lecture 2 water in foods

8/9/2019 Lecture 2 Water in Foods

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WATER


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WATER'S IMPORTANCE

SolventMost molecules dissolved in water

ReactantWater's involvement in hydrolysis reactions

ProductWater's involvement in condensation reactions

Heat transfer mediumE.g. oiling! steaming! cooling


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WATER'S IMPORTANCE

#e$ture%uiciness! mouthfeel

Snac& foodsegeta les

MeatPreservationHighly (erisha le foods usually have high water activity

E.g. read vs. crac&er or cereal

EconomicsMore water added ) more *

+,-ERS# ,-/,0 #HE PH S/ 3 ,- HEM/ 3PR4PER#/ES 45 W #ER /S /MP4R# ,# /, #HES#+- 45 544- ,- PR4 ESS/,0


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PHYSICAL & CHEMICALPROPERTIES OF WATER

Water has very uni7ue (ro(erties not shared y othersimilar hydrogen com(ounds or com(ounds of similarweight

Why8 9 this is e$(lained y the uni7ue structure of H 24

Compound Melting point Boiling pointH24 :; 1::;

H2S


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STR CT RE OF WATER

#etrahedral arrangement#wo free electrons of 4act as H< ond acce(torswhile H acts as donor

Highly electronegative 4(ulls electrons from H!ma&ing H ehave li&e aare (roton5orms a di(ole ecauseof the electronegative 4


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STR CT RE OF WATER

Because of the -/P43Eand #E#R HE-R 3structure we can getstrong H!"ondingWater ca(a le of ondingto 6 other water molecules+ni7ue (ro(erties of waterfrom other hydridesH< ond ,4# a static(henomenon

# de(endent


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PHASE CHAN#ES OF WATER


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WATER $APOR

Water is CfreeD and devoid of any H< onds3arge in(ut of energy needed

an endothermic (rocess

3arge dissi(ation of same energy needed to ma&ewater lose &inetic energyan e$othermic (rocess

Waters latent heat of va(ori ation is unusually

highto change 1 3 from li7uid to va(or need A"@.6 &cal


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LI% I WATER

E$tensively H< ondedH< ond formation de(endent on #

With increasing # get more mo ility and increased fluidity

T (C) en*it+ ,g-m . ) $i*/o*it+ m 0 -*)

: @@@.@ 1.?=@A

A 1:::.: 1.A"A

2A @@?.1 :.==61:: @A=.6 :.2@6


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ICE

5orms when e$actly 6 H< ondsare formed etween watermolecules

#o get this order a lot of energyneeds to e adsor ed y theenvironment

#he strong H< onding in iceforms an orderly he$agonal

crystal lattice> H24 molecules

Has 6F more thermalconductivity than water at same

tem(erature


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C1n go 23om ICE to #AS

BASIS FOR

FREEZE DRYING4 SUBLIMATION


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PROPERTIES OF ICE

rystalli ationrystal growth occurs at free ing (ointRate of crystal growth decreases with decreasing tem(erature

,ucleation < affects ice crystal si e.

Slow free ing results in few nucleation sites and large! coarsecrystalsSolutes slow ice crystal growth

5ast free ing results in many nucleation sites and small! finecrystalsHeterogeneous nucleation

usually caused y a foreign (article! such as salt! (rotein! fat! etc.Homogeneous nucleation

very rare! mainly occurs in (ure systems


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PROPERTIES OF ICE

S+PER 443/,0Water can e cooled to tem(eratures elow itsfree ing (oint without crystalli ation

When an ice crystal is added to su(ercooled water!tem(erature increases and ice formation occurs


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PROPERTIES OF ICE

5ree ing induced changesin foods Ge$am(les-esta ili ation of emulsions5locculation of (roteins/ncreased li(id o$idationMeat tougheningellular damage3oss of water holding ca(acity

E$am(leI Effect of free ing on seafoods


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WATER SOL TE INTERACTIONS

A**o/i1tion o2 51te3 to 6+d3op6ili/ *u"*t1n/e*Bound water < occurs in vicinity of solutes

Water with highly reduced mo ilityWater that usually won't free e even at


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WATER SOL TE INTERACTIONS

Ioni/ pol13 *olute*React readily with water and mostare usually solu le in water Water H -R #ES the ionsharge interactions due to waters

high -/E3E #R/ 4,S# ,#an easily neutrali e charges dueto its high di(ole moment

3arge ions can rea& waterstructure

Have wea& electric fields

Small ions can induce morestructure in water

Have strong electric fields


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WATER SOL TE INTERACTIONSNonpol13

+nfavora le interaction with water Water around non


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EFFECT OF SOL TES ON WATERBoiling point

a(or (ressure is e7ual to atmos(heric(ressureStrongly influenced y water < soluteinteraction

Solutes decrease va(or (ressure andthus increase oiling (ointSucrose :.A2; Nmol,a l 1.:6; Nmol

ATMOSPHERIC PRESSURE

VAPOR PRESSURE


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So does it ta&e longer orshorter to oil an egg inBaguio8 Why8

90C 100C

1 atm Gsea level

mountains

EFFECT OF SOL TES ON WATER


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Raoult'sLaw3et's go ac& to our egg!what would ha((en if you

added salt8

Re/ommended t61t +ou 1dd *1lt to 51te3 1t 6ig6 1ltitude*


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F3ee7ing point lo5e3ing 5ree ing (oint can get e$tensivede(ression via solutes

lter a ility of water to form crystalsdue to H< ond disru(tion

Sucrose ; Nmol,a l


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W61t e8pl1in* 1ll t6i*9Raoult's law

P : P ; -< =o3

P ;!P-P ;: 8->>?>M

P ) va(or (ressure of solutionO P ) va(or (ressure (uresolventO F1 ) mole fraction of soluteO $ ) grams solutes in

solutionO AA.AM ) moles of water (er liter

#his relationshi( is not only im(ortant for e$(laining theconce(ts of de(ressing free ing (oint and elevating oiling(oint

lso e$(lains the conce(t of 51te3 1/ti@it+


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O*moti/ p3e**u3e o2 *olution*#here is a tendency for a system containing water and asolution se(arated with a mem rane to e at e7uili rium#he (ressure needed to ring the two solutions at e7uili riumis called 4SM4#/ PRESS+RE#he more the solution has of dissolved solutes Ge.g. salt thehigher its osmotic (ressurean use this in food (rocessing and (re(aration

E.g. ris(ing salad items/ncrease turgor


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Su321/e ten*ionWater surface ehavesdifferently than ul& (hase

3i&e an elastic film-ue to une7ual inward forceResist formation of a newsurface thus forming surfacetension


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Water has high surface tension?2.?A dynesNcm G2:;

Because of the high surface tension s(ecial

considerations are needed in food (rocessing#o affect it one canI/ncrease # Gmore energy reduces surface tension

dd solutes,a l and sugars increase surface tension

m(hi(athic molecules reduce surface tension


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Ioni71tion o2 51te3 Water can ioni e into hydronium GH "4 and hydro$yl G4H < ions#ransfer of one (roton to the unshared s( " or ital of anotherwater molecule

Pu3e 51te3 Qe7 ) E7uili rium Gor ioni ation constant

Qe7 ) H "4 4H .Aontrolled y three com(onents

Phos(hate! citrate! car onate

Eggs5resh eggs < (H ) ?.>

fter storage for several wee&s < (H ) @


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EFFECT OF SOL TES ON WATERE$am(les of Cman madeD (H control

5ood additives < /-+3 ,#Sitric acid < (ectin Jellies

(H must e around 2.@


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E$am(les of Cman madeD (H control cidulants < leavening agents

+sed in the a&ing industry to give rise Grelease of 4 2 A


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WATER ACTI$ITY

So! &nowing the a w of afood com(onent one canselect the (ro(eringredients for a(articular food (roduct5or e$am(le! it is(ossi le to create a multi

WATER ACTI$ITYSor(tion isotherms also e$(lain the levelof water inding in a food Gi.e. ty(es ofwater

#y(e /I #ightly C oundD water Gmonolayer+navaila leN+nfree a le Gat


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WATER ACTI$ITY

/m(ortance of a w in foods5ood sta ility directlyrelated to a w/nfluences storage!

micro ial growth! chemicalV en ymatic deteriorations!etc.

$it C lo**


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WATER ACTI$ITYitamin and (igment sta ility

scor ic acid very unsta le at high a wSta ility est in dehydrated foods < ty(e // water Pro lem with intermediate to high moisture foodsMust consider (ac&aging for these foods

En yme sta ilityHydration of en yme-iffusion of su strate Gsolu ility,ot significant in dehydrated foods3ittle en yme activity elow ty(e // water E$ce(tionsI in some cases we get activity at a w

5ro en foods3i(ases Gwor& in a li(id environment

lecture 2 water in foods

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