Lecture 9: High and Low Temperatures Flashcards
Why doesn’t UHT milk sell well in the US? Does it have to do with it’s microbial safety or it’s taste?
It tastes different. US consumers don’t like the cooked taste. The milk is perfectly safe.
What are the 2 stages of crystal formation in freezing?
See slide 6. Can you describe what is going on with “nucleation” and “crystal growth”?
How do rapid and slow freezing impact crystal formation?
Rapid freezing causes more nucleation and tiny crystals. Slow freezing causes more growth and larger crystals. This is summarized on slide 6.
What are some ways that thawing of a food product (the example used was vegetables) can promote bacterial growth?
See slide 10, focusing on how the tissue will break down, both releasing nutrients and giving microorganisms access to the inside of tissues.
How does B. cereus cause sweet curdling in milk?
A proteolytic enzyme cleaves casein proteins. These chewed up proteins coagulate and curdle the milk. No acid is involved.
What process is the F value used in?
See slide 18.
What does “hermetically sealed” mean?
Air tight
Can you describe in words, what happens to the flow of water across a bacterial membrane, as the freezing process progresses?
This is what slide 8 was all about; you should also be able to describe from this process why slow freezing is more detrimental to bacteria than fast freezing.
Can you describe in words, what cryoprotectants are and how do they protect microbial cells during the freezing process?
Revisit the video from slide 9 if not. In essence, the cryoprotectants change the temperature at which the liquid outside the cell freezes.
What two intrinsic/extrinsic factors are altered when a food is frozen?
Temperature and water activity; see slide 11 if you don’t remember why water activity is affected!
What are the two main goals of pasteurization?
Eliminate pathogens, and reduce spoilage organisms.
What are the three types of pasteurization, and the time/temperatures used?
LTLT; also called vat pasteurization, 63 C for 30 minutes
HTST; 72 C for 15 seconds; most common heat treatment given to milk in the US;
UHT; 140-150 C for 2-3 seconds
What are some of the advantages of aseptic packaging?
No need to maintain a cold chain, increased destruction of microorganisms compared to pasteurization, reduced destruction of certain vitamins compared to pasteurization, less energy needed to maintain quality of food during shipping.
The time/temperatures used for pasteurization are designed to target what category of microorganisms?
Pathogens. Remember that these standards are designed to protect public health, so these processes do not need to eliminate spoilage organisms that are only a food quality concern.
What are two issues concerning Clostridium tyrobutyricum in milk?
Revisit slide 16 for a description of this organism; it’s the cheese industry that cares the most about this organism; the answer has to do with two products formed during metabolism: CO2 and butyrate.
