salad dressing science - uc...
TRANSCRIPT
STEM%Outreach%at%CU%Denver%Activity'Description''
Salad%Dressing%Science'Contributed'by:'Rebecca'Zabinski'and'Cierra'Walker'
Adapted'from:'sciencefriday.com''Purpose:'to'introduce'emulsifiers'in'the'context'of'homemade'salad'dressing''Background%'
Water'molecules'are'composed'of'two'hydrogen'atoms'and'an'oxygen'atom.'The'structure'in'which'these'atoms'are'bonded'creates'positive'and'negative'charges'at'opposite'ends'of'the'molecule.'As'a'result,'other'molecules'with'similar'electric'charges'mix'well'with'water'and'are'called'hydrophilic.'Molecules'that'have'an'even'distribution'of'electric'charge'do'not'mix'well'with'water'and'are'called'hydrophobic.''Emulsifiers'are'molecules'used'to'prolong'the'mixture'of'hydrophilic'molecules'with'hydrophobic'molecules.'For'example,'emulsifiers'are'used'to'maintain'the'desired'consistencies'in'margarine,'ice'cream,'bread,'chocolate,'and'salad'dressing.'
'Overview%%
This'activity'explores'the'behavior'of'emulsifiers'and'their'effectiveness'in'the'context'of'home'made'salad'dressing.'Specifically,'students'will'compare'the'separation'times'of'oil'and'vinegar'mixtures'using'different'emulsifiers.'
'Materials%''
–'5'50mL'test'tubes'(per'group)'' –'75mL'(5'Tbs)'of'olive'oil'(per'group)'
–'75mL'(5'Tbs)'of'white'vinegar'(per'group)'M'5mL'(1'tsp)'of'each'of'the'following'(per'group):''
tomato'paste'mustard'garlic'powder'salt'
–'Clock'or'stopwatch''Protocol''
1. Write'down'the'question'this'experiment'was'designed'to'answer'and'state'your'hypothesis.'
2. Clean'five'50mL'test'tubes.'3. Label'the'five'test'tubes'control,'tomato'paste,'mustard,'garlic'powder,'and'salt.'
Into'the'nonMcontrol'test'tubes,'add'5ml'(1'tsp)'of'the'ingredient'corresponding'to'the'test'tube’s'label.'
STEM%Outreach%at%CU%Denver%Activity'Description''
4. Into'every'test'tube,'add'15mL'(1'Tbs)'of'olive'oil'and'15mL'(1'Tbs)'of'white'vinegar.'Observe'the'layering'of'the'oil'and'vinegar'in'the'control'test'tube.'
5. Vigorously'shake'each'test'tube'for'about'5'seconds'to'mix'the'ingredients.'As'soon'as'you'stop'shaking,'start'the'stopwatch'and'watch'for'signs'of'separation.'
6. When'most'of'the'oil'has'separated'from'the'vinegar,'record'the'amount'of'time'it'takes'each'test'tube'to'separate.'If'the'oil'and'vinegar'have'not'separated'after'15'minutes,'record'“over'15'minutes.”'
7. Repeat'time'trials'as'desired.''Discussion%Questions''
M'How'do'we'measure'separation?'How'do'we'know'if'an'ingredient'is'an'emulsifier?'
M'Did'the'control'test'work?'Why'does'separation'occur?'M'Based'on'the'data,'which'ingredients'are'likely'emulsifiers?'Why'are'or'
aren’t'they?'Is'this'what'was'expected?'M'Is'there'discrepancy'among'separation'times'for'different'groups?'What'
might'cause'differences'in'separation'times?'M'Which'ingredient'would'you'recommend'for'making'salad'dressing?'
'Modifications%and%Extensions''
The'experiment'can'be'run'with'a'variety'of'potential'emulsifiers.'Students'could'also'be'challenged'to'determine'which'ingredients'in'common'salad'dressing'recipes'are'hydrophilic,'hydrophobic,'or'emulsifiers.'Additionally,'students'can'be'challenged'to'experimentally'find'the'best'emulsifier'from'among'a'list'of'ingredients'in'salad'dressing'recipes.'''The'conversation'surrounding'hydrophilic'and'hydrophobic'molecules'can'be'supplemented'with'the'fatty'acids'in'animal'cell'membranes,'which'create'hydrophilic'and'hydrophobic'regions'that'aid'in'transporting'nutrients'in'to'and'out'of'cells.'
'Some%References%%http://www.sciencefriday.com/blogs/08/15/2014/saladMdressingMscienceMemulsions.html''http://www.foodnetwork.com/recipes/articles/50MsaladMdressingM''recipes.html?oc=linkback''''Attachments''Slides'with'introduction'and'protocol'overview''
Compiled'by'Axel'Brandt'as'part'of'the'CU'Denver'Community'STEM'Clubs'program.'Special'thanks'to'
h"p://www.npr.org/blogs/the
salt/2014/06/25/325189711/kandinsky@on@a@plate@art@inspire
d@salad@just@tastes@be
"erC
Defi
niFo
nsC
• Hydroph
ilicC
• Hydroph
obicC
Defi
niFo
nsC
• Hydroph
ilicC=ChydroC+Cph
iliaC
• Hydroph
obicC=ChydroC+Cpho
biaC
H2OCW
aterCisChydroph
ilicC
h"p://www.scien
cefriday.com
/blogs/08/15/2014/salad@dressing@scien
ce@emulsion
s.htmlC
CH3(CH
2)nC00HCOilCisCaCfa"yCacidC
mostly
Chydroph
obicC
h"p://www.oliveo
ilsou
rce.com/page/chem
ical@characterisFcsC
Emulsifie
rsC
h"p://dkcorporaF
on.trade
india.com/emulsifie
r@for@paints@solvents@vegetable@oil@4
12944.htmlC
How
$do$we$an
swer$scien
-fic$que
s-on
s?$
The$Scien-
fic$M
etho
d$
RossCetCa
l.,C2005C
SaladCDressingCScienceCExpe
rimen
tC
• Que
sFon
C
• Hypothe
sisC
• Co
ntrols:C
– NegaF
veC
– Po
siFveC
SaladCDressingCScienceCExpe
rimen
tC
• ProtocolC
– Add
CvinegarCand
CoilCtoCcon
trolCtu
beC
– Add
Cvinegar,Coil,Cand
Cemulsifie
rCtoCte
stCtu
besC
– ShakeCtoCm
ix,Cthe
nCmeasureCsep
araF
onCFmeC
1@15minC
– Re
cordCdataCandCanalyzeCresultsC
SaladCDressingCScienceCExpe
rimen
tC
• MaterialsC
– OilC
– VinegarC
– 4CTestCtu
besC
– TomatoCpasteC
– MustardC
– GarlicCpow
derC
– 1CtspCC
– ClockCorCstopw
atchC
– Em
ulsifie
rCdataCshe
etC
MakingCsureCourCexperim
entCw
orks:C
UsingCcon
trolsCinCscien
ceC
• How
CdoCweCmeasureCsep
araF
on?C
– TimeCtheCcontrol:Cvine
garCandCoilC
• How
CdoCweCknow
CwhatCa
CposiFveCre
sultCforCanC
emulsifie
rClooksClike?C
– SeparaFo
nCFm
eCisClongerCth
anCcon
trol.C
AnalyzingCResultsC
• Re
cordCyou
rCgrou
pCresultsConCtheCbo
ard.C
• DidCth
eCcontrolCtestCw
ork?CCW
hyCdoe
sCseparaFo
nCoccur?C
• DidCth
eCmixturesCwith
CtheCem
ulsifie
rsCta
keCm
oreCorClessC
FmeCtoCsep
arateCthanCyou
rCcontrol?CIsCth
isCwhatCyou
Cexpe
cted
?CCW
asCitCre
plicated
CbyCothe
rCgrou
psCinCth
eCclass?C
• Ba
sedCon
Cyou
rCob
servaF
onsCofCsep
araF
onCFme,CwhichC
emulsifie
rCwou
ldCyou
Crecommen
dCusingCforCmakingC
saladCdressing?CC
CellCmem
branesCareCm
adeCofCfa"yCacidsC