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Chapter 6

Chapter 6. Fermented Food Products. Products from Microorganisms. Food and food related products Whole cells products Cheese and yogurt Fermented fruits and vegetables Organic acids Alcoholic beverages Flavoring agents: amino acids and nucleotides. Non-food products Enzyme

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Chapter 6

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  1. Chapter 6 Fermented Food Products

  2. Products from Microorganisms • Food and food related products • Whole cells products • Cheese and yogurt • Fermented fruits and vegetables • Organic acids • Alcoholic beverages • Flavoring agents: amino acids and nucleotides

  3. Non-food products • Enzyme • Vitamins • Antibiotics • Biotech drugs

  4. Organic Acid 1. Lactic acid fermentation Lactic acid - A Natural Product It is made by fermentation of different sugars (glucose, sucrose, or lactose) by means of the genera lactobacillus, streptococcusand pediococcus.

  5. Streptococcus thermophilus Lactobacillus bulgaricus

  6. Lactobacteriaceae • Gram positive, rods or cocci • Obligate anaerobes (no respiratory chain) • Catalase negative (often aerotolerant)

  7. Homolactic fermentation(homofermentation) •Glucose degraded via EMP pathway, with lactic acid as the only end product glucose + 2 ADP + 2 Pi ➞ 2 lactic acid + 2 ATP • Important in dairy industry (yogurt, cheese)

  8. homofermentation

  9. Heterolactic fermentation(heterofermentation) • Glucose degraded via phosphoketolase pathway (PK) • In addition to lactic acid, also ethanol and CO2 produced glucose + ADP + Pi ➞ lactic acid + ethanol + CO2 + ATP

  10. phosphoketolase pathway (PK) G → →xylulose 5-phosphate phosphoketolase acetyl phosphate + glyceraldehyde 3-phosphate pyruvate ethanol lactic acid C6H12O6＋ADP+Pi→CH3CHOHCOOH＋CH3CH2OH＋CO2+ATP

  11. Homofermentationvs. heterofermentation

  12. How to recognize heterofermentation strain in lab? （1） Production of C02 （2） Gram staining

  13. Lactic acid production process

  14. Lactic acid in Food • Lactic acid is naturally present in many foodstuffs, such as cheese, yogurt, soy sauce , fermented meat and pickled vegetables, etc. • It serves as either a flavoring agent, pH regulator or a preservative.

  15. Food Trends Health Convenience Value Taste

  16. What is Yogurt A semi-solid casein gel formed by the action of specific lactic acid bacteria on milk Fermented milk

  17. Microbes used in Yoghurt Involved • Lactobacillus bulgaricus and/or acidophilus • Streptococcus thermophilus • They work better together than they do • separatelybecause…. • Acid production rate is much higher • Formation of typical yogurt flavour and texture

  18. Ingredients and Function • Lactose is partial converted to lactic acid, which makes digestion easier for lactose-intolerant people. • Containing higher amino acid than milk. • Lactic acid causes the milk proteins (casein) to coagulate into a semisolid curd and also restricts spoilage bacteria. • Freshly prepared yogurt contains 10,000,000,000 (109) bactria per gram.

  19. Main Families of Lactic Bacteria Fig 1: Lactobacilli (Small Intestine) Large Intestine Small Intestine Fig 2: Bifidobacteria (Large Intestine)

  20. Yogurt Production Milk Selection Cooling to 42-45℃ Dry Matter Standardization Inoculation Homogenization Deaeration Sterilization Denaturing protein Heat Treatment

  21. Yogurt variations 1. Set yogurt：pouring the inoculated milk into pots and fermenting it, normally consumed by use of a spoon or sold into customers’ containers. 2. Stirred yogurt:fermented in bulk, stirred and then dispensed into pots.

  22. Two types of yogurt Inoculation Flavoring Ferment Fill Retail Container Break Ferment Stir/Cool Cool/Store Fill Set yogurt Stirred yogurt

  23. Cone Bottom Processor

  24. CHEESE CHEESE

  25. Basic Cheese-making Steps 1. Collect/deliver milk 2. Pasteurize milk 3. Add starter culture 4. Add rennet and CaCl2 5. Cut the curd and Heat 6. Separate curd from whey 7. Salt the curd (dry salt) 8. Package and ripen cheese

  26. Rennin, an acid protease from calves’ stomach , that partially hydrolyses the milk protein (casein) and leads to coagulationin the presence of Ca2+ to form “curds.” The liquid portion of the milk at this time is called “whey.”

  27. Pasteurization

  28. Separate the curd from the whey

  29. Salting

  30. Package, Coat Cheese andRipening

  31. Q: What’s the difference between yogurt making and cheese making?

  32. Citric acid Citric acid is a weak organic acid found in citrus fruits(lemon). It is a good, natural preservative and is also used to add an acidic (sour) taste to foods and soft drinks.

  33. Aspergillus niger • Well-known production organism of citric acid and other organic acids. • Also a well-known over-producer of enzymes, in particular starch-degrading enzymes and plant cell-wall degrading enzymes.

  34. Phosphofructokinase

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