evanthebioguy
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Help with glucose project

Hello there,

So, I was going through the Procedures section of my experiment. Recently, I completed the section of "Testing the Glucose Strips." Because my glucose test strips were showing colors that were two concentrations off from what they should be at thirty seconds, I adjusted my read out time to sixty seconds.

Then, I started looking ahead at the procedure for "Testing Invertase Activity" and found that I did not understand the directions.
What does the experiment procedure mean when it says "If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%"). Depending on where this happens in the Experimental Procedure, you may need to then perform a 1:10 dilution and re-test the sample. You will get more accurate results if you start diluting your samples once the glucose concentration is getting close to 1%."

More specifically, what does that last sentence mean? How would we know to perform a dilute solution once it starts getting close to 1% if we don't know whether the solution will reach the 2% before thirty seconds. Especially in this case with the enzyme, it would be very hard to test another glucose strip that quickly.

Secondly, if I'm reading my test strips after an entire minute, then should I still perform a 1:10 dilution if the test strip turns the darkest concentration before thirty seconds?

I've also been using room temperature tap water when it does not specify distilled water. Is that right?

I need the answer to these questions as soon as possible so that I can finish my project. It will be due very soon.

Thank you!

- Evan

koneill18
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Re: Help with glucose project

Hi Evan,

Here's an excerpt from the "Testing Invertase Activity" section of the procedure that is a little more specific than what you read in the "Technical Note" box:

"Remember that the glucose readings are most accurate if you dilute your sample once the glucose concentrations reach about 1%. If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%") and quickly perform a 1:10 dilution using 1 drop of your test solution (as described in the Technical Note on the third bullet point) to determine the actual percentage of glucose in the sample. Take a glucose reading of the 1:10 dilution."

Whenever it says 30 seconds in the procedure, I think it's fine to replace that with 60 seconds since that's the reading time that worked for you. So if you take a glucose reading and find that it's at 2% after 60 seconds, you can go ahead and perform a quick dilution by adding one drop of your test solution to nine drops of water. You can put the nine drops of water in a bottle cap ahead of time so that, in the moment, you only have to add the one drop of the test solution and it'll be faster. If the glucose concentration rises more slowly, then you can hold off on diluting the sample until it reaches 1%.

Since the procedure in the "Testing the Invertase Activity" section specifies to use distilled water, I would use the distilled water for every part of the experiment that requires water because you want to keep all of your experimental conditions the same. If you test your glucose test strips in tap water and then start using them in distilled water later in the experiment, that could theoretically make a difference.

Katelyn

evanthebioguy
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Occupation: Student

Re: Help with glucose project

Hello Katelyn,

I greatly appreciate your reply. I do feel like I still need a little bit more clarification.

After reading the excerpt, I am still very confused about diluting my sample once the glucose concentrations reach about 1%. How will I know that I will need to perform a 1:10 dilution around 1% if I do not know whether or not the sample I am testing will reach 2% before thirty seconds? In other words, how do I know when to perform a 1:10 dilution and when the best time is to perform a 1:10 dilution?

Are you saying that I should go ahead and perform a 1:10 dilution if it nears 1% really quick?

I find it might be difficult to determine the color if I perform a 1:10 dilution and then it does not end up reaching 2% before thirty seconds are up and then my results might be inaccurate.

I was thinking about using one kind of water throughout my entire experiment too, to keep conditions the same. However, as I was looking through the ingredients for the experiment, I happened to notice both types of water are listed. Hence why I decided to utilize both types of water already throughout my experiment, using distilled water when specified, room temperature tap water when not directly specified, and simply referred to as water. Should this be an issue? I thought that's why they included both types of water under ingredients.

Lastly, I was looking ahead at procedure three, which I am going to try to perform later today, and was looking at the calculations. How am I supposed to know the "original sucrose concentration" of my food samples? And how am I supposed to calculate the "original sucrose concentration" without having the "percentage of sucrose converted"?

Thanks! I hope to finish this experiment today.

koneill18
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Joined: Thu Aug 06, 2020 8:22 am

Re: Help with glucose project

Hello!

So for the "Testing Invertase Activity" part of the procedure, you start by making your 10% sucrose solution. Then you use a glucose test strip to determine the amount of glucose in the solution at your 0 minute time point. It should be 0% since you haven't added the invertase yet. Next you'll add the invertase and start taking glucose measurements every 5 minutes for the first 30 minutes. The invertase enzyme should convert the sucrose to glucose gradually over time, but let's say that for some reason it starts producing glucose at a fast rate. So after 5 minutes, you dip your glucose strip into the solution, wait 60 seconds, and then look at what color you got. I'm saying 60 seconds here instead of 30 seconds since that's the readout time that you said worked better for you. If the strip tells you that you're already at 2% glucose, then you can go ahead and make the 1:10 dilution. After you make the dilution, take another glucose reading. This reading should be below 2%. You just have to multiply whatever value you got by 10 to get your actual glucose reading since you just did a 1:10 dilution. So if your glucose reading is about 0.5%, that means your actual glucose concentration is 5%. This helps you get a more precise glucose measurement since the strip only goes up to 2%.

The other possibility is that the glucose conversion will happen more gradually. So for example, let's say when you take your first reading at 5 min, the glucose concentration is around 0.1%. Then you would keep going and take another reading after 5 more minutes. After a few more readings, you'll find that the color on the glucose strip indicates that the glucose concentration is getting close to 1%. At that point, you can go ahead and do a 1:10 dilution. If you accidentally miss the 1% point and your glucose concentration is already over 2%, that's okay. You can just go ahead and do the dilution then. The dilution doesn't have to happen exactly at 1%. You just want to try to do it before you get to 2% because your measurements will be more accurate that way. The strip can only tell you that your concentration is at 2% or above, but diluting the sample helps you calculate exactly what percentage above 2% you have.

I see what you're saying about both types of water being listed under Materials. In that case, it should be fine to go ahead and just use the tap water when it doesn't specify to use distilled water.

When it says "original sucrose concentration," that refers to the sucrose solution that you made in step one of "Testing Invertase Activity." So in this case, the original sucrose concentration in your homemade solution was 10%. So you would plug the number 10 into the "original sucrose concentration" part of equation 1. Then you would plug in your glucose concentration at the linear time point to get the percentage of sucrose converted. Equation 2 is meant for figuring out the sucrose concentration in all of your food samples. So you would take the value for percentage of sucrose converted that you got from equation 1 and insert that into equation 2 to calculate the original sucrose concentration in your food samples.

I hope this helps clarify things for you. Let me know if something is still unclear!

evanthebioguy
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Joined: Sun Dec 06, 2020 8:48 pm
Occupation: Student

Re: Help with glucose project

Hello,

It is still unclear. If I substitute 10% for the original sucrose concentration in the equation, I am going to end up receiving an original sucrose concentration in the second equation every single time. How is the second equation helpful if I am just calculating a value that I already supposedly have from the first equation?

I figure there is more to this, specifically in finding the original sucrose concentrations than just utilizing the 10% from a previous procedure. I say this because after performing the calculations using the 10% to calculate the percentage of sucrose converted for my ketchup, that I ended up getting 200%. That is impossible.

When I ended up testing ketchup in the procedure, I ended up getting 20% glucose concentration before adding invertase (2% calculated from 1:10 dilution and multiplied by 10), and 20% at the linear "time test point." I would figure this would mean I have 0% of sucrose in this solution, as the amount of glucose did not increase.

When I utilized 10% as the original sucrose concentration in my calculation, for % of sucrose converted for ketchup, I got 200% (20/10 x 100), which seems impossible.

I do not feel that I am utilizing the values right. Shouldn't the original sucrose concentrations in each food be different and not 10%?

How can I calculate these original sucrose concentrations? Should I try to research specific %'s on the internet for each food sample?

Lastly, does the concentration of glucose calculated before adding invertase play any role in the calculations for original sucrose concentration or percentage of sucrose converted? I know the formulas state to only use "glucose concentration at linear test point", but for some reason, I feel there is more to this.

I would love anyone's assistance as this project is due very very soon. Thank yoU!

evanthebioguy
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Joined: Sun Dec 06, 2020 8:48 pm
Occupation: Student

Re: Help with glucose project

Also, in every one of my food samples, I performed a 1:10 dilution because it was viscous. So in my calculations would I also multiply the 10% sucrose solution, we're supposedly using to calculate % of sucrose converted, by 10? Is this the main problem I am running into with utilizing the 10% sucrose solution for calculations?

koneill18
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Re: Help with glucose project

Hello,

Once you calculate the percentage of sucrose converted in equation 1, that value is going to stay constant every time you use equation 2. You're using equation 2 to calculate the original sucrose concentration in each of your foods, which should be different for every food. So if you substitute 10% for the original sucrose concentration in the first equation along with your glucose concentration at the linear time point, then you'll get the percentage of sucrose converted. Then you take that value for the percentage of sucrose converted that you just calculated and plug that into equation 2 along with the glucose concentration at the linear time point that you got for each food. Each food that you tested will have a different glucose concentration at the linear time point, so when you take that number and divide it by the percentage of sucrose converted that you got from equation 1, then you should get different original sucrose concentrations for each food. I think you had it backwards and you were using the original sucrose concentration from equation 1 in equation 2 instead of using the percentage of sucrose converted. You're only using the 10% sucrose value in equation 1, not in equation 2. That's probably why all of your numbers weren't making sense.

If you did a 1:10 dilution for all of your food samples, then you should multiply the glucose concentration that you got by 10. The glucose concentrations are the only number that you'll multiply by 10.

evanthebioguy
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Joined: Sun Dec 06, 2020 8:48 pm
Occupation: Student

Re: Help with glucose project

Hello,

I have been using exactly what you described. I have been using the percentage of sucrose calculated from equation 1 and plugging that into the denominator when for equation 2 when calculating for original sucrose concentration.

My Results:

Ketchup: @ linear test point: 20%

% of sucrose converted = 20 / 10 (original sucrose concentration you said to use) x 100 = 200%
* 200% sucrose converted does not make sense.

original sucrose concentration = 20 (glucose conc. @ linear test point) / 200 (% of sucrose converted, derived from step 1) = 10%

For each one of my food samples, I have gotten 10%. I suppose there are different original sucrose concentrations for each food.

What should I do?

koneill18
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Joined: Thu Aug 06, 2020 8:22 am

Re: Help with glucose project

Hi Evan,

When you did the "Testing Invertase Activity" part of the procedure, what value did you get for the glucose concentration at the linear time point? That is the value that you should be using in equation 1- not the linear time point for the ketchup. You're only using the glucose concentration at the linear time point for the ketchup in equation 2.

So in your equation 1, the place where you wrote 20 is the place where you should write the glucose concentration at the linear time point that you got from the "Testing Invertase Activity" part of the procedure where you were just working with the 10% sucrose solution.

% of sucrose converted = glucose concentration at the linear time point for 10% sucrose solution / 10 (original sucrose concentration) x 100

Then you would take that value and put it in the denominator of equation 2 with your ketchup glucose concentration (20%) in the numerator. That should give you the real original sucrose concentration.

Does that make more sense?

evanthebioguy
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Re: Help with glucose project

Hey,

That makes so much more sense now! I am going to try that! Thank you so much!

koneill18
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Joined: Thu Aug 06, 2020 8:22 am

Re: Help with glucose project

Oh good, I’m glad! Let me know if you run into any other problems.

evanthebioguy
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Joined: Sun Dec 06, 2020 8:48 pm
Occupation: Student

Re: Help with glucose project

Hello,

So I started calculating my original sucrose concentrations. I ended up getting 40%, 100%, 800%, 200% 150%, and 200%
. This still does not seem right. Not sure what I have done wrong.

Any ideas?

I have to turn this in today.

koneill18
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Joined: Thu Aug 06, 2020 8:22 am

Re: Help with glucose project

What number did you get for your percent of sucrose converted? And what were your glucose concentrations at the linear time point for each of your foods?

evanthebioguy
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Joined: Sun Dec 06, 2020 8:48 pm
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Re: Help with glucose project

Hello,

For % of sucrose converted, I got 2.5%. This was found with 0.25/10 x 100.

Linear time point: 20 minutes, concentration of 0.25%

Glucose Concentration at the linear time point for each of my foods:

Peanut Butter: 1.5%
Ketchup: 20%
Ranch: 5%
Orange Juice: 3.75%
Bananas: 5%

koneill18
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