Chapter 2 THERMAL PROCESSING PRINCIPLES

1. 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

2. Vocabulary • microbial population elevated temperature viability vegetative Salmonella spp., Listeria or Escherichiacoli-anyClostridium botulinum function of time logarithmic microbial spores abruptly semilogarithmic coordinates decimal reduction time, or D--value food spoilage microorganisms decimal reduction curve

3. 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

4. Microbial Populations Versus Time

5. Microbial Population Versus Time

6. 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.

7. 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 .

8. Survivor Curves at Different Temp.

9. 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.

10. Thermal Resistance Curve

11. 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 Z—value.

12. Thermal Death Time Curve

13. 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.

14. 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.

15. Thermal Death Time Versus Temperature

16. Establishment of Product Shelf Life • Factors influence the heat resistance of microbial. • When product safety is concerned. • When product shelf life is concerned.

17. 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

18. Comparison of D for Microbial Population

19. Some Low Acid Foods

20. When product safety is concerned • The Low Acid Canned Food (LACF) • Food and Drug Administration • l2-D process for low--acid canned foods

21. When product shelf life is concerned

22. INFLUENCE OF THERMAL PROCESS ON PRODUCT QUALITY

25. F versus T for MP & Quality Attributes

26. INTRODUCTION TO PROCESS CALCULATIONS • Lethal Rate Curve • Time/Temp. Process & LR • LR Curve for Thermal Process

27. Lethal Rate Curve

28. Time/Temp. Process & LR

29. LR Curve for Thermal Process

30. 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?