Food Packaging

Takashi Kadoya

• Publisher: Academic Press
• Year: 2012
• Print ISBN: 9780123935908
• eBook ISBN: 9780080923956
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

This book describes the basic principles of food packaging, as well as recent advances in new materials. The Japanese are world leaders in this area, and detailed information on certain aspects of their industry are presented in this volume.- Sanitation and waste of food packaging materials- Food packaging and energy in Japan- New trends in the technology of food preservation- Fresh and processed food packaging

Part I

Fundamentals of Foods

Chapter 1

Physical Properties and Microbiology of Foods

Toshimasa Yano Department of Agricultural Chemistry, The University of Tokyo, Tokyo, Japan

NOMENCLATURE

a Activity

a_w Water activity

C Specific heat capacity (J/kg ⋅ K)

f Fugacity (Pa)

f^o Fugacity for reference state (Pa)

h^E Excess partial molar enthalpy (J/mol)

p Water vapor pressure in equilibrium with food (Pa)

P₀ Saturation vapor pressure of pure water (Pa)

P' Condensation vapor pressure in a capillary (Pa)

q Heat flux (J/m² ⋅ s)

r Radius of capillary (m)

R Gas constant (J/mol ⋅ K)

t Time (s), or temperature (°C)

T Temperature (K)

T_f Freezing point (K)

V_L Molar volume of condensed water (m³/mol)

x Distance in x direction (m)

X^v Volume fraction

X^w Weight fraction

α Thermal diffusivity (m²/s)

θ Contact angle (rad)

λ Thermal conductivity (W/m ⋅ K)

μ Chemical potential (J/mol)

ρ Density (kg/m³)

σ Surface tension (N/m)

ϕ Volume fraction of dispersed phase

Subscripts

c continuous phase

d dispersed phase

e effective value

F fats

i ith component

m mean value

s solids

w water

I PHYSICAL PROPERTIES OF FOODS

A Moisture Sorption Equilibrium and Water Activity

1 Moisture Sorption Equilibrium

Any food material sorbs, or desorbs, moisture in a package until the moisture sorption equilibrium is reached. The sorption includes both the adsorption of moisture onto the surface of solid materials and the absorption of moisture into the solid or liquid materials. Knowledge of the moisture sorption equilibrium is necessary in order to control the physical, chemical, biochemical, and microbiological reactions that may occur during storage and distribution of packed foods. Since the moisture permeability of packaging material is much less than the rates of moisture sorption and desorption of foods, the atmosphere inside the package may be in the moisture sorption equilibrium, although the equilibrium changes slowly due to moisture permeation through the packaging material.

Figure 1 shows schematically the moisture sorption equilibrium as a function of the relative humidity at a constant temperature. Generally, hysteresis is observed for many foods. Upon desorption from a high water content, the equilibrium water content of foods is higher than that upon sorption from a low water content.

Figure 1 Moisture sorption isotherms of rice flour: sorption, desorption, — 26 °C, --- 45 °C.

The occurrence of hysteresis has been explained from many points of view. Change in food structure is one of the most likely explanations. The effect of impurities in porous structure is another. However, the most significant and useful explanation may be of an “ink bottle” structure (McBain, 1935). Suppose a water-filled cylindrical space of radius r₂ connected to the atmosphere through a capillary of radius r...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Foreword
• Preface
• Part I: Fundamentals of Foods
• Part II: New Food Packaging Materials: An Introduction
• Part III: Food Packaging and Energy
• Part IV: Packaging Systems and Technology of Food Materials
• Part V: New Trends in the Technology of Food Preservation
• Part VI: Packaging Fresh and Processed Foods
• Part VII: Physical Distribution and Food Packaging
• Index