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LAB 4 Chemical Analysis: Detecting Sugars, Proteins and Lipids.

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Presentation on theme: "LAB 4 Chemical Analysis: Detecting Sugars, Proteins and Lipids."— Presentation transcript:

1 LAB 4 Chemical Analysis: Detecting Sugars, Proteins and Lipids

2 Detection of Organic molecules using stains materials: – Onion – Potato – Apple – Peanut stains: – Benedict’s - presence of reducing sugars – Biuret’s – presence of proteins – Sudan IV – presence of fats – Potassium Iodide presence of starch/polysaccharides

3 Potassium Iodide starch divided up into two fractions – amylose – helical and unbranched – amylopectin - branched amylose forms a blue-black complex when it combines with the iodide ions found in a potassium iodide solution made for detecting starches this potassium iodide solution is also called Lugol’s reagent – actually a mixture of potassium iodide (soluble)and elemental iodine (insoluble) – results in a soluble solution containing triiodide the Lugol’s reagent interacts with the coiled structure of the amylose fraction of the starch – blue black color – specifically the triiodine molecule interacts with the polysaccharide no color produced by amylopectin or monosaccharides or dissacharides

4 Benedict’s Reagent used to detect the presence of reducing sugars reducing sugar – sugar that in its open form bears aldehyde group – all monosaccharides (reagent converts fructose to glucose) – maltose, lactose in nature – many foods possess both closed ring and open linear forms of sugars under heat - copper of the reagent reacts with the aldehyde of the sugar to turn a specific color Open, reducing form of glucose aldehyde

5 Benedict’s Reagent copper is reduced by the sugar to form copper oxide (red, insoluble) – color denotes amount of reaction (i.e. approximate amount of reducing sugar) – green - 0.5% sugar many dissacharides produce this color – yellow – 1.0% – red - 2% or more many monosaccharides produce this color sucrose is not detected by this reagent – not a reducing sugar many polysaccharides such as starch begin with a reducing sugar – may not be sufficient to turn the reagent’s color Open, reducing form of glucose aldehyde Benedict’s Sugar Copper Oxide

6 Biuret’s Reagent chemical reagent that detects the presence of peptide bonds presence of peptide bonds can produce a pink to violet color – pink – short chain polypeptides – violet – longer proteins – spectrophotometers can be used to measure the absorbance of these colored solutions = protein concentration biuret = chemical compound with the formula H 2 NC(O)NHC(O)NH 2 yet Biuret’s reagent doesn’t contain biuret – it gives a positive reaction same as the peptide-like bonds in the biuret molecule BR = potassium hydroxide and copper – potassium hydroxide increases the pH of the solution (alkaline) – copper forms violet-colored complexes in the alkaline environment of the test the copper sulfate of the reagent water BR albumin BR + albumin

7 Sudan Staining several different kinds of Sudan stains – all are used to stain lipids – different colors – Sudan III = red – Sudan IV = black Sudan IV stains lipid droplets black in slide preparations also can stain in liquid preparations Sudan III staining = oil and water

8 Explanation of results Benedict’s – Onion – reddish color (+ve) – Peanut – blue (-ve) – Apple - +ve – Potato – yellowish color (+ve) Biuret – Onion – +ve (pink) – Peanut - +ve (purple) – Apple – -ve (blue) – Potato – -ve (blue) Sudan IV Potassium Iodide – potato, apple – black staining, +ve result – peanut, onion – little to no staining peanut – kind of gray???

9 Explanation of results Onion: +ve Benedict’s, +ve Biuret 1% protein (sulfurous odor of the onion) 4% sugar – glucose, fructose and sucrose – fructose the most – sugar content increases with maturation 2% soluble fiber in flesh – insoluble fiber in the skin 0.1% fat 98% water Peanut: +ve Biuret, +ve Sudan IV – 25% protein – source of the essential amino acids histidine and arginine – 48% fat (7% saturated, 24% mono, 16% poly) – 41% considered oil numerous fatty acids – palmitic, stearic, oleic, linolenic, linoleic – 0% sugar; 1% cellulose, 9% fiber – 21% carbohydrates – NO SIMPLE SUGARS -presence of reducing sugars -presence of proteins -presence of fats -presence of proteins

10 Explanation of results Apple: +ve Benedict’s – 85% water – 0.3% protein – 11 types of amino acids – 0.4% fats – 12% carbohydrates – all three monosaccharides + starch – 2.3% fiber – 0.6% organic acids – e.g. citric acid Potato: +ve Potassium Iodide – 78% water – 2.2% protein – 0.1% fat – 18% starch – 0.4% fiber -presence of reducing sugars -presence of starch -not enough proteins or fats -presence of starch -not enough proteins or fats


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