CHAP 3 PCOG CARBOHYDRATES Flashcards
- a group of compounds composed of carbon,
hydrogen and oxygen - polyhydroxy aldehyde or polyhydroxy ketones or compound that on hydrolyses
produce either of the above (aldehydes or ketone)
Carbohydrates
General Formula of CARBOHYDRATES?
CnH2nOn
► crystalline, soluble in water and sweet
in taste
► Example: glucose, fructose, sucrose,
etc.
Low molecular weight carbohydrates
► amorphous, tasteless and relatively
less soluble in water’
► Example: starch, cellulose, inulin, etc.
High molecular weight
carbohydrates (polymers)
Primary Functional Groups
►Aldose
►Ketose
►Alcohol - sugar alcohol
(mannitol/ sorbitol)
►Carboxyl - sugar acid
(lactic acid/ tartaric acid/
citric acid
General test for carbohydrates
- The test is positive with soluble as well as
insoluble carbohydrates. - It consists of treating the compounds with *αnaphthol and concentrated sulphuric acid which gives purple color.
- soluble carbohydrate: appears as a ring with
sulphuric acid; form a layer below the
aqueous solution. - insoluble carbohydrate (such as cotton
wool/cellulose): color will not appear until the
acid layer is shaken to bring it in contact with
the material.
Molisch Test
Specific test for Ketones.
- A crystal of resorcinol is added to the
solution and warmed on a water bath with
an equal volume of concentrated
hydrochloric acid. - A rose color is produced if a ketone is
present (e.g. fructose, honey or hydrolyzed
inulin).
Seliwanoff’s Test
Test for Deoxysugars
-
Dissolved in acetic acid containing a trace
of ferric chloride and transferred to the
surface of concentrated sulphuric acid. - At the junction of the liquids, a reddishbrown color is produced which gradually becomes blue
Keller-Kiliani Test
Specific test for reducing sugar* or
the presence of free or potential
aldehydes.
- Positive result: red-orange precipitate
Benedict’s Test
A test used to distinguish monosaccharides and disaccharides
- Positive result: little dark red precipitate at the bottom of the test tube
- Monosaccharides: appears within 2-3 minutes
- Disaccharides: does not appear or appears after 10
mins
Barfoed’s Test
A test for pentoses and nucleotides that contain the pentose sugar.
- Furfural which is formed from a pentoses yields blue-green compound when treated with orcinol in the presence of ferric
ions (Bial’s reagent)
Bial’s Test
► convert electromagnetic energy into chemical potential.
LIGHT REACTION
► consists of the enzymatic reactions that utilize the energy
from the light reactions to fix carbon dioxide into sugar.
DARK REACTION
►a 5-C sugar
►Syn: Wood sugar
►Sources: Corn corbs & heart of deciduous trees
►Use: Diagnostic aid for cystic fibrosis(genetic disorder found among Caucasians- 1:2500)
► use to measure how much is absorbed in the intestine
Xylose
► Physiological sugar
► β-D glucose - most abundant in
nature
► Sources: Grapes (Vitis vinifera) - most abundant source
► Determined by: Benedict’s test
► Uses: in the production of wine
(White wine- peeled-off), liquid glucose- syrup
DEXTROSE/ GLUCOSE
► “Fruit sugar”
► found free in nature
► Reducing sugar: Seliwanoff’s test
►sweetest monosaccharide
► Uses:
1. For diabetic
2. Ingredient in infant feeding
3. Fructose injection - less
frequently used than glucose
Fructose/ Levulose
►more found in animals than in plants
►”milk” - not found free in nature
►a component of nerve cells
(neurons) - “galactocerebroside”
►Gaucher’s Disease - lack of galactocerebrosidase
►Mucic acid & Osazone test= crystals
GALACTOSE
►insoluble osazone crystals
MANNOSE
► “Table Sugar”
► Glucose + Fructose
► Glycosidic bond: α-1,2
► No free carbonyl carbon (non-reducing sugar)
► Molasses
► residual dark colored syrup after complete
crystallization of sucrose; Food and ethanol industry.
Uses:
► Demulcent, Sweetening agent; masks taste,
Coating agent, Preservative, Production of syrups, Retards oxidation
SUCROSE
Sources of sucrose:
►Sources:
► Sugar cane (Saccharum officinarum)
► Sugar beet (Beta vulgaris)
► Sugar maple (Acer saccharum)
►Glucose + Glucose
►Glycosidic Bond: α-1,1
►a non-reducing sugar
►found in seaweeds
TREHALOSE
► “Beer Sugar or Malt Sugar”
► Glucose + Glucose
► Glycosidic Bond: α-1,4
► sugar from grains (barley) - beer:
fermented grains
► product of the germination of
barley through the process called
“Diastatic Fermentation”
MALTOSE
►”Milk Sugar”
►Glucose + Galactose
►Glycosidic Bond: β-1,4
►Sources: Cow’s milk (Bos taurus); product of
crystallization of whey (from the manufacture of cheese)
LACTOSE
► Fructose + galactose
► Glycosidic bond: β-1,2
► semi-synthetic sugar prepared from
the alkaline rearrangement of lactose
► no enzyme is available for hydrolysis
► Lactulose –> Lactic acid + Acetic acid
LACTULOSE
