Chemical Tests for Carbohydrates PDF

MOLISCH’S TEST MUCIC ACID TEST/GALACTIC ACID TEST  It is a chemical test for the presence of  It is a test for detection of the presence of CARBOHYDRATES. Monosaccharides give a galactose and/ or lactose....

MOLISCH’S TEST MUCIC ACID TEST/GALACTIC ACID TEST  It is a chemical test for the presence of  It is a test for detection of the presence of CARBOHYDRATES. Monosaccharides give a galactose and/ or lactose. rapid positive test. Disaccharides and polysaccharides react slower.  REAGENTS: Concentrated Nitric acid  This test was discovered by Hans Molisch  PRINCIPLE: Galactose is oxidized by nitric acid to form mucic acid crystals. Mucic acid (C6 H10 O8)  REAGENTS: Molisch reagent (alpha- naphthol in is an insoluble dicarboxylic acid that forms 95% ethanol) and Concentrated Sulfuric acid characteristic sandy crystals.  PRINCIPLE: The test reagent dehydrates  POSITIVE RESULT: Formation of a crystalline pentoses to form furfural and dehydrates precipitate. hexoses to form 5-hydroxymethyl furfural. The furfurals further react with -naphthol present in TAUBER’S BENZIDINE TEST  It is a test for the detection of the presence of the test reagent to produce a purple product pentoses (furfuryl diphenyl meline dye)  REAGENTS: 4% solution of benzidine in glacial  POSITIVE RESULT: Purple or Violet ring forming acetic acid at the interface between the acid and test layers  PRINCIPLE: Pentoses like ribose and arabinose  Use Stratification Method reacts with the test reagent to form a cherry red product  Negative in Cellulose  BENZIDINE: carcinogenic ANTHRONE TEST FEHLING’S TEST  It is a chemical test for the rapid detection of  It is used to differentiate between aldehyde or carbohydrates in samples, most especially body ketone functional groups. Ketones (except alpha- fluids. It is also used in cellulose assays. hydroxy ketones) do not react. An example for its use is to screen for glucose in urine, thus  REAGENTS: (10- hydroanthracen -9- one in detecting diabetes. It is also used to test for sulfuric acid) reducing monosaccharides and disaccharides.  PRINCIPLE: Anthrone, when dissolved in  This test was discovered by Hermann von concentrated sulfuric acid and mixed with a Fehling carbohydrate solution, forms a blue or green colored product  REAGENTS: Fehling's reagent A - Copper (II) sulfate pentahydrate in distilled water.  POSITIVE RESULT: Formation of a blue or green  Fehling's reagent B - Rochelle's salt (potassium product sodium tartrate tetrahydrate) and Sodium hydroxide in distilled water  Test for urine, saliva, and other body fluids  PRINCIPLE: An aldehyde is first added to the SELIWANOFF’S TEST Fehling solution & then the mixture is heated.  This test is utilized for the differentiation of Aldehyde oxidizes to acid and red precipitates of aldoses and ketoses. Only ketoses (like fructose Cuprous oxide are formed The cupric ion is and sucrose) yield a positive result in this test. complexed with the tartrate lon. Contact with an aldehyde group reduces it to a cuprous ion,  REAGENTS: (Resorcinol in Hydrochloric acid) which then precipitates as red Cu₂O (copper(1) oxide). Ketones (except alpha-hydroxy ketones)  PRINCIPLE: The test reagent dehydrates and aromatic aldehydes do not respond to the ketohexoses to form 5-hydroxymethylfurfural. Fehling test. 5- hydroxymethylfurfural further reacts with resorcinol present in the test reagent to produce  POSITIVE RESULT: Formation of a brick-red a red product within two minutes. Aldohexoses precipitate react to form the same product, but do so more slowly.  Fehling A must be first before Fehling B  POSITIVE RESULT: Formation of a RED product  Fehling B: Be serve as BUFFER SOLUTION (pure sucrose)/ Orange  Cuprous oxide: brick red precipitate BENEDICT’S TEST TOLLEN’S TEST  It is a chemical test used to detect the presence  It is a chemical test used to detect the presence of reducing sugars (sugars with a free aldehyde of aldehyde groups. Tollens' test can be used to or ketone group). It is also a test for detecting ascertain whether the compound is a ketone or glucose in urine an aldehyde.  This test was discovered by Stanley Rossiter  This test was discovered by Berhard Tollens Benedict.  REAGENTS: 5% Silver nitrate  REAGENTS: Benedict's reagent-Copper (II) 10% Sodium hydroxide sulfate in a citrate buffer solution (Sodium Dilute Ammonium hydroxide (7 ml of citrate and Sodium carbonate). concentrated Ammonia in 100 ml. distilled water.  PRINCIPLE: The copper sulfate (CuSO₂) present in Benedict's solution reacts with electrons from  PRINCIPLE: Ag+ ions react with OH of" aqueous the aldehyde or ketone group of the reducing ammonia to produce a brown precipitate of Ag₂O sugar to form cuprous oxide (Cu₂O), a brick which is dissolved on addition of an excess of precipitate. The final color of the solution aqueous ammonia under the formation of depends on how much of this precipitate was [Ag(NH3)2]. The silver diamine complex is formed, and therefore the color gives an reduced by glucose and other reducing sugars to indication of how much reducing sugar was metallic silver while they are oxidized to present. carboxylic acids like glucose is oxidized to gluconic acid.  POSITIVE RESULT: Formation of a brick red precipitate  POSITIVE RESULT: Formation of Silver mirror BARFOED’S TEST  It is a chemical test similar to Benedict's test, but determines if a carbohydrate is a monosaccharide or a disaccharide. Barfoed's reagent reacts with monosaccharides to produce cuprous oxide at a faster rate than disaccharides do.  This test was discovered by Christen Thomsen Barfoed  REAGENTS: Barfoed's reagent-neutral, crystallized copper acetate in water and glacial acetic acid.  PRINCIPLE: This chemical test is based on the reduction of copper (II) acetate to copper (1) oxide (Cu₂O) by reducing sugars like the monosaccharides, which forms a reddish brown precipitate. Disaccharides may also react, but the reaction is much slower. A number of other substances, including sodium chloride, may interfere.  POSITIVE RESULT: Formation of a brick red precipitate BIAL’S TEST  It is a chemical test used to distinguish a pentose (5 carbons) from a hexose (6 carbons) monosaccharide.  REAGENTS: Orcinol in 95% ethanol with 10% FeCl2.6H₂O solution.   PRINCIPLE: The presence of pentoses or their derivatives which can form furfural upon heating INVERT SUGAR in acidic medium (dehydration reaction) yields a  is table sugar (also known as sucrose) broken into positive result. Furfural formed from pentoses the molecular bonds of glucose and fructose. reacts further with orcinol in the presence of FeCl, to give off blue-green hue of the solution  The result is a thick-as-honey, clear liquid that (condensation reaction). boasts all the benefits of conventional sweeteners, plus additional features  POSITIVE RESULT: Formation of a green to deep blue colored product.  Invert sugar is also known as inverted sugar, invert sugar syrup, and trimoline. LUGOL’S TEST  It is a chemical test used to distinguish polysaccharides from monosaccharides and disaccharides.  This test was discovered by Jean Guillame Auguste Lugol  REAGENTS: lodine and Potassium iodide  PRINCIPLE: This chemical test is based on the color change of Potassium iodide from yellowish brown to a blue-black colored product upon addition to a polysaccharide solution like starch ARTIFICIAL SWEETENERS  POSITIVE RESULT: Color change from yellowish  Any synthetically produced, intensely sweet brown to blue-black substance developed for use in reduced-calorie or dietetic foods and beverages. Unlike natural sugars, artificial sweeteners do not promote tooth decay, and they contribute few if any calories to the foods they sweeten.  Major sweeteners include aspartame, saccharin, the cyclamates, and sucralose ASPARTAME  It is the name for an artificial, non-saccharide sweetener. In the European Union, it is known under the E number (additive code) E951. Aspartame is the methyl ester of a phenylalanine/aspartic acid dipeptide. Character Reducing sugar Non reducing  It has been the subject of controversy since Its sugars initial approval in 1974. Foods containing this Nature Reduce cupric Don’t form brick- substance must be labeled so as to notify ions of Fehling’s red precipitates reagent and with Fehling’s individuals with phenylketonuria, a rare disease Benedict’s reagent and that requires control of dietary phenylalanine. reagent to Benedict’s The latest scientific evidence indicates that cuprous ions to reagents aspartame is safe at current levels of human produce brick-red consumption precipitates.  This sweetener is marketed under a number of Structural Have free Don’t have free trademark names, including Equal, NutraSweet, peculiarity carbonyl group carbonyl group (either aldehyde and Canderel, and is an ingredient of or ketonic group) approximately 6,000 consumer foods and beverages sold worldwide, including diet sodas Examples All Sucrose and all and other soft drinks, instant breakfasts, and monosaccharides polysaccharides others. It is also one of the main sugar substitutes maltose, lactose, etc. used by people with diabetes.  the digestive tract, being transformed (fermented) by bacteria there. Soluble fiber also SACCHARIN absorbs water to become a gelatinous substance  The basic substance, benzoic sulfide, has that passes through the body. Insoluble fiber, effectively no food energy and is much sweeter however, passes through the body largely than sucrose, but has an unpleasant bitter or unchanged metallic aftertaste, especially at high concentrations. In countries where saccharin is  Food sources of dietary fiber are often divided allowed as a food additive, it is used to sweeten according to whether they provide products such as drinks, candies, medicines, and (predominantly) soluble or insoluble fiber. To be toothpaste. precise, both types of fiber are present in all plant foods, with varying degrees of each according to  It was banned in Canada in 1977 as a result of a plant's characteristics. studies suggesting a link with bladder cancer in animals. In the United States, although saccharin  Potential advantages of consuming fiber are the was banned in 1977, Congress has invoked a production of health-promoting compounds series of moratoriums that have kept it on the during the fermentation of soluble fiber, and market with warning labels. insoluble fiber's ability (via its passive water- CYCLAMATES attracting properties) to increase bulk, soften  The patent for cyclamate was purchased by stool and shorten transit time through the DuPont but later sold to Abbott Laboratories Intestinal tract. which undertook the necessary studies and submitted a New Drug Application in 1950. Abbott Intended to use cyclamate to mask the bitterness of certain drugs such as antibiotics and pentobarbital. In the US in 1958 it was designated GRAS (Generally Recognized as Safe).  Cyclamate was marketed in tablet form for use by diabetics as an alternative tabletop sweetener, as well as in a liquid form. Since 1969, its sale and use has been banned by the Food and Drug Administration in the United States.  Cyclamate is 30-50 times sweeter than sugar, making it the least potent of the commercially used artificial sweeteners. Some people find it to have an unpleasant aftertaste, but generally less so than saccharin or acesulfame potas sium. It is often used synergistically with other artificial sweeteners, especially saccharin. SUCRALOSE  It is a zero-calorie sugar substitute artificial sweetener. In the European Union, it is also known under the E number (additive code) E955. Sucralose is approximately 600 times as sweet as sucrose, twice as sweet as saccharin, and 3.3 times as sweet as aspartame. It can be used in baking or in products that require a longer shelf life. FIBERS IN THE DIET  Dietary fiber (fibre), sometimes called roughage, is the indigestible portion of plant foods that pushes food through the digestive system, absorbing water and easing defecation.  Dietary fiber can be soluble (able to dissolve in water) or Insoluble (not able to dissolve in water). Soluble fiber, like all fiber, cannot be digested. But it does change as it passes through