Examples of fermented product

Examples of fermented product

Examples of fermented product

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

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

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

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

Undesirable changes in food fermentation

i) Vinegar in wineii) Proteolysisiii) Lipolysisiv) Toxinv) Odd coloursvi) Odd flavoursvii) Bad odours

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

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

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

Types of bacterial food fermentation

Principle of alkaline food fermentation

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

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