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PSU_Exp202lycopene - EXP 202 Column Chromatography TLC and...

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EXP 202 1 Column Chromatography, TLC, and Visible Spectroscopy of Vegetable Pigments Adapted by J. Bortiatynski from Operational Organic Chemistry, A Problem-Solving Approach to the Laboratory Course , John W. Lehman, Prentice Hall, New Jersey, 1999, pages 74-79 and from R. Minard and Annette Squillario Chem 36 Lab Experiments. Introduction: The orange and red pigments that are in fruits and vegetables such as tomatoes and carrots are hydrocarbons known as carotenoids . The two common carotenoids, which incidentally are precursors to Vitamin A, are lycopene and β -carotene. Lycopene has 13-carbon-carbon double bonds and is one of the most unsaturated compounds found in nature. It has antioxidant properties that is known to prevent digestive and cervical cancer. β -carotene, the other caroteniod pigment found in tomatoes, carrots and other leafy vegetables is converted to Vitamin A in the intestinal wall and is stored in the liver. The structure of lycopene and β -carotene is shown below, note the number of double bonds and their geometry. Lycopene β -Carotene CH 2 OH Vitamin A C 20 H 30 O Consumer groups are always questioning whether or not the packaging of foods changes their nutritional value. Does the processing of tomatoes into tomato paste and its subsequent packaging reduce the content and the structural integrity of the lycopene and β -carotene in it? Another thing to consider, does the structural integrity and or nutritional value of lycopene and β -carotene change with shelf life? In this experiment, you will extract these pigments from tomato paste, separate and isolate them using column chromatography, and then characterize them by UV/Vis spectroscopy. Where would you expect to see the UV/VIS maxima for these pigments? The isolated lycopene can be isomerized from one geometric isomer to the other by if allowed to stand too long in the presence of light, heat or acids. Prolonged exposure to heat can occur during processing. When isolating the lycopene is it is also important to work rather quickly because the natural acids in tomatoes and prolonged exposure to oxygen can also induce this isomerization. Washing with a weak base will help reduce the amount of natural acids. When the isomerization takes place the λ max is shifted to
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EXP 202 2 shorter wavelengths so what does that mean in terms of the energy need to induce the absorption? You will measure the λ max after isolation and then induce an artificial isomerization using iodine. The change in intensity of the λ max after the isomerization is an indication of the amount of degradation that occurred during processing. If only small changes in the intensity of the maxima after isomerization is observed then this could indicate pigment alteration during processing. If you were working for one of the watch dog organizations to examine food quality after packaging can you draw any conclusions regarding the processing of tomato paste by examining just one brand of product? If lycopene is found in tomatoes why use tomato paste rather than tomato sauce?
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