There are several factors that govern the fermentation process, including temperature, salt concentration, water activity, pH, oxygen availability, and nutrients. Fermentation can produce desirable changes like lactic acid production or undesirable changes such as off flavors or toxins. The main types of bacterial fermentations are lactic acid fermentation, acetic acid fermentation, and alkaline fermentation. Fermentation can also be classified based on the culture media used, including solid-state fermentation and submerged fermentation.

1. Examples of fermented product

2. Examples of fermented product

3. Examples of fermented product

4. Factors governing fermentation
1. Temperature
• Bacteria- optimum temperature-20 to 300C
• Thermophiles- 50 to550C
• LAB- 18 to 220C
• Leuconostoc species- 18 to 220C
2. Salt concentration
• LAB – high salt concentrations, begin
metabolism & produces acid

5. Factors governing fermentation
3. Water activity
• Bacteria- high water activity (0.9 or higher)
• Yeast and fungi- lower water activity
4. Hydrogen ion concentration (pH)
• Optimum pH for most m.o.- neutral (7.0)
• Acid tolerant (reduced pH levels)- Lactobacillus and
Streptococcus species

6. Factors governing fermentation
5. Oxygen availability
• Bacteria- anaerobes, aerobes or microaerophilic
(some lactobacilli)
• aerobic fermentations- oxygen is one of the limiting
factors, determines the type, the amount of
biological product obtained , substrate consumed,
energy released from the reaction. Exp- acetobacter
require oxygen for the oxidation of alcohol to acetic
acid

7. Factors governing fermentation
6. Nutrients
• All m.o. require nutrients/ energy
• Fermentative bacteria require carbohydrates-
either simple or complex.
7. Inhibitors
• Chemical compounds can inhibit the growth &
activity of m.os.
• Prevents metabolism, denature proteins,
damage the cell

8. Undesirable changes in food fermentation
i) Vinegar in wine
ii) Proteolysis
iii) Lipolysis
iv) Toxin
v) Odd colours
vi) Odd flavours
vii) Bad odours

9. Types of bacterial food fermentation
1. Lactic acid fermentation
• most desirable food fermentation, sour dough bread,
sorghum beer, fermented milks, fermented
vegetables.
• Lactobacillus, Leuconostoc, Pediococcus
and Streptococcus
• Homolactic fermentation:
Glucose 2 lactic acid
• Heterolactic fermentation:
Glucose lactic acid+ ethanol+ CO2

10. Types of bacterial food fermentation
2. Acetic acid fermentation
• Vinegar from fruit juices and alcohols
• acetic acid bacteria/ acetobacter- convert alcohol to
acetic acid in the presence of oxygen
Alcohol acetic acid + water

11. Types of bacterial food fermentation
3. Alkaline fermentation
• With protein rich foods. Exp soybeans, legumes and
also plant seeds
• Bacillus species- Bacillus subtilis, Bacillus pumilus etc.
• Bacillus subtilis is the dominant species causing
hydrolysis of protein which increases the alkalinity of
the substrate.
• Provide protein rich, low cost foods from leaves,
seeds and beans

12. Types of bacterial food fermentation
Principle of alkaline food fermentation

13. Types of fermentation based on culture media
A. Solid-state fermentation
• m.os. grow on a moist solid with little or no ‘free
water’
• Example- mushroom cultivation, bread making,
manufacture of miso (soy paste), tempeh (soy cake),
gari (cassava) etc.
• Subdivided into aerobic (koji fermentation) &
anaerobic (sausage production by acid-forming
bacteria) process

14. Types of fermentation based on culture media
B. Submerged fermentation
• May use a dissolved substrate, suspended in large
amount of water
• e.g. pickling vegetables, producing yogurt, beer, wine
& soy sauce
• Subdivided into aerobic (citric acid production by
Aspergillus niger) & anaerobic (yogurt) process