Bacterial Groups in Food Science

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Questions and Answers

What is the main characteristic that distinguishes pathogens from spoilage microorganisms?

Pathogens do not spoil food. (correct)

Spoilers cause foodborne diseases.

Pathogens cause undesirable odors.

Spoilers are harmful to human health.

What is one of the roles of indicators in food microbiology?

To prevent food preparation contamination.

To indicate safety and quality of foods. (correct)

To enhance flavor in food products.

To accelerate microbial spoilage.

Which of the following is NOT a primary source of microorganisms found in foods?

Water

Animal hides

Vacuum sealed packaging (correct)

Soil

In microbial taxonomy, which level indicates the specific type of organism?

Species Signup and view all the answers

What percentage of DNA homology is required to consider two strains the same in nucleic acid hybridization?

90% Signup and view all the answers

Which of the following best describes the term 'binomial nomenclature'?

A two-part name system for categorizing species. Signup and view all the answers

Which of the following best describes spoilage microorganisms?

They cause visible growth and undesirable changes in food. Signup and view all the answers

What comparison is typically made in the microbial taxonomy of strains?

Examining nucleotide base sequences of 16S rRNA. Signup and view all the answers

What is a positive effect of lactic acid bacteria (LAB) in foods?

Used as starter cultures for fermented foods Signup and view all the answers

Which group of bacteria is known for fermenting carbohydrates into butyric acid?

Butyric acid bacteria Signup and view all the answers

What is the primary outcome of the fermentation process performed by acetic acid bacteria?

Production of acetic acid Signup and view all the answers

Which bacteria are known for causing undesirable odors due to protein hydrolysis?

Proteolytic bacteria Signup and view all the answers

What do lipolytic bacteria primarily hydrolyze?

Complex triglycerides Signup and view all the answers

Which bacteria are commonly involved in the Swiss cheese production process?

Propionibacterium Signup and view all the answers

What kind of bacteria are capable of hydrolyzing pectin?

Pectolytic bacteria Signup and view all the answers

Which of the following is a characteristic of saccharolytic bacteria?

They convert disaccharides and polysaccharides into monosaccharides Signup and view all the answers

Which type of bacteria is characterized by its ability to grow at low pH levels?

Aciduric bacteria Signup and view all the answers

Which bacterial group is known to produce gas during the metabolism of nutrients?

Gas-producing bacteria Signup and view all the answers

What characteristic distinguishes halotolerant bacteria?

Survive in high salt concentrations Signup and view all the answers

What is a defining feature of thermophilic bacteria?

Thrive at temperatures above 41°C Signup and view all the answers

Which type of bacteria cannot grow in the presence of oxygen?

Anaerobes Signup and view all the answers

What does 'spp.' represent in bacterial nomenclature?

A shorthand for multiple species within a genus Signup and view all the answers

Which of the following is a characteristic of Homofermentative lactic acid bacteria?

Ferments sugar and produces primarily lactic acid Signup and view all the answers

What is the correct interpretation of the term 'biovar'?

A subspecies that exhibits a specific biochemical activity Signup and view all the answers

Which of the following correctly describes molds?

Multicellular and filamentous Signup and view all the answers

How are viruses commonly identified according to the content?

Through the diseases they cause or their numerical designations Signup and view all the answers

Which of the following molds is primarily used in blue cheese production?

Penicillium roqueforti Signup and view all the answers

What is the main product of sugar fermentation by Heterofermentative LAB?

Lactic acid and other byproducts Signup and view all the answers

Which taxonomic level is indicated by the term 'subsp.'?

Subspecies classification Signup and view all the answers

What type of spoilage does Pichia cause in food products?

Formation of pellicles Signup and view all the answers

What does the term 'serovar' refer to?

A variant distinguished by its antigenic properties Signup and view all the answers

Which yeast is known for causing rancidity in butter and dairy products?

Candida Signup and view all the answers

Which of the following yeasts can ferment lactose?

Torulopsis versatilis Signup and view all the answers

What is a typical characteristic of Rhodotorula yeasts?

They form pink to red pigments. Signup and view all the answers

What type of food spoilage is primarily caused by Saccharomyces cerevisiae?

Leavening of bread Signup and view all the answers

Which of the following describes Torulopsis yeast?

Is spherical to oval in shape Signup and view all the answers

Which type of mold is recognized for producing toxins such as citrinin?

Penicillium Signup and view all the answers

Study Notes

Important Bacterial Groups in Foods

Lactic Acid Bacteria (LAB): Ferment sugars; homofermentative LAB produce primarily lactic acid (e.g., Pediococcus, Streptococcus, Lactococcus, some Lactobacillus species); heterofermentative LAB produce lactic acid and other products (e.g., ethanol, acetic acid, CO2) (e.g., Leuconostoc, some Lactobacillus species). Can have positive (starter cultures in fermented foods) or negative (food spoilage, slime, sourness, turbidity) effects.
Butyric Acid Bacteria: Ferment carbohydrates into butyric acid, CO2, and H2 (e.g., Clostridium butyricum); cause food spoilage.
Propionic Acid Bacteria: Mostly Propionibacterium; ferment carbohydrates into propionic acid; used in Swiss cheese production; found in raw milk, cheese, and dairy products.
Acetic Acid Bacteria: Oxidize ethanol to produce acetic acid; Acetobacter aceti is used in vinegar production.
Proteolytic Bacteria: Hydrolyze proteins using extracellular proteinases; cause food spoilage with undesirable odors (amines, H2S, indole compounds, mercaptans, fatty acids); examples include Clostridium, Bacillus, and Pseudomonas.
Saccharolytic Bacteria: Hydrolyze disaccharides and polysaccharides into monosaccharides (e.g., Bacillus, Clostridium, Aeromonas, Pseudomonas, Enterobacter).
Lipolytic Bacteria: Hydrolyze triglycerides into fatty acids and glycerol; cause rancid smells (e.g., Clostridium, Pseudomonas, Staphylococcus, Micrococcus).
Pectolytic Bacteria: Hydrolyze pectin using pectinase (e.g., Erwinia carotovora).
Coliforms: Gram-negative, non-spore-forming bacteria; ferment lactose to acid and gas in 48 hours at 35-37°C; not all are fecal; do not survive pasteurization; indicate GMP adherence in processed foods.
Thermophilic Bacteria: Grow well above 41°C (e.g., Campylobacter jejuni, some Streptococcus, Lactobacillus, Bacillus stearothermophilus).
Psychrotrophic Bacteria: Grow at refrigeration temperatures (e.g., Listeria monocytogenes, Pseudomonas, Yersinia enterocolitica, Aeromonas).
Halophilic Bacteria: Tolerate high salt concentrations (≥10%) (e.g., Vibrio parahaemolyticus, Staphylococcus, Bacillus).
Aciduric Bacteria: Survive low pH (<4.0) (e.g., Lactobacillus, Pediococcus, Lactococcus, Streptococcus).
Gas-Producing Bacteria: Produce gases (CO2, H2, H2S) during metabolism (e.g., Propionibacterium, Escherichia, Enterobacter, Clostridium).
Slime-Producing Bacteria: Produce slime from polysaccharide synthesis (e.g., Xanthomonas, Leuconostoc, Klebsiella).
Aerobes: Require oxygen for growth (e.g., Pseudomonas, Bacillus, Flavobacterium).
Anaerobes: Cannot grow in the presence of oxygen (e.g., Clostridium).

Microorganisms and Food

Pathogens: Cause foodborne illnesses; do not necessarily spoil food.
Spoilers: Cause undesirable changes in food (visible growth, slime, gas, acid, odor, color changes); do not necessarily cause illness.
Beneficial Microorganisms: Starters (e.g., Acetobacter aceti for vinegar) and probiotics; indicators of food safety and quality (e.g., coliforms).

Microbial Taxonomy and Nomenclature

Taxonomy ranks: Kingdom, Division, Class, Order, Family, Genus, Species. Above family ranks are less used in food microbiology.
Characteristics used in microbial taxonomy: base composition (G+C content of DNA), nucleotide sequence (16S rRNA), and nucleic acid hybridization.
Binomial nomenclature: genus and species names (italicized, genus capitalized). Subspecies use trinomial epithets. Other designations include serovar, biovar, and phagovar to differentiate strains. "spp." denotes multiple species in a genus.

Important Molds in Foods

Penicillium: Blue to blue-green colors on foods; some species produce toxins (e.g., citrinin); P. roqueforti is used in blue cheese production.

Important Yeasts in Foods

Saccharomyces: Round, oval, or elongated cells; S. cerevisiae is used in baking and alcoholic fermentation; also causes food spoilage.
Pichia: Oval to cylindrical cells; unable to ferment or assimilate lactose; forms pellicles; used in some oriental food fermentations.
Rhodotorula: Pigment-forming (pink to red); causes food discoloration (e.g., R. glutinis, R. mucilaginosa).
Torulopsis: Spherical to oval cells; spoils fruit juice concentrates, acid foods, and milk; some ferment lactose (e.g., T. versatilis).
Candida: Spoils high-acid, high-salt, and high-sugar foods; forms pellicles; can cause rancidity in dairy products.

Primary Sources of Food Microorganisms

Soil, water, plants, food utensils, animal feeds, animal hides, animal feces, air, dust, food handlers, and food ingredients.

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Description

Test your knowledge on important bacterial groups involved in food production and spoilage. This quiz covers topics such as Lactic Acid Bacteria, Butyric Acid Bacteria, and the roles of various bacteria in food fermentation processes. Assess your understanding of how these microorganisms impact food quality and safety.