Lecture 6: Temperature and Gaseous Environments

Question 1

What pathogen would be the largest concern for lunch meat kept in the refrigerator? How would only keeping the meat for a short period of time decrease the risk associated with the lunch meat?

Answer 1

Listeria monocytogenes. It is a psychrotroph so while it can grow in lunch meat it grows at an extremely slow rate. Keeping the lunch meat for a shorter amount of time wouldn’t allow much growth to occur.

Question 2

How does the Z-value of a microorganism differ from D-value?

Answer 2

See slides 7-13 in the “Temperature” lecture.

Question 3

What is the difference between Controlled Atmosphere storage (CA) and Modified Atmosphere storage (MA)?

Answer 3

See slides 2 and 3 in the “Gaseous Environments” lecture.

Question 4

Where is Modified Atmosphere storage (MA) most commonly seen? Why is it commonly seen here?

Answer 4

See slides 3-6 in the “Gaseous Environments” lecture for where it is seen. It is seen there because the gases effect not only the types of microbes able to grow but can also enhance the color of the product.

Question 5

What non-microbial issue does flushing packaging with only CO2 cause?

Answer 5

Acidifying the food. See slide 6 from the “Gaseous Environments” lecture for the specific acid.

Question 6

What category of foods are often stored under high oxygen conditions during MAP? Why is this?

Answer 6

Fresh, red meats. Oxygen is used to maintain the red color of the meat. (but what is the mechanism by which it does this?)

Question 7

For MAP, three different gasses are commonly used. What is the general rationale for using high and low oxygen? High and “low” carbon dioxide? What is the point of adding nitrogen? (note “low” is in quotes, as this low level is still higher than atmospheric levels)

Answer 7

Revisit slide 4 for the answers

Question 8

Meat stored under atmospheric gas concentrations are most susceptible to spoilage by what broad category of microorganisms? If MAP is used to increase carbon dioxide levels, how does the ecology of this product change?

Answer 8

Most meats will be spoiled first by aerobic psychrotrophs such as Pseudomonads. Increasing the carbon dioxide decreases growth of these, while allowing for growth of spoilage lactic acid bacteria