food tests!

starch present

iodine solutions turns from brown to blue-black

starch absent

iodine solution remains brown

biuret test procedure

add 2cm3 of sodium hydroxide to 2cm3 of food sample and shake thoroughly

add 1% copper (II) sulfate solution, dropwise, shaking after every drop

protein present (biuret test)

mixture turns from blue to violet

protein absent (biuret test)

mixture remains blue

alcohol emulsion test procedure

add 2cm3 of ethanol to a test tube with food sample and mix thoroughly

add 2cm3 of water to the mixture and shake 

no fat (alcohol emulsion test)

mixture remained clear

fat is present (alcohol emulsion test)

a white emulsion is formed

benedicts test tests for?

all reducing sugars except sucrose, which is not a reducing sugar

reducing sugar absent (benedicts test)

mixture remains blue

reducing sugar present — 0.5 to 1g%

mixture turns from blue to green with ppt

reducing sugar present — 1g% to 1.5g%

mixture turns from blue to yellow with ppt

reducing sugar present — 1.5g% to 2g%

mixture turns from blue to orange-red with ppt

reducing sugar present — >2g%

mixture turns from blue to brick-red with ppt

benedicts test procedure

1) place 2cm3 of food sample in a test tube

2) add 2cm3 of benedicts solution to the food sample and mix

3) heat in a boiling water bath for 2-3 minutes