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Test for reducing sugars (Benedict's Test)

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Additional reading materials for Chapter 5: Nutrition Carbohydrates: Mono-, Di- and Polysaccharides Below is the flowchart to show the relationship between monosaccharides (simple sugars), disaccharides (complex sugars) and polysaccharides (e.g. starch and glycogen). Important things to note: (a) Glycosidic bonds are chemical bonds that hold / join molecules of monosaccharides together. (b) Chemical formulae of monosaccharides, disaccharides and polysaccharides. (c) Polysaccharides are macromolecules, meaning they are very large molecules (made up of many many small monosaccharide molecules joined together in straight or branched chains). (d) Examples of monosaccharides, disaccharides and polysaccharides. Test for reducing sugars (Benedict's Test) Given an unknown solution, you are to find out if it contains reducing sugars ... so you have to carry out the reducing sugar test (Benedict's test). NOTE: What are reducing sugars?? A reducing sugar (all monosaccharides and some disaccharides) will produce a brick-red ppt when boiles with Benedict' s solution. Non-reducing sugar: Sucrose Procedures: 1. To 2 cm 3 of the unknown solution in a test-tube, add an EQUAL VOLUME (that is the same volume as the unknown solution used: 2 cm 3 ) of Benedict's solution (blue). 2. Shake the mixture and heat it by immersing the test tube into a boiling water bath (beaker of boiling water) for 5 minutes. 3. Observe the appearance of the heated mixture after 5 minutes. ...read more.


through these clogged vessels. This increases the risk of heart disease (if the blood vessels that supply blood to the heart muscles are clogged). Dietician recommends ... Take less animal fats. Replace butter with margarine. Test for fats (Ethanol emulsion test) Test for fats in liquid food Given an unknown solution, you are to find out if it contains fats ... Procedures: 1. Place 2 cm 3 of the unknown solution into a dry test tube . Add about 2-5 cm 3 of ethanol (alcohol) into the test-tube. 2. Shake vigorously for about 1 minute (allowing time for the ethanol to dissolve / extract out the fats). 3. Pour the mixture into another test-tube containing 2-5 cm 3 of water . Shake the mixture thoroughly. Observations: Upon mixing with water, a cloudy white emulsion is formed, indicating the presence of fats. In the absence of fats, the mixture should remain clear and colorless. Test for fats in solid foods Given peanut seeds, you are to find out whether they contain fats ... Procedures: 1. Cut the peanut seeds into small pieces and place them into a dry test-tube . Note: Cutting them into smaller pieces increases the surface area of the food for the extraction of oil by ethanol ... ...read more.


Given an unknown solution, you are to find out whether it contains proteins ... Procedures: 1. To 2 cm 3 of unknown solution in a test-tube, add 1 cm 3 of sodium hydroxide solution . Shake thoroughly. 2. Add 1% copper sulphate solution (light blue), drop by drop , shaking the mixture after each drop . 3. Observe color changes. Observation: A violet / lilac color is formed, indicating the presence of proteins. In the Control Expt. the mixture remains light blue, indicating the absence of proteins. Complete proteins VS Incomplete proteins The proportion of protein in plant food is much lower than that in animal food . Proteins that come from animals are complete proteins . What are complete proteins? Complete proteins are proteins that contain all essential amino acids . Then ... what are essential amino acids? Essential amino acids are amino acids that the body cannot synthesize/make and must be obtained from our daily diet . Proteins from plants are incomplete proteins which lack some of the essential amino acids. For vegetarians to obtain the proper amounts of all essential amino acids, they must eat a mixture of 2 or more incomplete protein foods at each meal. Sources of complete proteins Sources of incomplete proteins Main functions of the 3 major classes of food Mian function of proteins: Main function of fats: Energy values of food Table below shows the energy values of each main class of food: ...read more.

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