Lecture 4: Antimicrobials and Water Activity

Question 1

What are the four kinds of antimicrobial barriers?

Answer 1

See slide 7.

Question 2

Allicin and isothiocyanates are examples of what kind of microbial inhibitor?

Answer 2

See slides 9-10.

Question 3

Improper cooling/washing of a warm cantaloupe with cold water, lowering the pressure inside and pulling microbes in, is a failure of what antimicrobial barrier?

Answer 3

Biological Structure. Think about the eggshell example from class.

Fun fact: This was a potential explanation for the Listeria monocytogenes cantaloupe outbreak of October 2011. Several other methods of contamination were also found but the above explanation was also considered.

Question 4

In what ways can eggs inhibit gram positive and gram negative bacteria?

Answer 4

See slide 11.
Example: lysozyme can digest a G+ cell wall an EDTA can chelate the outer membrane of a G- exposing the cell wall to lysozyme.

Question 5

When are microbes most vulnerable to preservatives and inhibitors?

Answer 5

When they are actively growing (log phase)

Question 6

What are some problems we face when trying to incorporate essential oils into foods as an inhibitor?

Answer 6

Reference slides 12-13.

Incorporating hydrophobic oils into hydrophilic substances. Flavor imparted my the oil may be undesirable.