Factors affecting Microbial Growth in food Food Preservation concepts

1. By:
Dr. Waleed Foad
MSc.Public Health in Nutrition
Clinical Nutrition Specialist
European Society of Gastrointestinal Endoscopy (ESGE)
Member of the American Society of Nutrition
Email: wfoad@outlook.com

2. Microbial Growths affecting Food
Most important microbial growths are:
1. Bacteria: are single-celled living micro-
organisms. The most common form of
food poisoning is bacterial food poisoning.
2. Fungi.
A Fungus: is a single-celled or multicellular
organism. Fungi can cause infections in humans
or only spoil Food.

3. Microbial Growth
 Understanding factors that influence microbial growth is
essential to maintaining food quality
 In production and preservation
 Microbial Growth and multiplication is influenced by:
1. Food (nutrients for bacteria).  F
2. Acidity (Suitable pH)  A
3. Time.  T
4. Suitable Temperature.  T
5. Oxygen (Most of them, but not all).  O
6. Moisture (Water content) M
Remember: Bacteria need “FAT TOM” to Multiply

4. Nutrient availability in Food
 Nutrients present in a certain food determine the
organisms that can grow in these foods
 Harmful bacteria and spoilage bacteria grow best in
high protein food such as poultry and seafood.
 Fungi and moulds need more Carbohydrate
nutrients in food, and cause food spoilage rather than
food poisoning. E.g.
 Dairy products, juices and pastries.

5. Acidity of Food
 Important in determining which organisms can Live in specific
foods
 Many microorganisms are inhibited by acid conditions
 Exception include lactic acid bacteria
 Lactic acid bacteria used in fermentation process
 Also prime cause of spoilage of unpasteurized milk and other
foods
 Fungi are able to survive at relatively low pH
 Most acid foods spoil from fungal contamination as opposed to bacteria
 pH can determine bacteria’s ability to produce toxin
 Toxin production of many organisms is inhibited by acid pH

6. Chemical Preservatives
•Chemical preservatives are usually derivatives of acids
that kill the microorganisms by slightly increasing the
acidity of the food. They can be:
•Organic: Benzoates; Propionates; Sorbates
antimicrobial agents-act vs. mould etc.
•Inorganic: Sulfites (SO2
2-); Nitrites/Nitrates(NO2
-/
NO3
-)
•Some concerns about safety!!

7. Microbial Growth: Time Factor
 The least time should be given to Raw food till it is
processed (e.g.. Cooked, Eaten, Preserved, ..etc.)
 Because, under suitable microbial growth
conditions, bacteria can multiply by dividing in two
every 10-20 minutes.
 After 6 hours, 1 bacterium can multiply into 262,144
bacteria, more than enough to cause food poisoning.

8. Temperature of food
Under ideal conditions, bacteria multiply rapidly between
5°C and 60°C (the danger zone for food).
 Below 5°C, bacteria multiply slower.
 At freezing temperatures, bacteria stop multiplying and
become dormant. Freezing does not kill bacteria.
 Most bacteria are killed at temperatures above 60°C.

9. Temperature Danger Zone
5°C and 60°C

10.  Cooking:
 Can destroy many organisms
 Alters characteristics of food
 If heat is uneven some organisms may survive in
undercooked portion of food
 Refrigeration:
 Preserves food by slowing growth rate of spoilage
organisms
 Many organisms unable to multiply in low
temperatures
Home Food Preservation

11. Food Preservation:
Temperature Controlling
1. Pasteurization:
 Heating foods under controlled conditions at high temperatures for
short periods
 Reduces number of spoilage organisms
 Does not alter taste of food significantly
2. Freezing:
 Stops microbial growth
 Water unavailable due to ice formation
 Portion of organisms remaining can grow when food is thawed

12. Oxygen availability in Food
 Presence or absence of oxygen affects type of
microbial population
 Obligate aerobes cannot grow under anaerobic
conditions (e.g. Staph. A.)
 Obligate anaerobes will grow only in anaerobic
conditions (e.g. Clostridia)

13. Food Preservation:
Oxygen Deprivation
Examples: Smoked Food, Vaccum and Canning.

14. Moisture
Water availability in Food
 Foods vary dramatically in terms of water availability
 Fresh meats and milk have high water
content
 Supports microbial growth
 Breads, nuts and dried foods have low water
availability

15. Food Preservation: Water Reduction
Inhibiting Microbial Growth by
decreasing water content of Food.
Methods:
 Drying. (e.g. Fruits, bread, powdered milk)
 Salting. (e.g. meat, fish)
 Preserving in concentrated sugar
form(fruit)

16. Food Preservation: Water Reduction
Drying

17. Food Preservation: Water Reduction
Salting

18. Food Preservation: Water Reduction
Concentrated Sugar Preservation.

19. Preservation using Multiple techniques.
 Compined 2 or more techniques for food
preservation may be used, Example:
 Canning: Heating and oxygen deprivation.
 Pasteurization: Heating and oxygen deprivation.
 Salted Fish Canning: Salting & oxygen deprivation

20. Preservation using Multiple techniques.
Freeze Drying

21. For Further Support:
Dr. Waleed Foad
Email: wfoad@outlook.com