MadSci Network: Biochemistry

Re: Why does salt preserve meat?

Date: Mon May 10 10:55:15 1999
Posted By: Robert LaBudde, Staff, Food science, Least Cost Formulations, Ltd.
Area of science: Biochemistry
ID: 926283459.Bc

Salt performs several functions in preserving food:

1. Salt shifts the growth conditions to favor Gram-positive instead of 
Gram-negative bacteria. Most human pathogens are Gram-negative. These 
include Salmonella, Escherichia coli and Clostridia. There are only a few 
Gram-positive pathogens, such as Listeria and Staphylococcus.

2. Salt removes available water from the food by changing the osmotic 
pressure. This makes it harder for bacteria to obtain water to grow. The 
availability of water in food is called "water activity", and every 
species of bacteria has a minimum water activity below which it won't 
grow. Most pathogens will not grow below a water activity of 0.92 (pure 
water is 1.0).

3. Salt in itself eventually becomes poisonous to the microbes by creating 
an electrolyte imbalance within the cell.

4. A brine (salt / (salt + moisture)) of 3.5% will normally prevent 
serious pathogens (e.g., Clostridium botulinum) from growing. Brines of 
more than 10% will normally prevent all pathogenic bacteria from growing.

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