Soil is a very rich environment in microbes
and is a major source of contamination of
Escherichia, Micrococcus, Alkaligens, Flavobacterium, Pseudomonas, proteus, Aerobacter, molds and yeast are kinds of organisms that contaminate food from soil.
Air and water:- contamination.-
Factors influencing microbial activity in food
Nutrient found in foods
Organisms obtain their energy
metabolic activity mainly from the Hydrogen ion concentration (pH)
for carrying food.
The optimum pH for many microorganisms is near the neutral point of pH 7. However molds and yeasts as a rule are acid tolerant. This is one of the reasons why fungi are usually associated with acid foods especially fruits.
Many bacteria are not acid tolerant, accordingly, several acid like acetic, benzoic, propionic acids are used to preserve foods.
It has been found that pH of 4.5 or below is lethal to salmonellae and staphylococci.