Lecture 5: Wrapping up antimicrobials and water activity

Question 1

What is meant by “GRAS”?

Answer 1

Generally Recognized as Safe; go back to slide 14 from this lecture if you don’t understand what this means!

Question 2

What is nisin, pediocin, and MicroGard?

Answer 2

The first two are bacteriocins produced by Lactococcus lactis and Proionibacterium shermanii, respectively. MicroGard is the commercial name for pediocin. For additional information about it, visit this site: http://www.danisco.com/product-range/antimicrobials/microgardr/

Question 3

What is meant by “developed inhibitors”?

Answer 3

Antimicrobial compound that are produced in foods often by fermentative microorganisms. How many examples can you name?

Question 4

What are eugenol, carvacrol, thymol, and 4-hydroxy-3-methoxybenzaldehyde, and where do they come from?

Answer 4

They are all essential oils known to have antimicrobial activity, and they are commonly isolated from cloves, oregano, thyme, and vanillin

Question 5

Essential oils from cloves, cinnamon, oregano, thyme, sage, and vanillin are active against what types of microorganisms?

Answer 5

eugenol and cinnamon aldehyde = gram positive and negatives; carvacrol and thyme = gram positives and negatives with some activity against yeast and molds; sage (rosemary as well) = mainly gram positive bacteria; vanillin = molds and some gram positive bacteria

Question 6

Give an example of when natural oils are a problem in food fermentations?

Answer 6

See slide 12 of this lecture, oleuropein example

Question 7

Define and describe “water activity”

Answer 7

be able to describe the different definitions on slide 16; make sure you can describe how water activity differs from water content (see YouTube video under “Storytime” link of website if unsure).

Question 8

What are three ways of reducing the water activity of a food?

Answer 8

1) Remove water; 2) Add water-binding polymers; 3) add solutes such as salts and sugars.

Question 9

In general, how much salt or sugar is needed to decrease the water activity of a food to levels inhibitory to bacterial growth?

Answer 9

The basic answer is “a fair amount”. Remember from the lecture that the point was food needs to be really salty (perhaps 13-16% NaCl) or have lots of sugar (equivalent to ~50% sucrose) in order to reduce water activity to ~0.90-0.92 range.

Question 10

How is water activity measured?

Answer 10

See the YouTube video link from slide 19.

Question 11

What are the general water activity values of specific foods?

Answer 11

I don’t expect you to memorize the list on slide 20, but you should have a general idea of which types of foods have high activity (meats, eggs, fruits and vegetables, etc), which have a moderate level (cheeses, honey, jellies and jams), and which are so low that microbial growth is inhibited (cereal, sugar, crackers, etc)

Question 12

What water activity values in general inhibit the growth of spoilage (and most pathogenic) bacteria, spoilage yeasts, and spoilage molds?

Answer 12

See slide 21 for these values; it is important to know that bacteria typically require higher water activity than yeast, followed by molds.

Question 13

What bacteria mentioned is notorious for its ability to grow at a water activity lower than most? What water activity is this?

Answer 13

Staphylococcus aureus. The water activity needed for growth varies depending upon the strain of this bacteria, but in general 0.83-0.92 is typical.

Question 14

Besides bacterial growth, what other things can a low water activity prevent bacteria from doing?

Answer 14

Producing toxins (see examples slide 21) and spore germination (see examples slide 22)

Question 15

How are moist food, intermediate moisture food, and low moisture food typically defined?

Answer 15

Know the water activity values stated on slide 22

Question 16

What does “TCS” mean?

Answer 16

Time/temperature control for food safety; see slide 23 for the concept. Remember that this is a concept you will sometimes still see referred to as “potentially hazardous foods”

Question 17

What are the water activity and pH values that define non-TCS foods, and those requiring a product assessment?

Answer 17

You should know the tables on slides 23 and 24.

Question 18

What is meant by “hurdle effect”?

Answer 18

In nearly every food, there are multiple intrinsic and extrinsic factors controlling microbial growth. In most cases, none of these factors by themselves inhibit growth, but taken together they will.

Be able to describe a food product based upon the different hurdles it has.