food tests

Question 1

list 5 food tests

Answer 1

reducing sugars test
non reducing sugars test
starch
biuret
emulsion

Question 2

test for simple sugars or reducing sugars

Answer 2

benedict test
mash food mix with water
put each suspension in test tube and add equal amounts of benedicts solution
boil mixture
orange red precipitate forms

Question 3

test for complex non reducing sugars

Answer 3

hydrolysis neutralisation benedicts test
boil food with few drops of diluted hydrochloric acid to break down sugar
add sodium bicarbonate to neutralise mixture
when stops fizzing add benedicts solution
orange red precipitate forms

Question 4

test for starch

Answer 4

add few drops of iodine solution to food
blue black colour indicates starch is present

Question 5

for lipids ( grease spot

Answer 5

rub small piece of food onto filter paper
hold paper up to light to check if food left behind tanslucent mark
dry paper carefully to ensure not water
translucent greasy mark indicates food contains lipids

Question 6

for lipids emulsion

Answer 6

dissolve food in ethanol
pour solution in clean test tube with water
fat is not water soluble but will dissolve in pure alcohol
white cloudy emission

Question 7

proteins

Answer 7

biuret test
mash food and mix with water
add few drops of potassium hydroxide until solution clears
add few drops of dilute copper sulfate and shake
can use sodium hydroxide as replacement
violet or purple colour

Question 8

what are reducing sugars

Answer 8

all mono and disaccharides except sucrose

Question 9

what are non reducing sugars

Answer 9

all polysaccharides and sucrose

Question 10

what should you do when testing for protein

Answer 10

shake test tube after addition of each drop of copper sulphate before adding another drop
stop adding at first sign of pale violet colour

Question 11

what should you do doing the emulsion test

Answer 11

ensure bunsen burner is turned off since lipids and ethanol are flammable and need to be kept away from an open flame for safety