Introduction

Question 1

In respect too micro-organisms and viruses, what are the main causes of food-borne illness?

Answer 1

80% of causes are unknown

However the top 4 known causes are: Norovirus, Salmonella, Campylobacter and listeria Monocytogenes.

Question 2

In respect to micro-organisms and viruses, what cause(s) the most food borne illness by quantity?

Answer 2

Norovirus is responsible for the most illnesses

Question 3

In respect to micro-organisms and viruses, what cause(s) the most hospitalisations through food-borne illness?

Answer 3

Salmonella spp. and Capylobacter spp.

Question 4

In respect to micro-organisms and viruses, what cause(s) the most deaths through food-borne illness?

Answer 4

Salmonella spp. and Listeria monocytogenes

Question 5

Why is it important to study food microbiology?

Answer 5

Food is jam packed full of microorganisms, we need to study and evaluate these for the following reasons:

1 - Potential food-borne illnesses causing public health concerns.
2- Evaluate spoilage potential in products and how to prevent it
3- Fortify foods by using beneficial micro-organisms, such as kombucha and kimchi (fermentation)
4- We can also use food microbiology for the development of new food products.

Question 6

Where can natural flora be found in food materials?

Answer 6

Flora can be found in any plant-based food material naturally.
Animals can deliver this flora in many ways, the intestine has a high concentration of this flora and as a result faecal contamination of eggs, milk and meat is very possible. The animals can also be a asymptomatic carrier of pathogens.

Question 7

Where/How can flora be introduced by processing and handling?

Answer 7

Humans are a good source of contamination so any unsterilised physical contact (Chefs) can result in this contamination. Humans have a notable concentration of staphylococcus in their nose and skin.

Flora can be introduced in the many steps of processing, from harvesting, transport, processing, storage. Cross contamination is a big concern in these parts.

Question 8

What are some environmental factors that can introduce this flora?

Answer 8

Soil: this is a viable medium for many moulds, yeast and bacteria and can be contaminated with faecal matter.
Water: Water has a big relationship of contamination with soil especially in agriculture. contamination can occur from irrigation, animals, and sewage contamination. This can be introduced to food in the field or even by washing.
Atmosphere: Dust and water droplets and aerosols can all be sources of contamination. Gram positive bacteria, fungi, spores are able to be transmitted like this.

Question 9

What are the four phases that occur in microbial growth?

Answer 9

1) Lag
2) Exponential growth
3) Stationary
4) Death

Question 10

Place holder (picture) - exponential phase question

Answer 10

Place holder(picture) - exponential phase answer

Question 11

Place holder (picture) - doubling time question

Answer 11

Place holder(picture) - doubling time answer

Question 12

Regarding the four phases of growth, what methods can we employ against microbial growth?

Answer 12

We can extend the ‘Lag’ phase
We can reduce the Growth rate
We can inhibit the microbes
We can inactivate the microbes

Question 13

What category of factors can affect microbial growth?

Answer 13

Intrinsic factors: Physico-chemical properties of the food itself.
Extrinsic factors: Environmental such as storage environment.
Implicit factors: the properties and interactions of the micro-organisms themselves when in the food material.

Question 14

What intrinsic factors can affect microbial growth?

Answer 14

• pH.
• Water activity.
• Oxidation-reduction potential.
• Naturally present compounds that affect growth such as nutrient or even anti-microbial compounds.
• Compounds added as preservatives.

Question 15

What is the fastest growth ranges for Bacteria, yeasts and filamentous fungi?

Answer 15

Bacteria has a range of 6.0 - 8.0 pH, with an exception to LAB and Acetic acid bacteria which prefer 5.0 -6.0
Yeasts have a range 4.5 - 6.0
Filamentous fungi has a range of 3.5 - 4.0.

Question 16

At what pH limit do most foodborne pathogens cease to grow?

Answer 16

<4.4pH

Question 17

Why are weak organic acids better at dissociating cells?

Answer 17

Cell membranes are typically impermeable to strong acids because when the dissociate they create a Hydrogen ion [H+], cell membranes are typically non-permeable to these hydrogen ions (strong acid). Where as a weaker organic acid can permeate through the shell, such as an carboxylic acid [-COOH]

Question 18

What is water activity?

Answer 18

It is the measure of available water in a system, for example the water activity of pure water = 1.
To measure water availability in a complex system we can measure the vapour pressure of water in food and compare it too pure water at the same temperature.

Question 19

In food what is considered a high water activity, and what is considered intermediate?

Answer 19

High water activity = 0.98 and higher

Intermediate = 0.70 - 0.85

Question 20

What is the minimum requirement of water activity for most bacteria to grow?

Answer 20

0.91 -0.88

Question 21

What is the minimum requirement of water activity for most yeast to grow?

Answer 21

0.88

Question 22

What is the minimum requirement of water activity for regular moulds to grow?

Answer 22

0.80

Question 23

What effect does water activity have on toxin producers like moulds and staphylococci?

Answer 23

They have a minimal viable water activity that allows them to grow, but that may not allow them to produce toxins.
Staphylococci requires a water activity of 0.86, however cannot produce its toxin unless the water activity is 0.93.

Question 24

What is redox potential?

Answer 24

It is a measure of how easily a substrate reduces or oxidises,
If a substrate gains electrons it becomes reduced.
If a substrate looses electrons it becomes oxidised.