Water Activity in Foods

Fundamentals and Applications

Gustavo V. Barbosa-Cánovas, Anthony J. Fontana, Shelly J. Schmidt, Theodore P. Labuza, Gustavo V. Barbosa-Cánovas, Anthony J. Fontana, Jr., Shelly J. Schmidt, Theodore P. Labuza

• Publisher: Wiley-Blackwell
• Year: 2020
• Print ISBN: 9781118768310
• eBook ISBN: 9781118823354
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

This second edition of Water Activity in Foods furnishes those working within food manufacturing, quality control, and safety with a newly revised guide to water activity and its role in the preservation and processing of food items. With clear, instructional prose and illustrations, the book's international team of contributors break down the essential principles of water activity and water–food interactions, delineating water's crucial impact upon attributes such as flavor, appearance, texture, and shelf life.

The updated and expanded second edition continues to offer an authoritative overview of the subject, while also broadening its scope to include six newly written chapters covering the latest developments in water activity research. Exploring topics ranging from deliquescence to crispness, these insightful new inclusions complement existing content that has been refreshed and reconfigured to support the food industry of today.

1
Introduction: Historical Highlights of Water Activity Research

Jorge Chirife¹and Anthony J. Fontana Jr.²

¹Catholic University, Buenos Aires, Argentina

²ALS – Truesdail, Irvine, CA, USA

The concept of water activity (a_w) is more than 50 years old. William James Scott showed in 1953 that microorganisms have a limiting a_w level for growth. It is now generally accepted that a_w is more closely related to the microbial, chemical, and physical properties of foods and other natural products than is total moisture content. Specific changes in color, aroma, flavor, texture, stability, and acceptability of raw and processed food products have been associated with relatively narrow a_w ranges (Rockland and Nishi 1980). Next to temperature, a_w is considered one of the most important parameters in food preservation and processing (van den Berg 1986). This chapter is not a review of the literature on a_w but rather a highlight of some early key a_w research as it relates to microbial growth, moisture sorption isotherms, prediction and measurement of a_w in foods, and, to a lesser extent, the influence of a_w on the physical and chemical stability of foods.

Australian‐born microbiologist Scott (1912–1993) received his bachelor's degree from the University of Melbourne (1933) and a doctorate of science degree from the Council for Scientific and Industrial Research (CSIR) Meat Research Laboratory (1933). He then took a position as senior bacteriologist at the CSIR Division of Food Preservation and Transport from 1940 to 1960. In 1960, he moved to the Meat Research Laboratory, where he served as assistant chief of division until 1964 and officer‐in‐charge until 1972. In 1979, he became a fellow of the Australian Academy of Technological Sciences and Engineering.

Scott's early work was concerned with handling, cooling, and transport conditions that would enable chilled beef to be successfully exported to Britain. During World War II, he was concerned with the microbiology of foods supplied by Australia to the Allied Forces. After the war, he pioneered studies on the water relations of microorganisms. In 1953, Scott related the relative vapor pressure of food to the thermodynamic activity of water, using the definition a_w = p/p_o, where a_w is the water activity derived from the laws of equilibrium thermodynamics, p is the vapor pressure of the sample, and p_o is the vapor pressure of pure water at the same temperature and external pressure. He showed a clear correlation between the a_w of the growth medium and the rate of Staphylococcus aureus growth. The summary of his paper stated:

Table 1.1 Papers by Scott and Christian.

Author	Year	Title of Paper
Scott, W.J.	1953	Water relations of Staphylococcus aureus at 30°C
Christian, J.H.B. and Scott, WJ.	1953	Water relations of Salmonella at 30°C
Christian, J.H.B.	1955a	The influence of nutrition on the water relations of Salmonella oranienburg
Christian, J.H.B.	1955b	The water relations of growth and respiration of Salmonella oranienburg at 30°C
Scott, W.J.	1957	Water relations of food spoilage microorganisms

Fourteen food‐poisoning strains of Staphylococcus aureus have been grown in various media of known a_w at 30°C. Aerobic growth was observed at water activities between 0.999 and 0.86. The rate of growth and the yield of cells were both reduced substantially when the a_w was less than 0.94. The lower limits for gr...

Table of contents

• Cover
• Table of Contents
• Preface to the Second Edition
• Preface to the First Edition
• List of Contributors
• 1 Introduction: Historical Highlights of Water Activity Research
• 2 Water Activity: Fundamentals and Relationships
• 3 Water Activity and Glass Transition
• 4 State and Supplemented Phase Diagrams for the Characterization of Food
• 5 Water Mobility in Foods
• 6 Water–Solid Interactions in Food Ingredients and Systems
• 7 Water Activity Prediction and Moisture Sorption Isotherms
• 8 Measurement of Water Activity, Moisture Sorption Isotherm, and Moisture Content of Foods
• 9 Moisture Effects on Food's Chemical Stability
• 10 Water Activity and Physical Stability
• 11 Enthalpy Relaxation and Food Stability
• 12 Diffusion and Sorption Kinetics of Water in Foods
• 13 Applications for Dynamic Moisture Sorption Profiles in Foods
• 14 Effects of Water Activity (aw) on Microbial Stability as a Hurdle in Food Preservation
• 15 Baroprotective Effect from Reduced aw
• 16 Principles of Intermediate‐Moisture Foods and Related Technology
• 17 Desorption Phenomena in Food Dehydration Processes
• 18 Humidity Caking and Its Prevention
• 19 Selected Applications of Water Activity Management in the Food Industry
• 20 Water Relations in Confections
• 21 Applications of Probabilistic Engineering in Food Moisture Management to Meet Product Quality, Safety, and Shelf‐Life Requirements
• 22 Applications of Water Activity in Nonfood Systems
• 23 The Future of Water Activity in Food Processing and Preservation
• A AWater Activity of Saturated Salt SolutionsWater Activity of Saturated Salt Solutions
• B BWater Activity of Unsaturated Salt Solutions at 25°CWater Activity of Unsaturated Salt Solutions at 25°C
• C CWater Activity, Isotherm, and Glass Transition EquationsWater Activity, Isotherm, and Glass Transition Equations
• D DMinimum Water Activity Limits for Growth of MicroorganismsMinimum Water Activity Limits for Growth of Microorganisms
• E EWater Activity Values of Select Food Ingredients and ProductsWater Activity Values of Select Food Ingredients and Products
• F FWater Activity Values of Select Consumer and Pharmaceutical ProductsWater Activity Values of Select Consumer and Pharmaceutical Products
• Index
• End User License Agreement