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Acid Hydrolysis of Polysaccharides.

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Introduction

Acid Hydrolysis of Polysaccharides Introduction Carbohydrates are the most abundant and widely distributed food component in nature (70% of caloric value in the human diet). Also very heterogeneous group in structure, and physical properties. Classified as: Monosaccharides- glucose, fructose Disaccharides- sucrose, lactose, raffinose Polysaccharides - starch, cellulose Only monosaccharides are absorbed in the small intestine, oligo an polysaccharides must be hydrolysed before absorption Humans can digest only sucrose, lactose, malto-oligosaccharides and starch Non-digestible polysaccharides and lignin make up fibre Carbohydrates contribute to bulk, body, viscosity, stabilization of emulsions and foams, water holding, freeze thaw stability, browning, flavours, and texture attributes . Starch (amylose) molecules and cellulose are related to each other, they are both polysaccharides. Glycogen is also a polysaccharide, but it has a protein core. Alpha Amylose is a linear polymer. It is made up of many thousands of glucose units linked by alpha 1-4 bonds. Cellulose is a much larger molecule than the amylose type molecules. However, cellulose molecules bond to each other to form crystals with hydrogen bonds. ...read more.

Middle

A spectrophotometer will be used and this is a form of colour measurement and it assigns numerical values dependant on the level of absorption of solution in cuvette. Method: Take 12 test tubes and place in a test tube rack. Pipette 1ml of glycogen into 6 tubes, and 1 ml of other polysaccharide into the remaining 6 tubes. Take a clean pipette and add 1 ml distilled water, then using a 5ml pipette add 2 ml of 2M HCl to each tube. Cover with parafilm and pierce this with a pin. Place the 12 test tubes in a boiling water bath, making a note of the time. Using the test tube tongs, remove one tube of each polysaccharide solution from the water bath after 10 minutes. Upon removal-using a Pasteur pipette, take one drop of each solution and place in separate wells of the white spotting tile. Add one drop of iodine to each and mix, making note of the colour produced. Neutralise the rest of the solution in the tubes by adding 1ml of 4M NaOH to each. ...read more.

Conclusion

This produces a long, rigid molecule. * There are no side chains in cellulose as there are in glycogen. The absence of side chains allows these linear molecules to lie close together. * Because of the many -OH groups, as well as the oxygen atom in the ring, there are many opportunities for hydrogen bonds to form between adjacent chains. The result is a series of stiff, elongated fibrils - the perfect material for building the cell walls of plants. Therefore cellulose is much more resistant to hydrolysis than glycogen. Animals store excess glucose by polymerizing it to form glycogen. The structure of glycogen is similar to that of amylopectin, although the branches in glycogen tend to be shorter and more frequent. Glycogen is broken back down into glucose when energy is needed (a process called glycogenolysis), Therefore the breakdown on glycogen has to be easy. Unfortunately I didn't get the opportunity to use starch in the experiment as there wasn't enough time available. If I was to repeat the experiment I would have done more tests and a wider range of time, this is to improve the accuracy of my results. I would also use other polysaccharides to see if there is a trend. ...read more.

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