Growth of microorganisms
The growth of microorganisms is influenced by the following factors
1. Food supply: – Every living cell requires a source of energy to maintain its life processes and elements for the formation of its cell substance. Milk and most dairy products furnish all the food requirements of microorganisms.
2. Moisture: – The nutrition of the microorganism is accomplished by the acquisition of the food elements from an aqueous solution. Milk contains adequate moisture. Dry milk due to low moisture content prevents the growth of microorganisms.
3. Atmosphere: – Certain type of bacteria can grow only where there is an unlimited supply of oxygen in the atmosphere, while other cannot develop at all if traces of free oxygen are present. Between these two extremes, however, will be found a range of oxygen concentration which will satisfy the majority of bacteria. Molds grow best in an atmosphere rich in oxygen.
4. Chemical & physical environment: –
a) Acidity or pH: – Most common type prefers a pH from 5-6 to 7.5.
b) Preservatives: – Microorganisms are susceptible to the action of certain chemicals which either check growth or destroy the organisms.
c) Light: – Light is more or less harmful.
d) Concentration of nutrient solution: – High sucrose or salt content in product checks growth of micro-organisms.
5. Temperature: –
According their optimum growth temperature bacteria can be classified into:-
a) Psychotropic: – can grow at refrigeration temperatures (5-7 0C).
b) Mesophilic: – can grow at temperatures ranging between 20 0C and 40 0C.
c) Thermophilic (heat loving): – can grow at temperatures above 50 0C.