Food MicroBiology Study Guide

What is the maximum allowable standard plate count (spc) for raw milk

Must not exceed 100,000 cfu/ml

State the acceptable bacterial count and coliform limit in pasteurized milk

Spc= <20,000, Coliform - < 10 cfu/ml

Define somatic cells and explain their significance in milk quality testing

White blood cells+epithelial cells from udder tissue. High counts signal mastitis in cows and poor milk quality

Differentiate between aerobic, anaerobic, and facultative anaerobic

Aerobic requires oxygen, Anaerobic doesn't require oxygen, Facultative anaerobic can grow with or without oxygen

List three intrinsic factors and explain in detail

Ph- Acidic foods resist bacteria

Water Activity (aw)-most bacteria need <0.90, molds can grow at 0.7

Buffer Capacity- Resistance to pH changes (milk and meat have higher buffer capacity)

What are zoonotic pathogens?

Pathogens that can be transmitted between animals and humans (Bacteria, Viruses, Parasites, Fungi)

State three changes that make spoiled food unacceptable for human consumption

off-odors, discolorations, slimy textures

What produces mycotoxins, and how can they enter humans?

Produced by mold, contaminated grains, nuts, and dairy

List three ancient methods of food preservation

Salting, Drying, and fermentation

Define oxidation and reduction.

oxidation: loss of electrons

reduction: gain of electrons

Define Intrinsic and List three examples

Properties of food itself that influence microbial growth. Examples pH, moisture content, biological structures

What is water activity, and why is it important

measures the amount of "free" or "available" water that microorganisms can use for growth

What is the buffer capacity of food?

resistance to pH changes

Explain the difference between aerobic and anaerobic bacteria

Aerobic needs oxygen and anaerobic doesn't

Define extrinsic factors and three examples

imposed by the environment in which the food product is present. Examples: temperature, relative humidity, and gaseous environments

What are psychrophiles?

bacteria that grow in refrigeration temperatures (0-7 °C), ex, Listeria

What are mesophiles?

bacteria that grow best between 20-45 °C; most pathogens. ex. Salmonella and e.coli

What are thermophiles?

heat-loving bacteria that grow well at <45 °C. ex. Bacillus

Explain the relationship between temperatures and relative humidity in food storage

High temp+high rh causes spoilage, low temp+controlled rh preserves food

State the two main atmospheric gases with antimicrobial properties

Ozone (O3) and Carbon Dioxide (CO2)

What do high microbial counts in food indicate

Indicate spoliage, poor handling, and possible pathogens

List three consequences of high microbial counts

Spoliage, public health hazards, and production recall

Name two fungi commonly found in meats

Penicillium spp. and Aspergillus spp.

Name two types of yeast found in meats

Candida spp and Rhodotorula spp.

Why are comminuted meats more contaminated than non-comminuted meats

Increase surface area, internal distribution, and cross-contamination

What microorganism is widely used as an indicator of food sanitation

Coliforms/ E. coli show poor sanitation

State three control measures to prevent foodborne diseases

Protective equipment (PPE), autoclave, sterilizes media with steam under pressure, water bath maintains constant temp of samples

Define cryogenic freezing

The rapid freezing technique uses liquid nitrogen or CO2

State two methods of thermal processing

Pasteurization (kills pathogens but not all microbes), Sanitization (destroys all microbes)

Describe two types of freezing methods and how each destroys microbes

Slow freezing forms large crystals, causing physical damage and leakage of cellular contents, while quick freezing forms small crystals create osmotic shock and dehydration

Provide one example of a parasite and one type of food associated with it

Toxoplasma Gondii

State three extrinsic factors affecting microbial growth

Temperature, Presence, and concentration of gases, relative humidity

Explain how food preservation inhibits spoilage microorganisms

By creating conditions that either kill them or prevent their growth and reproduction

Raw milk must not exceed ________ SPC/ml

100,000

The process of heating food to destroy pathogens without affecting quality is called _______

Pasteurization

______ is the study of microorganisms in food

Food Microbiology

____ Are foreign objects sucg as glass or stones in food

Physical Hazards

______ are produced by molds and can cause food posioning

Mycotoxins

The unit for bacterial counts is _____

Colony- Forming

_____ and ________ are gases with antimicrobial Effects

Carbon dixode and Ozone

Listeria monocytogenes is an example of a _________ Hazard

Biological

Heavy metals such as mercury in food are example of _____ Hazard

Chemical

Glass Fragments in food are an example of_________ hazards

Physical

Yogurt is produced by bacteria from genus _________

Cactobaillus

_____ are protective garments worn in microbiology labs

PPE

A _____ bath us used to maintain constant temperatures for samples

Water

_____ residues in foods are examples of chemical hazards

Pesticide

An ______ sterilizes media and instruments with steam under pressure

Autoclave

_______ Is considered the most heat-resistant non-spore forming pathogen in milk

Coxiella Burnetii

The water activity of most fresh food is above ______

0

Harmful Microorganism are also called _____ and draw a growth curve and explain each phase in detail

Pathogens

What does SPC stand for in milk microbiology testing

A. Standard Plate Count

Which is not an intrinsic factor

C. Storage temperture

Which is a biological hazard

B. Salmonella

Which equipment sterilizes culture media?

B. Autoclave

Colony counts are expressed in

B. CFU/ml

Which is a chemical hazard?

B. Mercury

Which virus commonly causes foodborne outbreaks

A.Norovirus

Which microorganism is common in poultry

A.Salmonella

Which of the following is not a physical hazard

C. Heavy metals

Which method uses heat to preserve food

C. Pasteurization

Improper fermentation of meat products may allow growth of

B. Clostridium Botulinum

The bacteria used for cheese fermentation belong to genus

B. Lactobacillus

The Optimal growth temperature for mesophiles is

B. 20-45 °C

Which preservation technique removes water

D. Both a and b ( salting and drying)

Which cheese requires aging for safety

B. raw milk cheese

No organisms grow below aw 0.60

True

Psychrotrophs can grow at refrigeration temperatures

True

Salmonella is commonly found in poultry

True

Comminuted meats are less contaminated than cuts

False

High microbial counts indicate food spoilage

True

Cryogenic Freezing uses liquid nitrogen or CO2

True

Glass fragments in food are biological hazards

False

Coxiella burnetii is the most heat-resistant pathogen in milk

True

Fermentation always makes food unsafe

False

Water Activity influences microbial growth

True

Probiotics can provide health benefits

True

Pasteurization sterilizes food completely

False

Lactic acid bacteria are important in dairy fermentation

True

Relative humidity affects microbial growth

True

Discuss the role of probiotics and fermented foods in human health. In your answer, include: a) An example of a probiotic organism, b) Examples of fermented dairy and non-dairy foods, c) Benefits and potential risks of fermented foods

Probiotics and fermented foods support a healthy gut microbiota, aiding digestion, nutrient absorption, and immune function. Probiotics are live microorganisms that provide health benefits, such as Lactobacillus acidophilus in yogurt. Fermented foods like yogurt, kefir, kimchi, and kombucha supply these beneficial microbes and enhance nutrient availability. Benefits include better digestion, vitamin production (e.g., B vitamins), and stronger immune defenses. Some people may experience temporary digestive discomfort or issues with high-histamine foods.

Case Scenario: Mr. John owns a farm where he grows fresh produce and also raises chickens. Mary regularly purchases organic chicken and fresh produce from his farm. Question: Identify and discuss the potential food safety risks that may occur: • On John's farm (during production of fresh produce and chicken rearing) • During transportation of food products, During processing and distribution, • During food preparation and handling in Mary's home. In your essay, explain how each stage contributes to possible contamination and foodborne illness, and suggest preventive measures that could reduce these risks.

In Mr. John's farm case, food safety risks exist from farm to Mary's home. On the farm, cross-contamination from chicken waste can spread pathogens like Salmonella, preventable with Good Agricultural Practices (GAPs). During transportation, improper temperatures can promote bacterial growth, requiring refrigeration. Processing and distribution risks from dirty equipment or poor hygiene are controlled with Good Manufacturing Practices (GMPs). At home, illness often comes from using the same cutting board for raw chicken and salad, preventable by keeping raw meats separate from ready-to-eat foods.

Food Safety Across the Supply Chain: Discuss how biological, chemical, and physical hazards can enter food products at different points along the supply chain (farm production, processing, transportation, retail, and home preparation). In your essay, provide specific examples of each type of hazard and propose strategies for preventing them.

Food hazards are biological, chemical, or physical and can enter the supply chain from farm to fork. Biological hazards like Salmonella or Norovirus arise from contaminated water or poor hygiene and are controlled by HACCP and proper cooking. Chemical hazards, such as pesticide or cleaning residues, are prevented through proper chemical use and rinsing. Physical hazards like glass or metal can come from machinery, mitigated by metal detectors, X-rays, and worker controls. A safe food supply requires targeted prevention at every step.

Essay Question: Foodborne Pathogens and Public Health. Foodborne pathogens remain one of the greatest challenges in food safety, affecting both developed and developing countries. Question: Write an essay discussing the major foodborne pathogens that pose risks to human health. In your answer, include: At least three examples of bacterial pathogens (e.g., Salmonella, Listeria monocytogenes, Escherichia coli 0157:H7) and the foods they are commonly associated with. At least one viral and one parasitic pathogen, including routes of transmission. The health impacts of these pathogens on consumers. Control measures that can be applied at the farm, processing, distribution, and household levels to minimize their risks.

Foodborne pathogens are a major public health concern worldwide. Key bacterial pathogens include Salmonella (raw poultry, eggs), Listeria monocytogenes (ready-to-eat meats, soft cheeses), and E. coli O157:H7 (undercooked beef, contaminated produce). Viruses like Norovirus spread via the fecal-oral route, and parasites like Toxoplasma gondii are found in undercooked meat. Illness can range from mild gastroenteritis to severe complications such as kidney failure or meningitis. Risk reduction requires measures across the supply chain: Good Agricultural Practices (GAPs) on farms, HACCP during processing, and proper handwashing and cooking at home.