Microbes in Food

Question 1

What type of organism are bacteria

Answer 1

Prokaryotic

Question 2

What type of organism are yeast and moulds

Answer 2

Eukaryotic

Question 3

What is the difference between eukaryotic and prokaryotic cells

Answer 3

Prokaryotic have no nucleus and are smaller than eukaryotic

Question 4

What is the difference between yeast and moulds

Answer 4

Yeasts are unicellular, moulds are multicellular

Question 5

How do moulds grow

Answer 5

Asexually by increasing length, diameter and number of hyphae/hyphal branches

Question 6

How do you measure overall mould growth

Answer 6

Plot of colony diameter vs time

Question 7

How do yeasts grow

Answer 7

Multiply by budding (bud protrudes from mother cell and becomes a daughter cell) to form two full sized yeasts or a stay together in a chain

Question 8

What bacteria is used to make yogurt

Answer 8

Lactic acid bacteria (LAB)

Question 9

What is the function of LAB in making yogurt

Answer 9

Converts lactose into lactic acid which decreases pH to prevent pathogen growth, reduces the sugar content and helps develop the yogurt characteristics

Question 10

How does the action of LAB result in the development of different yoghurt characteristics

Answer 10

-Acidification of the milk causes precipitation and coagulation of proteins (thickening/gel formation) to form firm gels in set yogurt or weak gels in stirred yogurt
- beneficial probiotic strains
- acidic flavours and other quality markers

Question 11

Which bacteria is involved in cheese fermentation

Answer 11

LAB

Question 12

How does LAB produce cheese

Answer 12

Converts lactose to lactic acid therefore protein coagulation occurs to form a cheese curd

Question 13

What breaks down the protein in cheese during ripening

Answer 13

Exogenous enzymes

Question 14

Which yeast is associated with bread making

Answer 14

Saccharomyces cerevisiae

Question 15

Which type of organisms are sourdough associated with

Answer 15

LAB and wild yeast strains

Question 16

What is the function of s.cerevisiae in bread making

Answer 16

Metabolises sugars, producing CO2 and ethanol, more CO2 increases the volume of the dough (leavening) and produces alcohols and esters which provide crumb character

Question 17

Which yeast strain is associated with brewing ales

Answer 17

s.cerevisiae

Question 18

Which yeast is associated with brewing lagers

Answer 18

s.pastorianus

Question 19

What is the role of yeast in brewing

Answer 19

Metabolises maltose to produce ethanol and CO2 for carbonation, alcohol and flavour generation

Question 20

How are pickles fermented

Answer 20

Using a range of LAB found naturally on the produce (not added as a starter) that can survive the anaerobic, high salt brining conditions

Question 21

What is the function of the LAB in pickle fermentation

Answer 21

Metabolises sugars to lactic acid to suppress pathogen growth and generate flavour and quality

Question 22

What organisms are involved in olive fermentation

Answer 22

LAB alone or LAB and yeasts

Question 23

What is the function of the LAB and yeasts in olive fermentation

Answer 23

Production of acids lowers pH and prevents pathogen growth
Degrades oleuropein in olives (bitter phenolic antioxidant in olives)
Develops flavour and extends shelf life

Question 24

At what pH are pathogens unable to grow

Answer 24

4.5

Question 25

What is a microbial pathogen

Answer 25

A micro organism that has the potential to cause disease e.g. salmonella

Question 26

What are spoilage organisms

Answer 26

Organisms that cause food to be undesirable or unacceptable for consumption

Question 27

What is food spoilage

Answer 27

Change in food characteristics leading to loss of acceptability/ quality

Question 28

What are the losses as a result of food spoilage

Answer 28

- food availability for consumers - income

Question 29

What are the two types of food spoilage

Answer 29

Microbial and non-microbial

Question 30

What are the 3 classes of non microbial food spoilage

Answer 30

Physical, chemical and infestation

Question 31

What are the two classes of microbial food spoilage

Answer 31

Direct microbial growth and effect of microbial enzymes

Question 32

When is spoilage usually detected

Answer 32

At 10^6- 10^8 cells per g/ml/cm etc

Question 33

What is the order of growth rate fastest to slowest between moulds, yeasts and bacteria

Answer 33

Bacteria, yeasts, moulds

Question 34

What are the. 3 main types of spoilage organisms

Answer 34

Moulds, yeast and bacteria

Question 35

How can mould spoilage be reduced and why is this effective

Answer 35

Improved anaerobic packing as moulds are only major problem in foods stored for a long time in conditions unfavourable to yeast and bacteria

Question 36

Which type of food spoilage organism is most common

Answer 36

Bacteria

Question 37

What is microbial growth succession

Answer 37

The conditions dictate which species of microbe multiply rapidly and predominate, the predominant organisms produce metabolites and alter the food environment enabling another species to grow, and over time the predominant type can change

Question 38

What do refrigeration temperatures prevent

Answer 38

Growth of all thermophilic and many mesophilic organisms

Question 39

What is the optimum temperature for thermophiles

Answer 39

45 degrees celsius

Question 40

Which organisms are more temperature versatile and important in spoilage of chilled foods

Answer 40

Psychrotrophs

Question 41

How does initials microbial load affect shelf life

Answer 41

Smaller load (e.g. cleaning before storage of food product) increases shelf life

Question 42

What does the total microbial population depend on

Answer 42

Degree of hygiene, contamination and processing and preservation methods used

Question 43

What does contamination of food depend on

Answer 43

The presence of a source of microorganisms and their entrance to the food due to poor sanitation during handling/ processing