salad dressing science - uc...

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'

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