Microbiology ch 30 Food

How does boiling a home-canned food immediately before serving it prevent botulism?

Botulinum toxin is denatured by heat, becoming harmless.

Why is the temperature of the canning process for acidic fruits and pickles not as high as that required for canning beans?

C. botulinum does not grow or produce toxin below pH 4.5, so it is not a danger in highly acidic foods.

What creates the air pockets in bread?

CO2, produced through fermentation by Saccharomyces cerevisiae.

Which foodborne pathogen can cause hemolytic uremic syndrome?

E. coli O157:H7

Why did CDC personnel interview people who became ill within 24 hours after party, and not only people who became ill within 2-3 hours of the party?

Not everyone who ate the contaminated food would necessarily develop illness or go to the hospital within 2-3 hours. Factors such as how much food they ate must be taken into account.

Please match the food type with the pathogen commonly associated with it.

Raw (unpasteurized) milk and cheese = Listeria monocytogenes Poultry, eggs, milk = Salmonella species Oysters = Vibrio vulnificus Rice, meat, vegetables = Bacillus cereus Low-acid canned food = Clostridium botulinum

T/F : To make fermented sausages, meat is ground and combined with a starter culture and other ingredients (including sugar, salt, and nitrite). The sugar serves as a substrate for fermentation by the microbes since there isn't enough sugar for this process in the meat itself.

TRUE

T/F: The metabolism of lactic acid bacteria differs from that of most other microorganisms that can grow aerobically in that wost organisms that grow aerobically use aerobic respiration, lactic acid bacteria only ferment.

TRUE

Which microbial groups are most likely to spoil refrigerated foods?

Thermophiles Hyperthermophiles

Why do canned tomatoes require less stringent heat treatment than canned beans?

Tomatoes are more acidic than beans; their pH inhibits bacterial growth.

What part of the body would you expect to be affected by enterotoxin?

Intestines

A fermentation process known as ______ originated as a way of preserving vegetables such as cucumbers and cabbage.

pickling

Food preservation methods such as ______ and drying have been used throughout the ages

salting

At freezing temperatures, most bacteria

stop growing, but are not dead.

The main environmental factors that affect microorganism growth include chemical inhibitors, oxygen, pH, nutrients, moisture, and ______.

temperature

Production of vinegar from alcohol is carried out by oxidation via

the acetic acid bacteria—Acetobacter and Gluconobacter species.

The tart taste of yogurt, pickles, sharp cheeses, and some sausages is due to

the production of lactic acid as a by-product of fermentation in these foods by bacteria.

The ripening process during cheese production

uses metabolic activities of other microbes to produce textural and flavor changes in the cheese over time.

Which of the following is often added to wine to inhibit growth of the natural microbial populations on grapes?

Sulfur dioxide

In the brewing process, the sugar and nutrient extract obtained by soaking germinated grain in warm water is called

wort

Most spoilage bacteria cannot grow below an aw of

0.9

What is a generally minimum pH for growth and toxin production by Clostridium botulinum and other foodborne pathogens?

4.5

Forty people attended the lunch party. Of these, 35 were interviewed by CDC personnel. The remaining 5 people were not available for the interview. What percentage of people were questioned?

87.5%

The aw of a food product reflects which of the following?

Amount of water available

Please choose the equation that illustrates the production of alcoholic beverages.

Anaerobic reaction of Yeast + Sugar = Ethanol + Carbon Dioxide

What defines the safe temperature ranges for storage of foods?

Cessation of growth at low temperatures AND cell death at high temperature.

What is a common cause of wine spoilage?

Conversion of alcohol to vinegar by acetic acid bacteria naturally occurring on grapes.

Benzoic acid is an antimicrobial chemical naturally found in which of the following foods?

Cranberries

Which of the following has the natural antimicrobial preservative benzoic acid?

Cranberries

A camper carries dried meat, whole pecans (in shells), and cranberries on a week-long hike. Match the characteristics of each food type that prevent spoilage during that time.

Cranberries = Natural antimicrobials Whole pecans= Physical barrier Dried meat = Low aw

After it was cooked, the perlo was left at room temperature overnight. On the day of the party, the food was heated for an hour at a high setting in a slow cooker. Even though the perlo was effectively heated, people who ate it still got ill. What can you conclude from this information?

Enterotoxin A is heat stable (not destroyed by heat).

T/F : E. coli cells die at temperatures below 6° C.

FALSE

Why is an orange more likely to be spoiled by fungi than by bacteria?

Fruits are naturally more acidic than bacteria can tolerate, allowing acid-resistant fungi to grow without competition.

Which group of organisms most commonly spoils breads, fruits, and dried foods?

Fungi

Select the TRUE statements regarding foodborne intoxications.

Result from ingesting living microbes growing in/on a food product. May result after improper canning of certain foods. Can be avoided by vaccination. Symptoms usually include diarrhea.

Which of the following genera is used in bread, wine, and beer production?

Saccharomyces

Which of the following cause foodborne intoxications?

Shiga-toxin producing E. coli Clostridium botulinum Campylobacter species Lactobacillus species Salmonella species

What is the name of the organism causing the illness in the people who attended the lunch party?

Staphylococcus aureus

Which of the following organisms cause foodborne intoxication?

Staphylococcus aureus

Which of the following is NOT an intrinsic factor influencing the growth of microbes in food?

Storage temperature

During the production of soy sauce, the initial several days-long step is necessary in order to

allow for production of fermentable sugars, peptides, and amino acids that the salt-tolerant microbes involved in the process can ferment to produce soy sauce.

Spoiled foods are

any foods that have undergone an undesirable change due to microbial growth.

Canned pickles require less stringent heat processing than canned beans, because pickles

are more acidic.

Storage temperature and atmosphere are both examples of ______ factors, or environmental conditions, that can affect growth of microbes in food.

extrinsic

Production of soy sauce is a lengthy process of successive microbial growth. It involves a several days-long process of breaking down soybean/wheat mixture, followed by placing the resulting liquid into an 18% NaCl solution (brine) to allow secondary ______ of the mixture by salt-tolerant microbes. This secondary step produces flavor changes in the liquid over several months.

fermentation

Lactic acid bacteria are obligate ______ that are responsible for the tart taste of yogurt, pickles, sharp cheeses, and some sausages.

fermenters

Most bacteria require an aw (water activity) above 0.90 for growth. Which of the following is likely to spoil quickest?

fresh stew - aw 0.98