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Types of Food 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
Editor's Notes
- glutinous rice: low amylose content, sticky when cooked
- All chemical reactions that occur in living cells including digestion, divided into catabolism & anabolism
- Hydrolysis of tryglycerides into glyserol and free fatty acids
- water melon seeds (Ogiri in Nigeria) and sesame seeds (Ogiri-saro in Sierra Leone) and others where coconut and leaf proteins are the substrates (Indonesian semayi and Sudanese kawal respectively).
- Soy proteins are sequentially hydrolyzed into peptides, amino acids, and ammonia. Due to release of ammonia, the pH of thua nao rapidly reaches as high as 8 (or even higher). This alkaline nature not only provides a selective condition for certain bacteria (i.e., Bacillus spp.) but also causes difficulty for other microbes to grow. Ammonia is considered as a major chemical causing a strong smell to the product.
- Lactobacillus, Pediococcus, Micrococcus Miso/ koji -soy sauce Sausage- penicillium mould & bacteria LAB