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Food Chemstry

F1 Food groups

F.1.1 Distinguish between a food and a nutrient.

F.1.2 Describe the chemical composition of lipids

(fats and oils), carbohydrates and proteins. IBO 2007

Lke a maer, ood s composed o cemcas. hesecemcas are parcuary mporan because eyprovde e ue rom wc we gan our energy and e

maeras requred or essena body uncons, as we as

e budng bocks or e grow and regeneraon o our

bodes. A baanced de s va or good ea, ence e

need o sudy e cemsry o ood.

A ood may be consdered any subsance a we

deberaey ake no our mous and swaow. ha s

any naura or arca maera nended or uman

consumpon. Ideay, a ood mus conan one or more

nurens. Some oods are rc n nurens, wereas

oers ave very e nuren vaue. A nutrent s a

componen o ood a s used by e body o provde

energy, or or e grow and repar o ssue. he major

nurens are pds, carboydraes and proens. Oer

nurens are vamns and mneras, wc are requred

n muc smaer quanes. Waer, wc s essena

or bocemca processes o occur, s aso consdered a

nuren. A ack o ese nurens n e de evenuay

gves rse o malnourshment.

Lpds (as and os) are esers o a gycero (propan-1.2.3-

ro) and ree ay acds (ong can carboxyc acds) assown n Fgure 1701.

C

O

O

O R1

CH2

COR2

OCH

CO R1

CH2

Figure 1701 The chemical structure of lipids

F1 Food groups

F2 Fats and oils

F3 Shelf life

F4 Colour

F5 Genetically modified foods

F6 Texture

F9 Stereo-chemistry in food (HL)

(Note that HL material from F7, F8 and

F10 has been integrated)

Food chemistry is a study of the composition and

properties of food, the chemical changes it undergoes

during handling, processing and storage, and the

principles underlying the improvement of food. The

aim of this option is to give students an understanding

of the chemistry of important molecules in food

and the contribution that chemistry has made

(and continues to make) towards maintaining and

improving the quality and cost of food, adequacy offood supplies and food safety. Students should be able

to recognize some important structures and relevant

functional groups and to distinguish between them.

It is not necessary to memorize complex formulas, as

structures and examples of some food molecules are

given in the Chemistry data booklet. IBO 2007

17

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Here R1, R

2and R

3represen ong ydrocarbon cans,

wc may be e same or may be dferen. he

ydrocarbon cans may aso be sauraed, unsauraed

(conanng a carbon-carbon doube bond) or poy-

unsauraed (conanng a number o carbon-carbon

doube bonds). he naure o e R group deermnes e

pysca and cemca properes o e pd. For exampe,sauraed as end o be sods a room emperaure wereas

unsauraed ones (as n vegeabe os) are quds. Lpds

are a source o energy and are aso va n consrucng

ce membranes.

Carboydraes, as er name woud mpy, ave e

emprca ormua CH2O. Monosacchardes w

e genera ormua (CH2O)

n(n>2) are e smpes

carboydraes. Eac monosaccarde conans one

carbony group (C=O) and a eas wo ydroxy groups

(-OH). Condensaon o wo monosaccardes orms

a dsaccharde. Carboydraes comprse sugars and

poymers suc as sarc and ceuose derved rommonosaccardes. he man uncon o carboydraes s

as a source o energy, oug ey are aso used or ce

consrucon. One o e smpes sugars s gucose, sown

n Fgure 1702.

C

C

C

C

C O

H

H

H

OH

CH2OH

H

HO

H

OH

OH

Figure 1702 The chemical structure of carbohydrates

Proens are poymers o amno acds. A proens conan

C, H, O and N and some aso ave P and S. A ypca

secon o a proen s sown n Fgure 1703.

NHNHNH CHCH COCOCOCH

R3

R2

R1

Figure 1703 The chemical structure of proteins

Here R1, R

2and R

3represen e sde cans o e amno

acds nvoved and ey may be e same or dferen.

F2 Fats and ols

F.2.1 Describe the difference in structure

between saturated and unsaturated (mono-

and poly-unsaturated) fatty acids.

F.2.2 Predict the degree of crystallization

(solidification) and melting point of fats and

oils from their structure, and explain the

relevance of this property in the home and

in industry.

F.2.3 Deduce the stability of fats and oils from

their structure.

F.2.4 Describe the process of hydrogenation of

unsaturated fats.

F.2.5 Discuss the advantages and disadvantages

of hydrogenating fats and oils. IBO 2007

As saed n e prevous secon, as and os (somemes

reerred o coecvey as pds) are esers o gycero

(propan-1.2.3-ro) and ay acds (ong can carboxyc

acds). Reer back o Fgure 1701.

he groups R1, R

2and R

3, wc may be e same or

dferen, represen ydrocarbon cans, ypcay 15-25

carbon aoms ong, oug n mos os and as e oa

number o carbons n e can (ncudng e O-CO-

one) s even because ey are synessed rom wo carbon

uns. hese ydrocarbon cans may be sauraed (a C-

C bonds snge), mono-unsauraed (conanng one C=C)

or poy-unsauraed (conanng more an one C=C). In

any gven o ere s usuay a mxure o can engs

and degrees o sauraon, oug e reave proporons

o ese as an efec on e properes o e pd.

Cemcay os and as are smar, e man dference

beng n er meng pon w as beng sod a room

emperaure and os beng qud. he meng pon o e

pd and ardness (degree o crysany) o e sod wdepend on a number o acors:

he mean eng o e ydrocarbon cans.

he degree o unsauraon.

Weer e ydrocarbon can s cis- or trans-

around e doube bond.

option

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477

he onger e carbon can, en e greaer e moar

mass, e sronger e van der Waas orces and e ger

e meng pon. he presence o doube bonds means

a e ydrocarbon can s ess srag, so weakenng

e van der Waas orces by reducng e cose conac

beween e cans. As a resu e greaer e degree o

unsauraon, e ower e meng pon. he efec odoube bonds on e sragness o e ydrocarbon

can s muc greaer ese are cis- (H-aoms on e

same sde o e carbon can) an ey are trans- (H-

aoms on e oppose sde o e carbon can) as sown

n Fgure 1704.

C

C

C

C

C

HH

C

CC

C

H

C

C

C

H

trans-unsaturatedcis-unsaturated

Figure 1704 Cis and trans forms

As a resu cis-unsauraed os (e sor mos commony

ound nauray) ave ower meng pons an e

equvaen trans-unsauraed os.

Lpds a are sods a room emperaure (suc as coconu

a, buer and ard) end o ave sauraed ydrocarbon

cans and orm more crysane sods wc are

reavey ard. Os, wc are qud a room emperaure

and gve ess crysane, soter sods wen soded, are

unsauraed. Poy-unsauraed os (suc as sunlower o,

corn o and s o) ave ower meng pons and orm

soter sods an mono-unsauraed os (suc as ove o,

canoa o and peanu o).

As mg be expeced rom e underyng cemsry

(unsauraed ydrocarbons are muc more reacve

an sauraed ones) unsauraed os are ess sabe and

ereore keep ess we an sauraed as. he major

probem s reacon o e carbon-carbon doube bond

w oxygen (auto-oxdaton), especay n e presence

o g (photo-oxdaton), wc s wy e surace o

margarne s oten dscooured. Unsauraed pds are asomore prone o ydrogenaon and ydroyss as we as

enzyme-caaysed degradaon by mcrobes.

Unsauraed os are oten ydrogenaed usng ydrogen

a g pressure and a emperaure o abou 200oC n e

presence o caayss suc as ncke, o produce producs

a are more sauraed and n some cases uy sauraed,

as sown n Fgure 1705.

CC

HH

HH

CC

HH

HH

HH+ H H

Figure 1705 Using a catalyst to increase saturation

Ws s as some pracca advanages, suc as:

e produc s a sem-sod or sod, raer an a

qud, wc s more convenen or some cookng

ecnques.

e produc s more sabe because e rae o

oxdaon s decreased.

e exure (ardness and pascy) o e produc

can e conroed.

hs comes a a ea cos because mono- and poy-unsauraed as are eaer or e ear an sauraed

as. Aso para ydrogenaon can ead o e ormaon

o trans-as wc, as ey do no occur nauray, are

dicu o meabose and ence ey accumuae n

e ay ssues o e body. Trans-as aso cause an

ncrease n e eves o LDL coesero, wc can ead o

aerosceross (narrowng o e areres) and a resuan

ncrease n e probaby o srokes and ear probems.

F3 shelF lFe

F.3.1 Explain the meaning of the term shelf life.

F.3.2 Discuss the factors that affect the shelf life

and quality of food. IBO 2007

One probem w a oodsufs s a ey graduay

degrade so a because o canges n lavour, sme, exure

and appearance, or because o e grow o organsms,

ey become undesrabe and/or un or consumpon.

he eng o me a produc can be sored wou

s occurrng s known as s shelf lfe and obvousymaxmsng se e s desrabe.

hs degradaon can resu rom a number o dferen

processes.

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478

C w c

f cc w

Loss o waer rom mos oods can resu n em becomng

dry and cangng n exure. he ncreased exposure o

ar o e sod ood can resu n an ncrease n e raeo oxdaon eadng o a decrease n nuren vaue,

dscoouraon o e surace and rancdy. Conversey

dry oods absorb waer vapour rom e ar ey become

mos and more vunerabe o mcroba degradaon.

Cc c

Cemca canges occurrng wn e ood can resu

n pH canges (e.g. becomng sour) or e deveopmen

o oer undesrabe lavours. Cemca canges can aso

resu n coour canges n e ood and a decrease n s

nurona vaue. he presence o oxygen oten eads ooxdave degradaon o oodsufs.

l

Lg provdes energy or poocemca reacons o occur

eadng o rancdy, e adng o e coour o oodsufs

and e oxdaon o nurens, especay vamns.

t

As w a cemca canges, an ncrease n emperaure

eads o an ncrease n e rae o degradaon o oods.

Noe a waer s an mporan componen o ood.

I deermnes s exure, sotness and ow jucy s

dependng on ow e waer moecues are presen. hese

can eer be cemcay bonded o carboydrae and

proen poar groups amongs oers or be ree bu nked

va ydrogen bondng o proen and poysaccardes. A

cange n e orces o aracon a od carboydrae

or proen cans n pace w nluence ow muc waer

can od. hus a cange n pH or ncreased emperaure

dsrups ese orces, cangng e amoun o waer canod and us afecng exure, sotness and ow jucy

remans.

F.3.3 Describe the rancidity of fats.

F.3.4 Compare the processes of hydrolytic and

oxidative rancidity in lipids.

F.3.5 Describe ways to minimize the rate ofrancidity and prolong the shelf life of food.

F.3.6 Describe the traditional methods used by

different cultures to extend the shelf life of

foods. IBO 2007

One common orm o ood degradaon s rancdty n

pds. Rancdy s e deveopmen o unpeasan smes

n as and os, wc are oten accompaned by canges

n er exure and appearance. here are wo dsnc

ways n wc rancdy can deveop; hydrolytc rancdty

and oxdatve rancdty. In e ormer, e eser bond sbroken down n e presence o pase, ea and mosure

o yed ree ay acds. See Fgure 1706.

RCR COCOC OO HOHH2O+ +

oil/fat water glycerol free fatty acid

Figure 1706 Rancidity in lipids

he ree ay acds w 4-8 carbon aoms suc as buanoc

acd, exanoc acd and ocanoc acd ave an unpeasan

sme gvng a rancd sme and ase o mk and buer

(wc s made rom mk) a ave been sored oo ong.

Longer can acds are ess voae, so e sme s ess

noceabe, bu e presence o e ree ay acds suc as

pamc, searc and oec acds or aurc acd afecs e

exure o gve a ay or soapy ee o e produc, as or

exampe n od sampes o cocoae or cocoa buer. he

rae o ydroyss s sgncany ncreased by e presence

o enzymes, suc as pase, produced by mcro-organsms

and deep ryng, can produce a ydroyc reacon beween

e cookng o and mosure n e ood.

A second way n wc rancdy occurs s oxdave

rancdy (auo-oxdaon) wc nvoves e reacon o

e carbon-carbon doube bond n unsauraed pds woxygen rom e ar. hs resus n compex ree radca

reacons o produce a wde varey o producs, many o

wc ave unpeasan odours or ases. he presence o

g (wc can produce ree radcas eadng o poo-

oxdaon), and o enzymes produced by, or exampe,

mcro-organsms, acceeraes e rae a wc oxdave

rancdy occurs. Obvousy s s muc ess o a probem

w sauraed pds, bu n gy unsauraed pds, suc

as s os, oxdave rancdy can be a major probem.

option

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HL F.7.1 Describe the steps in the free-radical chain

mechanism occurring during oxidative

rancidity. IBO 2007

Auo-oxdaon s a ree radca process can reacon anvoves e reacon o oxygen moecues w e doube

bonds o unsauraed pds. Lke oer ree radca can

reacons ere are ree sages o e reacon:

he na ormaon o ree radcas as a very g

acvaon energy and usuay occurs by exposure o

unsauraed pds o g (poo-oxdaon) wc causes

omoyc sson o a carbon-ydrogen bond:

R-H R + H

Inaon may aso occur as a resu o e decomposon

o ydroperoxdes, a produc o e reacon, caaysed by

races o ranson mea ons.

p

Once ormed e ydrocarbon ree radcas reac rapdy

w oxygen moecues o orm peroxde radcas, wc

en absrac ydrogen rom oer subsrae moecues

reormng e ydrocarbon radcas:

R + O2 R-O-O

R-O-O + H-R R-O-O-H + R

hese propagaon reacons connue un a ermnaon

reacon desroys e ree radcas. As ese nvove radcas

encounerng eac oer ey are reavey rare and so

one naon sep can produce very many ydroperoxde

producs.

ths nvoves e remova o ree radcas rom e

sysem by reacons beween radcas. An nspecon o

e propagaon seps above sows a ere are ree

possbe combnaons:

R + R R-R

R-O-O + R R-O-O-R

R-O-O + R-O-O [R-O-O-O-O-R] R-O-O-R + O2

he ydroperoxdes ormed (R-O-O-H) n e propagaonsep are very reacve moecues and are graduay

convered o adeydes and keones. hese, and e ong

can ay acds a e adeydes are urer oxdsed o,

ave unpeasan smes and ases and s ese a are

responsbe or e spong o e ood.

Increasng e me requred or e onse o rancdy

s a major acor n ncreasng e se e o producs

conanng g proporons o os and as. here are

number o ways n wc rancdy can be conroed:

pckUsng opaque packagng and cooured gass boes w

reduce g nduced oxdave rancdy. Gas mpermeabe

wrappng m w reduce e exposure o e produc o

oxygen and waer vapour n e ar and e ree space n

e conaner soud be kep o a mnmum o reduce e

amouns o ese presen. Even beer s vacuum packagng

or ng e package w an ner gas. A good exampe s

poao crsps wc are usuay packed n ck o packes

ed w nrogen.

s

Rergeraon w reduce e rae o mos reacons a

produce rancdy and sorng a and o rc oods n

e dark w reduce e rae o poo-oxdaon, wc s

ess afeced by emperaure. Dary producs or exampe

are amos aways sored a ow emperaures. Reducng

e waer eve, by drying or smoking, and en sorng

away rom mosure reduces ydroyc rancdy and

dscourages e grow o mcro-organsms.

avhere are many subsances a can be added o oodsufs

o reduce e occurrence o rancdy. Some processng,

or exampe saltng (as n preparng bacon) and avng a

g sugar conen (as n preserves), reduces e amoun

o waer n e oodsuf by osmoss. hs reduces e rae

o ydroyc rancdy as we as makng e envronmen

ess suabe or e grow o mcro-organsms. Oer

subsances, suc as suur doxde and sodum sues used

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w ru producs, aong w sodum and poassum

nres and nraes used n curng meas, are reducng

agens and preven e oxdave reacons a or exampe

ead o e brownng o many subsances wen sored oo

ong.

acb

Many meods o deayng e onse o rancdy depend

on prevenng e grow o mcro-organsms n e

oodsuf. Tradonay n pcklng e use o vnegar

creaes an envronmen a s oo acdc or mcro-

organsms. Many oer organc acds and er sas

(ndcang a s s no purey a pH efec) are added

o dscourage e grow o mouds and bacera n oods.

Specc exampes ncude e addon o benzoc acd

and sodum benzoae o ru juces as we as propanoc

acd, aong w s sodum and cacum sas, o bread and

ceese. Fermentaton aso produces eano wc msbacera grow, so wne keeps muc beer an res

ru juce and dsed sprs, w an even ger acoo

concenraon, as onger s.

Que a ew o e meods menoned above, parcuary

ose n bold, ave been radonay used by cuures

wordwde or many cenures o preserve oodsufs.

F.3.7 Define the term antioxidant.

F.3.8 List examples of common naturally

occurring antioxidants and their sources.

F.3.9 Compare the structural features of the

major synthetic antioxidants in food.

F.3.10 Discuss the advantages and disadvantages

associated with natural and synthetic

antioxidants.

F.3.11 List some antioxidants found in the

traditional foods of different cultures that

may have health benefits. IBO 2007

An antoxdant s a subsance a can be added o ood

o ncrease s se e by deayng e onse o oxdave

degradaon. Many o e anoxdans work by reacng

w oxygen conanng ree radcas, so prevenng ese

speces degradng ood by, or exampe, oxdave rancdy.

here are many nauray occurrng anoxdans presen

n oods, common exampes beng:

Vamn C (ascorbc acd) - ound n crus rus

and mos green vegeabes.

Vamn E (a ocopero) - ound n nus, seeds,

soya beans, woe grans, and some vegeabe os

ke canoa o.

-caroene - ound n vegeabes suc as carros

and brocco as we as rus suc as omaoes and

peaces.

Seenum an mporan race eemen ound n

s, ses, mea, eggs and grans.

Increasngy, synec anoxdans are beng added o

oodsufs o ncrease er se e. Some o e mos

common are BHA (2- and 3-er-buy-4-ydroxyansoe),

BHT (3,5-d-er-buy-4-ydroxyouene), PG (propy

gaae), THBP (2,4,5-rydroxybuyropenone) and

TBHQ (erbuyydroqunone). Amos a ave penocype srucures, a s ey ave a ydroxy group aaced

o a benzene rng, a srucura eaure a s no ound

n nauray occurrng anoxdans. he use o synec

anoxdans s no wou conroversy as ere are many

wo ee a ey can ave armu sde efecs, bu ere

s no cear evdence on e ssue. Sudes ave owever

sown a nauray occurrng anoxdans, suc as

vamn C, vamn E and -caroene reduce e rsk o

cancer and ear dsease by reacng w ree radcas.

here are aso oer ea benes o ese as vamn

C s va or e producon o ormones and coagen,

ws -caroene can ac as a precursor or vamn A.

Even oug synec anoxdans are more efecve

an e naura ones. ey requre srcy enorced codes

or er sae use n oods. hese may be dicu o poce,

especay n deveopng counres and many ee a er

saey as ye o be sasacory proven.

ha beng sad many subsances radonay used n

dferen cuures as promong good ea are rc

n naura anoxdans. Common exampes o suc

oods ncude green ea, urmerc, oregano, bueberres,

cranberres and dark cocoae. Many cams are made or

ese suc as e owerng eves o LDL coesero, bood

sugar eves and g bood pressure as we as prevenngcancerous ce deveopmen. In many cases ese cams

ave no been subjeced o e srngen ess o modern

scence.option

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481

F.8.1 Explain the differences between the three

main types of antioxidants. IBO 2007

he anoxdans added o oods may nerere w e

auo-oxdaon process n a number o ways:

FreeradCalquenChers

hese are speces (represened as H-A n e equaon

beow) a reac w e ree radcas presen and produce

ess reacve ree radcas (A n e mecansm beow):

R-O-O + H-A R-O-O-H + A

here are aso many nauray occurrng anoxdans,

suc as ocopero (vamn E) a can be used as ree

radca quencers and many peope preer ese osynec anoxdans suc as BHA (2- and 3-er-buy-

4-ydroxyansoe), TBHQ (erbuyydroqunone) and

BHT (3,5-d-er-buy-4-ydroxyouene).

Chelatngagents

Free radcas may be ormed by e reacon o ranson

mea ons w e ydroperoxdes nay produced by

e auo-oxdaon reacon, or exampe:

R-O-O-H + Fe2+ R-O + OH + Fe3+

Chelatng reagents orm very sabe compex ons w

ranson meas and ence reduce e occurrence o

ese reacons. Many pans suc as rosemary, ea and

musard, conan naura ceang agens. Sas o EDTA

(eyenedamneeraacec acd) are somemes added as

arca ceang agens.

reduCngagents

Reducng agents (eecron donors) can reac w bo

oxygen n e ood and w e ydroperoxdes nayproduced by auo-oxdaon. Exampes o nauray

occurrng reducng agens ncude ascorbc acd (vamn

C) and caroenods. Arca preservaves a are

reducng agens, suc as suur doxde, sues and

nres, may ac n a smar manner.

F4 Colour

F.4.1 Distinguish between a dye and a pigment.

F.4.2 Explain the occurrence of colour innaturally occurring pigments.

IBO 2007

Many oods ave dsncve coours and we oten use e

appearance o e ood o judge s quay and resness.

he coourng maeras nauray presen n oods are

reerred o as pgments, bu dyes (.e. cooured compounds,

eer synec or rom a dferen naura source) are

oten added o enance e appearance o processed

producs. hese dyes, wc are usuay waer soube,

ave o be orougy esed o prove a ey are sae

or uman consumpon. Bo groups o compounds owe

er coour o e ac a ey absorb ceran requenceso vsbe g, ws relecng oers wc are abe o

smuae e rena n e eye. For exampe green spnac

ooks green because absorbs red g and bue g, bu

does not absorb (and ence relecs) green g.

Note that the structures of the pigments shown overleaf all

involve extensive delocalised-bonds (HL material).

F.4.3 Describe the range of colours and sources

of the naturally occurring pigments

anthocyanins, carotenoids, chlorophyll and

heme.

F.4.4 Describe the factors that affect the colour

stability of anthocyanins, carotenoids,

chlorophyll and heme.

F.10.1 Compare the similarities and differences

in the structures of the natural pigments:

anthocyanins, carotenoids, chlorophyll and

heme. IBO 2007

here are varous groups o compounds a are ound asnaura pgmens n oods. Some o e mos common o

ese are sed beow aong w e way a cookng,

wc, as we as subjecng em o ea, may nvove

canges o pH and an acceeraon o oxdave reacons

wc can mody er coour:

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anthoCyanns

hese are e mos commony ound pgmens. hey

are responsbe or red, pnk, purpe and bue coours

ound n berres as we as e coour o beeroo and red

cabbage. Anthocyanns aso cause e coour o manylowers. Some ypca anocyanns are sown beow;

w be noed a ey a ave very smar 3-rng C6C

3C

6

srucures w conjugaed doube bonds, bu ey vary

n e number and poson o e ydroxy groups and

akoxy sde cans. Anocyanns are oten ound bonded

o sugar sde cans wc aso mody er precse coour.

Reer o Fgure 1707.

OH

O

+

HO

OH

OH

Pelargonidin

OH

O+

HO

OH

OH

Cyanidin

OH

OH

O+

HO

OH

OH

Delphinidin

OH

OH

Figure 1707 The structure of some anthocyanins

he srucure o anocyanns s very dependen on pH,

no ony because o acd base efecs, bu aso because o

e efec o pH on e ease o ydraon reacons. As

a resu e coour o oods cooured by anocyannscan vary sgncany durng e cookng process,

especay wen mxed w acdc or akane ngredens.

Anocyanns orm compex ons w mea ons suc as

Fe3+ and A3+, ence proonged conac w ese meas,

rom wc saucepans are oten made, may aso conrbue

o canges n coour durng e cookng process. A

g emperaures, ke many organc compounds,

anocyanns decompose and s may ead o brownng

n some cookng processes.

here are our cosey reaed srucura orms o

anocyanns wc are oten n equbrum, e exac

poson dependng on acors suc as pH and emperaure,

wc aows ese compounds o be used as acd-base

ndcaors. he mos brgy cooured orms (A and B

beow) owever are sabe a ow emperaure and, or A,

a ow pH. he srucures o ese orms and e equbrankng em are usraed beow, w e canges n

srucure gged:

he absorpon specra o e anocyanns ereore vary

w pH, causng e coour canges dscussed above. A

ow pH e lavyum caon (AH+) predomnaes and e

mxure s red, a neura pH vaues ere s a suicen

concenraon o ydroxde ons or s o ydroyse and

e souon becomes amos coouress as s convered

o e carbno pseudobase (B) and cacone (C). A even

greaer pHs e lavyum caon (AH+) n equbrum

w s s convered o e qunoda base (A) so a e

equbra are sted o yed s produc and e souonurns bue. hs s usraed n e Fgures 1708 and

1709.

R2

R1

O

OROR

OH

OR2

R1

O+

OROR

OH

HO+H+

+H

R2

R1

O

OROR

OH

HOHO

R2

R1

O

OROR

OH

HO OH

+OH

+OH

Quinoidal base (A) Flavylium cation (AH+)

Carbinol pseudobase (B) Chalcone (C)

Figure 1708 Colour changes in anthocyanins

Absorption

Wavelength / nm700600500400300

pH = 7

pH = 13

pH = 1

Figure 1709 Absorption of anthocyanins at various pH

levels

Flavanones, o wc quercen (sown beow) ound as

e coourng maera n red grapes and many berres s

a ypca exampe, are cosey reaed o anocyanns. See

Fgure 1710.

option

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O

OH

OH

O

HO

OH

OH

Figure 1710 Quercetin

Carotenods hese are wdey ound n a vng ngs,

especay n agae. hey are responsbe or yeow, orange

and red coours and, as we as beng responsbe or

e coour o carros, ey cause e coour n bananas,

omaoes and safron. Because er ow eves n grass are

concenraed n mk as ey aso gve buer s coour.

Caroenods aso ave nurona vaue because ey can

be convered no vamn A, as we as beng efecve

anoxdans. he srucures o some ypca caroenodsare usraed beow. he essena eaure o caroenods s

e ong ydrocarbon can, wc may aso ave mey

groups aaced. In some cases ere may be rng srucures

a e ends o e can, n oer cases no. Smary some

careenods ave ydroxy groups near e end o e can

or on e rng, wereas oers, somemes caed carotenes

(see Fgures 1711, 1712), ave a ydrocarbon srucure.

Vamn A, as can be seen rom Fgure 1713, s very cosey

reaed o e caroenes wc ac as precursors or .

HO

OH

Figure 1711 Xanthophyll a typical carotenoid

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

Figure 1712 Beta-carotene

CH3

CH3 CH3CH

3

CH3

OH

Figure 1713 Vitamin A

Caroenods are sabe under mos condons used or

processng oods so e oss o coour occurs, oug

eang can cause some dscoouraon and e trans-

coordnaon around doube bonds o cange o cis-

coordnaon. he presence o e poyunsauraed

ydrocarbon can means a, ke poy unsauraed os

caroenods are subjec o oxdave degradaon. As coud

be expeced, s s acceeraed by g, wc can produce

ydroperoxde ree radcas and wc s caaysed by e

presence o ranson mea ons. hs oxdaon as we ascausng dscooraon aso means a e caroenods can

no onger be convered o vamn A.

Astaxanthn s a red pgmen cosey reaed o caroenods

(compare e srucures). Wen s ound nauray s

usuay bonded o proens, wc mody e requences

o g absorbs so a gves e bue and green coours

ound n ve obsers and crabs. Hg emperaures dsrup

e bondng o e proen, ence e sarng cange n

coour wen ese anmas are cooked. Lke caroenods

acs as an anoxdan, ence e ea benes ascrbed

o eang e ses o srmps and prawns. hs pgmen s

aso responsbe or e pnk coour o samon mea.

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

O

O

HO

OH

Figure 1714 Astaxanthin

Chlorophyll

hs s e green cooured pgmen responsbe or

caaysng e poosynec process n green pans and

ence s wdey ound n green vegeabes. In e srucure

(See Fgure 1415), wc s acuay a o coropy

a, noe e presence o magnesum a e cenre o e

rng. here are acuay wo very cosey reaed orms o

coropy, coropy a and coropy b, wc dfer

ony n weer a sde can s a mey group (a) or an

adeyde group (b).

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N

NN

N NMg

O

O

OO

O O

In chlorophyll b this sidechain is an aldehyde group

Figure 1715 Chlorophyll a and b

Durng cookng pan ces break down and s reeases

acds, decreasng e pH o e souon. Ws sabe n

neura and akane souon, n acdc souon ydrogen

ons dspace e magnesum on rom e rng no

souon, resung n a coour cange o ove-brown.

hese canges aso make e pgmen ess sabe o g

and photodegradaton can occur.

heme

hs s e red pgmen ound n e red bood ces o

ger anmas. Is srucure s sown n Fgure 1716. Noe

e smary o srucure o a o coropy, bu n s

case ron(II), raer an magnesum s ound a e cenre

o e rng. he essena eaures o bo coropy and

eme are e panar rng sysems n wc e mea on s

bonded o our nrogen aoms, wc ac as lgands. hs

s reerred o as a porphyrn rng.

NN

N N

CO2H

CH3

CH3CH3

CH3

CO2H

Fe

Figure 1716 The Heme group

In musces, eme s ound assocaed w myoglobn, a

proen moecue, and s as a purps-red coour. I

bnds easy o oxygen moecues, ence s roe n oxygen

ransporaon, and s resus n a coour cange o

brg red. A muc sower reacon w oxygen, caed

auto-oxdaton, resus n e oxdaon o e ron romron(II) o ron(III), ormng metmyoglobnand e coour

canges o a browns red coour, wc s consdered ess

desrabe. hese canges are summarsed n e dagram

beow:

-O2

[Ox]

O2-Fe2+-Mb Fe2+-Mb Fe3+-Mb

+O2

[Red]

Brg red Purpe-red Brown-red

he coour o e mea can be preserved by sorng n

an oxygen ree envronmen, by vacuum packng , or

packng n an ner gas (suc as CO2), usng poymers

w ow gas permeaby.

F.10.2 Explain why anthocyanins, carotenoids,

chlorophyll and heme form coloured

compounds while many other organic

molecules are colourless.

F.10.3 Deduce whether anthocyanins and

carotenoids are water- or fat-soluble from

their structures. IBO 2007

I s neresng o enqure wy a o ese compounds

absorb g n e vsbe regon o e specrum and

ence appear cooured. he answer o s s a ey

a ave exensve sysems o deocased -bondng. he

greaer e exen o deocasaon, e coser ogeer n

energy e bondng and anbondng -orbas become.

Hence e regon n wc poons can exce an eecron

rom one o e oer sts rom e uravoe regon

option

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(as n benzene) no e vsbe regon. In e srucures

drawn e exensve sysem o deocasaon s ndcaed

by aernae snge and doube bonds (conjugaed doube

bonds). In anocyanns s can be seen o exend over

a ree rngs and cosey reaed moecues n wc s

does no occur (suc as carbnol, see beow, n wc

s dsruped by e sp3

ybrdsed carbon ndcaed). SeeFgure 1717.

R2

R1

O

OH

OH

OH

HO

HO

sp3 hybridised

carbon breaks the

delocalised -system

Figure 1717 Carbinol

In caroenods, even oug e rngs emseves are no

uy deocased, e deocased sysem spreads rom e

secons o e rngs coses o e can and aong e

enre ydrocarbon can. In coropy and eme e

deocased sysem s essenay e rng a surrounds

e cenra mea on, oug does exend sgy no

some o e sde cans. he coour o e ood depends

on e releced raer an e absorbed g, ence

coropy, wc absorbs red and bue g, appears

green because g o s waveeng s releced raer

an absorbed.

I can be seen a anocyanns ave many ydroxy

groups aaced o er rng srucure. hese can ydrogen

bond o waer moecues and as a resu anocyanns end

o be waer soube. In conras caroenods ave a ong

ydropobc ydrocarbon can and e ydroxy groups

on e rngs are no suicen o coner waer souby, so

caroenods are soube n os and as.

F.4.5 Discuss the safety issues associated with

the use of synthetic colourants in food. IBO 2007

Many synec dyes are que bocemcay acve and

ence pose ea reas. I s obvousy mporan a

suc maeras are no used o coour oodsufs, ence

n mos counres e dyes a can be used n oods are

reguaed and ere are auores responsbe or esng

and censng ood addves. Unorunaey ere are no

nernaona sandards on s and coourng maeras

permed n one counry may be banned n anoer, posng

dicues or nernaona rade. Synec dyes, suc as

maace green and sudan red, are somemes ound n

mpored oodsufs even oug ey are no permed

n many counres. Anoer probem s a ws sor

erm, acue oxcy s easy o es or, cronc efecs are

ess easy o prove, especay w subsances a may be

suspeced o avng ong erm carcnogenc efecs.

F.4.6 Compare the two processes of non-

enzymatic browning (Maillard reaction) and

caramelization that cause the browning of

food. IBO 2007

Cookng oods oten causes em o urn brown and s

coour cange s oten used as an ndcaon o weer

ey ave been suiceny cooked. here are wo dsnc

processes a ead o s coour cange. he rs process

s known as e Mallard reactons (ater e Frenccems Lous-Came Maard). hese are responsbe

or e sme and coour cange o many common cookng

processes, suc as grng mea, oasng bread, mang

barey and makng udge (Maard reacons are aso used

n some se-annng reamens.). In ese condensaon

reacons e adeyde group n reducng sugars (suc as

gucose and acose) reacs w e ree amno group o an

amno acd, or amno groups on e sde cans o pepdes

and proens. Because ere s suc a varey o possbe

reacans, many Maard reacons are known and over

a ousand dferen producs ave been dened. he

poymerc ones are oten brown and ence responsbe or

e coour cange, ws e ower moar mass producs

are oug o be responsbe or many o e aromas o

cookng and resung canges n lavour. he equaon or

e rs sage o ese reacons can be wren as:

HO-CH2-[CH(OH)]

4-CH=O + H

2N-CHQ-COOH

HO-CH2-[CH(OH)]

4-CH=N-CHQ-COOH + H

2O

Reducng sugar + Amno acd

Ina condensaon produc

he na producs en poymerse o orm brown

pgmens (known as meanodns). Maard reaconsusuay ony occur a emperaures over abou 140oC,

oug er rae vares sgncany, especay w e

naure o e amno acd nvoved. Cysene s one o

e eas reacve, wereas ysne s muc more reacve,

so oods a conan a o o s (suc as mk) brown

ready (as or exampe n e ormaon o udge).

he second process s reerred o as caramelsaton. hs

occurs wen oods w a g carboydrae concenraon,

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especay sugars, are eaed and sar o deydrae. Inay

s process eads o poymersaon and produces a wde

varey o producs responsbe or e appearance o e

brown coouraon. I connued s evenuay eads o

e producon o carbon and e burnng o e ood:

Cn(H2O)n n C + n H2O

he rae o caramesaon vares w e sugar nvoved,

w rucose, ound n rus, beng e mos easy

caramesed. Exremes o pH, bo g and ow, aso

promoe caramesaon. Because e Maard reacon

requres proens or amno acds, e brownng o oods

a do no conan ese, suc as makng ofee rom

sugar, or e crsp sugar oppng ocrme brule, resus

rom caramesaon. In pracce owever e brownng o

ood on cookng usuay nvoves bo processes.

F5 genetCallymodFedFoods

F.5.1 Define a genetically modified (GM) food.

F.5.2 Discuss the benefits and concerns of using

GM foods. IBO 2007

Modern boogca ecnques mean a s possbe o

arcay mody e DNA sequence o mcro-organsms,

pans and anmas. Usng organsms moded n s

way, s possbe o produce oods a are dferen rom

ose a occur nauray. Foods produced rom ese

organsms are coecvey known as genecay moded

(or GM) oods. here are a number o possbe advanages

o GM oods, some o wc are sed beow.

p c

he yeds rom many pans and anmas are reduced bypess and dseases. Genetc modicaton can ncrease

er ressance o ese, reducng e need o rea w

erbcdes, pescdes, vaccnes ec., a o wc add o

producon coss and may eave poenay oxc resdues

n e ood. Exampes are e producon o poaoes

a are ressan o unga dseases and bananas a are

ressan o aack by nemaodes.

v

Many crops are geograpcay med because o e

condons requred or er grow. Genec modcaon

can enabe e producon o varees a can grow n

a wder range o cmac condons as we as produce

greaer yeds and maure n a sorer me. Exampesare e deveopmen o ger yedng rce varees and

maze a can grow n areas o ower rana.

pc f c

v c

Genec modcaon can be used o enabe pans and

anmas o produce producs a ey woud no normay

produce, suc as boogcay acve moecues a can be

used as medcnes. Exampes are GM ens a ay eggs

conanng uman nereron and cows a produce mkrc n nuronay desrabe omega-3 ay acds.

here are owever many peope and organsaons a

are very concerned abou e proeraon o genecay

moded organsms and ood produced rom em. he

man reasons or s concern are:

a gm f f?

Some peope wo ave no probems w naura oods w

deveop aergc reacons o GM varees. he composon

o GM oods may be dferen rom e equvaen naura

oods and ence suby aer e baance o our des.

W c f gm f

c?

Even oug genecay moded pans are curreny

med o ceran arms, ere s e rsk a poen rom

em w escape no e wd popuaon w unoreseen

consequences.

d w b

c ic?

Genec modcaon s a reavey recen ecnque. Do

scenss undersand enoug abou e process, or coud

we be amperng w ngs a coud ave a caasropc

efec we curreny canno predc?

option

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F6 texture

F.6.1 Describe a dispersed system in food.

F.6.2 Distinguish between the following types ofdispersed systems: suspensions, emulsions

and foams in food.

F.6.3 Describe the action of emulsifiers. IBO 2007

he exure o ood depends on s pysca properes, suc

as s ardness and s eascy. hese are amos aways

afeced by cookng, suc as mea and vegeabes becomng

soter as er ce srucure breaks on eang or bscus

becomng crsp as waer s os. Conrass n exure, suc

as a crsp crus on sot bread, are very aracve o e

paae. A creamy exure s someng a s oten sougn oods and oten s comes rom a dsperse system,

.e. a sabsed, macroscopcay omogenous mxure o

wo mmscbe pases. here are many ypes o dsperse

sysems and er namng depends on e pysca saes o

e componens, ose mos mporan n ood cemsry

a conan a qud as one componen:

lqudsold

In ac ere are wo ypes o dsperse qud-sod sysems

a do no separae; a suspenson or sol comprses sod

parces suspended n a qud, wereas as a gel as qudparces suspended n a sod medum. An exampe o a

so woud be bood n wc e sod red and we ces

reman suspended n e pasma, or e ne precpae o

suur a orms wen very due acd s added o aqueous

sodum osuae. A ru jey, n wc waer s rapped

n a proen marx woud be an exampe o a ge.

lqudlqud

A sabe bend o wo mmscbe quds s known as

an emulson. Mayonnase, wc s a suspenson o o

dropes n an aqueous sysem woud be a good exampe.

lqudgas

Agan ere are wo ypes o sabe dsperse qud-gas

sysems. Foams are comprsed o gas bubbes rapped n

a qud medum. Wpped cream or egg wes, woud

provde a good exampe. Aerosols, wc comprse qud

dropes suspended n a gas, may we be responsbe or

many o e smes o ood and cookng.

A queson a arses w dsperse sysems s wy eydo no separae. In ac oten ey do, bu ony very

sowy. Gravy, couped w e dferng denses o

e componens w oten cause a dsperse sysem o

sowy see ou. Some dsperse sysems, reerred o as

collods, do no owever separae. Oten s s because

e suspended parces are eecrcay carged and ence

repe eac oer. In ood preparaon subsances, known as

emulsiers, are requeny used o promoe mxng o e

wo pases, and sabsers are oten added o sow down

TOK What conflict of concepts and values

are raised by GM foods?

I you ave suded Opon D you may remember e

TOK Box on scenc responsby and you suded

Opon E I sad a e abou reasonabe doub and e

mparay o scenc opnon. hese wo concepssor o come ogeer n e dea o accepabe rsk

wc s wa probaby governs e GM ood debae.

I don nk any scens manans a s oay

rsk ree, nor does any envronmenas deny a

ere are uge poena advanages. he debae woud

seem o be over weer one juses e oer. Facs,

even wen agreed on by bo sdes o e debae (n

se a rary), can somemes be manpuaed by

sascs o back bo causes, bu s rare o see a

debae on s ssue a cenres around e dferng

nerpreaons o agreed acs, or even e reasons

wy one sde nds unaccepabe a parcuar body o

evdence quoed by e oer sde.

Our scenc name s Homo sapiens, bu maybe

Homo emotionalis mg be more approprae? Do we

use ogc or e mporan decsons n e wc

unversy o go o, wo o ge marred o, wa knd

o pzza o order? he answer s a resoundng No.

We mg use ogc o narrow ngs down a e b

(e.g. w e weaer, ood and rends) bu wen

comes down o our na ca s a gu reacon, an

emoona one. Knowng a, bo sdes ave red o

move e dscusson o an emoona eve, oug s

as been aceved w specacuary more success by

e envronmenas obby. Do a search with Google

to see what I mean.

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er separaon. Emusers are moecues a can bond

o bo pases so ey are ound a e surace beween e

pases and ence are known as surfactants. hs s very

smar o e acon o soap as sown n Fgure 1718.

This part of the molecule bonds tothe phase surrounding the globule

This part of the molecule bonds tothe phase inside the globule

Figure 1718 The action of soap

In ood preparaon one o e mos commony used

emusers s ecn, a pospopd wc occurs

nauray n egg yoks. As can be seen rom s srucure

beow, ecn as many carge cenres and oxygen aoms

a one end o e moecue wc bond srongy o waer(ydropc). I aso as wo ydrocarbon cans wc

w end o break e ydrogen bonds n waer, bu be

unabe o orm any bonds o er own o repace ese.

As a resu ese pars o e moecue w avod waer

(ydropobc) and bond o e non-aqueous pase. See

Fgure 1719.

PO

O

O

O

O

N+O

O

O

Hydrophilic

Hydrophobic

Figure 1719 Lecithin is an emulsifier

In mayonnase, made by beang o and vnegar w egg

yoks, e ydropc end o ecn w bond o e

vnegar and e ydropobc ydrocarbon as w bond

o e o. Eac o drope w ereore be surrounded

by a ayer o ecn moecues. Noe a s mporan

o pyscay bea e mxure so a sma dropes o

e suspended pase are ormed, maxmsng e surace

area on wc e suracan can be adsorbed. Sabsersare oten aso added o sabse dsperse saes. Inorganc

pospaes, suc as rsodum pospae, are efecve a

sabsng emusons. Ces oten preer mea bows or

beang egg wes and recen researc as sown a

mnue races o e mea are n ac ncorporaed no

e oam and sabse .

F9 stereo-Chemstry nFood

F.9.1 Explain the three different conventions

used for naming the different enantiomeric

forms. IBO 2007

You may reca a a moecue conans a cra carbon

aom (one a s bonded o our dferen groups) en

wo dsnc spaa arrangemens o e moecue, caed

enanomers, are possbe. hese enanomers are mrror

mages o eac oer and ave denca pysca and

cemca properes, excep a one o em w roae

e pane o poarsaon o pane poarsed g n acockwse drecon, ws e oer w roae e pane

o poarsaon o pane poarsed g n an ancockwse

drecon. he cockwse roang enanomer s sad

o be dextrorotatory, {+ or (d)}, and as a posve

specc roaon vaue, ws e oer enanomer s

sad o be laevorotatory, {- or (l)}, and as a negave

specc roaon vaue. Weer s dexroroaory or

aevoroaory does no owever gve any ndcaon as o

e spaa arrangemen o e componens, er absoue

conguraon. Unorunaey ere are wo separae

sysems used o ndcae s.

he rs sysem, known as e D,L sysem ( s mos

unorunae a upper case D and L are used or s and

ower case dand lor e oay unreaed dexroroaory

and aevoroaory) s an oder convenon and used or

sugars and amno acds. In s e absoue conguraon

o e moecue s reaed o a o gyceradeyde, e

absoue conguraon o wc was dened orgnay by

guesswork. Forunaey a correc guess now conrmed by

X-ray crysaograpy. See Fgure 1720.

O=C-HH-C=O

Mirror images

*C

HOOH

CH2OHHHOCH2 H

*C

D - glyceraldehyde L - glyceraldehyde

Figure 1720 D and L forms of glyceraldehyde

he absoue conguraon o oer sugars abou eac cra

cenre s en named by anaogy, a s, e moecue s

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vewed aong e can w e C=O poned away, e D-

somer as e OH group on e rg. he sysem s aso

apped o amno-acds, were a useu rue o umb s e

CORN rule. he moecue s vewed w e C-H bond

ponng away rom e observer (orunaey e same as

n e R,S sysem beow). I e groups COOH, R, NH2

(were R- s e sde can) are arranged cockwse arounde carbon aom en s e D-orm. I ancockwse,

s e L-orm.

Consder appyng s o e aanne (2-amnopropanoc

acd) enanomer usraed n Fgure 1721.

C

COOH

H

C

HOOC

NH2

NH2

R (=CH3)

Looking along the C-H bond

with the H pointing away

R (=CH3)

Anti-clockwise

Figure 1721 The CORN rule

I can ereore be seen, appyng e CORN rue, a s

s L-aanne (COOH -> R -> NH2

ancockwse). In ac

amos a nauray occurrng amno acds are e L-orm.

hese are usuay aseess, wereas e synec D-amno

acds ase swee. Conversey mos nauray occurrng sugars

are e D-orm, wc ase swee. Oten e enanomer

a does no occur nauray canno be meabosed by our

bodes.

he second sysem, e R,S system (or CIP system, ater

Can, Ingod and Preog, wo rs proposed ) s used or

mos oer groups o compounds. In s sysem ere are

ree seps:

1. he aoms bonded o e cra carbon are

ranked n order o ncreasng aomc number

(H

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490

O

H

O

H

(R) (S)

Figure 1724 R and S forms of the molecule carvone

he R-orm (wc s aevoroaory, as a sme and lavour

o spearmn, ws e S-orm as a sme and lavour

o caraway seeds. Smary e cosey reaed moecue

monene as a +(d)-enanomer wc smes o oranges

and a -(l)-enanomer a smes o emons.

Somemes a naura lavour s a pure enanomer, because

bosyness ends o be sereospecc, wereas e

synec equvaen s oten a racemc mxure (a mxure

o equa amouns o e enanomers) because s s

muc easer o synesse. An exampe o s s apa-onone, one o e lavours presen n raspberres were

e naura maera s e pure R- apa-onone. he

oxcy o moecues can aso vary remendousy beween

e dferen enanomers, as became ragcay apparen

n e adomde dsaser.

questons For opton F

Noe a quesons nended or HL sudens ony are

marked w an asersk [*].

F1 Food Groups

1. Dsngus beween a ood and a nuren. Is

possbe o ave a ood a s no a nuren?

Wa abou a nuren a s no a ood?

2. Descrbe e common cemca srucure o os

and as? Gven s common srucure, n wa

way do os and as dfer and ow may s be

expaned.

3. Proens are comprsed o many 2-amno acd

uns. Draw e srucura ormua o a ypca2-amno acd and sow ow amno acds jon

ogeer o orm proens. Wa name s gven o

e bond nkng e amno acd uns?

4. Gucose as e cemca ormua C6H

12O

6.

To wa group o cemca compounds does

beong? Name a ood componen a comprses

many gucose uns joned ogeer. Gve an

exampe o a ood a s rc n s componen.

5. For e oowng oods, deny rsy e major

ood group a ey beong o and aso gve e

major use a s made o s by e body.

Ove o Four Honey

Eggs Rce Cocoae

6. he major ood groups are carboydraes,

pds and proens. Expan wy s a oer

subsances, suc as mneras, vamns and waer

can be consdered as nurens.

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F2 Fats and oils

7. Ove o s many mono-unsauraed, wereas

sunlower o s many poy-unsauraed. Expan

wa s mean by ese erms. How woud youexpec e meng pons o ese wo os o

compare? Expan wy s s so.

8. Mos nauray occurrng unsauraed os are e

cis-somer, bu ydrogenaon o poy-unsauraed

os can gve e trans-somer o unsauraed os.

Expan ow cis- and trans- somers dfer and

sae wa dferences you woud expec beween

ese somers rsy w regard o meng pon

and secondy w regard o nurona vaue.

9. You are pannng o make a srawberry candy

w a exure smar o cocoae by bendngogeer a pd base, sucrose, ood coourng and

arca srawberry essence. Wa knd o pd

woud you coose or s? Jusy your coce.

10. Gong rom ard, roug ove o o canoa o o

corn o e degree o unsauraon ncreases. How

woud you expec e cemca saby o ese

pds o vary? Expan s.

11. Vegeabe os are requeny ydrogenaed.

Gve e reagens and condons used or ese

reacons. Gve wo advanages or e ood

ndusry o dong s and wo ea concerns

a e genera pubc mg ave abou e

producs.

F3 Shelf life

12. Gve ree specc exampes o canges you mg

noce n specc oods a woud ndcae a

ey ad been n sorage beyond er se e.

13. Many cuures ave radona ways o preservng

oods. Some a are common across a number

o cuures are ermenaon, pckng, sang and

dryng. For eac o ese gve an exampe o a

ood a s preserved n s way and expan e

reason wy s meod o preservaon works.

14. Wa s mean by e erm rancdy? Sae wc

ood group becomes rancd and gve wo canges

you coud make o e way n wc e ood s

sored wc woud decrease s efec.

15. Addng anoxdans can ncrease e se e o

oods. Wa s mean by e erm anoxdan and

wa ype o ood degradaon does comba?

Name one synec and one nauray occurrng

anoxdan used n oods.

16. Rancdy can occur by wo dsnc processes. Descrbe

a way n wc subsances become rancd a

) afecs a ypes o pds.

) afecs unsauraed pds muc more an

sauraed ones.

In e case o e aer wa oer condons are

key o acceerae e reacon?

17. I you were wanng o ncrease your consumpon

o anoxdans, name wo oods a you woud be

advsed o ea more o and or eac ood name e

acve anoxdan presen n .

18. In ood sorage oten:

) e mosure eve s kep very ow.

) e packagng excudes ar.

) e wrappng s opaque.

v) e produc s sored a a ow emperaure.

Expan ow eac o ese w ep o ncrease e

se e o e produc.

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31*. Anocyanns, caroenods and coropy a

ave very dferen srucures. Wy s a a

are cooured?

32*. Wen beeroo s boed e waer becomes

a brg purpe coour, bu wen carros are

boed e coouraon o e waer s noced,bu carros are red, e o becomes orange

cooured. Use your knowedge o e compounds

responsbe or e coour o ese vegeabes o

expan ese observaons.

33*. I a moecue o -caroene was subjec o caayc

ydrogenaon, woud you expec e produc o

be cooured? Expan.

F5 Genetically modified foods

34. Brely descrbe e process by wc a pan or

anma can be moded o produce a genecay

moded (GM) ood.

35. Gve ree separae ways n wc genec

modcaon mg mprove e yed rom a ood

crop.

36. As we as mprovng e vaby o pans and

anmas, genec modcaon can aso resu n

nove subsances beng produced by organsms.

Gve a specc exampe o suc a modcaon.

37. Many peope are opposed o e nroducon o

genecay moded pans and anmas. Expan

wa er major concerns are.

F6 Texture

38. Wa pysca properes o a ood conrbue o

s exure? Dsperse sysems oten dspay gy

desrabe exures. Wa s mean by a dspersesysem?

39. hree common dsperse sysems are suspensons,

emusons and oams. Dsngus beween ese

n erms o e saes o e componens.

40. he producon o sabsed dsperse sysems

oten depends on addves suc as emusers and

sabsers. Expan e roe o ese wo groups o

subsances and name a synec exampe o eac.

41. Wa caracerscs do a emusers ave?

Expan ow ese caracerscs aow an

emuser o produce a sabe dsperse sysem

rom wo mmscbe componens.

42. As we as requrng an emusyng agen, e

producon o an emuson aways nvoves

vgorous beang o e componens. Expan wy

s mecanca agaon s necessary.

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F7 Stereochemistry in food

43*. Wa s mean by an absoue conguraon?

Pace e oowng subsuens n ncreasng

order or e R-S sysem o ndcang absoueconguraons:

-CO-CH3

-CH2-CH

3-F -C=CH

2

-OH -CO-OH

44*. Is e compound sown e D or L enanomer o

e amno acd eucne?

C

COOH

H

C4H

9

H2N

45*. Draw e R-somer o 2-coropropanoc acd.

46*. Is e compound usraed beow e R-somer or

e S-somer o 2-meybu-3-ena?

C

CO-H

H

CH=CH2

CH3

47*. Draw e D-somer o e 4-carbon sugar

eryruose (HO-CH2-CO-CH(OH)-CH

2OH).

48*. he specc roaon o nauray occurrng

sucrose s +66.5. Is dexroroaory or

aevoroaory? Wa woud be e specc

roaon o s enanomer?

49*. Expan ow may be possbe o e weer aood coourng conanng a cra cenre comes

rom a naura or a synec source.

50*. Gve a specc exampe o a compound or wc

e wo enanomers ave dferen smes or

ases.

option

Food F

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