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Stomach Acid Simulation with Enzymes/Digestion

Postby lorikidd » Thu Dec 06, 2018 10:59 am

My son is in 5th grade and working on his science project. He is trying to create a new material to replace single-use petroleum based plastic bags that can be digested by sea turtles.

Part of his experiment is testing the digestibility of the new material in a simulated sea turtle stomach. He spoke with a sea turtle scientist and found out that the stomach acid and enzymes in turtles is comparable to that of humans.

He does not have a science lab at his school so we are working with him at home to set this up. After much research we believe that the below is an accurate representation of the stomach acid mixture.:

A 'batch' of stomach acid would include the following:

1000 mL of .15M HCL
5 g of table salt
5 g of potassium chloride

Enzymes (Just sort of guessing on amounts here)
Proteases - 30 mL pineapple juice per liter of stomach acid
Lipase - 30 mL of a 5% solution per liter of stomach acid
Amylase - 30 mL of a 60% solution per liter of stomach acid (the description says 'This solution contains 60 weight % amylase' which I assume to mean 60%
Nucleases - couldn't find a source for these.

He’s going to use two 2,000 mL glass beakers for the stomach and fill them with above solution. We’re going to stir the solutions 2-3 times an hour for 2 minutes during the day (they will not be stirred in the night). He’s planning to put a heating pad under the beakers to heat the solutions. This will be set up in our garage. I was thinking we’d open the garage door during the day for ventilation but it’s getting cold here so that could mess up the temperature of the solution.
He is thinking that he’ll run this test for 1 week because he learned that if the material doesn’t digest in a sea turtle’s stomach within a week it will start to have health problems.

We wanted to know if you feel that the above stomach acid and enzyme formula (contents and ratios of each) will accurately simulate the stomach and digestion. And will the heat and stirring plan suffice? Also, any advice on safety precautions we all need to take during this process would be greatly appreciated. My son has done some research on this but we want to double check.

Thanks so much for your help!

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Re: Stomach Acid Simulation with Enzymes/Digestion

Postby lynnsamuelson » Fri Dec 07, 2018 10:19 pm

Hello Lori,

It looks like you and your son have done a lot of research the this project and are thinking through methods before you begin. Good job on both of these things.

To answer you questions, I'm not an expert on stomach acid, but that solution looks like a good recipie base on what I found online. When you are working with strong acids like HCL, be sure to wear gloves and safety glasses while working with the solutions (including stirring).

As for using heating pads in the garage for a week with these solutions, consider the following.

1. Hydrochloric acid fumes are dangerous and heating those solutions will cause more to vaporize. The fumes are both corrosive ( and thus could cause damage to property in the garage) and a health hazard.

2. What temperature are you heating the solution to and how do you intend to keep it uniform and consistent? Also, how do you intend to account for evaporation over the course of the week?

Because of 1 and 2 I would suggest you consider testing the new material's ability to break down over a shorter period of time. Preferably one you could do in a fully ventilated area. Maybe you could keep the experiment outside during the night or increase the frequency of stirring and do the experiment over 1 or a couple of days.

Since the point of this part of the experiment is to test whether the new material will break down better than a plastic bag, mimicking the 1 week time frame of the sea turtle's stomach and more important to compare which material breaks down better. Demonstrating the new material breaks down better is the first step to showing it is safer for sea turtles. For this, set-up an experiment with a normal piece of plastic and one with your new material and examine each at the end of the experiment.

3. Light can also be a contributor in the breaking down of a material. Since stomachs are in the dark, consider wrapping the experiment in aluminum foil to account for this.

Feel free to follow-up as you have more questions.

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Re: Stomach Acid Simulation with Enzymes/Digestion

Postby lorikidd » Sat Dec 08, 2018 10:21 am

Thank you so much for your reply! Very good suggestions on keeping the stomach dark and testing a piece of plastic.

We were going to try to keep the stomach solution at 98.6 degrees F. Do you think the heating pad idea is a good solution?

And do you think the amount of stirring time is good?

And one more question, will the concentration of HCL that he's going to use be dangerous in the garage? I know you suggested that we perform the test outside at night because of the chemicals. We thought that since it's not a full concentration that it would be safer and OK in that set up, but I'm not familiar with the chemicals or chemistry aspect of this.

Thank you!

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