Dairy Microbiology Notes PDF

# Dairy "Microbiology" ## Microorganisms - Are organisms that are microscopic (invisible to the naked eye) - May be unicellular (consists of only one cell): Bacteria - Multicellular (consists of many cells) Fungi/Molds ## Microbiology: The Study of Microorganisms - **Anton van leeuwenhoek:** Cal...

# Dairy "Microbiology" ## Microorganisms - Are organisms that are microscopic (invisible to the naked eye) - May be unicellular (consists of only one cell): Bacteria - Multicellular (consists of many cells) Fungi/Molds ## Microbiology: The Study of Microorganisms - **Anton van leeuwenhoek:** Called the father of microbiology. - Was the first to observe bacteria. Called them **Animalcules**. - He couldn't make a connection between microorganisms and dairy products. - He stated that there were forms of life that couldn't be seen by the naked eye ## What's the relation between microorganisms and dairy products? - Not all microorganisms are harmful. - There are many microorganisms useful. - Certain types of microorganisms can be used as starter culture ## Starter Culture - Are microorganisms that can be used, added in the manufacture of dairy products. - Convert lactose to lactic acid. - **Yogurt starter culture:** - _Streptococcus thermophilus_ - _Lactobacillus bulgaricus_ (helpful) - **Butter starter culture:** - _Lactococcus lactis subsp. lactis_ - _Lactococcus lactis subsp. cremoris_ - _Lactococcus lactis subsp. lactis diacetylactis_ ## The PH of fresh milk: 6.6 - 6.8 - Addition of starter culture can convert lactose into lactic acid. - **Production of Lactic acid decreases PH from 6.8 to 4.6.** This is the **ISP (isoelectric point)**, where casein precipitates (forms curds). - **Production of flavor components:** (production of acetaldehyde). - **Lipolytic and proteolytic activity:** - **Lipolytic:** degradation of fats, lipids present in milk - **Proteolytic:** degradation of proteins - **Inhibition of Certain types of microorganisms:** - (Production of inhibitor substances). - _Lactococcus lactis subsp. lactis_ when grown in milk, produces inhibitor substances, such as Nisin (bacteriocin). ## We associate microbes with spoilage, infection of food, but not all microbes are harmful. ## Certain types of microbes cause spoilage. - **Spoilage (Changes in the normal state of food)** - **Normal state of food:** Smell/color/odor/viscosity/nutritional value ## Harmful microbes: _Pseudomonas_ (aerobic rods) - It has the ability to produce certain types of enzymes. - **Lipase:** - Lipase is an enzyme that is present naturally in milk - The substrate of lipase is milk fat. ## Composition of milk fat: 89% of milk fat is triglycerides. - 3 Fatty acids + Glycerol - Phospholipids - Sterols ## Microbial lipase, which is produced by _Pseudomonas_, is more resistant to pasteurization than the lipase present naturally in milk. ## _E. coli_ (facultative anaerobic bacteria). ## Coliform bacteria - **_E. coli_:** characterized by production of acid and CO2 (holes). It converts sugar into acid and CO2, causing gassing effect. - **_Clostridium tyrobutyricum_** - "Anaerobic bacteria," an example of spore former bacteria. ## Spore former bacteria: Bacteria that can grow under different conditions. - **Temperature of pasteurization:** - 63℃ for 30 minutes or 72℃ for 15 seconds. - **_Bacillus, Clostridium_** When exposed to difficult conditions, such as pasteurization, they can produce spores that reduce (resist) the temperature of pasteurization. ## Shelf life of Pasteurized milk: 3-15 days at refrigerator temp. ## Shelf life of Sterilized milk: Kils all types of microbes (UHT) - About 6 months using high temperature ## Spore forming bacteria: _Clostridiumn_ - Can ferment to produce gases and puteric acid (RAS): - **Cause late gassing effect in hard cheese (RAS).** ## Early gassing effect: _E.coli_ ## Late gassing effect: Spore-former bacteria: "_Clostridium_" ## Certain types of microorganisms that cause poisoning by toxins - **_Staphylococcus aureus_**: Cause food poisoning (G+) - **_Clostridium botulinum_**: Produce toxins that attack the nervous system(disease called **botulism** (attacks the nervous system)). ## What are the factors effecting the growth of microbes? ### 1. Requirement of O2 - **Obligate aerobes:** _Pseudomonas, Bacillus_ - **Obligate anaerobes:** _Clostridium_ - **Facultative anaerobes:** _E.coli_ - **Microaerophiles:** Need few amounts of O2: _Streptococcus_ (2-10%) O2 ### 2. Temperature - **Psychrophils:** (cold loving) - **Mesophils** - **Thermophils:** >45 ℃ ### 3. PH - Most bacteria prefer neutral pH: 6-8. - Yeast and mold prefer acidic medium. ## Yogurt - **When we want to isolate yeast and mold from dairy products, we use a medium called PDA and add tartaric acid before pouring the medium into the plate.** ### PDA (Potato Dextrose Agar) - Used to isolate yeast and mold from dairy products. - Tartaric acid reduces the pH of the medium to 3.5. -At this pH, most bacteria can't grow, while yeast and mold can grow. ### 4. Water (87%) - Two types of water: - **Free water:** Which is important to microbes - **Bound water:** ### 5. Nutrition - **Autotrophic** - **Heterotrophic** ## Types of microbes: - **Bacteria:** (including bacteria, yeast, molds, viruses) - **Virus:** A small infectious agent that replicates only inside living cells. - They can't reproduce by themselves. - **Bacteriophage:** Attacks bacteria ## Difference between bacteria, yeast, and molds. ### Bacteria ( prokaryotes) - Nucleic acid does not include DNA. - DNA is not associated with histone proteins. - Cell wall: Peptidoglycan - reproduce by binary fission. ### Yeast, molds (eukaryotes) - Nucleus included with DNA - DNA associated with histone proteins. - Cell wall: Peptidoglycan protein - Reproduce by budding ## What is the difference between homofermentative and heterofermentative? ### Homofermentative: - Can ferment sugar and produce acid as a main end product: (lactic acid) - **_Clostridium_ and _Bacillus_.** ### Heterofermentative: - Can ferment sugar and produce acid and gasses (byproducts) as CO2, ethanol: **_Leuconostoc_** ## Fungal Spoilage: - Fungi cause off odor. ## Coliforms, _E. Coli_: Present naturally in the intestine ## Why is _E. coli_ used as indicator organism to determine the hygiene condition of dairy products? - _E. coli_ is present naturally in the intestine of animals. - So it is present in dairy products (an indicator for fecal origin, it can grow at 44℃). ## _E. coli_ is also used to determine the efficiency of Pasteurization. ## Penicillium: Used in roquefort cheese ## _Bacillus stearothermophilus_: Cause flat sour spoilage ## _Clostridium tyrobutyricum_: Cause late bloating in Ras cheese ## How can we reduce the growth of microorganisms? 1. **Reduce pH by adding acid.** 2. **Adding salt or sugar** 3. **Removing water (dry milk)**: Shelf life of dry milk is 1 year or more (decreasing the water content by 2%, increasing the shelf life). 4. **Adding additives** 5. **Freezing (ice cream after processing at –20℃)** ## Food Poisoning: - It is the illness you may get after eating spoiled food. ## Types of Microbes ### Bacteria: - Unicellular: They can be seen using a light microscope. (consists of only one cell) - Prokaryotes: Don't have a nucleus, but have structures like chromosomes. - Multiply by simple cell division (binary fission). - The bacterial cell divided into two equal cells (daughter cells). - Cell wall of bacteria contain diaminopelic acid (amino acid) (solid) ### Yeast - Eukaryotes: Single cell, larger than bacteria, oval shape - Reproduce by budding (asexual) contain nucleus - Yeast and mold prefer to grow in acidic media (low PH, ~3.5). - Have a complex cell wall (Glucan, manan, pectin) - Optimum growth temperature: 15-40℃ ### Molds: - Sexual and asexual reproduction. - Multicellular eukaryotes. - Certain types produce mycotoxins as _Aspergillus flavus_ - Contain a nucleus. - Grow in the form of hyphae. - Food production: _penicillium roquefort_ (for Roquefort cheese). ### Virus: - Each bacteriophage is specific to a certain type. - Smaller than bacteria. - Can't reproduce by itself. - Seen by electron microscopes. - A small infectious agent that replicates only inside the living cells. - Viruses can infect all types of life forms. ### Bacteriophage("Attack bacteria") - When starter cultures are infected with bacteriophage, the fermentation process will stop. - Consists of DNA, RNA coated with protein (capsid) + tail (nucleic acid).