Microbial Growth Factors

The above graph is expressing the changes in the growth rate of microorganisms. There are 4 phases: 
  • A = Lag phase: At this stage, the microbes are adjusting themselves with the new environment + synthesize essential components for their lives
  • B = Log phase: Microbes produce lots of metabolites + increase in numbers rapidly
  • C = Stationary phase: Numbers of population start to be steady (no increase or decrease) with ongoing metabolites production. Nutrients are running out + wastes start to increase.
  • D = Death phase: Microbes start to die (Numbers of population are decreasing).
In order for microbes to grow, they need mainly carbon (C) sources, nitrogen (N) sources, and oxygen (O) sources with some factors as well. These factors are categorized into 2 types: Intrinsic factors + Extrinsic factors.

Intrinsic factors include:
  • pH: Most bacteria are inactivated at pH lower than 4.5 (acidic foods). However, some types of molds and yeasts can withstand very low pH. Below are some pH ranges for various types of microorganisms.
  • Moisture content / Water activity (Aw): Different ranges of Aw in foods can cause chemical reaction + microbial growth. Most fresh foods have Aw around 0.99.