Control of microorganisms in foods

1. Control of Microorganisms in
Foods

2. Control of Microorganisms in Foods
• For efficient production of bioprocessed food = to
stimulate growth and increase the viability of
desirable microorganisms.
• In contrast, w.r.t spoilage and pathogenic
microorganisms = to minimize their numbers or
completely eliminate them from food.
• Several methods are used to achieve these goals by
1. Controlling access of the microorganisms in foods
2. Physically removing the microorganisms present in
foods
3. Preventing or reducing the growth of
microorganisms and germination of spores present
in foods
4. Killing microbial cells and spores present in foods.

3. Control of Microorganisms in Foods
• a control method is more effective when
a food has fewer microbial cells and
when the cells are in the exponential growth phase and
are injured
• Spores are more resistant than vegetative cells
• Gram-negative cells are generally more susceptible
than Gram-positive cells to many control methods
• Bacteria, yeasts, molds, phages, and viruses differ in
sensitivity to the methods used to control them
• Different species and strains of the same species
also differ in sensitivity to these control methods.

4. Control or Preservation Methods
discussed in this section are:
1. Control of Access (Cleaning and Sanitation)
2. Control by Physical Removal
3. Control by Heat
4. Control by Low Temperature
5. Control by Reduced Aw
6. Control by Low pH and Organic Acids
7. Control by Modified Atmosphere (or Reducing O–R Potential)
8. Control by Antimicrobial Preservatives
9. Control by Irradiation
10. Control by Novel Processing Technologies
11. Control by a Combination of Methods (Hurdle Concept)

5. 1- Cleaning and Sanitation
• UV radiation
• Steam
• Vaccum Cleaning
• Hot air

6. 1- Chlorine sanitizers
• Hypochlorite
• Chlorine dioxide
• Organic Chloramines
• These are stable at acidic ph and more reactive
at alkaline ph
• It react with SH group of protein

7. 2- Iodophores
• Alkyl phenoxypolyglycol
• They are active for gram +ve and gram –ve
bacteria
• Mechanism: they will oxidize the SH group of
protein

8. 3- Hydrogen peroxide
• It kill both vegetative cells, spores and eggs

9. 2- Control by Physical Removal
• Physical methods
1. Washing
2. Filteration
3. Drying
4. Trimming

10. Control by heat
• Smoking
• Pasteurization
• Mechanism: The permeability of cell membrane
will increase
• These will change the formation of ribosomal
DNA, RNA and different proteins
• The enzymes will denature
• Exponential stage is more prone to heat

11. 4- Control by temperature
• Methods
1. Ice Chilling
2. Refrigeration

12. 5- Control by reduced AW (Water
Content)
• 2 types of water
1. Free water---Involves in microbial growth
2. Bound water---Hydrophiliic, Colloids and
solutes---not available for biological function
• Low water content inside--- cause turgor
pressure, then it cause osmotic
shock/plasmolysis

13. Mechanical Drying
• Tunnel drying
• Roller drying
• Spray drying
• Freeze drying:
-80 C for few min
Instant vaccum

14. 6- Control by Anti-microbial
Preservatives
• Nitrite
• EDTA
• Enzymes

15. 7- Control by modified atmosphere
(Reducing O-R potential)
• 3 methods
1. CAP
• Atmosphere is altered
• Continous monitoring
• Expensive
2- MAP
• Air is removed and particular gas flushed in
3-Vaccum packaging
• Removal of air and sealing the package