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Chapter: Microbiology

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Factors that influence the growth of the microorganisms

Many factors that influence the growth of the microorganisms in food. Some of the factors are intrinsic and some others are extrinsic.

Factors that influence the growth of the microorganisms

Many factors that influence the growth of the microorganisms in food. Some of the factors are intrinsic and some others are extrinsic.

a)     Intrinsic factors: The intrinsic factors include pH, moisture content, oxidation-reduction potential, nutrient status, antimicrobial constitu-ents and biological structures.

 

a)     Intrinsic factors: The intrinsic factors include pH, moisture content, oxidation-reduction potential, nutrient status, antimicrobial constitu-ents and biological structures.

 

i.                  pH : It has been well established that most of the microorgan-isms grow best at pH values around 7.0, while few grow below 4.0. Bacteria grow at more pH than molds and yeasts.

 

ii.                  Moisture content: The preservation of foods by drying is a direct consequence of removal of moisture, without which microorganisms do not grow. The water requirements of microorganisms should be defined in terms of the water activity (aw) in the environment. Water activity is defined by the ratio of the water vapour pressure of food substrate to the vapour pressure of pure water at the same tempera-ture (aw=P/po). The aw of most fresh food is above 0.99. The minimum value of aw for the growth of the microor-ganisms in foods should be around 0.86.

 

iii.                  Oxidation reduction potential: The O/R potential of a sub-strate may be defined generally as the ease with substrategains electrons. When an element or compound loses elec-trons, the substrate is said to be oxidized, while a substrate that gains electrons becomes reduced.

 

iv.                  Nutrient content: In order to grow and function normally, the microorganisms of importance in foods require water, source of energy, source of nitrogen, vitamins and related growth fac-tors and minerals.

 

v.                  Antimicrobial constituents: The stability of foods against attack by microorganisms is due to the presence of certain naturally occurring substances that have been shown to have antimicro-bial activity. Some species contain essential oils that possess antimicrobial activity. Among these are eugenol in cloves, alli-cin in garlic, cinnamic aldehyde and eugenol in cinanmon.

 

 

b)          Extrinsic factors: These include those properties of the storageenvironment that affect both the foods and their microorganism. The following extrinsic factors affect the growth of microorgan-isms: Storage temperature, pH, presence and concentration of gases in the environment.

 


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