2 Sterilization Process Engineering Hosahalli S. Ramaswamy and R. Paul Singh CONTENTS 2.1 Introduction 2.2 Principles of Thermal Processing 2.3 Thermal Resistance of Microorganisms 2.3.1 Survivor Curve and D Value 2.3.2 Thermal Death Time (TDT) and D Value 2.3.3 Temperature Dependence and z Value 2.3.4 Reaction Rate Constant (k) and Activation Energy (E a ) 2.3.5 Lethality Concept 2.4 Heat Transfer Related to Thermal Processing 2.4.1 Conduction Heat Transfer 2.4.1.1 Steady-State Conduction 2.4.1.2 Unsteady-State Conduction 2.4.1.3 Solution to Unsteady-State Heat Transfer Problem Using a Spherical Object as an Example 2.4.2 Convection Heat Transfer 2.4.2.1 Steady-State Convection Heat Transfer 2.4.2.2 Unsteady-State Convection Heat Transfer 2.4.3 Characterization of Heat Penetration Data 2.4.4 Heat Penetration Parameters 2.4.5 The Retort Come-Up Time 2.5 Thermal Process Calculations 2.5.1 The Original General Method 2.5.2 The Improved General Method 2.5.3 The Ball-Formula Method 2.5.3.1 Come-Up Time Correction and the Ball-Process Time 2.5.4 The Stumbo-Formula Method 2.5.5 The Pham-Formula Method References 2.1 INTRODUCTION Conventional thermal processing generally involves heating of foods packaged in hermetically sealed containers for a predetermined time at a preselected temperature to eliminate the pathogenic microorganisms that endanger the public health as well as those microorganisms and enzymes that deteriorate the food during storage. The original concept of in-container Copyright © 1997 CRC Press, LLC