1/0 8–12Brussels sprouts −3/−2 6–10Red beet −0.5/+0.5 16–26Celery −0.5/+1 26Asparagus +0.5/+1 2–4Spinach −1/0 2–4Tomato +1/+2 2–4Onion −2.5/−2 40a Kept in pods.

.r

vegetables and vegetable products

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