Thermal processing Sterilization/pasteurization Appertization Canning

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.

HEAT TRANSFER MODES: Conduction Convection Radiation

CONDUCTION Transport of energy due to direct molecular interaction without appreciable displacement of molecules.

CONVECTION Transport of energy from one point of fluid to another point by actual movement of fluid itself. MODES OF CONVECTION: Natural convection Forced convection

RADIATION Transport of energy in the form of electromagnetic waves between materials across the space.

HEAT PENETRATION TEST 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.

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

Primary Objectives of Canning are: to kill microorganisms to keep away microorganisms

Microorganisms: public health hazard economic spoilage

Public health hazard 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.

Economic spoilage is due to un-processing: sporeformers from the genera Bacillus sporeformers from the genera Desulfotomaculum sporeformers from the genera Clostridium

FOOD CONTAINERS: Metal containers Glass containers Retort pouches

Double seam

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.

Pasteurization < 100 oC Classification of thermal processes based on processing temperature Sterilization >100 oC Pasteurization < 100 oC

Hot pack/hot fill processes Classification of thermal processing based on method of product packaging Terminal processes Aseptic processes Hot pack/hot fill processes

Food classification Low acid food pH > 4.6 Acid food pH  4.6

“Acid” Foods pH ≤ 4.6 Generally all fruits Tomatoes, with added acid Sauerkraut and fermented pickles Foods to which large amounts of acid are added 20

“Low Acid” Foods pH > 4.6 Generally all vegetables Meats Poultry Seafood Soups Mixed canned foods 21

Retorting consist of : heating phase: removal of air, come-up time (CUT) , holding time at processing temperature cooling phase

Types of retorts: Still retorts (nonagitating retorts): vertical, horizontal, malo, hydrostatic. Agitating retorts: sterilmatic, orbitort, rotomat, Flame sterilizers Aseptic systems

Still retort - vertical retort

Still retort -hydrostatic retort

Agitating retort - Sterilmatic

Agitating Retort - ORBITORT

Effect of heat on microorganisms 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 times 330 min at 100 oC 150 min at 104 oC 36 min at 110 oC 10 min at 116 oC 5.27 min at 118 oC 2.78 min at 121 oC 1.45 min at 124 oC 0.78 min at 127 oC

The destruction of microorganisms is affected by: their inherent resistance by environmental influences during the growth and formation the heating time & temperature pH humidity protective effect of food components: fat, proteins, salt

Order of destruction of microorganisms The death of bacteria exposed to wet heat is of logarithmic order. The logarithmic order means that theoreti- cally the survivors can be reduced to less than one. Thus the number of survivors may become very small such as one survivor in million units etc.

The 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, DT 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 destruction is described by the equation U =DT *(log N0 - log Nu) U - the equivalent heating time at proces- sing temperature N0 - the initial numbers of microorga- nisms Nu -the number of microrganisms after heating

Survivor Curves at Different Temperatures.

Comparison of D for Microbial Population

THERMAL 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) 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.

Thermal Death Time Curve

The 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 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 equation: Log FT = ( Tref - T)/Z + Log Fref Z = 10/log Q10 Q10 - 2.2- 4.6 dry heat Q10 - 8 - 20 wet heat

Lethal 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

Sterilization value of heat process, F F = Dref * (log N0 - log NF ) F =  t *  Li F = ∫ L *dt