LSCI 230 - Food microbiology

Type of organisms in blue cheese and Roquefort + causes ripening (spore, bacteria, or other + name of organism)

Spore: Penicillium roquefortii

Where does the blue cheese mold grow?

In the holes that were drilled in the cheese

Bacteria that causes ripening in Cheddar

Lactic acid bacteria only

Enzyme used for cheese ripening

Rennin

Bacteria used in Oka cheese

Geotrichum

In which cheese does propionbacteria produce propionic acid + acetic acid for ripening?

Swiss cheese

Bacteria used for cheese curdling

Lactic acid bacteria

What do the lactic acid bacteria do during the curdling process?

Ferment lactose and produce lactic acid to promote development of curd and whey

What protein does rennin cleave?

Casein

True or false: most use both rennin and lactic acid bacteria for cheese curdling

False: they use one or the other

What material must be removed from curd to allow it to thicken?

The whey

Benefits of adding salt to cheese curd

• Promotes extraction of water

• Inhibits growth of spoilage organisms

• Adds flavour

Protein found in milk

Casein

Two cultures of bacteria found in yogurt

Streptococcus thermophilus and lactobacillus bulgaris

At what temperature are yogurt bacteria incubated at?

42 degrees C

Casein can be denatured by rennin or by the ____ produced by Lactobacillus bulgaris

acid

True or false: raw milk already contains lactic acid

True, it’s usually pasteurized afterwards though to remove potential pathogens

Lactic acid bacteria are Gram (+/ -), (obligate anaerobes/aerotolerant anaerobes) and shaped as rods or cocci

• +

• aerotolerant anaerobes

Yield of homofermentative fermentation

Lactic acid

Yield of heterofermentative fermentation

Lactic acid AND flavorful compounds

How does lactic acid reduce food spoilage and improve storage qualities?

a) degrades pathogens

b) ferments lactose

c) lactic acid reduces pH

c)

Name 2 types of yeast and mold strains

• Saccharomyces

• Aspergillus

The 2 main microorganisms involved in fermenting food

• Lactic acid bacteria

• Yeasts

Types of organisms found in Camembert/Brie for ripening

• Penicillium (mold)

• Brevibacterium (bacteria)

Where are the microorganisms in brie found?

a) bottom

b) inside

c) on the sides

d) surface

d)

True or false, the ripening process in brie usually takes longer than blue cheese?

False: brie = 1-5 months vs blue cheese 3-6 months

Enzyme secreted by microorganisms in brie, responsible for softening the cheese

Proteases

Difference between making white whine and red whine

Red whine keeps the red grape’s skin while white whine removes all of the grape’s skin and only extracts the juice

Compound used to kill wild yeasts in wine

Metabisulfite (Na₂S₂O₅)

2 disadvantages of using wild yeast

• Uncontrollable —> we won’t necessarily get the results we want

• Can’t tolerate too much alcohol (10% give or take)

Sugar in sweet wine is (all/mostly) fermented and (fully/mostly) fermented in dry wine

• Mostly (some left after fermentation)

• Fully

Name 2 types of lab grown yeasts used for wine making

• S. cerevisiae

• S. ellipsoideus

Name 2 advantages of lab grown yeast

• Resistant to metabisulfite

• Tolerates 12-14% alcohol content

1. Grains of barley germinate and produce ____

2. This step is called: a) Malt, b) Malting, c) Mashing, d) WORT

• Amylase

• b)

Barley grains are dried and then crushed during

a) Malt

b) Malting

c) Mashing

d) WORT

a)

After the malt is soaked in warm water for a few hours, the amylase will degrade starch into fermentable sugars (glucose/maltose) during which step?

a) Malt

b) Mashing

c) Wort

d) Malting

b)

During which step does filtering take place?

a) Malt

b) Mashing

c) Wort

d) Malting

c)

Plant added to wort before it is boiled. Contains antimicrobial properties

Hops

What organisms do hops inhibit?

Lactic acid bacteria

When is yeast added to the beer?

a) after the Wort cools down

b) Before malting

c) Before mashing

d) at the very beginning of the process

a)

Yeast used in lager beer (6-12°C)

Saccharomyces carlsbergensis

Yeast used in ale (carried by CO2 during fermentation, 14-23°C)

Saccharomyces cerevisiae

What processes are used in beer polishing (name at least 2)

Filtration, carbonation, pasteurization

What is special about yeasts in light beers?

They are genetically manipulated to use all sugars in the wort

What isn’t added while making distilled alcoholic beverages?

a) Water

b) Hops

c) Lab grown yeast

b)

True or false: wort isn’t boiled in whiskies + lactic acid bacteria is added

True

True or false: the process of making vinegar involves fermentation

False

Bacteria that oxidize ethanol in vinegar

Acetobacter (acetic acid bacteria)

Acetobacter are:

a) Anaerobes

b) Anaerobe aerotolerant

c) Facultative anaerobes

d) Strict aerobes

d)

Complete the formula: ____ —> ____ —> Acetic acid

• Ethanol

• Acetaldehyde

In absence of ethanol, what compounds will acetic acid oxidize?

CO2 and H2O

True or false: More than 10% of food in North America is spoilt and unsuitable for consumption

True

Name some factors affecting spoilage

• Types of microorganisms involved

• Extent of growth of microorganisms

• Temperature

• Availability of oxygen

• pH

• Moisture content of food

• Chemical composition and physical state

• Surfaces vs insides, grinding distributes the surface contaminant

True or false: spoilt food may be safe to eat

True

True or false: microorganisms thrive in food with high water activity

False

What is a_w?

Availability of water to microorganisms

SOlutes dissolved in water (increase/reduce) availability of water to microorganisms

Reduce

True or false: fresh food has an aw higher than 0.95

True

True or false: most spoilage microorganisms can grow to an aw as low as 0.8

False

True or false: molds can grow in food with a_w < 0.9, unlike bacteria and yeasts

True

Specialized organism that grows at aw < 0.8, lives in dry environment with low osmolarity

Xerophiles

Specialized organism that grows at aw < 0.8, lives in environment with and high sugar and with high osmolarity

Osmophiles

Specialized organism that grows at aw < 0.8, lives in environment with high salinity

Halophiles

Bacterial strain that can grow at aw > 0.83

Staphylococcus aureus

Bacteria that can grow at low T° are:

a) Cryophiles

b) Thermophiles

c) Psychrotrophs

c)

Cold food should be kept below ___ °C

4.5

3 bacteria that can grow at 4.5°C

• Yersinia enterocolitica

• Listeria monocytogenes

• Clostridium botulinum

Hot foods should be kept above ___ (steam table).

60°C

True or false, most bacteria can grow at pH 3.8

False, most grow at pH = 5

Bacteria that thrives at pH 4

Lactic acid bacteria

Molds and yeasts can grow at:

a) pH = 5

b) pH = 7

c) pH = 4

d) pH =/< 4

d)

True or false: most spoilage organisms are found in acidic food at 4.5 pH and under

False, has to be under pH of 4.5

True or false: molds require oxygen

True

Types of foods that microorganisms can use are determined by what?

Enzymes needed to degrade nutrients in the food

Enzymes required in meat + type of organisms that can colonize it

• Proteases and lipases

• Bacteria and molds

Vegetables are high in ___, ___ and _____

• Cellulose

• Starch

• Pectin

Fruits are high in ___ and ____

• Sugars

• Pectin

Enzymes required to degrade nutrients in fruits/vegetables (3)

• Saccharase

• Pectinase

• Cellulase

What organisms can thrive on vegetables/fruits

a) bacteria and mold

b) mold and yeasts

c) bacteria, mold and yeasts

d) mold

c)

Toxins cause this. Symptoms appear quickly:

a) food poisoning

b) food infection

a)

Organisms live and multiply in the host + symptoms may take longer to develop, and illness could be due to tissue invasion, production of toxins or both

a) food poisoning

b) food infection

b)

What is NOT a cause of food-borne disease?

a) Inadequate reheating

b) Presence of yeast in beer

c) Cheese from unsafe source

d) Lapse of 12 h or more between preparation and consumption

b)

Bacteria that produces AB-type neurotoxin

Clostridium botulinum

Difference between infant botulism and adult botulism

Infant botulism: bacteria will grow in the host

What protects Clostridium botulinum from heat?

Endospores

Botulism contains (aerobic/anaerobic) bacteria

ANaerobic

True or false: heating food will kill the toxin but not the organisms

True, especially if the organism forms endospores

Most common form of food poisoning

Staphylococcal food poisoning

Type of toxin that causes staphylococcal food poisoning

Enterotoxin (SE)

What eneterotoxigenic bacterial strain produces SE?

Staphylococcus aureus

SE enterotoxin is heat (stable/labile)

Stable

S. aureus colonizes the skin and ____ of 20-30% of humans

Upper respiratory tract

True or false, S. aureus is halotolerant

True

Salmonella enterica: type of transmission route used

Zoonose (animal to human)

WHere does Salmonella grow in humans?

Intestinal tract

True or false: salmonella uses T3SS and T4SS to propagate

True

What kills Salmonella enterica?

Cooking

Symptoms of Salmonella enterica are caused by invasion and destruction of ____ epithelium

Intestinal

Salmonella must multiply (before/after) food is eaten to cause an infection

Before

True or false: E. coli O157:H7 colonizes kidney

False —> the toxins infect the kidney, not the bacteria itself