Chapter%202%20THERMAL%20PROCESSING%20PRINCIPLES

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Chapter 2 THERMAL PROCESSING PRINCIPLES

• INFLUENCE OF ELEVATED TEMPERATURES ON MICROBIAL
  POPULATIONS
• ESTABLISHMENT OF PRODUCT SHELF LIFE AND SAFETY
• INFLUENCE OF THERMAL PROCESS ON PRODUCT QUALITY
• INTRODUCTION TO PROCESS CALCULATIONS

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Vocabulary

• microbial population elevated temperature
  viability vegetative Salmonella spp., Listeria or
  Escherichia coli-any Clostridium botulinum
  function of time logarithmic microbial spores
  abruptly semilogarithmic coordinates decimal
  reduction time, or D--value food spoilage
  microorganisms decimal reduction curve

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Vocabulary

• thermal resistance curve thermal resistance
  constant or Z--value, thermal death time (F)
  survivor curve linear relationship commercial
  sterilization yeast and molds acidity, or pH
  low--acid anaerobic Low Acid Canned Food
  pathogen Spoilage probability quality attributes
  heat-sensitive nutrients flavor, texture, and
  color over-processing lethal rate lethality

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Microbial Populations Versus Time
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Microbial Population Versus Time
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survivor curve

• When the microbial populations as a function of
  time are presented on semilogarithmic
  coordinates, a linear decrease in microbial
  population with time is observed. It is the
  survivor curve. It is emphasized that these
  relationships occur when the environment around
  the population is at a constant temperature
  throughout the period of exposure.

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Definition of Decimal Reduction Time

• On survivor curve, the time required for a one
  log cycle reduction in microbial population is
  the decimal reduction time (D), or D--value .

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Survivor Curves at Different Temp.
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thermal Resistance Curve

• A plot of decimal reduction time as a function of
  temperature on semilog coordinates results in a
  linear relationship. This linear relationship is
  the thermal resistance curve for a given
  microbial population.

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Thermal Resistance Curve
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Definition of Thermal Resistance Constant (Z)

• On Thermal Resistance Curve , the temperature
  increase required to cause a one log cycle
  reduction in the decimal reduction time is
  defined as the thermal resistance constant (Z),
  or Zvalue.

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Thermal Death Time Curve
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Definition of Thermal Death Time (F)

• Thermal death time (F) is defined as the time
  required to achieve a stated reduction in the
  microbial population at a given temperature (in
  minutes), or F--value.

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Relations Between F D

• Each log cycle reduction in the microbial
  population on the thermal death curve represents
  a decimal reduction time, or D-value F--values
  may be expressed as multiples of D--values. The
  most common of these relationships is F 12D for
  Clostridium botulinum in commercial
  sterilization.

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Thermal Death Time Versus Temperature
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Establishment of Product Shelf Life

• Factors influence the heat resistance of
  microbial.
• When product safety is concerned.
• When product shelf life is concerned.

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Factors Influence the Heat Resistance of Microbial

• Species of microorganisms.
• Acidity or pH .
• Oxygen (some of the spores with high thermal
  resistance are anaerobic).
• Water activity
• Food composition

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Comparison of D for Microbial Population
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Some Low Acid Foods
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When product safety is concerned

• The Low Acid Canned Food (LACF)
• Food and Drug Administration
• l2-D process for low--acid canned foods

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When product shelf life is concerned
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INFLUENCE OF THERMAL PROCESS ON PRODUCT QUALITY
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F versus T for MP Quality Attributes
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INTRODUCTION TO PROCESS CALCULATIONS

• Lethal Rate Curve
• Time/Temp. Process LR
• LR Curve for Thermal Process

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Lethal Rate Curve
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Time/Temp. Process LR
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LR Curve for Thermal Process
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Problems

• What is D-value, What is decimal reduction curve
  or survivor curve,?
• What is Z-value, What is thermal resistance
  curve?
• What is F-value, What is thermal death time
  curve?
• What are the relationships between them?