Lecture 5

Question 1

Psychrotrophic microorganisms

Answer 1

Food packaging and refrigeration

• convenience, preserve freshness, increase shelf life
• Vacuum packaging and modified atmosphere packaging
• Ideal storage: Vacuum Packaged/MA treated (no oxygen) and chilled (<5 degrees)
• Expected shelf life 20 - 60 days

Question 2

What is microbial food spoilage?

Answer 2

Spoilage as a consequence of microbial growth in a food or of release of microbial enzymes in the food

Question 3

Microbial monitoring and modelling

Answer 3

• To predict how long - under normal storage and transport conditions - food will remain acceptable for consumption i.e.g shelf life
• To determine the current status - with respect to spoilage- of a food that has been stored for some time

Question 4

Ground beef potential E.coli

Answer 4

E. coli O157:H7

Question 5

Spoilage indicators

Answer 5

1. Sensory (S)
2. Microbiological (M)
3. Chemical (C)

Question 6

Sensory indicators

Answer 6

Use of human senses to assess colour, odour, flavour and texture.
- Panel of trained human evaluators assess products.
Advantage: Quick
Disadvantages:
- Effects may only be noticeable when spoilage is well advanced and bacterial levels are high
- sensory measures work best when combined with microbiological and/or chemical measures

Question 7

Plating technqiues to detect bacterial growth:

Answer 7

Aerobic plate count (APC) - counts for specific foods, e.g. fresh chilled meat and vacuum packed foods - 2-7 days at 10-20 degrees
Standard plate count (SPC) - mesophilic APC

Question 8

Methods for detecting food spoilage

Answer 8

Electrical impedance - rapid measure of microbial growth