MadSci Network: Microbiology

Re: Can molds grow in the absence of air?

Date: Tue Jan 18 08:13:26 2000
Posted By: Edward Richter, Faculty, Food Microbiology, The Ohio State University
Area of science: Microbiology
ID: 948150927.Mi

For the most part, Molds are obligate aerobes. This means that they require oxygen (not specifically "air") to complete their metabolism.

However, many molds have the ability to reproduce (grow) at very low concentrations of oxygen gas. Organisms which are obligately anaerobic can not grow in the presence of oxygen. An example of an obligate anaerobe is the bacterium Clostridium botulinum. Examples of obligately aerobic microorganisms include molds and Pseudomonas species of bacteria (the bacterium which causes your lunch meat to get slimy).

Other types of microorganisms can grow both in the presence or absence of oxygen gas. These organisms are classified as facultatively anaerobic. Examples include yeast, Salmonella, and Escherichia coli.

It is very difficult to remove all of the oxygen from a chamber (bread box). Most vacuum packaging can only reduce the oxygen concentration to approximately 0.5%. This is still enough oxygen for some molds to grow. We rarely see moldy soda because there is no oxygen in the can. The atmosphere has been replaced with carbon dioxide. Some food manufacturers have used this information to package foods for longer shelf life in what is called modified atmosphere packaging (MAP). This is a situation where all of the air is removed and the atmosphere is replaced with a specific concentration of gas such as CO2, N and H2 (carbon dioxide, nitrogen or hydrogen gas). What you have suggested is what the French refer to as sous-vide (under vacuum). If you had an airtight container and a 2-way valve you could remove as much air as possible with your pump. If you had an oxygen scavenger or could introduce a neutral gas such as CO2 then you might be able to reduce the oxygen content low enough to inhibit mold.

Try this experiment:

  1. Store some bread with no air removal.
  2. Store bread with just the air removed.
  3. Place a soda water (carbonated water) bottle in the container along with your bread and remove the air .
  4. Place a candle (lighted) in the container along with your bread and let the flame remove the oxygen.

obligate: adjective (-gt, -gt)1. Able to exist or survive only in a particular environment or by assuming a particular role: an obligate parasite; an obligate anaerobe. 2.Absolutely indispensable; essential.

facultative: facultative (fk1el-ttv) adjective 1.Of or relating to a mental faculty. 2.a. Capable of occurring or not occurring; contingent. b. Not required or compulsory; optional. 3.Granting permission or authority. 4. Biology. Capable of functioning under varying environmental conditions. Used of certain organisms, such as bacteria that can live with or without oxygen.

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