Science Buddies: "Ask an Expert"

I am currently working on a variation of the Sucrose and Glucose and Fructose Oh My! project. The problem is, I cannot figure out how to measure the original sucrose concentration from the glucose concentration. I know that I use the linear time point to determine the final sucrose concentration but how do I find the original sucrose concentration? I tested invertase activity on apple, orange, pineapple and tomato juice. Is the word “sugar” interchangeable with sucrose or is it also fructose?

For example, the apple juice has 1.8 g of sugar per 15 mL of apple juice (the size of one sample). By testing the glucose concentration, I found it had 5% glucose before adding the enzyme invertase to catalyze the sugar and turn more into glucose. After this process, it had 7.5% glucose. How do I determine how much sucrose was present before? I can use the equation given in the experiment ( original sucrose concentration X glucose concentration at linear time point = percentage of sucrose converted) after if I know the before amount.

Once again, how do I find the ORIGINAL sucrose amount of the juice?

Please get back ASAP, as the rough draft is due Tuesday.

Thank you,

Sierra

Hello,

The 1.8g sugar amount (that I assume you are getting from the apple juice label) is probably reporting the total amount of all sugar forms: glucose, sucrose, and fructose. In order to determine the total amount of sucrose you would have to measure the amount of glucose after invertase has broken down all of the sucrose. After taking an initial glucose measurement, add invertase and check the glucose levels periodically until it stops increasing. At this point you can assume that all of the sucrose has been converted to glucose and can then calculate the original sucrose (ending glucose % minus starting glucose %). After you have this value you can use the linear time point for all subsequent measurements and you will be able to calculate the percentage of sucrose converted at the linear time point.

One thing to keep in mind is that since each beverage will have a different concentration of starting sucrose, the linear time point will be different for each one. The reason for this is that speed that invertase converts sucrose is dependent on how much sucrose there is to begin with.

I hope this was helpful. Please post again if you need further help. good luck!

Caleb

Thank you SO much! That makes sense. If you don't mind me asking, what do you do as a biotechnology scientist?

I am a scientist at a company that makes clinical diagnostic tests. So I'm involved in developing and improving the tests for people who are trying to get diagnosed with autoimmune diseases (like lupus or celiac disease) or infectious diseases (like Herpes, Measles, or Mumps viruses). Most of my work is in the disciplines of molecular biology, which means the manipulation of DNA and genes, and biochemistry, which is purifying, modifying and testing proteins. Testing the enzymatic activity of the protein invertase like you are doing in your project could be described as a biochemistry experiment. There are also many other disciplines that contribute to making clinical diagnostic products, like chemists, engineers, and software developers.

I'm glad I was able to help with your project. I'd be happy to answer any other questions you have about the project or science careers.

Caleb