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Stomach acid : Science project

Postby AksAks » Sat Jan 02, 2021 8:40 am

Hello ScienceBuddies team,

I’m looking for help on a 6th grade science project.
My daughter plans to test the reaction of stomach acid on different foods and also determine if the food increases the acidity level or decrease.
After doing some research online, we purchased 0.1M HCl to perform this experiment. We have made sure to purchase all safety items like apron, goggles, mask and Certified experiment apparatus.
To test it out, we placed very small amounts of food in a small amount of acid. But there has not been much of a change.
Need help with below questions:
1. How do we acquire enzymes?
2. How to determine how much food vs hcl ratio should we use? Was trying to keep the quantities small as worried about using large amounts of hcl and the fumes it could generate.
3. Do we need to keep it warm? Again worried about the fumes.
4. Anything else we are possibly missing?
Thank you,

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Re: Stomach acid : Science project

Postby probiotics » Sun Jan 03, 2021 6:00 pm


This sounds like a really cool project! Learning more about how our bodies function is very important and I'm sure your daughter will have a great time conducting this experiment!

Your choice of acid to simulate the stomach acid is a great choice! HCl is very similar to the gastric juice commonly found in our bodies. However, you may not want to use HCl directly. Instead, as directed in the project linked below, you can mix it with a specific amount of sodium chloride and distilled water to create a more representative stomach acid! When mixing materials, make sure that add the acid to the water and not the other way around!


I'm not sure exactly why there was no interaction with the food when placed in the HCl! My guesses are that the ratio of food to HCl may be too low! Hypothetically, there should be enough HCl to cover the entire piece of food. The rate of chemical reactions relies on the surface area of the reactant! By increasing the surface area of the food in contact with the HCl, you may be able to see better results! This could mean more HCl or ripping the food into smaller pieces. If you are worried about fumes, the project linked above creates a 0.01 M hydrochloric acid solution, which is less concentrated and would create fewer fumes. As always, make sure that the project is completed in a well-ventilated area to ensure no impacts to your health!

In order to model the stomach more accurately, you may want to incorporate some movement of the acid and food. The food in our stomachs does not stay still at all times, so it would be interesting to add this component to your experiment!

As per enzymes, there are a few specific ones found in gastric juice. A breakdown of the most common ones are as follows:

- Pepsin (Proteases): split proteins. You may have heard that pineapples are a fruit that can "eat you back." This is a reference to the fact that pineapples naturally contain two types of proteases. As such, pineapple juice could be a source of this enzyme. You could also purchase from Carolina Biological!
- Lipase: split fatty acids. This can be purchased from a site such as Carolina Biological. Here is a link:
- Amylase: split carbs. Also found on Carolina Biological. A smaller, 2.5g packet for 8 dollars is also available, and may be a better choice!

After purchasing/collecting these enzymes, the next step would be to find the concentrations in gastric juice so you know how much to add! The paper linked below states that the concentration of Pepsin is around 0.5–1.0 mg per ml!


As pepsin is the primary enzyme in the stomach, it would be safe to assume that the other enzymes would have a lower concentration. However, I'm unable to find published concentrations of the other enzymes. Therefore, an estimate would most likely be the best choice!

Hypothetically, it would be best to keep your mixture at body temperature (97.7–99.5 °F) to better simulate the stomach. However, as this would create more fumes, it is not advisable unless you can perform the experiment in a very well ventilated area like a garage with the door open or outside.

I hope this helps! Let me know if you have any more questions!

Thanks, Probioitcs

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Re: Stomach acid : Science project

Postby AksAks » Tue Jan 05, 2021 5:36 pm

Wow! Thank you so much Probiotics!! I really appreciate the time taken to explain it so well and all the links shared.
You may be right on the quantity used, we used about 4ml of 0.1M HCl for about a teaspoon of each food item.

We will try it again with
- breaking the food into smaller bits
- adding some movement
- keeping it warm
- more quantity of HCl

Thank you once again!!

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