Food microbiology

Question 1

Examples of Prokaryotic cells

Answer 1

bacteria cells

Question 2

What are gram positive bacteria

Answer 2

Gram-positive are purple and have a thick peptidoglycan cell wall layer above cytoplasmic membrane

Question 3

What are gram negative bacteria

Answer 3

Gram-negative are pink and have a thin peptidoglycan layer with an additional outer membrane composed of lipopolysaccharide

Question 4

Properties of gram positive bacteria

Answer 4

It is heat resistant

Question 5

Properties of gram negative bacteria

Answer 5

Gram-negative bacteria outer membrane can help it evade immune system & limit entry of antibodies & sanitizers

Question 6

Which factors can increase risk of food contamination

Answer 6

biological layers such are biofilms which are resistant to cleaning sanitizers and tough, dormant resistant structures called endospores that are resistant to heat

Question 7

What is mold able to form

Answer 7

Mold form long filaments called hyphae which further group together to form mycelium

Question 8

How are proteins spoilt

Answer 8

Proteins are hydrolyzed into peptides causing bitter taste, foul-smelling amines, ammonia or sulfur containing volatiles such as hydrogen sulfide

Question 9

How are lipids spoilt

Answer 9

Triglycerides are hydrolyzed into microbial lipase giving rise to free fatty acids causing hydrolytic rancidity

Question 10

How are carbohydrates spoilt

Answer 10

Carbohydrates when broken down can be mushy, organic acids are produced, unsightly pigments are synthesized by accumulation of too many spoilage bacteria cells or production of dextran

Question 11

What are low acid foods

Answer 11

Foods with pH higher than 4.5

Question 12

What are the differences between yeast and mold and bacteria

Answer 12

Yeast & mold can grow at temperatures, pH and water conditions that may not be feasible for bacteria. It can also produce mycotoxins. Yeast is unicellular while mold is multicellular

Question 13

What are bacteria that can tolerate higher levels of salt

Answer 13

halophiles

Question 14

What are bacteria that can tolerate higher levels of sugar

Answer 14

osmophiles

Question 15

What are strong odor attributed to

Answer 15

Enterobacter or Serratia species

Question 16

What happens in Food intoxications

Answer 16

Microorganism produce toxins that are ingested by humans

Question 17

What is Staphylococcus aureus

Answer 17

aerobic Gram-positive cocci, it is found due to unhygienic handling of food. It is heat stable

Question 18

What is Clostridium botulinum

Answer 18

anaerobic Gram-positive bacilli. It is widely distributed in soils, water & environment. It forms heat-resistant spores & is a risk for low-acid canned foods as it thrives in neutral environment

Question 19

What is Aspergillus flavus

Answer 19

It produces alfatoxins

Question 20

What is salmonella

Answer 20

Salmonella are Gram-negative facultative anaerobes & are associated with under-processed meat & feces

Question 21

What is Listeria monocytogenes

Answer 21

Gram-positive rod that is well known for being able to grow at low temperatures

Question 22

What is Escherichia coli

Answer 22

Escherichia coli is a Gram-negative bacteria that is on-pathogenic & found in feces of humans & animals

Question 23

What are Toxicoinfections

Answer 23

This happens when the pathogen grows to high numbers in the food, gets ingested, and then produces toxins in the human body

Question 24

What are Bacillus cereus & clostridium penfringens

Answer 24

Gram-positive & are found in soil.
They produce heat resistant spores but do not grow well in low temperatures

Question 25

Is processing at higher temperature for shorter periods better than lower temperatures for longer periods

Answer 25

higher temperature for shorter periods

Question 26

Best temperature to grow microorganisms

Answer 26

10℃ to 35℃

Question 27

What are the temperatures to keep hot and cold food

Answer 27

Best to keep hot food at above 60℃ & cold food below 5℃

Question 28

What are extrinsic factors

Answer 28

Factors which affect the external environment of the food

Question 29

What are intrinsic factors

Answer 29

Intrinsic factors are conditions within the food which affects the growth of microorganisms

Question 30

What is fermentation

Answer 30

Fermentation is the metabolic process that takes place during desired microbial growth resulting in evident physical & chemical changes to food materials

Question 31

What can fermentation produce

Answer 31

Organic acids, vitamins, anti microbial compounds, ammonia carbon dioxide, sugars

Question 32

What are the 2 most common lactic acid bacteria used in fermenting yoghurt

Answer 32

Lactobacillus delbrueckii subsp. Bulgaricus & Streptococcus thermophilus

Question 33

Why are 2 species used

Answer 33

Lactobacillus delbrueckii is able to grow quickly but is only able to lower the pH to about 5.5 after which the growth is inhibited by low pH. Streptococcus thermophilus grows slowly but can bring the pH down to 4.5

Question 34

What species can bring down the bacteria slowly

Answer 34

Lactobacillus plantarum, Leuconostoc spp & Pediococcus spp

Question 35

What are some examples used to produce alkaline fermented foods

Answer 35

Bacillus subtills Gram-positive ferments Natto while Rhizopus oligosporus mold ferments tempeh

Question 36

What is used in the fermentation of bread dough

Answer 36

Saccharomyces cerevisiae.

Question 37

What is alcoholic fermentation

Answer 37

sugars are converted into alcohol

Question 38

What are some examples of metabodies

Answer 38

alcohol, organic acids & other anti-microbial compounds that can inhibit growth of other microorganisms