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Questions and Answers
What significant contribution did Louis Pasteur make regarding bacteria?
Which of the following was a method of food preservation developed between 8000 and 1000 B.C.?
What structure did Pasteur use in his experiments to prevent bacteria from contaminating liquids?
What is a key characteristic of eukaryotic cells compared to prokaryotic cells?
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Which morphological group of bacteria did Antony van Leeuwenhoek observe?
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What major aspect of microbiology was NOT demonstrated by Louis Pasteur?
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What is a characteristic of molds compared to yeasts?
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Which of the following is true regarding the cell walls of eukaryotic cells?
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What is the calculated generation time (G) based on the provided formula?
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Which of the following factors is considered an intrinsic factor affecting microbial growth in food?
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Which pathway is NOT one of the major pathways for fermentable monosaccharide metabolism?
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What type of food preservatives are Reuterine and Diacetyl classified as?
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What is the role of bacteriocins produced by lactic acid bacteria?
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Which of the following components is associated with microbial metabolism of food carbohydrates?
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Which of the following is considered an extrinsic factor influencing microbial growth in food?
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Which of the following is a type of organic acid that can be used as a food preservative?
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What is the primary composition of the cell wall in molds?
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Which of the following correctly identifies bacterial shapes?
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What distinguishes an enveloped virus from a non-enveloped virus?
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Which group of microorganisms includes both Bacillus and Clostridium and is noted for foodborne illness?
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What is the process through which spores can remain dormant for years before reverting to vegetative cells?
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Which of the following factors does not prevent spore germination?
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What are the smallest microorganisms mentioned that do not contain organelles?
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What kind of reproduction do molds use to form spores?
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Which of the following viruses is most associated with foodborne outbreaks?
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In terms of generation time, what does the letter 'G' represent?
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What is the role of contaminated soil and water in foodborne diseases?
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Which of the following is NOT a source of microbial contamination in foods?
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What is the first step in the sporulation process of bacteria?
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What happens to mold and yeast spores when exposed to high heat?
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What is the approximate size range of bacteria as specified?
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Study Notes
Microbiology History
- Antony van Leeuwenhoek observed bacteria in saliva, rainwater, vinegar, and other materials between 1676-1683
- He described three morphological groups: cocci, bacilli, and spirilla
- He observed that some bacteria were motile
- Louis Pasteur demonstrated that bacteria in boiled infusions could only grow if contaminated by dust particles in the air in 1861
- Pasteur disproved spontaneous generation and proved that bacteria reproduce through biogenesis
- Pasteur, while working at a university in Lille, France, was asked to explore the reasons for souring in alcoholic beverages
- He used a swan-neck flask to prove that bacteria could not reach the liquid if trapped in the long neck, preventing souring
- When the flask was tipped and bacteria reached the liquid, it would turn sour
- Early food preservation methods were developed between 8000 and 1000 BC, including drying, cooking, baking, smoking, salting, sugaring, low-temperature storage, storage without air, fermentation, pickling, and spicing
- These methods likely aimed to delay food spoilage
Types of Microorganisms
- Yeasts and molds are eukaryotic, with cells much larger than prokaryotic cells.
- Yeasts are unicellular, while molds are multicellular.
- Eukaryotic cells have rigid cell walls and thin plasma membranes.
- The cell wall does not contain peptidoglycan but is composed of carbohydrates, and plasma membrane contains sterol.
- Molds are nonmotile, filamentous, and branched.
- The cell wall of molds is composed of cellulose, chitin, or both.
- Molds are composed of filaments called hyphae.
- Bacteria are unicellular, ranging in size from 0.5–1.0 × 2.0–10 μm.
- Bacteria have three forms: spherical (cocci), rod-shaped (bacilli), and curved (spiral).
- Bacteria lack organelles in their cytoplasm.
- Viruses are noncellular entities or particles.
- Bacterial viruses are called bacteriophages.
- Viruses are composed of nucleic acids surrounded by a protein capsid.
- Some bacteriophages have an envelope surrounding the capsid, known as enveloped viruses.
- Viruses can cause foodborne diseases in humans, with hepatitis A and norovirus being significant contributors to outbreaks.
- Both hepatitis A and norovirus are single-stranded RNA encased in a capsid.
- Protozoan parasites are eukaryotic cells associated with water and foodborne outbreaks linked to fresh produce.
- Animals, livestock, pets, and humans can carry these parasites, serving as sources of contamination.
- Contaminated soil and irrigation water are environmental sources of contamination.
Microbial Sporulation and Germination
- Molds, some yeasts, and some bacteria form spores.
- Molds form spores through both asexual and sexual reproduction.
- Yeasts that form spores (sexual ascospores) are known as Ascomycetes (true yeasts).
- Ascospores form through the conjugation of two yeast cells.
- Only a few bacterial genera form spores.
- Foodborne sporeformers include Bacillus, Alicyclobacillus, Clostridium, and Desulfotomaculum.
- Bacterial cells produce endospores (inside a cell, with one spore per cell).
- Spores are more resistant to physical and chemical antimicrobial treatments than vegetative cells.
- Spores are metabolically inactive or dormant for years and can germinate into vegetative cells in suitable environments.
- Foods can be contaminated by spores from various sources.
- In a suitable food environment, spores will germinate, grow, and produce effects (desirable or undesirable).
- Mold and yeast spores are sensitive to heat and can be prevented from growing by storing foods in the absence of air.
- Bacillus, Clostridium, and Desulfotomaculum are associated with food spoilage and foodborne diseases.
- Spores are of special interest and importance in food processing due to their high heat resistance.
- Canning of low-acid foods requires high heat treatment to achieve commercial sterility that kills spores of all pathogenic bacteria.
- Nitrites, low pH, low AW, or high salt are used to prevent spore germination.
Sources of Microorganisms in Foods
- Various sources can contribute to microbial contamination in foods, including:
- Animals, Birds, Fish, and Shellfish
- Air
- Soil
- Sewage and manure
- Water
- Humans
- Food ingredients
- Food processing or harvesting equipment
Microbial Growth Characteristics
- Generation time or doubling time is the time it takes for a single cell to divide into two.
- The formula to calculate generation time (G) is: G = 0.3 x t / (log10 z - log10 x), where:
- G is the generation time (in minutes)
- 0.3 is a constant value
- t is the duration of study (in minutes)
- log10 x is the initial cell number per milliliter or CFUs/mL
- log10 z is the final cell number per milliliter or CFUs/mL
Factors Influencing Microbial Growth in Food
- Intrinsic factors of a food influence microbial growth, including:
- Nutrients
- Growth factors
- Inhibitors (or antimicrobials)
- Water activity
- pH
- Oxidation-reduction potential (Eh)
- Extrinsic factors also influence microbial growth, including the environmental conditions of storage:
- Temperature
- Relative humidity
- Gaseous environment
- Relative humidity and gaseous conditions influence the AW and Eh of the food.
Microbial Metabolism of Food Components
- Carbohydrates are metabolized by microorganisms, including:
- Degradation of polysaccharides
- Degradation of disaccharides
- Degradation of monosaccharides
- Fermentable monosaccharides are metabolized through five major pathways:
- Embden-Meyerhoff-Parnas (EMP) pathway
- Hexose monophosphate shunt (HMP) pathway
- Entner-Doudroff (ED) pathway
- Two phosphoketolase (PK) pathways (pentose phosphoketolase and hexose phosphoketolase)
Food Biopreservatives of Microbial Origin, Bacteriocin, and Nanotechnology
- Antimicrobial Compounds of Food-Grade Bacteria:
- Organic Acids, Diacetyl, Hydrogen Peroxide, and Reuterine are used as food preservatives.
- Bacteriocins of Lactic Acid Bacteria as Food Preservatives:
- Bacteriocins are produced by certain bacteria and are used as food preservatives.
- Food Ingredients and Enzymes of Microbial Origin:
- Microbial Proteins and Food Additives (Amino acids)
- Organic Acids
- Microbial Enzymes in Food Processing
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Description
Explore the pioneering work of scientists like Antony van Leeuwenhoek and Louis Pasteur in the field of microbiology. This quiz examines key historical developments, including the discovery of bacterial morphology and the disproval of spontaneous generation. Test your knowledge on early food preservation methods and the significant breakthroughs that shaped modern microbiology.
