14 - physical methods for food preservation Flashcards
what is the Decimal reduction time (D value)
the time it takes of a 10-fold reduction in the number of survivors at a given temperature
What are the factors that will affect the heat transfer
- product type 2. container shape 3. container size 4. container material 5. agitation 6. temperature of heating medium
The greater the D value and the more ___ is an organism
resistant
The higher the temperature and the ___ is the D value
smaller
what is the thermal resistance plot
What is the survivor plot
A large Z value indicates that an organism is ____ to heat
resistant
What is the F value
The time in minutes it takes for a population of a specific organisms (specific temperature and z value) to acheive a target level. For c. bottulinum it is 12D.
What is the difference between the D value and the F value?
•The difference between D value, which defines the time it takes to reduce the population by 1 log, F value represents the time it takes to get the population to a specific level (i.e. 101 or sterile)
What is the F value of C. Botulinum if the D value is 0.21
•C. botulinum has a D121C value of 0.21 minutes, and a Z value of 10C. Therefore, to achieve commercial sterility at F121C you multiply 0.21 minutes by 12 which equals 2.52 minutes
•Commercial sterility of food products is the application of heat that renders the food free of:
- Microorganisms capable of reproducing in the food under normal non-refrigerated storage and distribution temperatures
- Viable microbial cells or spores of public health significance
What are the mechanisms of bacteria that make them more resistant to heat?
- higher GC in DNA
- Crosslinking disulfide bonding
•. if the aw, pH, or antimicrobial constituents are already stressing the bacteria out, you’ll need ____(less/more) heat to kill them
less
Aspectic processing is not used for __ and ___
low acid foods and particulat containing foods
are toxin affected by freezing?
no
How does freezing will presrve foods
because of the freeze/thaw cycle that can effect the cells
becuse of the freezing that stops the metabolic activity of most food-borne microorganisms
Because it will rduce the water activity (only xerotolerant can grow –> some yeast and fungo can)
•Gram-____ bacteria survive freezing better than Gram-___ bacteria
positive survive better than gram -
Are parasite destroyed by freezing
yes
which is better to kill microbial cells rapid or slow freezing
slow freezing because bigger crystals
Organisms that can resist the freezer needs to be :
xerotolerant (low Aw)
cryophilic, psychrophilic or psychrotrophic (cold resistant)
___water is essential for microbial growth and survival
Unbound
What is the formula of the water activity
Aw = P / P0
What is the relation between the equilibium relative humidity and the Aw
ERH (%) = aw x 100
T or F : the relation between the moisture content of foods and the Aw is linear
false
What are the 3 categories of foods based on their Aw
High moisture (over 0.9) Intermidiate moisture foods (between 0.65 and 0.9) Dry foods (lower than 0.65)
Maple syrup is an ___ moisture food
intermidiaite
__ and ___ can be an issue for maple syrup
yeasts and molds
when boiled at lower temperautres, the maple syrup can be spoiled by ____
spoiled by LAB
What is the minimal Aw that is needed by spoilage bacteria
0.95
What is the minimal Aw that is needed by Listeria, and V.paraheamolyticus
o.91-0.95
What is the minimal Aw that is needed by S.aureus
0.85
____ have aw requirements that are lower than those of bacteria
Yeasts
Can molds produce toxins in xerophilic conditions
no
What is the organisms you are most likely to find in xerophilic conditions
molds
is there any spoilage yeasts
yes
Why is there no mold growth at higher Aw
because bacteria grow and they will produce fungicides
T or F : lowering the Aw will kill the microorganisms
False, it will only inhibit their growth but they can stay dormant and multiply when there is an increase in the Aw
what is another factor other than Aw in the presrvation by decreasing water availability that will inhibit the microorganisms
the humectant used to lower the Aw, for example glycerol will permetate the bacterial membrane and have different effect than the sucrose
How does the ionizing radiation works
using the gamma and x-rays to target the DNA because of the creation of rective oxygen species
the ____ the genome, the greater the resistance to ionizing radiation
smaller
What is the advantage of gamma radiation
•The advantage is radiation has a high penetration power, and the energy is constant over the duration of the treatment, it is a continuous source that doesn’t need to be turned off
What is redappertization?
. Involves a high dose (10 to 75 kGy) to produce commercial sterility
What is Radicidation?
. Involves medium dose (1 to 10 kGy) to produce an equivalent effect to thermal pasteurization – effective against vegetative bacteria but spores are not inactivated
What is Radurization
Involves low dose irridation (0.05 to 1 kGy) to control the presence of insects in grains or stop the sprouting of potatoes, or delay fruit ripening (because it lower ethylene production)
What is HPP ?
•High pressure processing (HPP) involves treating food with pressures in the range of 100 to 600 MPa, which will inactivate most bacteria, yeasts, molds, and viruses (spores survive)
What is PEF?
application of shor burst of high voltage between two electrodes (food inbetween) to eliminate vegetative cells
Does HPP kills spores
no
Does PEF kills spores
no
