Food Microbiology and Fermented Foods
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Questions and Answers

Which enzyme is specifically associated with the breakdown of pectin in fruits?

  • Protease
  • Pectinase (correct)
  • Amylase
  • Cellulase

What type of linkages are found in the structure of cellulose?

  • γ-1,6-linkages
  • β-1,4-linkages (correct)
  • α-1,4-linkages
  • δ-2,4-linkages

Which bacteria is known to cause soft rot in celery and carrots?

  • Clostridium botulinum
  • Erwinia carotovora (correct)
  • Lactobacillus plantarum
  • Bacillus subtilis

Which of the following fungi is associated with decay in citrus fruits?

<p>Penicillium citrinum (C)</p> Signup and view all the answers

What is the main composition of pectin found in fruits?

<p>Galacturonic acid (B)</p> Signup and view all the answers

Which factor is NOT directly mentioned as affecting microbial growth?

<p>Light exposure (C)</p> Signup and view all the answers

What is the primary by-product produced by lactic acid bacteria during fermentation?

<p>Lactic acid (A)</p> Signup and view all the answers

Which microorganisms are primarily responsible for spoiling proteins in an anaerobic environment?

<p>Pseudomonas and Acinetobacter (D)</p> Signup and view all the answers

Which fermented product is NOT produced from milk?

<p>Kimchi (B)</p> Signup and view all the answers

What is the role of yeast in fermentation?

<p>To convert glucose into ethanol (A)</p> Signup and view all the answers

What type of organism is Escherichia coli?

<p>Unicellular organism (C)</p> Signup and view all the answers

What is the significance of crystal violet retention in bacterial cells?

<p>Helps to distinguish between G+ and G- cells (B)</p> Signup and view all the answers

Which of the following factors significantly affects microbial growth?

<p>Nutrients (A)</p> Signup and view all the answers

What does water activity (aw) measure in bacteria?

<p>Availability of unbound water for growth (B)</p> Signup and view all the answers

What type of organisms depend on other bacteria to survive?

<p>Predominant organisms in a food source (A)</p> Signup and view all the answers

Which of the following statements about sporulation is correct?

<p>It helps bacteria form spores to survive unfavorable conditions. (A)</p> Signup and view all the answers

Why do bacteria require higher water activity levels than other organisms?

<p>Bacteria depend on a greater availability of unbound water. (B)</p> Signup and view all the answers

What shapes can bacteria exhibit?

<p>Spherical, spiral, rod-shaped (A)</p> Signup and view all the answers

What is the optimal pH range for bacteria?

<p>6.5-7.5 (A)</p> Signup and view all the answers

Which type of microorganism requires reduced oxygen conditions to grow?

<p>Facultative anaerobes (D)</p> Signup and view all the answers

At what temperature do thermophiles optimally grow?

<p>50-80°C (D)</p> Signup and view all the answers

How does low temperature affect microbial activity?

<p>Decreases metabolism and fluidity (C)</p> Signup and view all the answers

Which of the following best describes the hurdle concept?

<p>It indicates factors that disrupt the growth of microorganisms. (D)</p> Signup and view all the answers

What is the optimal pH range for molds?

<p>4.5-6.8 (B)</p> Signup and view all the answers

Which type of microorganisms can survive in conditions with some oxygen, but not at high levels?

<p>Microaerophilic (B)</p> Signup and view all the answers

What effect does high protein food have on microbial growth?

<p>Provides a shielding effect against high temperatures (A)</p> Signup and view all the answers

Which of the following bacteria is primarily known for being a pathogenic lactic acid bacterium found in unpasteurized milk?

<p>Listeria (A)</p> Signup and view all the answers

Among the listed bacteria, which one is a psychrotrophic organism that can cause spoilage during packaging?

<p>Pseudomonas (B)</p> Signup and view all the answers

Which of the following is NOT categorized as a lactic acid bacterium?

<p>Clostridium (B)</p> Signup and view all the answers

What is the primary characteristic of bacteria such as Bacillus cereus and Clostridium perfringens?

<p>They are spore-forming organisms. (A)</p> Signup and view all the answers

Which of the following pathogens is known for being a major concern in food safety due to its presence in unpasteurized milk?

<p>Mycobacterium (D)</p> Signup and view all the answers

Which organism is characterized as both a spoilage bacterium and a thermophilic pathogen?

<p>Clostridium perfringens (D)</p> Signup and view all the answers

Which microorganism is classified as a lactic acid bacterium that can lead to food spoilage in dairy products?

<p>Micrococcus (A)</p> Signup and view all the answers

Which grouping includes both harmful pathogens and spoilage organisms typically associated with dairy products?

<p>Lactic acid bacteria and psychrotrophic organisms (B)</p> Signup and view all the answers

Which of the following is NOT a source of microorganisms in nature?

<p>Raw food products (C)</p> Signup and view all the answers

What characteristic is associated with microorganisms found in soil?

<p>Poorly active and mostly spore-forming (B)</p> Signup and view all the answers

How do microorganisms typically acquire entry into food?

<p>During handling and processing (C)</p> Signup and view all the answers

Which environment is most likely to contain microorganisms that are less active?

<p>Soil environments (C)</p> Signup and view all the answers

Which process could allow microorganisms to survive in food?

<p>Preservation treatments (B)</p> Signup and view all the answers

What is a common misconception about the relationship between microorganisms and processed foods?

<p>Processed foods are entirely free of microorganisms (B)</p> Signup and view all the answers

Where can microorganisms NOT be found?

<p>In space (A)</p> Signup and view all the answers

Which of the following represents the type of microorganisms primarily associated with food?

<p>Aerobic bacteria (B)</p> Signup and view all the answers

Flashcards

Prokaryotic Cell

A single-celled organism lacking a nucleus and membrane-bound organelles.

Bacterial Shapes

Bacteria come in various shapes: coccus (spherical), bacillus (rod-shaped), and spirillum (spiral).

Sporulation

Bacterial response to unfavorable conditions where they produce a dormant resistant structure (spore).

Microbial Growth Factors

Nutrients, water activity (aw), and other conditions affect how well bacteria grow.

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Chemotrophy

Bacteria that get energy from chemical reactions (not sunlight).

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Phototrophy

Bacteria that obtain energy from sunlight.

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Water Activity (aw)

Measure of available water for microbial growth.

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Bacterial Water Requirements

Bacteria need more water than yeasts or molds.

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pH Range

Microorganisms have a specific pH range they can tolerate for survival and optimal growth. This range varies depending on the type of microbe.

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pH Affects Metabolism

pH affects the transportation of molecules in and out of the cell membrane. It also influences proteins, potentially causing them to denature or precipitate, interrupting cellular metabolism.

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Aerobic Microorganism

A microbe that requires oxygen for growth, like molds. They rely on an oxidized environment.

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Facultative Anaerobe

Microorganisms that prefer oxygen but can still grow in its absence, like Salmonella species. They can adapt to both oxidized and reduced environments.

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Microaerophile

Microbes that need oxygen for growth but only at low levels, like Campylobacter. This means they don't do well in high oxygen environments.

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Psychrophiles

Microorganisms that thrive in cold temperatures, typically between 10 and 15 degrees Celsius.

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Mesophiles

Microorganisms that thrive at moderate temperatures, typically between 30 and 37 degrees Celsius. They are commonly found in humans and animals.

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High Temperature Effects

High temperatures can cause enzyme inactivation and protein denaturation, leading to cell death. However, high-protein foods offer some shielding effect.

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Microbe Habitats

Microorganisms can be found in diverse environments like air, land, water, and even inside living organisms like humans.

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Sources of Microorganisms in Food

Microorganisms can be introduced to food during production, handling, and storage.

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Raw Food Contamination

Raw foods are a common source of microbial contamination, as they are likely to harbor microorganisms.

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Food Processing Contamination

Microorganisms can be introduced to food during handling and processing, like during preparation, packaging, or transportation.

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Survived Preservation

Some microorganisms can survive the preservation methods applied to food, like heat treatment or refrigeration.

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Types of Microorganisms in Food

There are various types of microorganisms found in food, including bacteria, yeasts, and molds.

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Spore-Formers

Some microorganisms can form spores, which are highly resistant structures that can survive harsh conditions.

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Human Colon Microorganisms

The human colon contains a complex community of microorganisms, which play a crucial role in digestion and other bodily functions.

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Pectin

A complex carbohydrate found in many fruits, composed of galacturonic acid linked by 1,4-linkages. It contributes to the texture and firmness of fruits.

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Pectinase

An enzyme that breaks down pectin, found in some microorganisms. It can cause fruits and vegetables to soften or rot.

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Cellulose

A complex carbohydrate found in vegetables. It consists of glucose molecules linked together by β-1,4-linkages.

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Cellulase

An enzyme that breaks down cellulose. It is produced by certain bacteria and fungi.

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Soft Rot

A type of bacterial decay affecting vegetables like celery and carrots, often caused by Bacillus polymyxa and Erwinia carotovora.

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Lactic Acid Bacteria (LAB)

A group of bacteria that produce lactic acid as a primary byproduct of fermentation. They are commonly found in dairy products and play a crucial role in food preservation.

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Spore-Forming Bacteria

Bacteria that can form resistant structures called spores in harsh conditions. These spores are highly resistant to heat, drying, and disinfectants.

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Pseudomonas

A genus of bacteria that can cause spoilage in dairy products, especially at cold temperatures.

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Psychrotrophic Organisms

Microorganisms that can grow at low temperatures, often found in refrigerated foods.

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Listeria

A genus of bacteria that is a common foodborne pathogen, particularly in dairy products.

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Coxiella

A genus of bacteria that can cause Q fever, a serious illness often associated with unpasteurized dairy products.

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Mycobacterium

A genus of bacteria that can cause tuberculosis and other diseases. They are sometimes found in dairy products, particularly unpasteurized milk.

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Unpasteurized Milk

Milk that has not been heated to kill harmful bacteria. It can be a source of various pathogens.

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Food Spoilage: Carbohydrates

Lactic acid bacteria break down carbohydrates into sugars, producing foul odors and lowering the pH, leading to food spoilage.

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Food Spoilage: Proteins

Pseudomonas, Acinetobacter, and molds break down proteins anaerobically, forming off-odors and leading to food spoilage.

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Fermentation: Lactic Acid

Fermentation is the conversion of sugars into byproducts. Lactic acid bacteria use this process to lower pH, crucial in making foods like yogurt.

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Fermentation: Beer

Yeast ferment grain products like barley to produce alcohol. Glucose is converted to ethanol, the key ingredient in beer.

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Food Source: Microbial Origin

Microorganisms found in food come from the raw ingredients and can be acquired during handling, processing, and storage.

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Study Notes

Food Microbiology and Fermented Foods

  • Food microbiology involves the study of microorganisms in food, including their growth, sources, effects on food, and methods for preservation and control.

Outline

  • What are microorganisms?
  • Factors affecting microbial growth
  • Sources of microorganisms
  • Food spoilage
  • Fermented foods

What are Microorganisms?

  • Small living entities: bacteria, viruses, protozoa, and fungi
  • Utilize organic matter to form inorganic compounds; not parasites or viruses
  • Eukaryotes vs prokaryotes: with or without a true nucleus
  • Scientific names: genus and species (e.g., Escherichia coli)

Bacteria

  • Unicellular organisms, 1 µm in length
  • Found everywhere (ubiquitous)
  • Crystal violet retention: Gram-positive or Gram-negative cells
  • Different shapes: coccus, bacillus, spirillum
  • Sporulation: response to unfavorable conditions

Factors Affecting Microbial Growth

  • Nutrients: Chemotrophic (lithotrophic or organotrophic) vs. phototrophic; dependent on other bacteria; organisms in a food imply ideal conditions for them to survive.
  • Water Activity (aw): A measure of water availability for growth; bacteria require higher aw (0.9) than yeasts (0.8) or molds (0.7); death if aw too low.
  • Acidity/Alkalinity (pH): Medium needs to be within a pH range; different optimal pH ranges for bacteria, yeasts, and molds; affects molecule transport and cell metabolism.
  • Oxygen: Aerobes require oxygen; facultative anaerobes can grow in presence or absence of oxygen; microaerophiles require some oxygen but not high levels; anaerobes cannot tolerate oxygen.
  • Temperature: Psychrophiles (10-15°C), psychrotrophs (20-30°C), mesophiles (30-37°C), thermophiles (50-80°C); low temperatures reduce metabolism and fluidity; high temperatures cause enzyme inactivation and denaturation.
  • Food Effects: nature of food has effect on survival & growth of microbes; high protein food → buffering effect; high: shielding effect from high protein/fat food; Low: switch metabolism to produce more unsaturated and short-chain fatty acids

Sources of Microorganisms

  • Found everywhere in nature (air, land, lakes, oceans, soil, shallow/deep water)
  • Human colon
  • Associated with raw food
  • Acquired during handling and processing of food
  • Survived preservation and storage treatments applied to food

Types of Microorganisms in Food

  • Spoilage organisms
  • Pathogenic organisms
  • Useful organisms

Food Spoilage

  • Carbohydrates [Complex]: Breakdown of polysaccharides (e.g., cellulose, starch); pectinase action; Bacillus polymyxa; Erwinia carotovora; Penicillium citrinum
  • Carbohydrates [Simple]: Breakdown of lactose (lactic acid); simple sugars (ethanol)
  • Proteins: Breakdown into amino acids; Clostridium sporogenes; sour odor; foul-smelling compounds; Lysine → cadaverine; Ornithine → putrescine; Alanine → pyruvate; Tryptophan → indole; Cysteine → hydrogen sulfide

Microbial Fermentation

  • Examples include milk fermentation (yogurt, cheese), cereal grain fermentation (beer), and other food products.

Milk Fermentation

  • Add lactic acid bacteria, 20°C, pH 4.6; protein ppt → uniform curd; Add enzyme (rennet), casein → gel; Combination of bacteria + rennet = softer coagulate.

Yogurt

  • Whole milk; heat at 85°C, 30 min, cool to 43°C; Inoculate Lactobacillus delbrueckii + Streptococcus thermophilus (1:1); Incubate at 43.3°C, 6 hrs; pH 4.2; growth stops.

Cereal Grain Fermentation (Beer)

  • Barley, rice, corn as raw materials; Germinated barley – activate enzyme; Cooked to form a mash and wort (38-77°C); Hops added; Inoculated with yeast (Saccharomyces cerevisiae ); pH drops to 4.0 at 10°C in 9 days; Products: ethanol and carbon dioxide.

Take-Home Messages

  • Microorganisms are found in various environments.
  • Factors like nutrient availability and temperature affect microbial growth.
  • Microorganisms can be beneficial (fermentation) or detrimental (spoilage).

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Description

Explore the fascinating world of food microbiology and the role of microorganisms in our food systems. This quiz covers key concepts such as microbial growth factors, sources of microorganisms, food spoilage, and the science behind fermented foods. Test your knowledge and dive deeper into how these tiny entities impact our food safety and preservation methods.

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