food tests Flashcards
what does qualalative mean
colour change
what is the test for starch called
iodine test
say the steps for the starch test
- add a few drops of iodine solution to the sample
what are the results for starch test
orange- negative
blue/black- postive
what is the reducing sugar test called
Benedict’s test
explain the steps for the reducing sugar practical
add 2 ml of Benedict’s reagent ( copper sulphate) to 2 ml of the sample and shake
-heat for a few minutes at 95 C in a water bath
what are the results of the reducing sugar test
positive- green/orange/brick red precipitate
negative is blue/ black
this test is semi qualative
what is the test for non reducing sugars called
benedicts test
what does the reducing sugar test apply to
all monosacchrides and most dissachrides except from sucrose because they reduce ions like Cu2+
what is the test for non reducing sugars called
benedicts test
explain the steps for the non reducing sugars test
first test a sample for reducing sugars to see if any present hydrolysis. Using a seperate sample, heat with dilute hydrocholric acid few minutes to hydrolyse the glycosidic bond
- neutralise the solution by gently adding small amounts of alkali
- heat for a few minutes
what are the results for non reducing sugar test
neg- blue
pos- brick red precipitate
what does non redcuing test apply to
sucrose because it doesnt reduce copper sulphate
what is the test for lipids called
emulsion test
explain steps for emulsion test
lipids doesnt dissolve in water but do dissolve in ethanol
dont start by dissolving water in sample.
-vigourously shake soke of the sample with 4 ml of ethanol
- decant the liquid into a 2 test tube, leaving any undissolve substance behind
