Physical Methods of Food Preservation Flashcards
What are the purposes of modern food preservation methods?
- increase shelf life
2. improve safety (inactivate/prevent pathogens)
What is “inactivation” of microbes in food?
damaging/reducing population to point where it will not recover
True/False; Physical methods of food preservation are rarely used today
false: still most common food preservation method
List the physical methods of food preservation:
- High temp
- Low temp
- Decrease Aw
- Ionizing irradiation
- High pressure
- Pulsed electric field
Describe the effect on bacteria as heat is increased:
enzyme activity and growth will increase -> reach optimum temp, peaks -> even higher temp will cause rapid decline/stop (cell death)
High heat will cause ____ in most bacteria. Why?
cell death damages membranes (collapse -> lysis), ribosomes, enzymes and proteins (denatured)
Describe the effects of high heat and very low temp on bacterial membranes:
low temp: membrane “gels” -> cannot transfer efficiently -> no growth
high temp: membrane lysis -> cell death
What is an issue with heat treatment in food?
overheating will damage quality of food
What factors affect heat transfer in food?
- product type
- container material (conductance)
- container shape (surface area)
- container size
- agitation
- heating medium temperature
What is the best container shape for fast heating of food?
small, tall, narrow
Liquids will heat (faster/slower) than solids
faster
What can be done to improve heating rate of viscous fluids?
agitation/mixing -> help better distribute heat
The (greater/less) the difference in temperature between product and heating medium, the greater the heat transfer
greater
The major parameters of heating processes for food:
time
temp
The microbial population will decline following a _____ pattern during heat treatment
logarithmic
What is a survivor plot?
depicts the inactivation of the bacteria population (logarithmic curve) over time
What is D value?
Decimal reduction time: time needed at given temperature to make a 1 log reduction (kill 90% of current population)
An organism with a high D value is (resistant/not resistant) to heat
resistant (take longer treatment)
Why might heat treatment times differ for different products?
- different bacteria -> different D values
2. different initial population (higher population need longer time)
As temperature increases, D value will (increase/decrease).
decrease
D value plotted vs. temperature gives a ____ plot. This follows a ___ pattern.
thermal resistance; linear
What is the z value?
thermal resistance constant
change in temp needed to decrease D value by 90%
negative reciprocal of slope on thermal resistant plot
The higher the Z value, the more _______ the organism
thermally resistant
________ measurements are taken to determine amount of time needed to sterilize food at a given temp
Lethality is represented by: ______
thermal lethality F value (minutes)
What is the difference between D value and F value?
D value: time for 1 log reduction
F value: time to reduce population to certain level (10^1 or 0)
F value is very important to consider in the ____ industry
canning
What standards are the canning heat treatments based on (especiallly low acid food)?
reducing C. botulinum population by 12 log
What is the difference between commercially sterile and sterile?
sterile: done by autoclaving; totally kills all microbes (extreme high heat, long time)
commercially sterile: free from microbes that can reproduce under common storage conditions; no viable cells/spores that could harm health
(less heat treatment to avoid totally destroying food)