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Thermal Process CalculationsOverview of the General Method, Ball Formula and NumeriCAL

IFTPS SOUTH EAST ASIA TECHNICAL OUTREACH SEMINAR

November 27, 2012

Terry L. HeyligerThermal Processing Manager

JBT FoodTechMadera, CA USA

Thermal Processing

Kill Bacteria in Food by exposing the product/container to HEAT (at a specific temperature) for an specific TIMETIME

HEATHEAT

Process Calculations Upon completion of the heat penetration test

one must analyze the time / temperature data and use the results of the analysis to calculate a thermal process that will render the product commercially sterile.

Process Calculations

A critical step in the design of a safe thermal process is the process calculation. It is important that one understands the calculation method employed as well as any conditions that may restrict the use of a particular method.

Sterility (Fo value) The General Method Ball Formula Method

Process Calculations

NumeriCAL

Sterility

Death of a microorganism is defined as when it has lost the ability to reproduce

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Commercial Sterility

1. Containers are free of viable microorganisms of public health significance

MINIMUM PUBLIC HEALTH

2. Containers are free of microorganisms capable of reproducing under normal conditions of storage and distribution

COMMERCIALLY STERILE

12D Concept Minimum Public Health

Minimum processes are established to reduce any population of the most heat resistant C. botulinumspores by 10-12 or 12 log cycles

or Reduce the probability of survival to:p y

1 C. botulinum spore in 1x1012

or

1 in 1,000,000,000,000

5 D Concept Commercially Sterile

Reduce the population of a common mesophilic sporeformer, C. sporogenes, by 5 log cycles or 10-5

D-value

Time in minutes to reduce the population of bacteria by 90% at a specific lethal temperature

Effect of Temperature on D-value

As exposure temperature increases the rate of bacterial death also increases

Effect of Temperature on D-value

Temperature (F) D-Value 111.1 20.0

115.5 7.3

121.1 2.0

126.1 .63

131.1 .20

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z-Value

Reflects the resistance of bacteria to different lethal temperatures.

Equal to the number of degrees (F or C) required to change the D-Value by 1 log cycle ( factor of 10)

Unit of LethalityF-Value

Sterilization value F expressed as the equivalent minutes at a specified temperature

Based on the destruction of a population of bacteria having a known z-value

Unit of LethalityFo-Value

Represents the equivalent minutes at 121.1oC (250F) at the slowest heating point in the container

Based on the destruction of a population of bacteria having a z-value of 10C (18oF)

Lethal Rate Value

The lethal-rate value assigned to each temperature is numerically equal to the reciprocal of the number of minutes required to destroy the same population of spores in one minute at the reference temperature, 121.1oC

L = 10 (T-121.1)/10

Lethal Rate Value

Temperature, (oC)

Minutes to Destroy Spores*

Lethal Rate Value

101.1 100 0.01

111.1 10 .1

121.1 1 1

131.1 .1 10

* Same Population of spores with know z-value of 10oC

Lethal Rate Table