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1. Dr H A Makroo
Department of Food Technology
Islamic University of Science & Technology
Kashmir 192122 India
Microbial Growth and Control

2. Microbial Growth
 Microorganisms grow or multiply in numbers when
exposed to a favorable environment, such as food.
 Their growth is associated with food spoilage,
foodborne diseases, and food bioprocessing.
 Growth is also important in isolating an unknown
microbial strain involved in food spoilage, foodborne
diseases, or food bioprocessing
Microbial Reproduction or Growth
An increase in the number or mass of vegetative cells
of bacteria, yeasts, and molds is customarily used to
reflect growth for microorganisms. Bacteria reproduce
by a process called transverse binary fission or,
simply, binary fission.
1. Earlier stage
2 Later stage
Final stage
Cell division in Lactobacillus cells
DNA
replication
and
separation
Partition
between the
DNA
Invagination and
septum formation
of a wall
Cell
separatio
n

3. Microbial Growth
Generation Time (or Doubling Time)
 The time that a single cell takes to divide into
two is called generation time.
 However, in practice, generation time is
referred to as the doubling time for the
entire population
Generation
Time
 The generation time of a microbial population
can be calculated mathematically from the
differences in population during a given time
period. Because of large numbers, the
calculation is done in logarithmatics (log10)
G is generation time (in minutes; also expressed as doubling
time, td, in hours)
0.3 is a constant (value of log10 2 and indicates doubling),
t is the duration of study (minutes),
log10 x is initial, and
log10 z is the final cell numbers
Parameters that influence the microbial
growth
 Nutrients
 Storage temperature,
 Acidity (pH),
 Water activity (AW),
 Oxidation-reduction (O-R) potential

4. Growth Curve
4. Death phase:
 The rate of cell
death is higher
than the rate of
cell multiplication
1. Lag phase:
 The population does not
change.
 During this time, the cells
assimilate nutrients and
increase in size.
 Although the population
remains unchanged
because of a change in
size, both cell mass and
optical density show
some increase.
2. Log phase:
 The cell number starts increasing, first slowly and then
very rapidly.
 The cells in the population differ initially in metabolic rate
and only some multiply, and then almost all cells multiply.
 This is the exponential phase, the growth rate at the
exponential phase follows first-order reaction kinetics and
can be used to determine generation time.
3. Stationary phase.
 At this stage, the growth rate slows down, because of nutrient shortage and accumulation
of waste products,
 Few cells die, and a few cells multiply, keeping the living population stable.
 However, if one counts the cells under a microscope or measures cell mass, both may
show an increase as dead cells may remain intact.

5. Sterilization
Process of destroying all forms of microbial life
Disinfection
Elimination of microorganisms from inanimate
objects and surfaces
Antimicrobial agents
Agents that inhibit the growth or completely
destroy the life of microorganisms
 Physical agents
 Heat
Dry heat
Moist heat
 Radiation
 Filtration
 Chemical agents
 Chemotherapeutic agents
Growth Control
MOIST HEAT
Autoclaving
Boiling
Free flowing steam
Pasteurization
DRY HEAT
Flaming
Hot air oven
Incineration (Burning)

6. Chemical Antimicrobial Agents
Mode of action
 Damage to cell wall or inhibition
of cell wall synthesis
 Alteration of the cytoplasmic
membrane permeability
 Alteration of the physical and
chemical state of proteins and
nucleic acid
 Inhibition of enzyme function
 Inhibition of protein and nucleic
acid synthesis
Qualities of good disinfectant
 High co-effecient of disinfection
 Stable
 Water soluble
 Non-toxic, non-corrosive
 Easy to use
 Cheap

7. Thank
You