Science Buddies: "Ask an Expert"

I need some help determining the original sucrose concentration for certain foods. I am doing the "Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food" project.
So the experiment says "original sucrose concentration x glucose concentration at the linear time point = percentage of sucrose converted"
So the linear time point of the 10% sucrose solution is 25 minutes and the glucose concentration at that time was 1.5 therefore the percentage of sucrose converted would be 15%? The experiment recommended to use the same linear time point for all the foods that I am testing and that is what i did.
I have much difficulty calculating the original sucrose concentration of my foods. So this was the results from one food:
Before invertase: 0.5%
After invertase at the linear time point (25 minutes): 2%
So how would I determine the original sucrose concentration? When the experiment says use the percentage of sucrose converted divided by the glucose concentration at the linear time point to determine the original sucrose concentration, would I use the percentage of sucrose converted as 15% divided by 2%? Would I use 15% as the percentage of sucrose converted for all my foods and only change the glucose concentration at the linear time point depending on the food? So for the results that I mentioned here, would I do 15 divided by 2 which equals 7.5<-- Is that the original sucrose concentration. Is what I'm doing right?
Please reply ASAP as this project is due in two days and I stumbled on this road block yesterday. Please.

Karth

Hi Karth,

I read over the instructions on analyzing the experimental data several times and I agree that it is confusing. The initial experiment you did with the invertase and 10% sucrose solution tells you how much glucose the enzyme is able to convert at the linear time point. In your case you said this turned out to be 15%. The amount of sucrose converted to glucose depends on the rate of the enzyme activity which is constant over the linear portion of the graph for a fixed amount of enzyme. That's why you measure the glucose at the half-maximal time point.

So you are correct. When you do the invertase reaction on the test solutions, you should divide the calculated % conversion, 15%, by the % of gluc that you measured at 25 min to get the original sucrose concentration.

Sybee