Thermal processing
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Transcript of Thermal processing
Thermal processingThermal processing
Sterilization/pasteurizationSterilization/pasteurization
AppertizationAppertization
CanningCanning
History
1810 Nicolas Appert about 1860 Luis Pasteur provides scientific
explanation 1920 Bigelow and coworkers described method
of calculation 1945 Otto Rahn applies the principle that
microorganisms die according to logarithmic order.
HEAT is the energy in transit due to a temperature difference between two regions and is always transferred from the region of higher temperature to the region of lower temperature.
Transport of energy due to direct molecular interaction without appreciable displacement of molecules.
CONDUCTION
Transport of energy from one point of fluid to another point by actual movement of fluid itself.
MODES OF CONVECTION:Natural convection Forced convection
CONVECTION
Transport of energy in the form of electromagnetic waves between materials across the space.
RADIATION
Process of putting a temperature sensitive element in food container and gathering temperature data over a time course during a thermal process. Reports on penetration tests need to state the type of thermocouple used and where the thermocouple was placed.
HEAT PENETRATION TEST
For penetration test the thermocouple should be placed in the coldest place of the container
for conduction heating product it is located at a geometric center of container
for convection heating products it is located 1/10 to 1/5 of the container height from the bottom of the container
Clostridium botulinum is the main public hazard b/c spores are heat resistant. Spores may survive when heat processing is insufficient. The health hazard is due to ability of Cl. botulinum to grow under anaerobic conditions and to produce toxin.
Public health hazardPublic health hazard
Economic spoilage is due to un-processing:Economic spoilage is due to un-processing:
sporeformers from the genera sporeformers from the genera BacillusBacillus
sporeformers from the genera sporeformers from the genera DesulfotomaculumDesulfotomaculum
sporeformers from the genera sporeformers from the genera ClostridiumClostridium
HEADSPACE
GROSS - vertical distance from the top of double seam or the top edge of the glass jar to the level of product in the container.
NET - vertical distance from the level of food to the inside surface of the lid (only metal containers).
A retort pouch does not have a true headspace, what is of importance is the volume of non con- densible gases.
Sterilization >100 oC
Pasteurization < 100 oC
Classification of thermal processes based on processing temperature
Terminal processes
Aseptic processes
Hot pack/hot fill processes
Classification of thermal processing based on method of product packaging
Food classificationFood classification
Low acid food pH > 4.6 Low acid food pH > 4.6 Acid food pH Acid food pH 4.6 4.6
““Acid” FoodsAcid” Foods
pH pH ≤≤ 4.6 4.6 Generally all fruitsGenerally all fruits Tomatoes, with added acidTomatoes, with added acid Sauerkraut and fermented picklesSauerkraut and fermented pickles Foods to which large amounts of acid are Foods to which large amounts of acid are
addedadded
““Low Acid” FoodsLow Acid” Foods
pH > 4.6pH > 4.6 Generally all vegetablesGenerally all vegetables MeatsMeats PoultryPoultry SeafoodSeafood SoupsSoups Mixed canned foodsMixed canned foods
Retorting consist of :Retorting consist of :
heating phase: heating phase: removal of air, come-up time removal of air, come-up time (CUT) , holding time at processing (CUT) , holding time at processing temperaturetemperature
cooling phasecooling phase
Types of retorts:Types of retorts:
Still retorts (nonagitating retorts): vertical, Still retorts (nonagitating retorts): vertical, horizontal, malo, hydrostatic.horizontal, malo, hydrostatic.
Agitating retorts: sterilmatic, orbitort, Agitating retorts: sterilmatic, orbitort, rotomat, rotomat,
Flame sterilizersFlame sterilizers Aseptic systemsAseptic systems
Effect of heat on Effect of heat on microorganismsmicroorganisms
Yeast are the least resistant, followed by mold and then bacteria. All vegetative cells are destroyed instantly at 100 0C . Spores of C. botulinum, C. sporogenes, C. bifermentans, C. butiricum, C. pasteurianum, C. perfringens,C. thermosaccharolyticum, D. nigrificans, and B. stearothermophilus are very heat resistance.
Equivalent processing timesEquivalent processing times
330 min at 100 330 min at 100 ooCC 150 min at 104 150 min at 104 ooCC 36 min at 110 36 min at 110 ooCC 10 min at 116 10 min at 116 ooCC 5.27 min at 118 5.27 min at 118 ooCC 2.78 min at 121 2.78 min at 121 ooCC 1.45 min at 124 1.45 min at 124 ooCC 0.78 min at 127 0.78 min at 127 ooCC
The destruction of microorganisms The destruction of microorganisms is affected by:is affected by:
their inherent resistancetheir inherent resistance by environmental influences during the by environmental influences during the
growth and formationgrowth and formation the heating time & temperaturethe heating time & temperature pHpH humidityhumidity protective effect of food components: fat, protective effect of food components: fat,
proteins, saltproteins, salt
Order of destruction of microorganismsOrder of destruction of microorganisms
The death of bacteria exposed to wet heat The death of bacteria exposed to wet heat is of logarithmic order.is of logarithmic order.
The logarithmic order means that theoreti- The logarithmic order means that theoreti- cally the survivors can be reduced to less cally the survivors can be reduced to less than one. Thus the number of survivors than one. Thus the number of survivors may become very small such as one may become very small such as one survivor in million units etc.survivor in million units etc.
The survivor curveThe survivor curve
The number of viable bacteria plotted on the logarithmic scale against the corresponding heating time (processing time) on the linear scale provides the graph known as the survivor curve.
DECIMAL REDUCTION TIME, DECIMAL REDUCTION TIME, DDTT
The time in minutes required to reduce the viable cells in suspension of bacteria to one tenth of their original value. The slope of semilogarithmic survivor curve determi -nes the decimal reduction time.
The logarithmic model for microbial The logarithmic model for microbial destruction is described by the destruction is described by the
equationequation
U =DT *(log N0 - log Nu)
U - the equivalent heating time at proces- sing temperature N0 - the initial numbers of microorga- nismsNu -the number of microrganisms after heating
THERMAL DEATH TIMETHERMAL DEATH TIME
The longest time when the unit test are positive for growth and the shortest time when the units are negative
The thermal death (TDT) curveThe thermal death (TDT) curve
The value of F plotted on the logarithmic scale against the corresponding tempe- ra ture on the linear scale provides graph known as TDT curve.
The thermal resistance curveThe thermal resistance curve
Values of DT plotted on the logarithmic scale against the corresponding temperature on the linear scale provide a graph called phantom thermal death time curve or thermal resistance curve.
Parameter ZParameter Z
The parameter Z represents the number of degrees of Fahrenheit, centigrade, or Kelvin necessary to cause the F-value or D value to change by a factor ten.
TDT curve is described by TDT curve is described by equation:equation:
Log FT = ( Tref - T)/Z + Log Fref
Z = 10/log Q10
Q10 - 2.2- 4.6 dry heatQ10 - 8 - 20 wet heat
Lethal rateLethal rate
It is described as minutes at T ref per minute at T. Can be calculated using the following equation:
L = Fref/FT = 10 (T -Tret)/ Z
Z = 10 C or 18 F, Tref = 121.1 C or 250 F