Food Microbiology

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Questions and Answers

What is the main process by which microbial growth alters food?

Hydrolysis (correct)

Sublimation

Photosynthesis

Fermentation

Which type of microbial growth is primarily associated with the spoilage of foods rich in carbohydrates?

Virus

Yeast

Mold (correct)

Bacterial

Which intrinsic factor can influence microbial growth in food?

Food composition (correct)

Mechanical handling

Packaging type

Temperature of storage

What is produced during the putrefaction of proteins?

Foul-smelling amines Signup and view all the answers

Which of the following is a characteristic of ergotism caused by Claviceps purpurea?

Hallucinogenic alkaloids Signup and view all the answers

What role do extrinsic factors play in microbial growth?

They involve environmental conditions like temperature. Signup and view all the answers

How does putrefaction affect the nutritional value of food?

It decreases the nutritional value. Signup and view all the answers

What type of microbial growth predominates in foods that are high in fats?

Bacterial growth Signup and view all the answers

What is one major difference between High-Temperature-Short-Time Treatment (HTST) and Low-Temperature-Long-Time Treatment (LTLT) regarding milk?

HTST preserves more nutrients in milk compared to LTLT. Signup and view all the answers

Which process best describes how microbes contribute to food safety?

Microbes can aid in food production and preservation. Signup and view all the answers

What distinguishes food spoilage from food poisoning?

Spoilage can happen without causing illness, while poisoning causes symptoms. Signup and view all the answers

What factor influences the choice of pasteurization method for a food product?

Desired sensory characteristics and nutrient preservation. Signup and view all the answers

Which of the following statements about microbes and food is true?

Microbes can both aid in production and cause spoilage or illnesses. Signup and view all the answers

Which of the following is a key learning objective related to food microbiology?

Recognizing that microbial activity can impact both food safety and quality. Signup and view all the answers

What might be a consequence of improper pasteurization techniques?

Potential growth of harmful microorganisms. Signup and view all the answers

What does the term 'spoilage' imply in the context of food microbiology?

It involves changes that make food unpalatable but not necessarily harmful. Signup and view all the answers

What is the role of bacteriophages that target Listeria monocytogenes in food safety?

They are sprayed onto meats to eliminate pathogens before packaging. Signup and view all the answers

How does relative humidity affect microbial growth?

Higher humidity levels promote microbial growth. Signup and view all the answers

What is the primary goal of food preservation methods established by Louis Pasteur?

To eliminate or reduce spoilage and disease-causing microbes while maintaining quality. Signup and view all the answers

What temperature is refrigeration typically set to, and what is its effect on microbial growth?

5 °C; it retards but does not stop microbial growth. Signup and view all the answers

What occurs during the canning process to prevent spoilage?

Food is heated in retorts to 115 °C for 25-100 minutes. Signup and view all the answers

What is a potential cause of spoilage in canned foods?

Improper heating during canning. Signup and view all the answers

What atmospheric condition promotes microbial growth in food packaging?

High oxygen levels. Signup and view all the answers

What is the significance of different pasteurization procedures?

Shorter heating times can improve flavor but may not eliminate all microbes. Signup and view all the answers

What factor may allow for the introduction of oxygen in cans during the cooling process?

Damage to the can. Signup and view all the answers

What method is commonly used to remove microorganisms from liquids for preservation?

Filtration. Signup and view all the answers

What is the primary purpose of Bacillus subtilis (PREEMPT) in poultry?

To limit colonization of the gut by competitive exclusion Signup and view all the answers

As of 2021, what percentage of Singapore's food is imported?

Over 90% Signup and view all the answers

What is the goal of the '30 by 30' plan launched in 2019 by the Singapore Food Agency?

To build capacity to meet 30% of nutritional needs locally by 2030 Signup and view all the answers

How much funding has the Singapore Food Agency allocated for the Agri-Food Cluster Transformation Fund?

$60M Signup and view all the answers

One of the challenges faced by Singapore regarding food production is:

The need for local food production to reduce reliance on imports Signup and view all the answers

What are some components that microorganisms can provide in food production?

SCP, lipids, vitamins, and nutrients Signup and view all the answers

What impact does Vibrio infection have on aquaculture?

Can lead to significant losses in fish stock Signup and view all the answers

What is a consequence of microorganisms growing in food?

They can cause illness in humans consuming contaminated food Signup and view all the answers

What is the primary purpose of hops in the beer brewing process?

To provide flavor and assist in clarification of wort Signup and view all the answers

Which type of fermentation is used for producing bread?

Aerobic fermentation Signup and view all the answers

What is the purpose of racking in the wine-making process?

To remove sediment produced during fermentation Signup and view all the answers

What is the role of Saccharomyces cerevisiae in bread production?

It ferments sugars to produce CO2 Signup and view all the answers

How is wort treated before fermentation begins?

It is mixed with malt and water to create mash Signup and view all the answers

Which type of yeast is commonly used in ale production?

Top yeasts Signup and view all the answers

What happens to the hydrolytic enzymes during the heating of malt mash?

They are inactivated Signup and view all the answers

Which of the following microorganisms is commonly used in probiotic supplements?

Lactobacillus acidophilus Signup and view all the answers

What effect does low pH have on microbial communities in food?

It promotes the growth of yeast and mold. Signup and view all the answers

Which of the following is a characteristic of antimicrobial substances found in food?

They can have chemical structures similar to antibiotics. Signup and view all the answers

How does the presence and availability of water affect microbial growth?

Higher water activity promotes microbial growth. Signup and view all the answers

What are bacteriocins?

Antimicrobial peptides secreted by bacteria. Signup and view all the answers

Which of the following compounds is known for its antimicrobial properties?

Allicin from garlic. Signup and view all the answers

What is the primary role of polyphenols in food?

They act as natural antioxidants. Signup and view all the answers

What can the physical structure of food, such as the outer skin of fruits, do?

Slow down microbial growth by acting as a barrier. Signup and view all the answers

Which of the following factors has the least impact on food spoilage?

Marketing strategies of food production. Signup and view all the answers

What happens during the spoilage of unpasteurized milk?

Acid production precedes putrefaction. Signup and view all the answers

What is the role of cooking in relation to microbial spoilage?

Cooking alters redox potential, affecting spoilage rates. Signup and view all the answers

Study Notes

Introductory Microbiology: Lecture 9 - Food Microbiology

Food microbiology is a critical area of study impacting food safety and quality.
Pasteurization methods (HTST and LTLT) influence nutrient composition and taste.
HTST (High Temperature Short Time): 72°C for 15 seconds.
LTLT (Low Temperature Long Time): 63°C for 30 minutes.
HTST is preferred for milk due to less damage to nutrients and sensory characteristics compared to LTLT.
Microbes significantly impact food via spoilage, illnesses, and food production.
Spoilage and poisoning are separate phenomena.
Food spoilage is a continuous process with infection linked to these processes (but different microbes involved).
Visual inspection of food cannot predict poisoning.

Learning Objectives

Understand how microbes contribute to food spoilage and the factors influencing this process.
Understand how food can be a vector for transmission of pathogenic microorganisms.
Understand how microorganisms cause illnesses due to food consumption.
Learn microbes' roles in food production, preservation, and consumption.
Recognize that food spoilage is a component of both food production and potential infection.

Impact of Microbes on Food Safety and Quality

Microbes significantly impact food.
Food spoilage affects food quality.
Foodborne illnesses directly affect human health.
Microbes are essential for food production processes.

Microbial Growth and Food Spoilage

Microbial growth in food alters its appearance and quality.
Microbial growth is a predictable, successive process.
Different food types undergo different spoilage processes.
Toxin production is possible.
Microbial growth is affected by intrinsic (food-related factors) and extrinsic (environmental factors) influences.

Intrinsic Factors

Food composition (carbohydrates, proteins, fats).
Mold predominates in carbohydrate-rich foods, hydrolyzing them.
Tomatoes are particular susceptible to food degradation.
Ergotism (hallucinogenic alkaloids) is associated with Claviceps purpurea in grains.
Various chemical reactions affect foods during microbial decomposition.

Intrinsic Factors (continued)

pH (impacts microbial community composition, chemical reactions).
Water activity (lower water activity inhibits microbial growth).
Oxidation-reduction potential (altered by cooking).

Antimicrobial Substances

Coumarins (fruits, vegetables).
Lysozyme (cow's milk, eggs).
Aldehydic and phenolic compounds (herbs, spices).
Allicin (garlic).
Polyphenols (green, black teas).

Microbial Product-Based Inhibition

Bacteriocins (bactericidal proteins active against related species).
Bacteriocins can influence susceptible bacteria by:
- Disrupting proton motive forces.
- Creating pores in cell membranes.
- Disrupting protein or RNA synthesis.
Examples include nisin from Lactococcus lactis and various bacteriophages.

Extrinsic Factors

Temperature (lower temperatures retard microbial growth, higher temperatures promote growth).
Relative humidity (higher relative humidity promotes microbial growth).
Atmosphere (oxygen promotes growth).
Modified atmosphere packaging (MAP).
Use of packaging technologies like shrink wrap and vacuum atmospheres.

Controlling Food Spoilage

Modern food microbiological era started in 1857 (Louis Pasteur).
Goal of preservation methods: eliminate/reduce spoilage microbes while maintaining quality.
Specific preservation methods: heat for different time periods.
Shorter heating times result in better flavor preservation.

Removal and Reduction of Microorganisms

Removal/reduction of microbes is common in water, wine, beer, juices, and soft drinks.
Filtration is a method commonly used.
Refrigeration retards growth but doesn't eliminate all microbes.
Extended storage may lead to spoilage/bacterial/growth.
Microbes still grow below -10°C.

High Temperature Preservation (Canning)

Food heating in special containers at 115°C for 25-100 minutes.
Kills most spoilage microbes, but not necessarily all food-related microbes.

Food Handling Contamination

Contamination during food handling is a concern for safety.

Food Safety Considerations (and Questions)

Questions about the safety of specific food products (e.g. Surströmming).

Water Activity

Dehydration techniques (e.g., lyophilization) to produce freeze-dried foods can eliminate bacterial growth.
Food preservation impacts directly with reduced water and increased solute concentration.
Xerophilic organisms can tolerate reduced water levels, grow at low water activities.

Chemical-Based Preservation

GRAS (generally recognized as safe) chemical agents: Organic acids, sulfites, ethylene oxide gas, sodium nitrite—inhibiting spore formation in meats—forming nitrosamines, pH affecting effect of chemical preservative.
Salt is a common food preservative.

Table 40.3: Major Groups of Chemicals Used in Food Preservation

Provides a list of food preservatives using various examples of usage and levels.

Food Safety and Radiation Techniques

Radappertization is used for extending shelf life or sterilization of specific foods (meat, seafood, fruits, vegetables).
Killing microbes in moist foods by producing peroxides (from water) by ionizing radiation.
Electron beams are used to kill microbes, but do not penetrate foods as deeply as gamma radiation.

Food Packaging

Modified atmosphere packaging (MAP) controls microbial growth by altering gases in stored food.
Other methods include using impermeable materials and vacuum technologies.
Using polylactic acid as an alternative to plastic.

Types of Food-Borne Disease

Foodborne infections: pathogens growing in food.
Common pathogens: Noroviruses, E. coli, Campylobacter jejuni, Salmonella, Listeria monocytogenes.
Food intoxications: toxins from microbes growing in food.

Foodborne Diseases (Continued)

Breakdown in hygiene can cause transmission of pathogens.
Fecal-oral route is a major transmission pathway.
Fomites are materials that can carry infection (clothes, utensils).

Specific Foodborne Pathogens

Salmonella, E. coli O157:H7, Campylobacter, Giardiasis, Listeria, Norovirus, Staphylococcal Food Intoxication, Aflatoxin, common pathogens leading to food illness.

Food-Borne Infection

Pathogens are ingested, grow, and invade tissues.
Raw foods (e.g., sprouts, raspberries, seafood) are important sources of contamination.
Pregnant women, young, old, and immunocompromised people are at higher risk for foodborne infections.

Food-Borne Intoxication

Ingestion of toxins produced by microorganisms.
Does not require microbial growth (in food) to produce symptoms (e.g., Staphylococcus aureus toxins, botulism, C. perfringens, Bacillus cereus toxins, mycotoxins).
Various types of fungus-derived toxins: Aflatoxins, fumonisins can affect grains, nut products, corn, and fish/shellfish.

Microorganisms and Food Production

Most food production processes involve fermentation.
Major fermentations are lactic, propionic, and ethanolic fermentations.

Fermented Milks

Most fermented milk products involve lactic acid bacteria (Lactobacillus, Lactococcus, Leuconostoc, Streptococcus).
Gram-positive, aerotolerant, survive under acidic conditions.

Fermented Meat and Fish

Sausages, hams, bologna, salami are fermented meats; fish (sushi), rice, vegetables, and tuna are fermented food.
Fermented meats are prepared for human consumption.

Effects of Culture on Meat and Products

Curing agents in fermented sausages work to prevent the growth of various pathogens (e.g in raw/ready to eat ham; Semi-processed raw meats use strains of bacteria that improve longevity.

Wines and Champagnes

Enolgy (wine production; crushing grapes, separating liquid from grapes).
Treatment with sulfur dioxide fumigant.
Saccharomyces cerevisiae or S. liposideus is used for consistent wine results.

Beers and Ales

Cereal grains as fermentation sources for beers and ales.
Using Malt (germinated barley grains).
Mashing, adding hops.
Inoculation (pitching) of wort with yeast.
Top and bottom yeasts.

Production of Breads

Involves growth of yeast (Saccharomyces cerevisiae) under aerobic conditions.
Maximizing CO2 production causes bread dough to rise.
Other microbes are used in specific bread types, like sourdough.
Spoilage can occur due to Bacillus species in bread.

Major Types of Cheese and Microorganisms (Table 40.6)

Contains a list of various cheeses along with the causative microorganisms.

Cheese as an Ecosystem (page 45)

Explains different aspects of cheese production from fresh cheese to aged cheese.

Probiotics and Standardization

Probiotics are live microorganisms that benefit the host.
Specific requirements exist to confer health benefits.
Examples: Lactobacillus, Bifidobacterium.

Good and Bad Bacterial Flora

Various bacteria are present in the human gut.
Bifidobacterium, Lactobacillus, Escherichia coli (some strains), beneficial varieties.
Campylobacter jejuni, enterococci faecalis, Clostridium difficile are also present.

Summary

Microorganisms are essential for food production and are also components that can cause food-related damage or illness.
Many various food sources impact health depending on their composition and microbial growth.

Studying That Suits You

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Description

Test your knowledge on the processes of microbial growth and its impact on food. This quiz covers various aspects including intrinsic and extrinsic factors, putrefaction, and types of food spoilage. Perfect for students and enthusiasts of food science and microbiology.