Lab Activity 3 Carbohydrates Reactions

Lab Activity 4 PolysaccharidesAlaa S BarakaIslamic university of GazaMarch 2013ContentInversion of sucroseIodine Test for PolysaccharidesHydrolysis of StarchMucic Acid Test For GalactoseUNKNOWN

sucrose

Non-reducing sugar: CHO- of D-glucosyl unit and C=O ofD-fructosyl unit are in glysosidic bond, no reducing end.

Inversion of sucrose

As a result, sucrose is easily hydrolyzed in very dilute acid or enzymes:SucroseGlu(+52.2) + Fru (-92)H+invertase (yeast, bacteria)or intestinal sucraseinvert sugar (equimolar mixture of D-glucose and D-fructose)[]D= +66.5[]D= -39.8Reagent:1% sucrose solutionConc. H2SO4Bendict reagentBarium hydroxide Ba(OH)2phenolphthalein,

ProcedureAdd 25ml of sucrose solution in a beakerAdd one drop of H2SO4Boil one minCool and neutralize with saturated Ba(OH)2Use phenolphthalein,as indicatorRemove the precipitate of barium sulfate by filtrationTest for BenedictIodine Test for PolysaccharidesIodine forms colored adsorption complexes with polysaccharidesBlue color with starchRed-blue or purple color with dextrinRed color with glycogenWith cellulose it gives no color

Reagent1%solutions of Starch, DextrineIodine solution (2% KI containing sufficient I2 to color it deep yellow)

Procedure1. In a test tube add 4 drops of the tested solution2. Add 1 to 3 drops of a dilute solution of Iodine solution.3. Compare the color obtained with that of water and iodine solution.

Hydrolysis of StarchReagents:1% starch solution, Benedicts solutionConc. HCl

ProcedurePlace 25 ml of 1% starch solution in a small beaker, add 10 drops of conc. HCl & boil gently.At the end of each min transfer 1 drop of the solution to the test plate and make the regular iodine test.Also at the end of each min transfer 3 drops of mixture to 5 ml portions of Benedicts solution in a series of test tubes.114. As the test proceeds, the reaction with iodine should become weaker & finally be negative.5. At this point place all test tubes containing Benedicts solution in a boiling water-bath for 3 min.6. Remove the tubes then allow to cool.7. Note the degree of reduction in each case compare with the rate of the disappearance of iodine reaction.

12Mucic Acid Test For GalactoseGalactose & any sugar gives galactose upon hydrolysis such as lactose, Raffinose and some gums give mucic acid on oxidation with HNO3Conc. HNO3 oxidizes galactose to mucic acid (a fine white gritty crystals separate, insoluble in water, but readily soluble in alkaline or ammonium carbonate solution & re-precipitated on the addition of nitric acid.13

Galactaric acidReagents2% solution of GalactoseConc. HNO314ProcedureTo 10 ml of 2% of galactose solt. In porcelain evaporating dish add 5ml conc. HNO3 Place the dish on top of a beaker filled with 2/3 distilled water.Evaporate (under hood) the contents of the dish on the boiling water bath to about a volume of 2 ml (it takes about 45 min boiling to reach the 2 ml).Remove the hot dish with tong and allow to cool.

156. add 5 ml of distilled water to the dish and mix well with a string rod.7. Note the insoluble mucic acid crystals from the oxidation of galactose.8. Transfer one drop of the liquid plus crystals to a clean microscope slide, examine with a low power microscope (10X).Note the gritty crystals of mucic acid.16