I have decided to use 10ºC, 20ºC, 30ºC, 40ºC, 50ºC, 60ºC, and 70ºC to get a good range of results, because in our pilot investigation, w only used the temperatures 20C and 40C. However, I wanted to see at what temperature, if at any, the enzymes became denatured, and at what temperature they began to work. I will do it 3 times to get reliable results.
Preliminary Results
My results
Conclusion
Looking at the results, I can see that as the temperature increased, the volume of the dough increased. E.g. after 30 minutes in the tube at 10C, the volume went from 23.3cm3 to 29.0cm3. Whereas in the tube at 50C, it went from 25.1cm3 to 101cm3.
The yeast increased in volume at 50C after 30 minutes, where the enzymes reached their peak at 101C, then fell as they were denatured at 30 minutes at 70C, and went back down to 76.7cm3. As I said in my prediction, when yeast respires anaerobically, bubbles of carbon dioxide in the tubes that were heated got trapped. This is because the anaerobic word equation for the respiration of yeast is:
Glucose = ethanol + Carbon dioxide (+ little energy)
The enzymes in the yeast worked best at higher temperatures than 20ºC, so the respiration rates increased; so more carbon dioxide was produced. At 70ºC, the dough stopped rising after 30 minutes. This is because high temperatures make all enzymes inactive. This is because of denaturation. Enzymes are proteins, which are damaged by high temperatures. Enzymes are biological catalysts, which are either ones, which break down complexed compounds to simple compounds, or vice-versa. A chemical reaction always involves a substrate changing into another. The substance, which is present in the beginning of the reaction, is called the substrate. The substance, which is made by the reaction, is the product, e.g. ethanol + CO2 from glucose and yeast. Enzymes have a very precise 3D shape, and each has a “duct” and has exactly the right size and shape for a molecule of the enzyme’s substrate to fit into it. This “duct” is known as the active site. When the substrate slots into the active site, the enzyme “tweaks” the substrate molecule, by pulling it out of shape and making it split into product molecules. These then depart from the active sit, which is then ready to repeat the process with another substrate molecule.
Most chemical reactions happen faster when the temperature is higher. At higher temperatures, molecules move around faster. This makes it easier for them to react together. Usually a rise of 10ºC will double the rate of the reaction. They are very sensitive to high temperatures. Once the temperature is above 100ºC, the enzyme will be damaged. When this occurs, it cannot catalyze its reaction so well, so the reaction slows down.
The water rehydrated the powdered yeast, sugar, and flour mixture, so it gave the enzymes a solution to work in. The carbon dioxide bubbles made the dough rise and expand, so we measured the enzyme activity by the CO2 amount, or by how much the dough raised. This was what happened in my pilot experiment. At 20ºC the volume of the dough was 25cm3, and after 30 minutes, it only went up by 2cm3, but in the cylinder at 40C, the volume increased from 25cm3 by 60cm3. The trend of the graph is to go up as the temperature increases, reaching its peak at 50C, where it is 101cm3, then going back down to 76.7cm3at 70C. It could be a curve. My graph is basically what I expected it to be, and a curve could be formed from it. The graph volume of the dough on the graph rises as the temperature does, which was just what I predicted would happen. Also, the graph declines at 101cm3 at 50C. However, I did not expect the dough to only raise ½ cm3 from 10C to 20C.
Fair Testing
We tried to make this a fair test by using:
- In all of them, the same amounts of sugar, flour, and yeast,
- A stirring rod – getting all the bubbles out from the mixtures,
- A clock to record measurements of the new volumes at the same times,
- A measuring cylinder to get 20cm3 of water each,
- The same apparatus all the way through.
Evaluation
I found that this experiment was successful, and provided relatively accurate results, however, a few things were difficult to do. When taking measurements of the volumes of dough after every five minutes, the top of the dough was very uneven, so it was hard to measure. Also, it was hard to pour the dough into the cylinders without spilling some of it around the sides of it. It was also to make it a reliable investigation. I have noticed that there are a few anomalies in my result, which I have circled on my graph, and on the results table. These are due to the problem we had with the uneven temperatures, in which the measuring cylinders with dough were in, as it was relatively difficult to maintain the temperatures in the water baths, as we continuously had to put some hotter or colder water into the baths. However, the results were reliable and accurate to support the conclusion, which also agreed with my hypothesis. As the temperature increased, the volume of the dough increased until it reached its peak, and the enzymes had reached their optimum temperature. Then the volume decreased because the enzymes were denatured.
I hav creatd another experiment which investigates the best temperatures at which yeast enzymes work best at. I want to investigate further into what exactly is the yeast enzymes’ optimum temperature, as it was 101cm3 at 50C, but as I mentioned before – the dough was at unevern temperatures, as it was hard to control it without the special abilities of laboratory machines. I know that the optimum temperature is between 40C and 50C.
Method
We will mix 1g of yeast, 0.5g of sugar, and 10g of flour, each in 4 beakers with 20cm3 of water, which will be measured with a measuring cylinder. Then we will pour it into measuring cylinders, but this time using a measuring cylinder with a larger opening, to avoid spilling the mixture around the edges of it. Then, the volumes in each of the 4 cylinders will be 25cm3
