MadSci Network: Biochemistry

Re: What would be a safe liquid to use to reproduce stomach acids?

Date: Wed Mar 3 14:05:30 1999
Posted By: Carl Custer, Staff, Office Public Health & Science, Scientific Research Oversight Staff , USDA FSIS OPHS
Area of science: Biochemistry
ID: 920383802.Bc

Hi Alex, I received the following from the Mad Scientist 
Subject: What would be a safe liquid to use to reproduce stomach acids?
Message ID Number: 920383802.Bc
"I would like to do an experiment on how long it takes certain foods to 
break down. I'd like to use some liquid as my 'stomach acid' and place 
different foods into the liquid.  Thanks so much 
for your help!"

The short answer: 
Hydrochloric acid (HCL) also know as Muriatic acid is the acid in the 
check out the following URLs for more info: 

BUT!!!  - - - it's not just the acid that digests the food.  There are 
enzymes (e.g. pepsin and rennin) and the mechanical stirring you stomach 
does.  See one of the URLs below. 
I did a quick web search for more info (because after 30 + years, I 
couldn't remember the names of the stomach enzymes, just the intestinal 
ones -- I work mostly with bacteria now) 

Here's how and some of what I found:
Using AltaVista (my fav search engine for science stuff)  
I entered: +"stomach acid" +enzyme +digest
and got the following URLs -- & a bunch of antacid commercials ;^(

These all contain the same info -- word for word -- without citing their 
source (sigh)
But, it's still excellent information that you could use as background 
material for your experiment.  Do cite your sources of information.

I went back to Alta Vista and entered +stomach +Hydrochloric
The first URL:

contained the following:
Hydrochloric acid in the stomach
 The hydrochloric acid in gastric fluid has several  functions: 
1)It provides the optimum pH for pepsin and rennin (an enzyme which digests 
milk proteins).   
2) it begins the digestion of some carbohydrates and  lipids through the 
chemical reaction of hydrolysis.
3) it denatures proteins and helps to soften tough connective tissue in 
4) it is a strong bactericide (it kills bacteria) and so protects the body 
from some of the harmful microbes which might enter the body in food. 

Interesting (to me any way) stuff:
1) HCl as a bactericide: Don't count on it.  
Escherichia coli O157:H7 (the "hamburger disease" bug) is very acid 
resistant; that's why it takes so few of these bacteria to cause disease 
because most of them survive the stomach acid.  Shigella is another acid 
resistant bacterial pathogen.  Also, acid-sensitive pathogens such as 
Salmonella have proven to be infective in small doses -- if they are 
protected from the stomach acid by being covered by the food, especially 
fatty food, such as chocolate, cheese, and even hamburger (good reason to 
chew your food well). 

2) Safety of HCL: Do heed the warnings at: but, HCl is unique from other strong 
acids in that it doesn't readily attack skin.  I used to illustrate this by 
holding a steel nail in my palm and spooning a little HCl over it.  The HCL 
would attack the nail, give off bubbles of hydrogen gas and not harm my 
hand -- BUT -- the chemical reaction would get pretty hot so I would have a 
cold water tap handy and a safe place to dump the acid (it eats the heck 
out of clothes and you may not notice where the droplets landed until your 
clothes are washed) 

3) Rennin:  
Renin is an enzyme that used to be commonly found in the grocery store as 
"rennet".   Rennet is used to make "rennet pudding" and cheese. 

References for additional reading:
Facts and Fallacies About Digestive Diseases. 1991. This fact sheet 
discusses commonly held beliefs about digestive diseases. Available from 
the National Digestive Diseases Information Clearinghouse, 2 INFORMATION 
WAY, BETHESDA, MD 20892-3570. (301) 654-3810. 

Larson DE, Editor-in-chief. Mayo Clinic Family Health Book. New York: 
William Morrow and Company, Inc., 1990. General medical guide with section 
on the digestive system and how it works. Available in libraries and 

Tapley DF, et al., eds. The Columbia University College of Physicians and 
Surgeons Complete Home Medical Guide, revised edition. New York: Crown 
Publishers, Inc., 1990. General medical guide with section on the digestive 
system and how it works. Available in libraries and bookstores. 

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