Help with Glucose Project

[deleted-276708]

Hi
I'm in 6th grade and doing a variation of the "How Sweet It Is!" Science Project. https://www.sciencebuddies.org/science- ... p049.shtml
I'm going to compare the glucose in fresh, frozen and juices fruits/vegetables. So far I have blueberries, pineapples, cherries, grapes, tomatoes and carrots.
I was wondering if there are other fruits/vegetables I could use. Also, should I thaw the frozen fruits/vegetables before using the glucose strips? What preparation do I need to do do for something dry like a carrot? Will the glucose strip be able to measure if the carrot is dry? Thanks for your help.

[deleted-249560]

The glucose test strips only work in liquids. So yes, you will have to thaw your frozen fruits and vegetables, and any solid will have to be turned to liquid. Something like a carrot could be a challenge if you don't have any appropriate juicing equipment at home. You could try grating the carrot finely over some plastic wrap, making sure to catch every last bit of liquid that drips out. The squeeze the gratings really hard to get the juice out that way. If you live near a shop that sells freshly made juice, they may be able to make you a small glass of pure carrot juice.

If the idea is to discover 'hidden' sugars in foods, think of things that may be a bit juicy but may not taste very sweet. Are there sugars in a potato? In a grapefruit?

Howard

[deleted-276708]

Thanks for your quick reply. I was wanting to compare which had less glucose depending on its form - if it was fresh, frozen or a juice. I wanted to see if a generality could be regarding all fruits/vegetables in general. Is this a valid question or will the fruit/vegetable glucose content be the same? We do have a juicer for the carrots but wouldnt that be the same if I tested 100% carrot juice?

[deleted-249560]

Whether something is fresh or frozen could have a lot of impact on the measured glucose content. Even fresh fruit at different times in the season is going to have differing content. The best you can do is make a determination with what's available today. You conclusion might include a discussion of whether a peach that ships in 'fresh' from South America will have the same sugar content as one you grow in your backyard this summer. I don't know whether you can generalize that freezing will have a specific effect. You'll get some data which will suggest an answer, even though you can't really generalize for all fruits and vegetables. There are a lot of variables - can you think of some? It's likely to come up during your discussion at the fair. One thing which the fruit/vegetable industry likes to brag about is that they pick the food at the peak of ripeness and freeze it immediately for the best flavor. If anyone cans food at your house during the summer and fall, you do the same thing. What effect might that have on sweetness and sugar content? Corn is a great example. If you bite it into it in the field it's sweeter than if you take it home first. The sugars start turning into starch that quickly.

I would expect that yes, if you have a juicer that can reduce a carrot to juice would be the same as buying a little cup of juice. My point was that many things sold as 100% carrot juice might be a little carrot mixed with some apple. You don't know unless you have control over it yourself or you buy it from a source with 100% integrity. In my case, I don't live near a juice stand like that, nor do I own equipment that can juice a carrot. I do have one of those serious industrial blenders they have at coffee shops that can blend iPads [https://www.youtube.com/watch?v=lAl28d6tbko]. That's not the same thing though, as a proper juicer.

It sounds like you have what you need to do a good job and I like the angle of comparing a frozen version of something to the fresh version.

Howard

[deleted-276708]

So I did the project this weekend and had some questions about the glucose strips. I did the control with the glucose tablets and got expected results. The color on the strips matched the bottle for each of the dilutions.
Now I have a question, when I read the strips when testing either the fresh, frozen or juice I placed it into the food for 30 seconds. I read the color immediately after taking it out of the food but noticed that some after a few seconds it kept on darkening. So, do I use the initial color right when it comes out of the food or do I need to wait to read the strip? Are there any other ways to measure the glucose other than the strips?

[deleted-249560]

That will depend on the specific glucose test strip you have. For the most part, you usually immerse the stick in the liquid, wait 1 or 2 second, touch the strip to the container briefly to wick away any excess liquid and then wait up to 2 or 3 minutes. The sticks we reference in the materials list are intended for urinalysis and may come with instructions just for urine. Other sticks I'm finding on the internet have additional instructions that suggest waiting longer for liquids other than urine.

If there are no specific instructions on the packaging, I think you have to wait a few minutes for it to finish changing. As a control. try testing your known glucose solutions with the sticks, wait perhaps 2 minutes for the change to complete and see if they accurately show the concentration. Or is that too long to wait for the sticks you have?

[deleted-276708]

These are the test strips I used
http://www.amazon.com/gp/product/B001BK ... UTF8&psc=1
I reread the directions and it says

1. Dip reagent end of strip in Fresh urine and remove immediately
2. While removing, draw edge of strip againsgt the rim of urine container to remove excess urine
3. Compare reagent side of test area with color chart at exactly 30 seconds.

That is the directions for testing glucose in urine would I follow the same for food?

I will have to redo my trial because I put the strip in the food for 30 seconds and then read immediately.

[deleted-249560]

The instructions I'm seeing on the web suggest that the dipping is the same for food as for urine, but you wait longer for any change before comparing the color.

If you dip the strip and remove after a second or two, how long does it continue to change? If it settles into a color without changing any further after, say, 30 seconds, then that's long enough. I'd suggest trying a control solution - dip the stick and remove after a second or two, knock off the excess liquid and wait 30 seconds. Did stop changing and does it indicate the concentration you expect? Wait another 30 seconds and read it again. Did it get darker? Since some brands say to wait 2 minutes, I'd suggest that any amount of time that causes your sticks to get a stable color (in the 30 second to 3 minute range) is the right amount of time. Once you've selected a method that seems to work for your control solution, follow that procedure exactly for all of your food samples.

Howard

[skuzniewski]

You might also want to have controls, one positive control and one negative control. The positive control could be a glucose solution and the negative control could be tap water. The controls can help to ensure that the experiment is working.

[deleted-276708]

Ok, so I tested the blueberry juice and I diluted 30mL of juice with 210 mL of water. The glucose test strip said 0.5%. I need help how I figure out the actual percentage of glucose. On the bottle of blueberry juice it says Total carbohydrates 24 g or 8% and sugars 19g. The serving size is 8 oz or 240 mL.

Can you explain how I calculate the percentage with the test strips and dilutions before I test my other foods. Thanks

[deleted-249560]

I'm not sure how to reconcile that data exactly, but this is what it looks like. If you have 19g of sugar in 240g of juice, that's about 8% sugar. You took 30g of that and added 210g of water to make 240g of dilute juice. 30/240 = 1/8, so the 8% figure gets divided down to 1% as an estimate of sugar percentage after you diluted it.

You measured 0.5% and not 1%. Why might that be? Probably not an error in dilution since you seem to be rather careful. We don't know what 'sugars' are in the juice. Blueberries have a good deal of fructose and if the strips are only detecting glucose levels, that could explain it. If half the sugars in your sample don't register on the strip, your numbers work out. You may need to research the relative concentrations of different sugars in the juice. The manufacturer might actually have that information if you ask. http://www.marksdailyapple.com/the-defi ... z3SXFX7YiG suggests that blueberries have a relatively equal glucose/fructose ratio so that backs up my theory. If it's right (blueberry sugar is 1/2 glucose), then your strip is properly showing the concentration of your dilution at 0.5%.

Howard