Debra Jones
The Manipulation of Digestion Rates of Starches, Proteins, and Lipids through the Fluctuation of
Temperature and pH, and the Observation of Iron Presence in Breakfast Cereals
The purpose of this experiment was to examine the chemical processes of the digestion of starches,
proteins, and fats, and to determine how temperature and pH affects enzyme activity. Digestion is the breakdown of
food particles so that they become more easily absorbed by the body. Digestion begins in the mouth with the
breakdown of starch into maltose. This is catalyzed by the enzyme amylase, which is found in saliva. Next, proteins
are broken down into amino acids in the stomach and the small intestine. Fats are digested by the secretion of bile
salts and pancreatic lipase in the small intestine. Each of these processes require different structures and are
dependent on different enzymes in order to be completed.
The first part of the experiment examined the digestion of Carbohydrates and the effect of pH and
temperature on the enzyme amylase. This was done by creating 4 different starch containing solutions. The first
contained only starch and water. The second solution contained 2% amylase solution and starch. The third solution
combined 2% amylase solution, 1% HCl, and 1% starch solution. The last tube contained 2% amylase solution that
had been boiled, and afterwards starch solution was added. These solutions were incubated in a 37°C water bath for
an hour. Lugol’s solution was then used to test for the presence of starch, and benedict’s solution was used to test
for the presence of sugar. It was found that the first solution contained only starch, the second solution contained
only sugar, the third solution contained both starch and sugar, and the fourth solution contained only starch. Based
on these results, it was concluded that the solution that contained HCl had some of its amylase enzymes denatured
due to the presence of both starch and sugar, and that the amylase that had been boiled had been completely
denatured due to the solution that contained the boiled amylase containing no sugar and only starch.
The second experiment tested the effects of pH on pepsin and its effectiveness of digesting proteins. This
was done by creating the following 5 solutions: tube one contained 3% pepsin solution and water, tube two
contained 3% pepsin and 1% HCl, tube three contained 3% pepsin, 1% HCl, and was placed on ice, tube four
contained HCL and water, and tube five contained 3% pepsin and 1% NaOH. Tubes 1,2,4, and 5 were then
incubated in a 37°C water bath for 90 mins. Biuret solution was then added to each of the tubes to test for protein
presence. Based on the results, tubes 4 and 5 had the greatest color change and had the lowest and highest pHs
respectively. Based on these results, it was determined that tubes 4 and 5 were the least digested out of the tested set.
This was believed to be due to the inefficiency of pepsin in high and low pH environments.
In the third experiment, the efficiency of fat digestion was examined by creating solutions of corn oil and
water and adding the following solutions to each of the tubes: tube one had nothing extra added, tube two had bile
salts added, tube three had liquid soap added, tube four had lipase solution added, tube five had lipase and bile salts
added, and tube six had lipase solution and liquid soap added. These solutions were then placed in a 37°C water bath
for 60 minutes, and the pH of each tube was measured at 20 minute increments. The results yielded little fluctuation
in pH, and were inconsistent with what had been predicted. It was thought that tube 5 would exhibit the highest rate
of digestion due to there being both lipase and bile salts being added to the solution, and that tubes 2 and 4 would
each exhibit digestion rates lower than tube 5 but higher than those of the other tubes.
The fourth experiment isolated iron from fruity rice crispies, rice crispies, and total by crushing up the
cereals, adding 250 mL of warm water to each, and stirring the mixture with a magnet for 10 minutes. It was found
that the total contained the most iron and the fruity rice crispies contained the least iron. It was predicted that the
total would have the greatest amount of iron found followed by rice crispies, and then the fruity rice crispies due to
each cereal containing 18 g, 9 g, and 1.8 g of iron per serving for each respective cereal.
Based on the results found, pH and temperature both affect the enzymes found in the digestive processes,
and influence the rate of digestion. Based on the data obtained temperature had the greatest influence and
completely halted the digestion of starches, while pH fluctuation in the digestion of starch, lipids, and proteins only
slowed the rate of digestion.