Science Buddies: "Ask an Expert"

I'm doing glucose, sucrose fructose oh my god uncovering hidden sugar in our food project
I need help of how to determine the percentage of sucrose converted to glucose after adding the invertase to each drink I am using in my experiment

Hi Sarah,

I think you are doing this excellent, but challenging project, adding invertase to samples and measuring the glucose concentration before and after adding the enzyme.

https://www.sciencebuddies.org/science- ... #procedure

1.Please confirm that you set up the standard curve with serial twofold dilutions of glucose.

2. Please also confirm that you tested the activity of the invertase to determine the linear time point and used that incubation time before measuring the glucose in the invertase-treated samples.

3. Also, if any of your samples tested out of range high, then you should have diluted them 1:10 and repeated the enzyme treatment.

4. And, did you calculate the percentage of sucrose converted by multiplying the glucose concentration at the linear time point for the 10% sucrose sample?

If you did all of this, then you can determine the original sucrose concentration in the sample by dividing the percent sucrose converted (from step 4) by the glucose reading of the sample.

If this is not clear, then read through the analyzing your results section of the original project guide, step-by-step to make sure you understand each step. If necessary, please post the data that you obtained for each step, and I'll use your data to do an example calculation.

Donna

Yes I did all the steps
For the linear point the glucose reading was 0.75% so as mentioned in the procedure 0.75% 10% = 7.5%
I measured several drinks for example sprite for which glucose reading before adding inverts was 1% and after adding invertase the reading was 2%
I used orang juice also the glucose reading before invertase was 1% and after adding invertase was 1.5%
For these reading how can I calculate the glucose converted to glucose and the original sucrose concentration.
Thank you so much for your help

Hi Sarah,

Thanks for posting your results;

I'm not sure there is enough information yet but you are making progress. The linear point is 0.075% x 10. this means that 7.5% of the total sucrose had been converted to glucose.

To calculate the original sucrose concentration in the sample, you need to divide 7.5 by the % glucose in the treated sample.

Here are the directions for the calculation from the project guide:

"b. Look at the data you collected in the "Testing the Foods for Glucose Concentration Before and After Adding Invertase" section. To determine the original sucrose concentration of each of your food samples, use Equation 1 and divide the percentage of sucrose converted (which you just determined) by the glucose concentration at the linear time point.
i. For example, if at the linear time point a food had a 2.5% glucose reading, and we calculated that the percentage of sucrose converted is 20%, then we could calculate that the original sucrose concentration of this food was 8% (20% divided by 2.5%)."

So the calculation for your Sprite samples is 7.5% divided by 2%, or 3.5 percent sucrose. For the orange juice, the calculation is 7.5% divided by 1.5% or 5%.

The numbers do not seem reasonable, so I think something is wrong with the numbers. Can you double check your data? I will double check the calculations and post again also.

Donna .

Hi Doona.
Thanks for your respond
I got the same results when I applied the equation but the results as you said not reasonable but even if I got different numbers the results always will be not reasonable because as The glucose readings got bigger the division result will be smaller according to the equation and that what confuse me, because it is a fact that sprite has greater sugar amount in it so it is reasonable to have larger glucose percent after adding invertase than the orange juice and because we using the same number of sugar converted for both the sprite and the juice the result number for the sprite will be smaller... the project due in two days and I'm really confused about these calculations.

Hi Sarah,

Thanks for your response. I have asked for help from another expert who is more familiar with this project. Hopefully we'll have a response for you sometime today.

Donna

Sarah - Donna has given you excellent input on this project and the calculations needed. I consulted with one of our scientists at Science Buddies who has done testing recently with invertase, and she has a few comments and questions to add to your discussion here.

Like Donna, she notes that the numbers seem low.

She said that your linear time point glucose concentration seems a little low. (This may vary, however, with the invertase and the glucose strips used.) But the food (Sprite and orange juice) glucose concentrations also seem low. She asks if you diluted them 1:10 before measuring them?

She suggests you make sure to dilute your samples and measure them again and see if you get more accurate results. She says that it is best to dilute the samples once you get around 1% reading with the glucose strips and notes that the strips may not work as well in the high range.

In terms of the calculations, Donna has explained the steps nicely. To summarize them again:

"First, you want to determine the percentage of sucrose converted to glucose from her linear point, as you did (original sucrose concentration x glucose concentration at linear point). As for the food, you choose the same linear point as you did with the sucrose solution before, and assuming that the invertase has the same activity in the food as in the sucrose solution, the conversion rate of sucrose (and thus the percentage of sucrose converted) should be the same in the food as in the sucrose solution for the same time point. This means that you can simply divide the calculated percentage of converted sucrose for the linear time point by the glucose you measured for the food and should get the original sucrose concentration in the food."

I hope this information helps.

Amy
Science Buddies

Hi Sarah,

Amy has given you some excellent suggestions and I know you don't have time to repeat the experiment, so here is my best advice for this situation, which is based on many actual science project with unexpected results.

Complete the project using the results and calculations that you have obtained. One nice thing about science fair projects is that there's no way to get a wrong answer. You have designed a controlled experiment and documented the results. Your results are empirical; they are what happened so go ahead and use them.

You should then make a conclusion that is based on your results and then note that the results do not seem to be reasonable. You can then discuss the possible reasons for the discrepancy between actual and expected results. Perhaps your amylase enzyme was not active enough; perhaps the glucose strips were giving inaccurate results; perhaps there really was more sugar in the orange juice sample you tested compared to the Sprite. If you tested each sample twice, be sure to mention that your results were reproducible. Try to think of other possibilities. Your discussion section will be very interesting for this project.

You should then state what you would do next to resolve the issue if you were to do the experiment again, which is to repeat the experiment with new reagents.

Make sure to review the teachers guidelines for the assignment and include all of the required details. Grading on science fair projects is usually done on a point count, so if you include all sections, you should get complete credit for the assignment.

I hope this helps. Do let us know if you have other questions.

Donna