Physical methods of food preservation Flashcards
Inactivation
the destruction of the organisms as judged by its inability to recover on microbiological media
which method of food preservation is most common?
physical methods
purpose of food preservation
- extended shelf life
- ensure food safety by inactivating pathogens or preventing their growth
High temperature treatment
- temperature exceeds the optimal temperature for an organism. The cell multiplication slows and eventually stops.
- additional temperature may result in cell death - denaturation
why is heat treatment effective
it can eliminate almost any microbial target and is customizable to the product and organism of concern.
- Risk: overheating may damage the product quality
- Major parameters: temperature and time
Heat transfer - what factors affect it (6)
- product type
- container material
- container shape
- container size
- agitation
- temperature of heating medium
survivor plot
depict the logarithmic nature of population inactivation over time
decimal reduction time (D value)
the time it takes of a 10-fold reduction in the number of survivors at a given temperature
-the greater the D value at a given temp, the more resistant that organism is to heat
What happens to the D value when the temperature increases?
the D value decreases
thermal resistance plot
when the D value is plotted against temperature (usually linear)
z value
thermal resistance constant
(the negative reciprocal of the slope on a thermal resistance plot)
-represents the change in temperature required to change the D value of a microorganism by an order of magnitude (10-fold)
-larger Z value: more heat resistant organism
Thermal lethality measurements
taken to determine the amount of time required to commercially sterilize food at a given temperature
F value
the time (in min) at a specific temperature required to achieve a targeted reduction in a homogeneous population having a specific z value -F value is important in the commercial canning industry
Difference between D value and F value
D value 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 (ie 10^1 or sterile)
Which organism + what test is used in the canning industry?
- C. botulinum: key pathogen in canned low acid foods.
- use the F value at a specific temperature to achieve commercial sterility.
sterilization
- the process of rendering a product free of any living organisms
- ex. autoclaving reders media sterile
- using sterilization would cause the food to become unacceptable quality (through excessive heating)
commercail sterilization
food free of
- microorganisms capable of reproducing in the food under non-refrigerated storage and distribution temperatures
- viable microbial cells or spores of public health significance
- ie heat-treated just enough to produce a safe and shelf-stable product
Important factor in heat resistnace?
state of dormancy: stationary phase cells are more resistant to heat than exponential phase cells and spore formation dramatically increases heat resistance
-stress: if aw, pH, or antimicrobial constituents are stressing them, less heat will be needed to kill them
Aseptic processing
- used in industry where foods and cans are sterilized separately and then foods are packaged under aseptic conditions
- product is heated by passing through a set of heat exchangers until the holding time and temp has been reached.
- passed through cooling exchangers
- used for fruit juices, dairy products, sauces (not particulate containing foods)