tests Flashcards
how to test for reducing sugars
-sample of food into solution
-add benedict’s reagent (contains CU2+ ions)
-if turn red, showing reducing sugars as CU2+ goes into CU+
how to test for non reducing sugars
hydrolase bonds to free up reducing sugars
steps for testing for non reducing sugars
-test sample for reducing sugars
-separate sample + boil with hydrochloric acid to hydrolase the sucrose into glucose and fructose
-cool solution and use sodium hydro carbonate solution to neutralise it
-test for reducing sugars again
steps for testing for protein
-test solution must be alkaline so add a few drops of sodium hydroxide
-add copper (II) sulphate solution(biuret solution)
(the peptide bonds that react with copper sulphate ions in biuret solution)
emulsion test for lipids
-Take a small sample of the substance you want to test
-Add a few drops (or enough to cover the sample) of ethanol (dissolves lipids present)
-Shake the test tube so the lipids (if present) dissolve in the ethanol.
- After shaking, add an equal volume of distilled water
-After adding water, shake the test tube again
-present = milky white or form a cloudy emulsion.
iodine test for startch
-the solution added is iodine dissolved in potassium iodide so u must say iodine solution
-turns blue black
-add to spotting tile with food
how to determine dilution factors
- if its 1:20, use 1ml stock solution and 19ml diluent so that you get 20 parts in total
-transfer one part of previous solution to another 19 part solution and continue
-will be a 20th of the beginning solution
what are biosensers
use detector and light source shone through a solution to determine concentration
example of biosensors in a weak glucose concentration
-light source –> less absorption in solution—> receives more light
example of biosensors in a strong concentration
-light source–> more absorption–> detector receives less light
what’s a colorimeter
-biosensor that measures the strength of a coloured solution by how much light passes through it
what colour does a colorimeter detect in benedict’s
-blue as not directing light through precipitate, rather the solution
what does it mean if there’s a higher concentration of glucose molecules at the start
-less light absorbed at end as more available glucose molecules to react with benedict’s so more orange solution
why would a lot of light pass through if theres less benedicts
benedict’s contains CU2+ ions which are blue, so more blue light passes through when theres less benedicts as light isnt absorbed by blue solution
comparison of biosensers at beginning and end of glucose reaction with a lot of glucose
- beginning detector recieves less light as copper ions havent reacted
-end, receives more light as low conc of CU2+ ions as its all reacted
what does lower glucose molecules mean
-means less reaction with CU2+ ions, lower transmission of light read by detector
whats the curved called that has glucose copnc on x axis and transmission of y
calibration curve
whats it called when when testing for glucose, u need to make up several glucose solutions of different known concentrations, way to do this
serial dilution
describe chemical reaction that causes colour change in startch test
the iodine (I2) forms a triiodide (I3-) which slips into the middle of the amylose helix causing colour change
alternate method to test for reducing sugars
-commercially manufactured test strips, dip into solution and compare colour with calibration card supplied
why is important to check there are no reducing sugars in the solution before carrying out non reduce test
interferance in results, reliability and validity
why is sucrose a non reducing
-no free aldehyde groups or ketone groups
chemical reaction that causes colour change to occur
reaction between nitrogen atoms in peptide chain and CU2+ ions, detects presence of peptide bonds
what is emulsion
a mixture of two immiscible (liquids that dont combine to form same solution) liquids, where one liquid is dispersed in the other in the form of small droplets.
