Calorimetry in Food Processing- Analysis and Design of Food Systems

Calorimetry in Food Processing:

Analysis and Design of Food Systems

The IFT Press series refl ects the mission of the Institute of Food Technologists to advance the science of food contributing to healthier people everywhere. Developed in partnership with Wiley-Blackwell, IFT Press books serve as leading-edge handbooks for industrial application and reference and as essential texts for academic programs. Crafted through rigorous peer review and meticulous research, IFT Press publications represent the latest, most signifi cant resources available to food

scientists and related agriculture professionals worldwide.

Founded in 1939, the Institute of Food Technologists is a nonprofi t scientifi c society with 22,000 individual members working in food science, food technology, and related professions in industry, academia, and government. IFT serves as a conduit for multidisciplinary science thought leadership, championing the use of sound science across the food value chain through knowledge sharing, education, and advocacy.

IFT Book Communications CommitteeBarry G. SwansonSyed S. H. RizviJoseph H. HotchkissChristopher J. DoonaWilliam C. HainesRuth M. PatrickMark BarrettJohn LillardKaren Nachay

IFT Press Editorial Advisory BoardMalcolm C. BourneFergus M. ClydesdaleDietrich KnorrTheodore P. LabuzaThomas J. MontvilleS. Suzanne NielsenMartin R. OkosMichael W. ParizaBarbara J. PetersenDavid S. ReidSam SaguyHerbert StoneKenneth R. Swartzel

A John Wiley & Sons, Inc., Publication



EDITOR

Gnl Kaletun

A John Wiley & Sons, Inc., Publication

Edition fi rst published 2009 2009 Wiley-Blackwell and the Institute of Food Technologists

Chapter 7 remains with the U.S. Government.

Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwells publishing program has been merged with Wileys global Scientifi c, Technical, and Medical business to form Wiley-Blackwell.

Editorial Offi ce2121 State Avenue, Ames, Iowa 50014-8300, USA

For details of our global editorial offi ces, for customer services, and for information about how to apply for permission to reuse the copyright material in this book, please see our website at www.wiley.com/wiley-blackwell.

Authorization to photocopy items for internal or personal use, or the internal or personal use of specifi c clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service are ISBN-13: 978-0-8138-1483-4/2009.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

Library of Congress Cataloging-in-Publication Data

Calorimetry in food processing : analysis and design of food systems/editor Gnl Kaletun. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-8138-1483-4 (alk. paper) ISBN-10: 0-8138-1483-9 (alk. paper) 1. FoodAnalysis. 2. Thermal analysis. 3. CalorimetryIndustrial

applications. 4. Food industry and trade. I. Kaletun, Gnl TX544.C35 2009 338.4'7664dc22

2009008348

A catalog record for this book is available from the U.S. Library of Congress.

Set in 11.5 on 13.5 pt Times by SNP Best-set Typesetter Ltd., Hong KongPrinted in Singapore

1 2009

Titles in the IFT Press series Accelerating New Food Product Design and Development (Jacqueline H. Beckley, Elizabeth

J. Topp, M. Michele Foley, J.C. Huang, and Witoon Prinyawiwatkul) Advances in Dairy Ingredients (Geoffrey W. Smithers and Mary Ann Augustin) Biofi lms in the Food Environment (Hans P. Blaschek, Hua H. Wang, and Meredith E. Agle) Calorimetry and Food Process Design (G n l Kaletun ) Nondigestible Carbohydrates and Digestive Health (Teresa M. Paeschke and William R.

Aimutis) Food Ingredients for the Global Market (Yao - Wen Huang and Claire L. Kruger) Food Irradiation Research and Technology (Christopher H. Sommers and Xuetong Fan) Food Laws, Regulations and Labeling (Joseph D. Eifert) Food Risk and Crisis Communication (Anthony O. Flood and Christine M. Bruhn) Foodborne Pathogens in the Food Processing Environment: Sources, Detection and Control

(Sadhana Ravishankar and Vijay K. Juneja) Functional Proteins and Peptides (Yoshinori Mine, Richard K. Owusu - Apenten, and Bo

Jiang) High Pressure Processing of Foods (Christopher J. Doona and Florence E. Feeherry) Hydrocolloids in Food Processing (Thomas R. Laaman) Microbial Safety of Fresh Produce (Xuetong Fan, Brendan A. Niemira, Christopher J.

Doona, Florence E. Feeherry, and Robert B. Gravani) Microbiology and Technology of Fermented Foods (Robert W. Hutkins) Multiphysics Simulation of Emerging Food Processing Technologies (Kai Knoerzer, Pablo

Juliano, Peter Roupas, and Cornelis Versteeg) Multivariate and Probabilistic Analyses of Sensory Science Problems (Jean - Fran ois

Meullenet, Rui Xiong, and Christopher J. Findlay) Nondestructive Testing of Food Quality (Joseph Irudayaraj and Christoph Reh) Nanoscience and Nanotechnology in Food Systems (Hongda Chen) Nonthermal Processing Technologies for Food (Howard Q. Zhang, Gustavo V. Barbosa -

C novas, and V.M. Balasubramaniam, Editors; C. Patrick Dunne, Daniel F. Farkas, and James T.C. Yuan, Associate Editors)

Nutraceuticals, Glycemic Health and Type 2 Diabetes (Vijai K. Pasupuleti and James W. Anderson)

Packaging for Nonthermal Processing of Food (J. H. Han) Preharvest and Postharvest Food Safety: Contemporary Issues and Future Directions (Ross

C. Beier, Suresh D. Pillai, and Timothy D. Phillips, Editors; Richard L. Ziprin, Associate Editor)

Processing and Nutrition of Fats and Oils (Ernesto M. Hernandez and Afaf Kamal - Eldin) Processing Organic Foods for the Global Market (Gwendolyn V. Wyard, Anne Plotto,

Jessica Walden, and Kathryn Schuett) Regulation of Functional Foods and Nutraceuticals: A Global Perspective (Clare M. Hasler) Sensory and Consumer Research in Food Product Design and Development (Howard R.

Moskowitz, Jacqueline H. Beckley, and Anna V.A. Resurreccion) Sustainability in the Food Industry (Cheryl J. Baldwin) Water Activity in Foods: Fundamentals and Applications (Gustavo V. Barbosa - C novas,

Anthony J. Fontana Jr., Shelly J. Schmidt and Theodore P. Labuza) Whey Processing, Functionality and Health Benefi ts (Charles I. Onwulata and Peter J. Huth)

vii

Dedication

For my parents, my son, and my husband for their patience and encouragement.

Hayatta en hakiki m r s it ilimdir. The truest guide in life is science.

Mustafa Kemal Atat rk, September 22, 1924

This book is also dedicated to the memory of the late Professor Michel Ollivon, a great scientist and an exceptional human being, who passed away on June 16th, 2007, during the preparation of the book.

Dedication

viii

ix

Table of Contents

Preface xiiiContributor List xvii

Part 1 Analysis of Food and Biological Materials by Calorimetry 3

Chapter 1 Calorimetric Methods as Applied to Food: An Overview 5

Gnl Kaletun

Chapter 2 Methods and Applications of Microcalorimetry in Food 15

Pierre Le Parlour and Luc Benoist

Chapter 3 High-Pressure Differential Scanning Calorimetry 51

Gnther W.H. Hhne and Gnl Kaletun

Chapter 4 Calorimetry of Proteins in Dilute Solution 67 G. Eric Plum

Chapter 5 Thermal Analysis of Denaturation and Aggregation of Proteins and Protein Interactions in a Real Food System 87

Valerij Y. Grinberg, Tatiana V. Burova, and Vladimir B. Tolstoguzov

x Table of Contents

Chapter 6 Heat-Induced Phase Transformations of Protein Solutions and Fat Droplets in Oil-in-Water Emulsions: A Thermodynamic and Kinetic Study 119

Perla Relkin

Chapter 7 Analysis of Foodborne Bacteria by Differential Scanning Calorimetry 147

Michael H. Tunick, John S. Novak, Darrell O. Bayles, Jaesung Lee, and Gnl Kaletun

Chapter 8 Coupling of Differential Scanning Calorimetry and X-Ray Diffraction to Study the Crystallization Properties and Polymorphism of Triacyglycerols 169

Christelle Lopez, Daniel J.E. Kalnin, and Michel R. Ollivon

Part 2 Calorimetry as a Tool for Process Design 199

Chapter 9 Overview of Calorimetry as a Tool for Effi cient and Safe Food-Processing Design 201

Alois Raemy, Corinne Appolonia Nouzille, Pierre Lambelet, and Alejandro Marabi

Chapter 10 Shelf Life Prediction of Complex Food Systems by Quantitative Interpretation of Isothermal Calorimetric Data 237

Simon Gaisford, Michael A.A. ONeill, and Anthony E. Beezer

Chapter 11 Use of Thermal Analysis to Design and Monitor Cereal Processing 265

Alberto Schiraldi, Dimitrios Fessas, and Marco Signorelli

Chapter 12 Importance of Calorimetry in Understanding Food Dehydration and Stability 289

Yrj H. Roos

Table of Contents xi

Chapter 13 High-Pressure Calorimetry and Transitiometry 311 Stanislaw L. Randzio and Alain Le Bail

Chapter 14 Calorimetric Analysis of Starch Gelatinization by High-Pressure Processing 341

Kelley Lowe and Gnl Kaletun

Chapter 15 Use of Calorimetry to Evaluate Safety of Processing 351

Hans Fierz

Index 369

Preface

xiii

The global food industry is very large, producing sales worldwide on the order of approximately U.S. $1 trillion. To remain competitive in this complex industry, it is vital that manufacturers optimize food - processing conditions, most importantly not only to ensure the safety of food products but also to produce affordable, healthy, and conve-nient products, with desired sensory attributes. The global scale of the food industry brings the new challenges of increasing transport and export and in turn new requirements for increased shelf life. Optimization of food - processing conditions as well as development of new products requires knowledge of the physical properties of the food products and their components as the variables that are relevant to processing and storage conditions. Detailed knowledge of physical properties enables manufacturers to prevent waste of time and resources caused by trial and error during product formulation and process design.

Many food - processing protocols involve application of heating or cooling over a broad range of temperature. Knowledge of a food s thermal properties as a function of temperature and composition is necessary for heat transfer and energy balance calculations used to rationally design these thermal - processing protocols. During process-ing, the food components go through conformational and phase changes that affect the state and texture of the fi nal food product.

Temperature - scanning calorimetry provides a useful tool for detecting, monitoring, and characterizing thermal processes in food materials. Moreover, calorimetry can be used to evaluate the effects of various physical and chemical stresses, including nonthermal treat-ments, on specifi c components by comparing the thermal profi les of pre - and post - treated food and biological materials to develop an

xiv Preface

understanding of the mechanism of processing - induced changes. The data generated from thermal analysis techniques also can be used to develop equations that predict the physical properties of pre - and post-processed foods as a function of processing and storage conditions.

Although the use of calorimetry to measure the physical properties of food materials has increased both in academia and in industry over the past 20 years, the analysis of data frequently is complicated by multiple overlapping transitions and kinetically controlled events that occur in food materials.

This book is designed to introduce the basic principles of calori-metry, applications of calorimetry to characterize food products, inter-pretation of the resultant data, and the use of these data for process optimization and product development. The book is organized in two sections. The fi rst section, consisting of eight chapters, focuses on the basic principles of calorimetry and its use for a wide range of materials from dilute solutions to solids. The second section, consisting of seven chapters, emphasizes the use of calorimetric data as a tool for process design and product development.

Chapter 1 provides an overview of calorimetry and the organization of the book. Chapters 2 and 3 focus on experimental design principles, calibration, data collection and analysis for microcalorimetry and high - pressure calorimetry. Chapter 4 addresses applications of ultrasensitive calorimetry to proteins and their interactions in dilute solution to char-acterize the thermal and thermodynamic stability and the thermody-namic origins of that stability. Chapters 5 , 6 , and 7 undertake the characterization of concentrated, multicomponent systems that are commonly observed in foods and complex biological systems such as bacteria. The fi nal chapter in this section, Chapter 8 , focuses on the use of an instrument that combines X - ray diffraction and high - sensitivity differential scanning calorimetry (DSC) in the same appa-ratus to simultaneously obtain complementary thermal and structural information for a sample.

Section Two of the book comprises Chapters 9 through 15 . Chapter 9 provides an overview of the use of phase transition information in development of phase diagrams that can be used for effi cient process design. Chapter 10 covers application of isothermal calorimetry for analysis of food stability, shelf life, and isothermal cooking processes. Chapter 11 describes application of thermal analysis to cereal - based products and mathematical treatment of the complex thermograms to

Preface xv

deconvolute the contributions from different components of the system. Chapter 12 reviews the use of calorimetric data for selection of dehy-dration parameters to produce products with improved storage stabil-ity. Chapter 13 describes the relatively new technique of scanning transitiometry and its specifi c application to gelatinization of wheat starch dispersions and for investigation of pressure shift freezing. Chapter 14 covers the application of calorimetry to characterize the impact of nonthermal treatment and to determine kinetic parameters during storage. Chapter 15 reviews the use of calorimetry to quantify the probability and potential severity of exothermic events such as formation of hot spots in dryers and to establish safe conditions for handling materials to prevent accidents in the food industry.

This book is designed to explain the capabilities of calorimetry for characterization of food and biological systems, which can range from single component, single - phase systems to multicomponent, multi-phase systems. Therefore, information described in the book will provide comprehensive insight for scientists who have experience with calorimetry as well as a basic understanding for beginners. This text may also be used as a textbook for a graduate - level course. The book is also intended to serve as a resource for food scientists, food tech-nologists, and food engineers working in the area of process design, optimization, and product development. The descriptions of the basic principles and potential uses of calorimetry to provide critical informa-tion for their respective areas and will serve as a bridge between these workers and specialists in calorimetry.

xvii

Contributors

Bayles, Darrell O. (Chapter 7 ) Dairy Processing & Products Research Unit, USDA - ARS - Eastern Regional Research Center, Wyndmoor, PA, USA

Beezer, Anthony E. (Chapter 10 ) The School of Pharmacy, University of London, London, UK

Benoist, Luc (Chapter 2 ) SETARAM, Lyon, France

Burova, Tatiana V. (Chapter 5 ) Nesmeyanov Institute of Organo - Element Compounds, Russian Academy of Sciences, Moscow, Russian Federation

Fessas, Dimitrios (Chapter 11 ) DISTAM, University of Milan, Milano, Italy

Fierz, Hans (Chapter 15 ) Swiss Safety Institute, Basel, Switzerland

Gaisford, Simon (Chapter 10 ) The School of Pharmacy, University of London, London, UK

Grinberg, Valerij Y. (Chapter 5 ) A.N. Nesmeyanov Institute of Organo - Element Compounds, Russian Academy of Sciences, Moscow, Russian Federation

xviii Contributors

H hne, G nther W.H. (Chapter 3 ) University of Ulm, Ulm, Germany (Retired)

Kaletun , G n l (Chapters 1, 3, 7, 14) The Ohio State University, Department of Food Agricultural and Biological Engineering, Columbus, OH, USA

Kalnin, Daniel J.E. (Chapter 8 ) YKI, Ytkemiska Institutet AB, The Institute for Surface Chemistry, Stockholm, Sweden

Lambelet, Pierre (Chapter 9 ) Nestl Research Center, Nestec LTD, Lausanne, Switzerland

Le Bail, Alain (Chapter 13 ) ENITIAA, UMR CNRS GEPEA (6144), Nantes, France

Lee, Jaesung (Chapter 7 ) Department of Food Science and Technology, The Ohio State University, Columbus, OH, USA

Le Parlou r, Pierre (Chapter 2 ) Thermal Consulting, Caluire, France

Lopez, Christelle (Chapter 8 ) UMR Science et Technologie du Lait et de l Oeuf, INRA - Agrocampus Ouest, Rennes Cedex, France

Lowe, Kelley (Chapter 14 ) Abbott Nutrition Products Division, Columbus, OH, USA

Marabi, Alejandro (Chapter 9 ) Nestl Research Center, Nestec Ltd., Lausanne, Switzerland

Nouzille, Corinne Appolonia (Chapter 9 ) Nestl Research Center, Nestec Ltd., Lausanne, Switzerland

Novak, John S. (Chapter 7 ) Dairy Processing & Products Research Unit, USDA - ARS - Eastern Regional Research Center, Wyndmoor, PA, USA

Contributors xix

Michel Ollivon (Chapter 8 , published posthumously) Universit Paris - Sud, Chatenay - Malabry, France

O Neill, Michael A.A. (Chapter 10 ) Department of Pharmacy and Pharmacology, University of Bath, Bath, UK

Plum, G. Eric (Chapter 4 ) IBET Inc., Columbus, OH, USA, and Rutgers, The State University of New Jersey, Department of Chemistry and Chemical Biology, Piscataway, NJ, USA

Raemy, Alois (Chapter 9 ) Nestl Research Center, Nestec Ltd., Lausanne, Switzerland

Randzio, Stanislaw L. (Chapter 13 ) Polish Academy of Sciences, Institute of Physical Chemistry, Warszawa, Poland

Relkin, Perla (Chapter 6 ) UMR 1145 (AgroParisTech, CEMAGREF, INRA), AgroParisTech, Department of Science and Engineering for Food and Bioproducts, Massy, France

Roos, Yrj H. (Chapter 12 ) Department of Food and Nutritional Sciences, University College Cork, Ireland

Schiraldi, Alberto (Chapter 11 ) DISTAM, University of Milan, Milano, Italy

Signorelli, Marco (Chapter 11 ) DISTAM, University of Milan, Milano, Italy

Tolstoguzov, V.B. (Chapter 5 ) Tolstoguzov consulting.com, Pully, Switzerland.

Tunick, Michael H. (Chapter 7 ) Dairy Processing & Products Research Unit, USDA - ARS - Eastern Regional Research Center, Wyndmoor, PA, USA

Analysis of Food and Biological Materials by Calorimetry

Part 1

Chapter 1

Calorimetric Methods as Applied to Food: An Overview

G n l Kaletun

Introduction 5 Calorimetry 6 An Overview of the Book 8 References 13

Introduction

Several thermal and nonthermal methods are applied to process and preserve food materials and to manufacture value - added products. The goals of food processing are to inactivate spoilage and pathogenic microorganisms and to maintain this status in storage during the intended shelf life of the product. During processing, changes take place in food components, including vitamins, lipids, carbohydrates, and proteins. Such changes lead to structural and functional changes in foods at the micro - and macromolecular levels that affect the physi-cal, organoleptic, and nutritional properties of the food.

Food materials are complex biological systems. Food products may have a broad range of structures spanning the three states of matter, including dilute to concentrated liquids, solids, and mixtures of multi-liquid, liquid - solid, liquid - gas, and solid - gas structures. The combina-tion of complex structures making up complex biological compounds makes the characterization of food systems challenging. To address the wide variety of compositions and structures, many biophysical techniques are uesd to characterize the structure and properties of food materials before and after processing to develop a fundamental

5

6 Calorimetry in Food Processing

understanding of the impact of processing and storage conditions. The data resulting from such studies can be used to predict the physical prop-erties of foods so that food processing and storage conditions are optimized.

Calorimetry

Among biophysical techniques, calorimetry presents itself as particu-larly well suited for analysis of food materials. Among many reasons, the fi rst is the relevance of the experimental protocols of calorimetry to the majority of processes employed in food preservation. Specifi -cally, because many food - processing methods involve thermal treat-ment (heating, cooling, freezing) of the materials, thermal characterization of food systems and their components leads to data that can be related directly to the processing protocols. Determination of thermal properties of food materials, such as specifi c heat as a func-tion of temperature, is essential for heat transfer and energy balance calculations (Kaletun 2007 ). Generation of a reliable database to develop equations predicting thermal properties of food materials for optimization of food processes can be accomplished by using calorim-etry. Moreover, food materials and their components go through con-formational and phase transitions during processing. Calorimetry data can be analyzed to evaluate the thermal and thermodynamic stability of various phases for a rational design of food product formulations and process conditions.

Differential scanning calorimetry, which measures heat capacity as a function of temperature, is a well - established thermal analysis technique that detects and monitors thermally induced conformational transitions and phase transitions as a function of temperature. During temperature scanning, depending on the complexity of the material, many peaks or infl ection points (one to several) refl ecting the thermally induced transitions can be observed. The direction of the peak corresponds to the nature of the transition, being heat absorbing (endo-therms) or heat releasing (exotherms). While melting of solids and denaturation of proteins display endotherms, crystallization of carbo-hydrates and aggregation of proteins manifest themselves as exotherms. The temperatures for the endothermic and exothermic transitions and

Calorimetric Methods as Applied to Food: An Overview 7

the heat involved in such transitions are measured using a calorim-eter. Infl ection points are indicative of glass transitions; that is, transitions from a glassy to rubbery state. The transition temperatures ( T peak or T g ) refl ect the thermal stability of the phase or state going through the transition. One can extract from calorimetry data values for the thermal and thermodynamic changes in free energy ( G ), enthalpy ( H ), entropy ( S ), and heat capacity ( C p ) of the various transitions in addition to determination of the bulk heat capacity of the material.

The basis for thermodynamic study of food materials is that the relevant initial and fi nal states (preprocessing and postprocessing states) can be defi ned and the energetic and structural differences between these states can be measured using calorimetric instrumenta-tion. To this end, calorimetry can be used to evaluate the effect of other physical and chemical variables by comparing the thermograms of the materials before and after exposure to the variable outside the calorimetry.

The basics of application of calorimetry to food materials are dis-cussed in detail in this book. However, it is important to start the discussion with a summary of the advantages of using calorimetry for study of biological materials. These advantages can be outlined as follows:

Direct measurement of the energetics of the transition is obtained ( H and C p ). The experimental results are not model dependent.

Calorimetry can be applied to a range of materials, pure or complex. Materials do not have to be optically transparent or have chromo-phores as required by spectroscopic methods.

Materials do not have to be uniform or have to be a homogeneous mixture. In fact, in addition to pure materials, the technique can be used to evaluate the interactions among the components in a complex system and how the interactions are altered by the processing.

Calorimetry does not require elaborate or destructive sample preparation.

Calorimetry is an established technique which has been around since the 16th century (Haines 1995 ). Today, the instruments are highly developed for accurate measurement of thermal events. The theory behind the technique is well developed, which facilitates interpreta-tion of the data (H hne et al. 2003 ).


While the technique is powerful, the validity and utility of the data depend strongly on the careful use of the equipment and correct inter-pretation of data. Some analytical methods provide results specifi c to materials; however, calorimetry data depends on the conditions used during the experiment (Haines 1995 ). One must be careful in choosing the calorimetry parameters:

1. Time scale: Especially in dynamic measurement systems, for events to be detected the experimental time scale should match the time scale of the observed event.

2. Magnitude of the heat fl ow: If the energy associated with the transi-tion is small, it can lead to ambiguities in its detection. Increasing the scanning rate enhances the signal; however, it may cause devia-tion from equilibrium conditions, which requires models beyond the standard equilibrium thermodynamics treatment of calorimetry data.

3. Moisture loss during experiment: Biological samples in general are high - moisture content materials. If the sample cell is not sealed well, the moisture content of the sample will change due to evapora-tion during the course of experiment. This may lead to overestima-tion of the transition temperature as well as the transition enthalpy change.

4. Interpretation of overlapping peaks: Biological samples may contain multiple components that undergo thermally induced transitions at similar temperatures. As a result, overlapping peaks may be observed on a differential scanning calorimetry (DSC) thermogram. Even if the origin of the event is known, because the peak temperatures may shift due to overlap, individual events may appear to happen at dif-ferent temperatures. The individual peaks can be resolved experi-mentally (Barrett et al. 2002, 2005 ), or the complex thermograms can be deconvoluted by using special software (Fessas and Schiraldi 2000 ).

An Overview of the Book

This book focuses on the basics of calorimetry and specifi c applica-tions for characterization of food systems. The material in this book is designed to provide food scientists, food technologists, and food engi-


neers with knowledge about the potential uses of calorimetry as a tool in process design and optimization as well as product development and improvement. The book consists of two sections. The fi rst section includes eight chapters describing the principles of calorimetry alone and coupled with other techniques as well as the use of calorimetry to characterize biological systems ranging from pure single phase to multicomponent and multiphase systems of solids, dilute and concen-trated solutions of macromolecules, emulsions, foams, and bacteria. The second section of the book is designed to illustrate the use of calorimetric data to guide engineers and processors in design and opti-mization of processes.

The multicomponent nature of the food materials presents a chal-lenge in that the specifi c component undergoing a conformational or phase transition may be in small quantity relative to the whole, thus generating an insuffi cient heat signal to detect. As an alternative to increasing the heating rate, the heat signal can be enhanced by increas-ing the sample size. In Chapter 2 , the challenges of increasing sample size and strategies to overcome these challenges by using micro-calorimetry are discussed.

The increased interest of consumers in minimally processed foods pushed the food research community to explore novel technologies that present alternatives to thermal processing. High hydrostatic pressure (HHP) processing has become the most promising alternative technol-ogy. Currently, HHP processing is implemented for several foods and has a market value of more than $500 million. The optimization of HHP processing requires knowledge of physical properties under con-ditions relevant to the pressures attained during the process. The design of calorimeters operating under the pressures used in industry is very challenging. Chapter 3 focuses on the design of a high - pressure calo-rimeter and the protocols to be followed for calibration, data collection, and analysis.

Applications of ultrasensitive calorimetry to proteins and their inter-actions in dilute solution are examined in Chapter 4 . Emphasis is placed on the practical aspects of collecting and analyzing differential scanning calorimetry (DSC) data to characterize the thermal and ther-modynamic stability and the thermodynamic origins of that stability in a protein in solution. The thermodynamics of association between a protein and a small molecule or another macromolecule are quantifi -able by application of isothermal titration calorimtery (ITC). The


design and execution of ITC experiments are described with emphasis on the information content of titration curves. Together or separately, DSC and ITC provide valuable tools for developing a predictive under-standing of protein stability and interactions as a function of tempera-ture and solution conditions.

Investigation of dilute systems is essential to elucidate the behavior of macromolecules thermodynamically. However, in biological systems and foods, dilute systems are rarely encountered. Commonly, macro-molecules exist in foods at high concentration and in complexes with other macromolecules and low - molecular - weight compounds. Heat denaturation and aggregation of proteins are common during food processing and affect the quality attributes of food. Therefore, Chapter 5 uses calorimetry to study the effects of pH, salts, alcohols, and poly-saccharides on thermal denaturation and aggregation of food proteins in order to elucidate the mechanisms of structure formation, structure - texture and structure - physical property relationships in foods.

Proteins also play an important role in development of emulsions and foams that are examples of multicomponent and multiphase food systems. Both the formation and the stability of such complex systems depends on the adsorption properties of proteins at oil - in - water or gas - in - water interfaces. Chapter 6 reviews the use of DSC in scanning and isothermal mode for monitoring effects of food composition and physi-cochemical environment on the conformation and structural modifi ca-tions of proteins in emulsions under the time - temperature combinations relevant to processing. The results presented in this chapter illustrates that a combination of thermodynamic and kinetic data obtained by using DSC in scanning and isothermal modes provide a better under-standing of emulsions and the ability to control structure - forming mechanisms in food systems.

The main goal of food processing is to manufacture foods that are stable and safe to consume, which requires the inactivation of bacteria to prevent spoilage and foodborne diseases. Thermal inactivation of microorganisms is associated with irreversible denaturation of mem-branes, ribosomes, proteins, and nucleic acids. DSC can be used to monitor the reversible and irreversible changes in the cellular compo-nents of bacteria. Chapter 7 describes using DSC to provide an insight into the mechanism of bacterial cell inactivation. Also illustrated is the utility of DSC data to quantitatively evaluate bacterial inactivation kinetics. Calorimetry can be used to evaluate the effect of food -


processing variables other than heat on bacteria. Chapter 7 describes the analysis by calorimetry of damage to bacterial cells due to chemi-cal, nonthermal, or antibiotic treatments and the relationship between the calorimetric data and loss of cell viability.

The data collected by calorimetry are complementary to data col-lected by other biophysical methods. Thermal analysis is a valuable tool to observe phase transition, but especially for complex systems, such as lipids, the thermal observables can be due to a variety of struc-tures forming during the heating or cooling process. Generally, another technique such as Fourier transform infrared spectroscopy or x - ray diffraction (XRD) is used in parallel to acquire structural information. Obtaining complementary data can be further improved by performing simultaneous DSC - FTIR (Yoshida 1999 ) or DSC - XRD (Yoshida et al. 1996 ; Ollivon et al. 2006 ) measurements on the same sample. Chapter 8 describes in detail the development of a new instrument, called MICROCALIX, combining XRD at both wide and small angles as a function of temperature (XRDT) or time (XRDt), and high - sensitivity DSC, in the same apparatus with scanning or isothermal modes over the temperature range 30 to +230 C. This approach enables one to obtain complementary thermal and structural properties information on the same sample in one experiment.

Foods exhibit thermally induced transitions over a temperature range between 50 C and 300 C. The thermal behavior of a food is mainly a refl ection of its major component, however, with some change due to interactions with other components. Chapter 9 focuses on the use of phase transition information in development of phase diagrams that can be used for effi cient process design. Heat of a solution as a parameter of great importance for food powder dissolution is also emphasized. The relevance of calorimetric data to the food industry is illustrated by specifi c examples.

Biological samples undergo changes even when they are kept at constant temperature. Changes, physical or chemical in origin, may produce heat that can be studied with isothermal calorimetry. However, detection and monitoring of small quantities of heat, especially at the initial stage of the physical or chemical event, requires using a high - sensitivity calorimeter. Chapter 10 focuses on application of isother-mal calorimetry, a relatively less - exploited application of calorimetry in comparison with DSC, for qualitative and quantitative analysis of food stability, shelf life, and isothermal cooking processes. Specifi c


examples are discussed, from simple ingredients to complex biological processes.

Cereal - based products are staple foods all around the world. Although the main component in such foods is starch, thermally induced transitions are highly affected by the presence of other com-pounds in cereals, including proteins, nonstarch carbohydrates, and lipids, either due to competition for available water or direct interac-tions. Chapter 11 provides a review of thermal analysis applications to cereal - based products and cereal processing. This chapter discusses in detail mathematical treatment of the complex thermograms to decon-volute the contributions from different components in the system.

Drying has been used as a method of food preservation since ancient times. In modern practice, water is removed by evaporation upon application of heat or by sublimation from a frozen product under vacuum. During the drying process, amorphous or partially crystalline states are formed. The thermal stability of the amorphous state is defi ned by the glass transition temperature, which depends strongly on the amount of water present in the food system. Chapter 12 reviews the use of calorimetric data for selection of dehydration parameters to produce products with improved storage stability. This chapter also discusses the relationship between the glass transition and collapse of structure in freeze - dried materials, fl avor retention by encapsulation of volatiles in amorphous systems, solids crystallization, lipid oxidation, nonenzymatic browning, and enzymatic changes.

Chapter 13 describes the relatively new technique of scanning tran-sitiometry developed by Randzio (1996) based on scanning of one of the three variables pressure, volume, or temperature and measure-ment of the other two, as well as the heat signal. This chapter also discusses the specifi c application of scanning transitiometry for gela-tinization of wheat starch dispersions and for investigation of pressure shift freezing. In addition, the technique is applied to the study of water, water in pork muscle, solutions of gelatin in water, and lipids.

Chapter 14 focuses on the application of calorimetry to determine the effects of high hydrostatic pressure on starch gelatinization as well as to characterize the recrystallization of the gelatinized starch during subsequent storage for calculation of starch recrystallization kinetic parameters. These results are used in selection and optimization of HHP processing parameters and storage conditions for foods contain-ing starch.


Foods show chemical reactivity leading to self - heating and self - ignition of hot spots. Especially handling of dry powders in bulk, such as in milling, drying, and packaging, can be dangerous due to potential dust explosions. Chapter 15 reviews the evaluation by calorimetry of the thermal consequences of exothermic decompositions in foods, describes the methodology for quantifying the risk in terms of its sever-ity and its probability, and discusses methods for collecting the stabil-ity data correctly. Specifi c cases of formation of hot spots in dryers, storage and hot discharge, and transport safety are discussed. The importance of establishing safe conditions for handling of materials in prevention of accidents in the food industry is emphasized.

References

Barrett A. , Cardello A. , Maguire P. , Richardson M. , Kaletun G. , and Lesher L. 2002 . Effects of Sucrose Ester, Dough Conditioner, and Storage Temperature on Long - Term Textural Stability of Shelf - Stable Bread . Cereal Chem , 79 ( 6 ): 806 811 .

Barrett A.H. , Marando G. , Leung H. , and Kaletun G. 2005 . Effect of Different Enzymes on the Textural Stability of Shelf - stable Bread . Cereal Chem , 82 ( 2 ): 152 157 .

Fessas D. , and Schiraldi A. 2000 . Starch Gelatinization Kinetics in Bread Dough, DSC Investigations on Simulated Baking Processes . J Therm Anal Calorim , 61 : 411 423 .

Haines P.J. 1995 . Thermal Methods of Analysis, Principles, Applications and Problems . Glasgow : Blackie .

H hne G.W.H , Hemminger , W. , and Flammersheim , H.J. Differential Scanning Calorimetry: an Introduction for Practitioners . 2nd Ed. Berlin; New York : Springer - Verlag , 2003.

Kaletun G. 2007 . Prediction of Heat Capacity of Cereal Flours: A Quantitative Empirical Correlation . J Food Eng , 82 ( 2 ): 589 594 .

Ollivon M. , Keller G. , Bourgaux C. , Kalnin D. , Villeneuve P. , and Lesieur P. 2006 . DSC and High Resolution X - Ray Diffraction Coupling . J Therm Anal Calorim , 85 : 219 224 .

Randzio S.L. 1996 . Scanning Transitiometry . Chemical Society Reviews , 25 : 383 . Yoshida H. , Ichimura Y. , Kinoshita R. , and Teramoto Y. 1996 . Kinetic Analysis of

the Isothermal Crystallization of an N - Alkane and Polyethylene Observed by Simultaneous DSC/FT - IR/WAXD Measurement . Thermochim Acta , 282/ 283 : 443 452 .

Yoshida H. 1999 . Structure Relaxation of N - Alkanes Observed by the Simultaneous DSC/FTIR Method. J Therm Anal Calorim , 57 ( 3 ): 679 685 .

Chapter 2

Methods and Applications of Microcalorimetry in Food

Pierre Le Parlou r and Luc Benoist

15

Introduction 15 The Heat Flux Calorimetric Principle 17 DSC versus Heat Flux Microcalorimetry 19

Comparison between DSC and Heat Flux Microcalorimetry 19 The Calvet Principle 22 Calibration 23

Description of Different Heat Flux Calorimeters Used for Food Characterization 26

High Sensitivity Heat Flux Calorimeter 26 The Mixing and Reaction Heat Flux Microcalorimeter 29

Methods of Microcalorimetry in Food 30 Heat Capacity Determination 30 Heating Mode 35 Mixing and Reaction Calorimetry 40 Pressure Calorimetry 43 Calorimetry under Controlled Relative Humidity 45

Conclusion 45 References 46

Introduction

Heat is involved at different steps in the preparation of foods, such as cooking and processing. During heating, cooling, or freezing, the food products undergo different types of transformations, including melting,


crystallization, gelation, gelatinization, denaturation, and oxidation. All these transformations occur in a certain range of temperature and are associated with heat variations. The thermal analysis techniques, and specifi cally differential scanning calorimetry (DSC), are used as a main approach for investigating the thermal properties of foods (Harwalkar and Ma 1990 ; Farkas and Moh csi - Farkas Csilla 1996 ; Schiraldi et al. 1999 ; Raemy et al. 2000 ).

However, in most food processing food ingredients are mixed or diluted with a liquid (water, milk) or with a powder (sugar, salt, yeast). For simulation of such transformations and interactions, the limited volume and the lack of in situ mixing constitute the major drawbacks of the DSC technique.

For such investigations, microcalorimetry (in the isothermal and scanning modes) is the ideal solution because it has the capacity to work on bulk materials and diluted solutions with a very high sensitivity. Microcalorimeters are found as reaction or solution calo-rimeters, pressure calorimeters according to the transformation to be simulated, and provide a wide range of experimental conditions for applications such as mixing, dilution, wetting, neutralization, and enzymatic reaction, which have relevance to food industry. For a food technologist, it is very important to understand various thermal and functional properties of food components and ingredients for fundamental research, food quality assurance, and for product development.

Although many articles have been published in the fi eld, to our knowledge a book dedicated to the very challenging fi eld of microca-lorimetric applications in food science has not been available.

Microcalorimetry, compared with DSC, still remains as a lesser - known technique. For a long time, it has suffered from a reputation as an old and slow technique (needing days of experimentation), of large instruments (microcalorimetry meaning microquantity of measured heat and not microsize instrument), and was used mainly by experts. Especially with the development of microcalorimetry in the biological and pharmaceutical fi elds (Ladbury and Chowdhry 2004 ; Craig and Reading 2007 ), there have been many advances in instrumentation in the last decade that facilitated the use of calorimeters in laboratories. Microcalorimetry benefi ts food research and opens new opportunities of experiments and applications that are to be described in this chapter.

Methods and Applications of Microcalorimetry in Food 17

The Heat Flux Calorimetric Principle

Existing calorimeters operate on the following principles:

the heat fl ux principle the heat - compensating principle the heat - accumulating principle

In this chapter, the heat fl ux calorimetric principle is described as it is used in most calorimeters for food characterization.

The heat fl ux calorimeter consists of a measurement chamber sur-rounded by a detector (thermocouples, resistance wires, thermisters, thermopiles) to integrate the heat fl ux exchanged by the sample con-tained in an adapted vessel. The measurement chamber is insulated in a surrounding heat sink made of a high thermal conductivity material.

The heat fl ux for a given sample at a temperature T s is equivalent to:

dq

dt

dh

dtC

dT

dts

ss

= +

(2.1)

where dh / dt is heat fl ux produced by the transformation of the sample or the reaction and C s is heat capacity of the sample, including the container. The heat fl ux dq s / dt is exchanged with the thermostatic block at a temperature T p through a thermal resistance, R , described by the following relation:

dq

dt

T T

Rs p s

=

(2.2)

Equation 2.1 shows that the thermal contribution due to the heat capac-ity of the sample and container is very large and will provide a major disturbance at the introduction of the container in the calorimeter. From Equation 2.2 , it is also evident that any temperature perturbation of the thermostatic block will affect the calorimetric measurement.

To solve these issues, a symmetrical calorimeter is preferred. Two identical calorimetric chambers, one housing a container with the sample and an identical reference container an inert material


(the reference container may also be empty) are placed in the thermo-static block at the same temperature, T p . The heat fl ux difference is measured between the two chambers.

dq

dt

dq

dt

dq

dt

dh

dtC

dT

dtC

dT

dts r

ss

rr

= = +

(2.3)

Here, C r is heat capacity of the reference, including the container, and T r is temperature of the reference.

Equation 2.2 becomes:

dq

dt

T T

Rr s

=

(2.4)

or by derivation

Rd q

dt

dT

dt

dT

dtr s

2

2=

(2.5)

By combining Equations 2.4 and 2.5 , the characteristic equation for the calorimetric measurement is obtained.

dh

dt

dq

dtC C

dT

dtRC

d q

dts r

ps= + ( )

2

2

(2.6)

TsCs

Heat sink

RThermostatic block

Heating elements

Tp

Sample + container

Figure 2.1. One - cell calorimetric principle.


If dh / dt corresponds to an endothermic transformation or reaction, the dh / dt value is positive. If dh / dt corresponds to an exothermic trans-formation or reaction, the dh / dt value is negative.

If the calorimetry is performed isothermally, the parameter dT p / dt is null. In a small perturbation of the temperature T p of the thermostatic block, the corresponding thermal effect will be minimized if the C s and C r heat capacities are similar. The last term R C s d

2 q / dt 2 (called as thermal lag) mostly depends on the thermal resistance or the time of response of the calorimeter and the heat capacity of the sample and the container. For a long period ( t >> RC s ) it will be negligible. Table 2.1 gives an overview of some endothermic or exothermic effects occur-ring in various types of food.

DSC versus Heat Flux Microcalorimetry

Comparison between DSC and Heat Flux Microcalorimetry

The differences between DSC and heat fl ux microcalorimetry are related mainly to the size of the sample and the sensitivity of the mea-surement but also to interactions between solid and liquid materials. To clearly understand the difference, it is important to analyze the technological principles that are behind each technique.

Table 2.1. Some endothermic and exothermic effects for different food types.

Food Type Endothermic Effect Exothermic Effect

Fat, oil Melting, lipidic transition Crystallization, oxidation Protein Denaturation Aggregation,

crystallization Enzyme Denaturation Aggregation, enzymatic

reaction Starch Gelatinization, glass

transition Retrogradation, oxidation

Milk Melting Crystallization, oxidation Hydrocolloid, gelatin Melting Gelation Carbohydrates Melting, glass transition Crystallization,

decomposition Yeast Fermentation Bacteria Growth, metabolism,

fermentation


International Confederation for Thermal Analysis and Calorimetry (ICTAC), in its nomenclature, considers two types of DSC: the heat fl ux DSC and the power - compensated DSC ( www.ictac.org ). Even if the measurement principles are different, the heat transfer from (or to) the sample is about the same. The detector for each DSC model is a plate - type design. The sample, contained in a metallic crucible, is placed and centered on the plate acting as a fl at - shaped sensor. A refer-ence crucible (empty or containing an inert material) is placed on the other plate. In plate DSC (heat fl ux type and power - compensated type), the heat exchange between the sample and the detector occurs through the bottom of the crucible, corresponding to a two - dimensional detec-tion. In fact, only a part of this heat transfer is measured, as a signifi cant part is dissipated through the walls and the cover of the crucible (Figure 2.2 ). The ratio of the heat fl ux measured by the sensor to the total heat fl ux produced by the thermal event, calculated by simulation using

Figure 2.2. Schematic of a plate - shaped DSC sensor.


thermal modeling software, shows that only around half of the heat fl ux is dissipated through the plate (Daudon 1996 ; Le Parlou r and Mathonat 2005 ). Figure 2.3 clearly shows that the effi ciency rapidly decreases with the temperature and the thickness of the plate. The effi ciency is also affected by the amount of the sample tested. Therefore, it is recommended to work with small amount of material (about 5 10 mg) when using a plate DSC to minimize the heat losses. The thermal conductivities of the crucible and the gas used in the experi-mental chambers also are very important parameters to be considered in the effi ciency of the heat exchange. For example, a very heat - conductive gas (helium) will favor the heat transfer between the crucible and the detector, but at the same time increase the heat losses. Hence, the calibration of a plate - type DSC (heat fl ux or power - compensated type) is very critical and has to be run with the experi-mental conditions selected for testing the sample.

The main difference between heat fl ux calorimetry and DSC (heat fl ux or power compensated type) is that in a microcalorimeter, the heat exchange between the sample and the detector is completely measured. Such a high effi ciency is achieved by applying the technological prin-ciple developed by Tian and Calvet.

Calorimeters are also designed on the power - compensating prin-ciple using a detector that surrounds the sample in the same way. MicroCal ( www.microcal.com ) and CSC (now TA Instruments)

50

40%

Flu

x 30

20

10

00 150 300

Temperature (C)

450 600

0.01 mm0.05 mm0.10 mm

Figure 2.3. Effi ciency ratio of a fl at - shaped DSC as a function of the sensor plate thickness.


( www.tainstruments.com ) have developed such ultrasensitive instru-ments, mostly used for the investigations of dilute liquids. Because these calorimeters operate with fi xed vessels, they are not well - adapted for the characterization of foods.

The Calvet Principle

The detection is based on a three - dimensional fl uxmeter sensor. The fl uxmeter element consists of a ring of several thermocouples in series (Figure 2.4 ). The corresponding thermopile of high thermal conductivity surrounds the experimental space within the calorimetric block. The radial arrangement of the thermopiles guarantees an almost complete integration of the heat. This is verifi ed by the calculation of the effi ciency ratio that indicates that an average value of 94% 1% of heat is transmitted through the sensor on the full range of tempera-ture of the Calvet - type DSC (Figure 2.5 ). In this setup, the sensitivity of the DSC is not affected by the type of crucible, the type of purge gas, or the fl ow rate. The main advantage of the setup is the increase

Figure 2.4. Schematic of the Calvet type calorimeter.


of the experimental vessel s size, and consequently the size of the sample, without affecting the accuracy of the calorimetric measurement.

Calibration

The calibration of the calorimetric detectors is a key parameter and has to be performed very carefully. In fact, the main purpose of the calibra-tion is to transform the electric signal (emf) provided by the thermo-couples of the detector expressed in microvolts ( V) in a thermal power (heat fl ux) signal expressed in milliwatts (mW). For DSC detec-tors, this conversion is achieved using metallic reference materials (Richardson and Charsley 1998 ). Although this recommended proce-dure is widely used, it has some limitations:

The calibration can only be performed at the temperature at which the reference material melts.

At low temperature, it is diffi cult to fi nd good reference materials. The calibration is mostly performed in a heating mode, but very

rarely in the cooling mode. The accuracy of the calibration depends on the purity and quality of

the reference materials.

For Calvet - type calorimeters, a specifi c calibration, so - called Joule effect or electrical calibration, has been developed to overcome the drawbacks described above (Calvet and Prat 1964 ). A dedicated vessel

Ratio of energy transmitted through the thermopile

9393.293.493.693.8

9494.294.494.694.8

95

0 100 200 300 400 500

T (C)

Rat

io o

f en

erg

y (%

)

Figure 2.5. Effi ciency ratio of a Calvet - type calorimeter versus temperature.


with a built - in electrical heater (platinum resistance) simulating the experimental vessel that contains the sample is introduced into the calorimeter at a given temperature. A well - defi ned electrical power (between 20 and 200 mW) is applied to the resistance. The calorimeter gives a corresponding deviation (Figure 2.6 ). The stabilized signal, expressed in microvolts, is directly correlated to the applied power, expressed in milliwatts. The main advantages of this type of calibration are as follows:

It is an absolute calibration. The use of standard materials for calibration is not necessary. The

calibration can be performed at a constant temperature, in the heating mode and in the cooling mode.

It can be applied to any experimental vessel volume. It is a very accurate calibration.

To understand the direct correlation between the electrical signal and the heat fl ux, consider that a power, W , is fully dissipated in a calibra-tion vessel (Figure 2.7 ) surrounded by a fl uxmeter composed of crowns of thermocouples (Figure 2.3 ). An elementary power, w i , is dissipated through each thermocouple giving an elementary variation of tempera-ture T i between the internal and external weldings:

w Ti i i= (2.7)

where i is the conductance of the thermocouple.

P

S

K=S/P

Figure 2.6. Joule effect calibration.


The corresponding variation of temperature generates an elementary electromotive force (emf) according to the Oersted law:

e Ti i i= (2.8)

where i is the thermoelectric constant of the thermocouple. By combining Equations 2.7 and 2.8 , for the thermocouples in

series, we obtain:

E e wi

i

ii= =

(2.9)

Because all the thermocouples are identical, Equation 2.9 can be expressed as follows:

E w E Wi= =

or (2.10)

Equation 2.10 shows that the power dissipated in the vessel is directly correlated with the heat fl ux. The term / corresponds to the calibra-tion factor of the calorimeter.

W

wi

ei g i

q i

Figure 2.7. Joule effect calibration principle.


Description of Different Heat Flux Calorimeters Used for Food Characterization

According to the Calvet principle, many different calorimeters have been designed with various temperature ranges, small and large volumes, with a broad range of sensitivity. In this chapter, we describe two different Calvet calorimeters ( www.setaram.com ) that are used worldwide in many food research laboratories.

High Sensitivity Heat Flux Calorimeter

The development of the very high sensitivity heat fl ux calorimeter ( www.setaram.com ) was mainly motivated by the limitations of the standard DSCs: small amount of sample, limited sensitivity, no possibility of interaction or mixing. It was designed to be used as a multipurpose calorimeter working in isothermal and scanning modes with batch and fl ow capacities on a signifi cant volume of sample (1 cm 3 ).

The calorimetric chamber is made of a highly thermal conductive block with two cylindrical cavities for the experimental vessels (sample and reference). The detectors are built with semiconducting Peltier elements, characterized for their high sensitivity compared with a standard thermocouple - based detector. For the temperature control of the calorimeter, two principles are used:

A thermostatic loop of liquid fl ows around the calorimetric block for a temperature range from 20 C to 120 C

Different shields with Peltier elements are located around the calo-rimetric block to extend the use at a lower temperature for a tem-perature range from 45 C to 120 C.

In both cases, the vessels are easily removed from the calorimetry block. This is a key point for the cleaning of the vessels when different types of foods, such as fatty compounds, gels, and proteins, are used. The tops of the calorimeters are opened to allow the introduction of fl uids (gas, liquid) by means of adapted and dedicated vessels. The thermostatic loop of liquid provides a prestabilizing ring at the upper part of the calorimeter that allows the liquid to preheat before entering the calorimetric chamber. According to the type of experiments to be


performed on food components, there are different experimental vessels for the batch or the fl ow applications (Figure 2.8 ).

The standard batch vessel is mainly used to investigate food com-ponents in a liquid or solid form in a closed system.

The batch - mixing vessel is composed of two chambers that allow isolation of each material before mixing in the calorimeter. The mixing operation is achieved by pushing the rod from outside. The batch high - pressure vessel is mainly dedicated to investigation of food components under pressure, especially for modifi cation of struc-ture (glass transition, polymorphism) when high pressure is applied. For such experiments, the calorimetric vessel is fi tted with a high - pressure gas panel (maximum pressure: 1000 bar) (Le Parlou r et al. 2004 ).

The fl uid - mixing vessel is designed to introduce a gas or a liquid into the vessel to interact with the sample inside. Before introducing a liquid, the liquid temperature is stabilized at the temperature of the calorimeter. The fl uid - mixing vessel makes possible the mixing of two liquids in situ in the calorimetric vessel using an adapted mixer. The entering liquids are prestabilized at the temperature of the calorimeter and are introduced through micropumps at variable fl ow rates. Table 2.2 gives an overview of the variety of applications that can be per-formed with the different vessels.

Figure 2.8. Standard and mixing vessels (batch), fl uid circulation vessel (fl ow).

Table 2.2. Applications of the MicroDSC technique versus the vessel and the heating mode.

Vessel Heating Mode Component Application

Batch Scanning Protein (animal, cereal )

Denaturation, aggregation, lyophilization

Isothermal Protein Crystallization Scanning Enzyme denaturation, stability Scanning Starch Gelatinization,

retrogradation, glass transition

Isothermal Starch Crystallization (stalling) Scanning Milk Melting, crystallization,

denaturation, aggregation Scanning Fat Melting, crystallization,

lipidic transition, polymorphism

Isothermal Fat Crystallization Scanning Hydrocolloids Melting, gelation Scanning Sugar Melting, crystallization,

glass transition (amorphism)

Isothermal Aroma Stability Batch high

pressure Scanning Fat, chocolate Polymorphism versus

pressure Starch Glass transition versus

pressure Batch

mixing Isothermal Enzyme Enzymatic reaction

Starch Wetting Dairy bacteria Yogurt processing Yeast Dough and bread processing Bacteria Bacteria growth, food safety

One fl uid vessel

Isothermal Oil Oxidative stability

Two - fl uid mixing vessel

Isothermal Enzyme Enzymatic reaction

28


The Mixing and Reaction Heat Flux Microcalorimeter

The mixing and reaction microcalorimeter ( www.setaram.com ) is used for larger amounts of materials to better fi t with the experimental needs of the food industry. The microcalorimeter can be used as a DSC for temperature scanning, but with large - volume samples. It is, however, more suitable for the applications in the isothermal mode. The micro-calorimeter has a large experimental volume (15 cm 3 ). It is built around a metallic conductive block with two cavities that contain the thermo-piles, which are made of crowns of thermocouples. The block itself is surrounded by the heating element and arranged in an insulated chamber. The calorimeter can be fi tted on a rotating mechanism to use with a special mixing vessel.

The microcalorimeter offers a large choice of experimental vessels for use with various applications. The most commonly used vessels in food research are as follows:

The batch standard vessel is designed for investigating transforma-tion during heating or cooling a large volume of samples in the solid or liquid form. It also can be used to determine heat capacity.

The batch high - pressure vessel is designed for simulation of reaction and decomposition under pressure in a closed vessel or under con-trolled pressure (max: 100 bar). It is used to defi ne safety conditions of some food - processing operations and also for simulation of super-critical gas extraction.

The gas - fl ow vessel is fi tted with two coaxial tubes and is used to produce a circulation of gas (inert or active) around the sample. It is used for investigation of oxidative stability of foods.

The mixing vessel using the rotating mechanism is divided into two chambers and separated by a metallic lid. One of the materials is placed in the lower chamber (i.e., powder) and the other material is placed in the upper chamber (i.e., liquid). The mixing of the two components is provided by rotating the calorimeter, the metallic lid acting as a stirrer. This mixing vessel is designed for investigation of liquid - liquid mixing (dilution, neutralization) or solid - liquid mixing (dissolution, hydration, wetting).

The membrane mixing vessel is used for mixing of viscous samples, often seen with food components and for applications in which the rotation of the calorimeter cannot be used. In such a vessel, the separation between both chambers is achieved with a thin membrane


(metal or PTFE). The vessel is fi tted with a metallic rod that is operated from outside the calorimeter. The mixing of components is obtained by pushing the rod to break the membrane. The rod is also used as a stirrer during the test.

The ampoule mixing vessel is designed for a slow dissolution process and for a wetting operation. The sample is sealed under vacuum in a breakable ampoule. The vacuum operation allows desorbing the surface of the solid sample for easier dissolution. The sealed ampoule and the solution are introduced into the vessel. By breaking the ampoule, the solid and liquid samples are brought into contact.

The Table 2.3 gives an overview of the major calorimetric applica-tions, either in scanning or isothermal modes.

Methods of Microcalorimetry in Food

Microcalorimetry offers a variety of methods that are applied to the characterization of foods and their components.

Heat Capacity Determination

Heat capacity plays an important role in thermal process and in refrig-eration applications. Heat loads, processing times, and industrial equip-ment sizes are infl uenced by the heat capacity of the material. Combined with thermal conductivity and thermal diffusivity, heat capacity data are needed for modeling of the thermal processes. Heat capacity varies with temperature and composition, as well as water content (Kaletun , 2007 ). Because food material can be in solid or liquid form, different ways of measuring heat capacity using the calorimetric techniques have been developed.

Heat capacity is thermodynamically defi ned as the ratio of a small amount of heat Q added to the substance to the corresponding small increase in its temperature dT :

C

Q

dT=

(2.11)

For processes at constant pressure, the heat capacity is expressed as:

C

H

Tp

p

= (2.12)


Table 2.3. Applications of the C80 calorimetric technique versus the vessel and the heating mode.

Vessel Mode Component Application

Batch standard Scanning Starch Gelatinization, retrogradation Salt Solubility Carbohydrate Melting, crystallization,

amorphism, decomposition Batch high

pressure Scanning Coffee Safety (roasting),

supercritical CO 2 extraction

Cereal Self - ignition, explosion (powder)

Starch Gelatinization under pressure, glass transition versus pressure

Fat, chocolate Polymorphism versus pressure

Gas fl ow Scanning, isothermal

Oil Oxidative stability

Mixing (reversing)

Isothermal Oil Neutralization Sugar Dissolution Salt Dissolution Enzyme Enzymatic reaction Hydrocolloid Binding

Mixing (membrane)

Isothermal Starch Wetting, gelatinization Yeast Fermentation

Mixing (ampoule)

Isothermal Food powder Wetting, dissolution

Although DSC is a technique well suited to measure heat capacity (Richardson and Charsley 1998 ), essentially only one procedure has been developed using a continuous heating mode for solid samples. In this chapter, another procedure is described using a step - heating mode.

Heat c apacity d etermination in t emperature - s canning m ode If there is no conformational or phase transformation for the tempera-ture range considered, the calorimetric signal for a given mass of sample heated at a constant heating rate dT / dt is relative to the follow-ing relation for the sample side:


dq

dtm c m c

dT

dtss p s cs p cs

= +( )( ) ( )

(2.13)

where m s and m cs are, respectively, sample mass and vessel mass (including the cover) and c p ( s ) and c p ( cs ) are, respectively, specifi c heat capacity of the sample and its vessel.

For the reference side, an empty vessel is used giving the corre-sponding signal:

dq

dtm c

dT

dtrcr p cr

= ( )( )

(2.14)

where m cr is reference vessel mass and c p ( cr ) is specifi c heat capacity of reference vessel (equal to c p ( cs ) ).

The resulting differential calorimetric signal dq / dt is given by the following equation:

dq

dtm c m c m c

dT

dts p s cs p cs cr p cr

= + ( )( ) ( ) ( ) (2.15) To get rid of the thermal effect generated by both vessels, the same

test (called blank test) is run with identical empty containers. The fol-lowing equation describes the blank test heat fl ow.

dq

dtm c m c

dT

dtbcs p cs cr p cr

= ( )( ) ( )

(2.16)

By subtracting the two calorimetric traces, the specifi c heat capacity of the sample is extracted (Figure 2.9 ).

c

m

dq

dt

dq

dt

dT

dtp s

s b( ) =

1

(2.17)

As described in the calibration section, the Joule effect technique allows conversion of calorimetric signal in milliwatts without the need of standard reference materials. Therefore, in Equation 2.17 , all of the parameters (sample mass, calorimetric signals, heating rate) are accu-


rately known to determine the specifi c heat capacity of the sample c p ( s ) (expressed in J.g 1 . C 1 ) at a given temperature. For DSC technique, a third test is needed using a standard reference material (sapphire) that has a known specifi c heat capacity.

c p d etermination in the t emperature s tep m ode The technique described in previous section is easy to use, but has a drawback regarding the accuracy of the c p determination. Using the temperature scanning mode, the sample is continuously heated and is never at the thermal equilibrium. However, c p is a thermodynamical parameter, defi ned at the thermal equilibrium. The temperature step mode has been developed to address this limitation. A temperature step is applied to the sample, and the thermal equilibrium is established (characterized by return of the baseline) after each step. If Equation 2.15 is integrated from time t 0 (beginning of the step) to time t n (return to the baseline), the corresponding equation is obtained:

Q m c m c m c Ttt

s p s cs p cs cr p crn[ ] = + ( )( ) ( ) ( )0 (2.18)

where c p corresponds to the mean c p value between the two tempera-tures defi ning the step of temperature. Q is obtained by integrating the corresponding surface defi ned by the calorimetric signal between t 0 and t n . The signal corresponding to the blank test is subtracted when

time

Heat flow (mW)

Ab

As

T

Figure 2.9. c p determination in the temperature - scanning mode.


an identical step of temperature is applied to obtain the fi nal equation for the mean c p of the sample.

c

mQ Q Tp s

sb( ) = ( )1

(2.19)

In Equation 2.19 , the result is independent of fl uctuations of the baseline between the tests contrary to that of specifi c heat determina-tion in temperature scanning mode.

c p d etermination for l iquids Both methods described above apply mainly for the c p determination of solid and powder foods. They also can be used for liquids, but the c p contribution of the vapor above the liquid sample must be accounted for to have an accurate measurement. The correction can be obtained by using a vessel designed for the c p determination of liquids (Cerdeirina et al. 2000 ). The vessel is a cylindrical container with a tube welded on the top (Figure 2.10 ). The liquid is introduced in the calorimetric vessel via the tube using a syringe with a long needle, which allows a complete fi lling of the vessel without a vapor phase. As the tube is opened, the liquid will freely expand when heating. The

Figure 2.10. Liquid c p vessel and principle.


c p determination is run for a given volume V of liquid, located in the calorimetric detection zone. If Q 0 is the differential calorimetric area corresponding to an increase T of the temperature of the calorimeter when the two vessels (sample and reference) are empty, Q 1 when the measure vessel is fi lled with a standard liquid of known heat capacity, and Q 2 with the liquid to be investigated, the following equations are obtained:

Q Q V T S cp1 0 1 1 = (2.20) Q Q V T S cp2 0 2 2 = (2.21)

where S is calibration coeffi cient of the calorimeter, V is volume of the vessel, 1 and 2 are masses of standard and sample, and c p 1 and c p 2 are heat capacities of standard and sample. The heat capacity of the liquid sample, at a given temperature, is obtained without needing to know and measure the corresponding volume V :

c

Q Q

Q Qcp p2

1 0

2 0

1

21=

( )( )

(2.22)

The determination of the specifi c heat capacity requires the measure-ment of the density of the liquid sample. This c p measurement does not need vapor phase correction.

Heat c apacity of f oods The specifi c heat of foods depends on their composition, specifi cally the water content (Kaletun 2007 ). Table 2.4 gives an overview of the specifi c heat of selected foods above and below freezing ( www.engineeringtoolbox.com ).

Heating Mode

Microcalorimetry is used under the various heating modes are described next.

Scanning c alorimetry The scanning mode (heating or cooling) is the usual method that applies to the standard DSC technique. A microcalorimeter also can


be used as a DSC, but with low or very low scanning rates (less than 2 C.min 1 ). Longer time of experimentation may be considered to be a disadvantage, but it provides a better resolution of different thermal processes.

Melting and c rystallization Physical state transformations (crystal-lization, melting, polymorphism) in fat samples are associated with thermal effects that are easily measured by DSC. Microcalorimetry used in the scanning mode allows improvement of the resolution of different effects because of low scanning rate, especially for charac-terization of emulsions (Relkin and Sourdet 2005 ).

Denaturation and a ggregation Proteins are the food components most studied by the microcalorimetric technique and include studies of conformation changes of food proteins (animal, vegetable, plant), food enzymes and enzyme preparations for the food industry, as well as effects of various additives on their thermal properties.

The denaturation and aggregation processes in thermal gelation of whey proteins were resolved with the microcalorimetric technique (Fitzsimons et al. 2007 ). Numerous previous studies of the thermal gelation of whey proteins, carried out on conventional (fast - scanning)

Table 2.4. Heat capacity data for some foodstuffs.

Food Category Type Cp before Freezing (J g 1 C 11 )

Cp above Freezing (J g 11 C 11 )

Fruit Apple 1.76 3.64 Grapefruit 1.84 3.81 Orange juice 1.8 3.73

Vegetable Cabbage 1.88 3.94 Potato 1.72 3.43

Meat Pork (bacon) 1.05 1.51 Pork (ham) 1.42 2.6

Fish Salmon 1.55 2.97 Carp 1.72 3.43

Dairy Butter 1 1.26 Cream 1.88 3.77 Milk (cow) 1.97 3.77 Milk (coconut) 1.76 3.98 Ice cream 1.67 3.1


DSC calorimeters (typical sample mass 15 50 mg), have shown only endothermic transitions. Slow transfer of heat into a large vessel (850 mg of sample) allows the exothermic heat fl ow from the slow aggregation process to keep pace with the endothermic heat fl ow from the more rapid denaturation process and give a detectable exotherm (Figure 2.11 ). The same resolution effect with a slow scanning rate has also been noticed on pea storage protein, vicilin (Bacon et al. 1989 ), on bovine serum albumin (Barone et al. 1992 , 1995 ), and on ovalbumin (Hagolle et al. 1997 ; Relkin 2004 ).

Gelation Microcalorimetry is applied to investigation of gels formed by biopolymers, such as carrageenan (Williams et al. 1991a , 1992 ), xanthan (Williams et al. 1991a , b ), gellan (Miyoshi et al. 1995 ; Robinson et al. 1991 ), agar (Cooke et al. 1996 ), pectin, and gelatin. Polysaccharides are widely used for their gelling and thickening properties in the food industry. In presence of a cation (for example, potassium K + ), a solu-tion of kappa - carrageenan gives an aggregate structure during heating. The temperature of transformation and the reversibility of the reaction

3.2

100

9085

83.1

3.0

2.9

Hea

t flo

w (

mW

)

2.8

2.7

2.6

2.5

2.440 50 60 70

Temperature (C)

80 90 100

Figure 2.11. DSC heating scans (1.0 C/min) of 3.0 wt.% WPI pH 7.0) in the presence of NaCl at the different concentrations (80, 85, 90, and 100 mM NaCl). From Fitzsimons et al. (2007) .


(melting/gelation) can be obtained from the calorimetry data. Furthermore, detection of the transition depends not only on the poly-saccharide concentration but also on the product type. For xanthan and gellan, the energy associated with the transition is very weak, and the high sensitivity of the microcalorimeter is needed.

Gelatinization and r etrogradation Microcalorimetry is used to charac-terize the gelatinization behavior of starches and interaction of starch with other food components, as well as phase transitions during baking processes (Eliasson 2003 ). Calorimetry in the scanning mode is used not only to study the order - disorder behavior of starch during gelatiniza-tion but also to study the recrystallization (retrogradation) during storage (Berland et al. 2003 ). Crystallization can also be investigated in the isothermal mode. A special calorimetric vessel has been designed to investigate the starch gelatinization during cooking of pasta (Riva et al. 1991 ).

Isothermal c alorimetry Isothermal calorimetry is commonly used to simulate a process that occurs at a constant temperature or to check the storage stability of a food component (Sch ffer and Lorinczy 2005 ). When reactions and transitions take place within a food system, the kinetic parameters of reactions and transitions are obtained from analysis of isothermal calo-rimetric curves (Riva and Schiraldi 1993 ).

Shelf l ife Shelf life of foods (Franzetti et al. 1995 ; Riva et al. 1997, 1998, 2001 ) is investigated using isothermal calorimetry by continu-ously monitoring the kinetics of microbial growth or enzymatic activ-ity in fresh foods, such as whole eggs, fresh milk, and fresh carrots (Figure 2.12 ), or growth of bacteria in milk (Berridge et al. 1974 ). There are studies in the literature reporting the evaluation of bacterio-logical quality of seafood (Gram 1992 ), characterization of the thermal consequences of irradiation of bacteria (Moh csi - Farkas et al. 1994 ), and microbial degradation (Teeling and Cypionka 1997 ; Andlid et al. 1999 ) by using isothermal calorimetry.

Oxidative s tability Thermal oxidative decomposition of edible oils examined by calorimetry can be used for predicting oil stability under normal or high pressure of oxygen.


Isothermal c rystallization The investigation of crystallization in the isothermal mode requires a high stability of the baseline of the micro-calorimeter combined with a high sensitivity because such a test may last many hours. This type of experimental protocol is applied to iso-thermal crystallization of proteins, isothermal crystallization of fats, or isothermal retrogradation of starch.

0.14

0.12

0.1T=21.7C

T=24.6C

T=19.6C

T=24.6C

T=19.6CT=14.6C

T=14.7C

T=14.7C

T=9.6C

A-PASTEURIZEDWHOLE EGG

B-PASTEURIZEDWHOLE MILK

C-FRESH CARROTS

0.08

0.06

0.04

0.02

00 2 4 6

Time / days

Time / days

Time / days

8

0 21 43 5 6 7 8

0 10.5 1.5 2 2.5 3

10

0.14

0.12

0.1

0.08

0.06

0.04

0.02

0

0.12

0.1

0.08

0.06

0.04

0.02

0

exo

HF

/ m

W g

1H

F /

mW

g1

HF

/ m

W g

1

exo

exo

Figure 2.12. Isothermal traces at different temperatures for pasteurized whole egg, pasteurized whole milk, and fresh carrots. From Franzetti et al. (1995) .


Step h eating in c alorimetry Step heating (or cooling) calorimetry is a technique that is between the two previously described modes. A small variation of temperature is applied to the sample by step. After each step, the sample is maintained at a constant temperature for a certain period of time. The relevance of the stepwise methods resides primarily in the ability to follow step by step the differential structural changes as a function of the tempera-ture. The technique was applied to follow the kinetics of the gelation of gelatine (Cuppo et al. 2001 ) (Figure 2.13 ).

Mixing and Reaction Calorimetry

For investigation of mixing and reaction processes in foods, the micro-calorimetry has major advantages over the DSC. As described previ-ously, the larger capacity of the calorimetric chamber allows the design of specifi c mixing vessels. Liquid - liquid or solid - liquid interactions are evaluated by mixing obtained by stirring or ampoule breaking.

Mixing can be performed by two different modes:

1. Batch mixing: The two components A and B are brought into contact in the mixing vessel. The heat of mixing corresponds to a given concentration of A or B.

0.100 5 10 15 20 25 30 35 40

0 5 10 15 20time / hours

T / C

25 30 35 40

0.08

0.06

0.04

0.02

0.0040

30

20

10

0

heat

flow

/ m

W g

1

Figure 2.13. Stepwise heating thermogram (from 0 to 40 C) of 4.5% gelatine (LH1e) in aqueous 0.1 M NaCl. From Cuppo et al. (2001) .


2. Flow mixing: The two components A and B at a given fl ow rate are pumped and mixed in the vessel. The concentration of the mixture can be adjusted by modifying the fl ow rate of A or B.

Dissolution, s olubility In food industry, solid - liquid and liquid - liquid interactions are often encountered, such as dissolution of powder (sugar, salt) and solubility of proteins, lipids, and fi bers. For such studies, the batch - mixing vessel is ideal because it provides information relevant to the start of the reaction and the corresponding kinetics.

Neutralization The batch - mixing vessel is also convenient for the investigation of any reaction occurring during a food process, such as neutralization of edible oils by soda. Raw edible oils contain free fatty acids that have to be neutralized before being used. The amount of soda necessary for neutralization has to be adjusted based on the acidity of the oil. The simulation of the operation was performed on a microcalorimeter using edible oil with variable acidities (Figure 2.14 ).

Binding A mixing calorimeter is useful to investigate the impact of the weak nonspecifi c physical interactions of the food biopolymers (proteins,

heat flow

4 mW

rape seed 8,8 %

peanut 3 %

peanut 0,85 %

exo

0 5 10 15 20 25

time (mn)

30

1

2

3

1

2

3

Figure 2.14. Neutralization of free acidity in edible oil by soda (C80).


polysaccharides) with each other and with the major low - molecular - weight ingredients of the multicomponent food colloids (sugars, mineral salts, small - molecule surfactants). The structure formation in the bulk aqueous phase and at the interfaces of colloidal systems, as well as the functional properties, depend on these weak interactions (Semenova 2007 ).

Enzymatic r eactions The example for the enzymatic reaction of transformation of maltose using

Calorimetry in Food Processing- Analysis and Design of Food Systems

Documents

Transcript of Calorimetry in Food Processing- Analysis and Design of Food Systems