This document discusses the intrinsic and extrinsic factors that affect the growth and survival of microorganisms in food. Intrinsic factors include nutrients, growth factors/inhibitors, water activity, pH, and redox potential. Extrinsic factors are environmental conditions like temperature, gaseous composition, salt concentration, and water quality. Different types of microbes have varying optimal ranges for these factors, such as psychrophilic, mesophilic, and thermophilic bacteria for temperature, and halophilic, halophobic, and halotolerant bacteria for salt concentration. The interplay between these intrinsic and extrinsic parameters determines whether conditions are suitable for microbial growth.

1. FACTORS (INTRINSIC AND EXTRINSIC) AFFECTING
THE GROWTH AND SURVIVAL
OF MICROORGANISMS IN FOOD

2. Intrinsic
parameters
• Parameters which are naturally present in fish called intrinsic
parameters.
• It includes nutrients, growth factors and inhibitors, water activity,
pH, oxidation reduction potential (redox potential).

3. A. Nutrients:
• They are very essential for growth of living cells, including bacteria.
• These nutrients include carbohydrate, proteins, minerals and vitamins.
• Water is not considered as a nutrient but it is essential medium for
biochemical reaction necessary for synthesis of energy.
• Fish is one of the highly nutritious commodities.
• The fish muscle contains around 15-23% protein.
• Bacteria attack the protein and break it down to peptides and amino acids

4. Mineral and vitamins in food:
• Microbes need several minerals in small amount such as phosphorus,
calcium, magnesium, iron, sulphur, manganese and potassium.
• Microbes also possess B group water soluble vitamins and fat soluble
vitamins in small amount in growth.

5. B. Growth factors and inhibitors:
 Food can also have some factors that can either stimulate; growth is
adversely affecting the growth of microbes.
 The exact nature of growth factors is not known but they are naturally
present in some foods, e.g. of growth factor is in curd that stimulate growth
of some lactobacillus species these factors can be added two row materials
during food bio processing or in to media to isolate some bacteria from
foods.
 Foods also contain many chemicals that can adversely affect microbial
growth. Some of the natural antimicrobial agents are lysozyme in egg,
agglutinin in milk.

6. C. Water activity (aw)
• Water activity is a major of the availability of water for biological function
and relates to water present in free form.
• The water activity of fresh fish is in the range of 0.95 -0.99.
• The free water in the fish is necessary for enzymatic and microbial activity.
• It is also necessary to transport nutrient and remove waste material,
synthesis cellular material and take part in other bio-chemical’s reactions.
• In general the minimum water activity values for the growth of microbial
growth are as follows.
Gram –ve bacteria – 0.93
Gram +ve bacteria – 0.90
But S. aureus can also grow at water activity of 0.85 and halophilic bacteria at
0.75. Fungi can grow at water activity range of 0.82- 0.85.

7. D. pH
• PH indicate the H+ ion concentration in a system and is expressed as [log-]
of H ion or proton concentration.
• The PH of fish and fish product has a profound effect on the growth and
viability of microbial cell.
• Each species of pathogenic bacteria has an optimum pH for the growth.
• In general mould and yeasts can able to grow at lower PH than that of
bacteria.
• Gram –ve bacteria are more sensitive to low PH than gram +ve.
Group PH Range
Moulds 1.5 to 9.0
Yeast 2.0 to 2.5
Gram +ve bacteria 4.0 to8.5
Gram –ve bacteria 4.5 to 9.0

8. E. Redox potential:
 Redox or oxidation reduction potential measures the potential different in a system
generated by a coupled reaction in which one substance is oxidized and 2nd substance
reduced simultaneously.
 Oxidation means loss of one electron and reduction means gain of one electron.
 The electrons donor that reduces an oxidize substance is called as reducing agent.
 Similarly the electron acceptor is called as an oxidizing agent.
 The redox potential designated as “Eh” is measured electrical unit of milli volt. The redox
potential of fish is influenced by its chemical composition, specific processing treatment
and storage condition.
 Fish stored in air will have higher reduced potential than stored under vacuum or modified
gases.
 The redox potential provides a useful scale for measuring the degree of
anaerobiosis. The redox potential of the environment at which different groups of
microorganisms usually grow is between +500 and +300 mV for aerobes, between
+300 and −100 mV for facultative anaerobes and between +100 and −250 mV or
more for anaerobes.

9. Extrinsic
parameters
It includes the environmental condition in which the fish is stored.
Following are the main extrinsic parameters.
1. Temperature
2. Gaseous composition
3. Salt concentration
4. Water quality

10. 1. Temperature:
 Microbial growth is accomplished through enzymatic reaction.
 It is well known that with every 100°C rise in temp, the catalytic rate of an
enzyme get double.
 Similarly the enzymatic reaction role is reduced to half by decreasing the
temp of 100°C.
 Foods are exposed to different temperature from the time of production
until conversion.

11. Each bacterial spp. has a range of temp in which it has optimum
growth depending on their temp difference bacteria are broadly
classify in to three groups.
1. Psychrophilic
2. Mesophilic
3. Thermophilic
 Psychrophilic bacteria:
They are called cold loving bacteria. They grow usually between
the ranges of 0 to 20°C. The optimum is 15°C. This groups includes
most of the bacteria causing spoilage to refrigerated or ice foods.
E.g. Pseudomonas, Alteromonas, Morax.

12.  Mesophilic bacteria:
They grow within temperature range of 20-45°C with an optimum temp of
37°C. Most of the pathogen belongs to this group.
E.g. Salmonella, Vibrio, Streptococcus etc.
 Thermophilic bacteria:
Bacteria which grow best at higher temperature come under this group. Their
growth temperature range is 45-65°C with optimum temperature of 55°C.
Certain bacteria causing spoilage of canned food belongs to this group.
E.g. Bacillus coagulants and B. stearothermophilus

13. Gaseous composition:
Depending on requirement of oxygen,
1. Aerobic Bacteria: Bacteria requiring presence of oxygen called Aerobic or
Aerobes.
Example - S. aureus
2. Anaerobic bacteria: Bacteria which can only grow in absence of oxygen
called anaerobic bacteria.
Example- C. botulinum

14. 3. Facultative: Bacteria growing in presence or absence of oxygen.
Example- Listiria monocytogen
4. Microaerohilic bacteria: Bacteria under this group can grow only in the
presence of very little oxygen (3 to 15%).
Example- lactobacillus, streptococci

15. Salt concentration:
Depending on requirement of salt concentration for bacterial growth, following
major groups have been classify,
a. Halophilic bacteria: Salt loving bacteria are called as halophilic bacteria.
Example- Vibrio
b. Halophobic bacteria: Bacteria which can survive even in small salt
concentration.
Example- Salmonella, E.coli etc.
c. Halotolerent bacteria: Bacteria that can survive higher salt concentration (>
10%).
Example- Bacillus micrococcus, Staphylococcus