Food Microbiology

Aerobic organisms produce energy via oxidative phosphorylation with O2 as terminal electron acceptor
Enzymes (SOD and catalase) disable toxic products of oxygen

Anaerobic organisms don’t have SOD or catalase, thus no growth at high redox potentials when O2 is present
Terms to describe oxygen preference:
  * ==Obligate aerobe==: Needs atmospheric O2 for growth.
  * ==Microaerophile==: Requires O2, but below 20%.
  * ==Facultative anaerobe==: Do not require O2, grows better with O2.
  * ==Aerotolerant anaerobe==: Grows equally well in presence or absence of O.
  * ==Obligate anaerobe==: Does not tolerate O2 and dies in its presence.
Classification of most important bacteria:
  * Bacillus is an Obligate aerobe
  * Campylobacter is an microaerophile
  * E.coli is an facultative anaerobe
  * LAB is an Aerotolerant anaerobe
  * Clostridium is an obligate anaerobe
Anaerobic environment means that the Eh is negative
Aerobic environment means that the Eh is positive
Oxygen is the most influential redox couple in food systems. It has a high E0 and is a powerful oxidizing agent. Increasing the access of air to a food material by chopping, grinding, or mincing will increase its Eh. This is all solved by excluding air.
  * Effects of other factors:
    * Processing means that the product will be more exposed to oxygen => higher Eh
    * Low pH => many H+ => higher Eh (Nernst equation) 58 increase for every level of pH.
    * Microbial growth => less O2 => lower Eh
Dissolving CO2 to carbonic acid which then dissociates to bicarbonate, which acidifies the product.
* o This has the most effect on molds, oxidative gram (-) bacteria

o And the least effect on: Gram (+) bacteria (lactobacilli) and some yeasts (Brettanomyces spp).

o Larger effect if no oxygen present and at lower temperatures, because of higher CO2 solubility.