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How Does the pH of a Solution Affect the Rate of Starch Digestion By Diastase

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Introduction

How Does the pH of a Solution Affect the Rate of Starch Digestion by Diastase Abstract: This investigation was designed to show the effect of pH on the activity of enzymes. I did this by making buffered 1% starch solutions and 2.5% diastase enzyme solutions and mixing 25 cm3 of both solution to each other and testing if the starch was broken down into maltose every 30 seconds. The experimental procedures were repeated 3 times for a range of 5 pH's of pH 3.45, pH 4.35, pH 6.27, pH 7.17 and pH 9.22. This plan worked and was very easy to prepare and implement. The enzyme used showed positive results and gave some unexpected results in respect to the research that I have done about the diastase group of enzymes. Aim: I am going to perform experiments to determine the optimum pH for the digestion of starch by the enzyme diastase and I will be measuring the time it takes the enzyme to digest the starch solution. Preliminary Work: I tested a wide range of pH's in my preliminary work. I started by testing buffered solutions at pH 1, pH 3, Ph 5, pH 7, pH9 and pH 12. This gave me a rough idea of where my enzyme was going to be active. After analysing my data I decided that pH's 3 and 9 were going to set the extremes to my range or different pH's. I decided to add pH 6 to my solutions to give a more rounded result and replace pH 5 by pH 4. ...read more.

Middle

The different diastases are Alpha-Amylase, Beta-Amylase, Fungal Amylase, Glucoamylase and Malt Diastase. [2] What is pH? The pH scale measures the concentration of aqueous H+ ions (protons). This controls the acidity of solutions. Thomas Lowry and Johannes Br�nsted independently came up with a definition for acids and bases in 1923. The Lowry-Br�nsted definition for acids and bases is: "An acid is a substance that can donate a proton (an H+ ion) and a base is a substance that can accept a proton". [10] There is a conventional accepted definition for pH and that is "-log10 [H+ (aq)]". The square brackets in this definition are there to show the concentration of H+ ions in mol dm-3. The pH scale depicts the concentration of ions present, as the number gets smaller, the concentration of H+ ions increases. A jump of 1, like from pH5 to pH4 for example, represents a tenfold increase in the concentration of H+ ions. [11] What is a Buffer Solution? A buffer solution is one that can resist changes to the concentration of the OH- ions and the H+ ions within the buffered solution. Buffer solutions usually withstand changes in pH when moderate amounts of acid or base are mixed within them. [11] The pH in a buffer solution can be calculated using the Henderson Equation. The Henderson Equation is: Ka = [H+ (aq)] eqm [A- (aq)] [HA (aq)] eqm [11] Apparatus and Glassware List ==> 10 x Spotting Tile ==> 2 x Spatulas ==> 2 x Glass Rod ==> Weighing scale accurate to 2 d.p. ==> 4 x 200ml Beakers ==> 2 x Funnel ==> 5 x 250ml Volumetric Flask ==> 1 x 500ml Volumetric Flask ==> ...read more.

Conclusion

I found that the enzyme that I used was inactive in pHs that are pH 7 and above. This tells me that the enzyme was denatured by neutral or basic conditions. My results have thus shown me that the enzyme that I have been supplied with would have a range from pH 3 to pH 6, the specific enzyme can then be determined as Glucoamylase and that the range of this enzyme is pH 3 to pH 6. The optimum pH is somewhere in the boundary of pH 4.0 to pH 4.9. Limitations to my experiments mean that I cannot guaranty this result although I can be certain which enzyme this is if I were to increase the number of trials that I did and if I use more accurate equipment and methods of measurement. I could also increase my experimental margin to the effect of pH on diastase in different temperatures. Another thing that could have affected my results was the accuracy of my equipment. Values that I am aware of will always be different from the actual result. The 250ml and 500ml volumetric flasks I used to make my stock solutions had an error margin of �0.05ml and the 25ml pipettes that I used to measure the solutions to mix has an error margin of �0.06ml. One other error in measurement came from the weighing scale as I could only measure accurately to 2 decimal places. After concluding my experimental procedures and analysing my results, I have decided that a more accurate range of pH's is needed for better accuracy for my result. Decreasing the sample time from 30 seconds to 15 seconds will also help me achieve more accurate results. ...read more.

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The background theory and account of the preliminary experiment are mostly very good quality. However, there is little discussion of variables and data presentation could be improved.

Marked by teacher Adam Roberts 17/09/2013

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