Page172Water and IceOWEN R. FENNEMAUniversity of WisconsinMadison, Madison, Wisconsin18Prologue: WaterThe Deceptive Matter of Life and Death182.1Introduction192.2 Physical Properties of Water and Ice202.3 The Water Molecule222.4 Association of Water Molecules242.5 Structure of Ice242.5.1 Pure Ice292.5.2 Ice in the Presence of Solutes29 2.6 Structure of Water302.7Water-Solute Interactions30 2.7.1 Macroscopic Level (Water Binding,Hydration, and waterHolding Capacity)312.7.2Molecular Level: General Comments312.7.3 Molecular Level: Bound Water322.7.4 Interaction of Water with Ions and Ionic Groups332.7.5 Interaction of Water with Neutral Groups Possessing Hydrogen-Bonding Capabilities (Hydrophilic Solutes)352.7.6 Interaction of Water with Nonpolar Substances372.7.7 Details of Water Orientation Adjacent to Organic Molecules382.7.8Hydration Sequenceof a Protein422.8WaterActivity and Relative Vapor Pressure422.8.1 Introduction422.8.2 Definition and Measurement442.8.3TemperatureDependence
Pag e 17 2 Water and Ice OWEN R. FENNEMA University of Wisconsin—Madison, Madison, Wisconsin Prologue: Water—The Deceptive Matter of Life and Death 18 2.1 Introduction 18 2.2 Physical Properties of Water and Ice 19 2.3 The Water Molecule 20 2.4 Association of Water Molecules 22 2.5 Structure of Ice 24 2.5.1 Pure Ice 24 2.5.2 Ice in the Presence of Solutes 29 2.6 Structure of Water 29 2.7 Water-Solute Interactions 30 2.7.1 Macroscopic Level (Water Binding, Hydration, and water Holding Capacity) 30 2.7.2 Molecular Level: General Comments 31 2.7.3 Molecular Level: Bound Water 31 2.7.4 Interaction of Water with Ions and Ionic Groups 32 2.7.5 Interaction of Water with Neutral Groups Possessing HydrogenBonding Capabilities (Hydrophilic Solutes) 33 2.7.6 Interaction of Water with Nonpolar Substances 35 2.7.7 Details of Water Orientation Adjacent to Organic Molecules 37 2.7.8 Hydration Sequence of a Protein 38 2.8 Water Activity and Relative Vapor Pressure 42 2.8.1 Introduction 42 2.8.2 Definition and Measurement 42 2.8.3 Temperature Dependence 44
472.9 Moisture Sorption Isotherms472.9.1 Definition and Zones502.9.2Temperature Dependence502.9.3Hysteresis
2.9 Moisture Sorption Isotherms 47 2.9.1 Definition and Zones 47 2.9.2 Temperature Dependence 50 2.9.3 Hysteresis 50
Page18522.10RelativeVaporPressure andFood Stability552.11 Molecular Mobility (Mm) and Food Stability552.11.1 Introduction572.11.2 State Diagrams592.11.3 Nine Key Concepts Underlying the Molecular MobilityApproach to Food Stability722.11.4 Technological Aspects: Freezing792.11.5 Technological Aspects: Air Drying792.11.6 Technological Aspects: Vacuum Freeze-Drying(Lyophilization)802.11.7 Technological Aspects: Other Applications of the MmApproach (Partial Listing)802.11.8 Technological Aspects: Estimation of Relative Shelf Life802.11.9 Technological Aspects: Relationship of Tg and Mm to RelativeVapor Pressure (p/po) and Moisture Sorption Isotherms822.11.10 Summary Statements Regarding the Mm Approach to FoodStability832.12Combined Methods Approach toFood Stability852.13 Concluding Comments About Water85Glossary: Molecular Mobility and Food Stability87Acknowledgments87Abbreviations and Symbols88Bibliography88ReferencesPrologue: Water-The Deceptive Matter of Life and Death
Pag e 18 2.10 Relative Vapor Pressure and Food Stability 52 2.11 Molecular Mobility (Mm) and Food Stability 55 2.11.1 Introduction 55 2.11.2 State Diagrams 57 2.11.3 Nine Key Concepts Underlying the Molecular Mobility Approach to Food Stability 59 2.11.4 Technological Aspects: Freezing 72 2.11.5 Technological Aspects: Air Drying 79 2.11.6 Technological Aspects: Vacuum Freeze-Drying (Lyophilization) 79 2.11.7 Technological Aspects: Other Applications of the Mm Approach (Partial Listing) 80 2.11.8 Technological Aspects: Estimation of Relative Shelf Life 80 2.11.9 Technological Aspects: Relationship of Tg and Mm to Relative Vapor Pressure (p/p0) and Moisture Sorption Isotherms 80 2.11.10 Summary Statements Regarding the Mm Approach to Food Stability 82 2.12 Combined Methods Approach to Food Stability 83 2.13 Concluding Comments About Water 85 Glossary: Molecular Mobility and Food Stability 85 Acknowledgments 87 Abbreviations and Symbols 87 Bibliography 88 References 88 Prologue: Water—The Deceptive Matter of Life and Death
Unnoticed inthedarknessofa subterraneancavern,awaterdroplettrickles slowlydownastalactite,followingapathleftbycountless predecessors, imparting, as did they, a small but almost magical touch of mineral beauty. Pausing at the tip, the dropletgrows slowly to full size, then plunges quickly to the cavern floor, as if anxious to perform other tasks or to assume differentforms. For water, the possibilities are countless. Some droplets assume roles of quiet beauty-on a child's coat sleeve, where asnowflake ofunique design and exquisite perfection lies unnoticed, on a spider's web, where dew drops burst into suddenbrlliance at the first touch of the moming sun; in the countryside, where a summer shower brings refreshment, or in the city,wherefoggentlypermeatesthenight air,subduingharshsoundswithaglazeoftranquility.Otherslendthemselvestothenoiseandvigorofawaterfall,totheoverwhelmingimmensityofaglacier,totheominousnatureofanimpendingstorm,ortothepersuasiveness of a tear on a woman's cheek.For others the role is less obvious but far more critical.There is lifeinitiated andsustained by water in a myriad of subtle and poorly understood waysor death inevitable, catalyzed under specialcircumstancesbyafewhostilecrystals ofice;ordecayat theforest'sfloor,wherewaterworksrelentlesslytodisassemble thepast so life can begin anew. But the form of water most familiar to humans is none of these; rather, it is simple, ordinary,anduninspiring, unworthy of special notice as it flows forth in cool abundance from a household tap.Humdrum,"galunks a frog inconcurrence, or so it seems as he views with stony indifference the watery milieu on which his very life depends. Surely, then,water'smostremarkablefeatureisdeception,forit isinrealitya substanceof infinitecomplexity,ofgreatandunassessableimportance, and one that is endowed with a strangeness and beauty sufficient to excite and challenge anyone making itsacquaintance2.1IntroductionOnthisplanet,water is theonly substancethat occurs abundantlyin all threephysical states.It istheonly commonliquid and isthemostwidelydistributedpuresolid,beingeverpresent
Unnoticed in the darkness of a subterranean cavern, a water droplet trickles slowly down a stalactite, following a path left by countless predecessors, imparting, as did they, a small but almost magical touch of mineral beauty. Pausing at the tip, the droplet grows slowly to full size, then plunges quickly to the cavern floor, as if anxious to perform other tasks or to assume different forms. For water, the possibilities are countless. Some droplets assume roles of quiet beauty—on a child's coat sleeve, where a snowflake of unique design and exquisite perfection lies unnoticed; on a spider's web, where dew drops burst into sudden brilliance at the first touch of the morning sun; in the countryside, where a summer shower brings refreshment; or in the city, where fog gently permeates the night air, subduing harsh sounds with a glaze of tranquility. Others lend themselves to the noise and vigor of a waterfall, to the overwhelming immensity of a glacier, to the ominous nature of an impending storm, or to the persuasiveness of a tear on a woman's cheek. For others the role is less obvious but far more critical. There is life—initiated and sustained by water in a myriad of subtle and poorly understood ways—or death inevitable, catalyzed under special circumstances by a few hostile crystals of ice; or decay at the forest's floor, where water works relentlessly to disassemble the past so life can begin anew. But the form of water most familiar to humans is none of these; rather, it is simple, ordinary, and uninspiring, unworthy of special notice as it flows forth in cool abundance from a household tap. “Humdrum,” galunks a frog in concurrence, or so it seems as he views with stony indifference the watery milieu on which his very life depends. Surely, then, water's most remarkable feature is deception, for it is in reality a substance of infinite complexity, of great and unassessable importance, and one that is endowed with a strangeness and beauty sufficient to excite and challenge anyone making its acquaintance. 2.1 Introduction On this planet, water is the only substance that occurs abundantly in all three physical states. It is the only common liquid and is the most widely distributed pure solid, being ever present
Page 19TABLE1Water Contents ofVarious FoodsFoodWater content(%)Meat53-60Pork,raw, composite oflean cuts5070Beef, raw, retail cuts74Chicken,all classes,rawmeat without skin6581Fish, muscle proteinsFruit8085Berries, cherries, pears90-90Apples, peaches, oranges, grapefruit90-95Rhubarb,strawberries,tomatosVegetables7480Avocado,bananas,peas (green)85-90Beets,broccoli,carrots,potatoes90-95Asparagus,beans (green),cabbage,cauliflower,lettucesomewhere in the atmosphere as suspended ice particles, or on the earth's surface as various types of snow and ice.It isessential tolife:asan importantgovernorofbodytemperature,asasolvent,asacarrierofnutrientsandwasteproducts,asareactantandreactionmedium,asalubricantandplasticizer,asastabilizerofbiopolymerconformation,asalikelyfacilitatorofthe dynamic behavior of macromolecules, including their catalytic (enzymatic) properties, and in other ways yet unknown, It istruly remarkable that organic life should depend so heavily on this small inorganic molecule, and, perhaps even more remarkable,that so few scientists are aware of this fact.Water is the major component ofmanyfoods, each having its own characteristic allotment of this component (Table 1).Water inthe proper amount, location, and orientation profoundly influences the structure, appearance, and taste offoods and theirsusceptibility to spoilage. Because most kinds offresh foods contain large amounts of water, effective forms of preservation areneeded if long-term storage is desired. Removal of water, either by conventional dehydration or by separation locally in the formof pure ice crystals (freezing),greatly alters the native properties of foods and biological matter.Furthermore, all attempts(rehydration, thawing) to return water to its original status are never more than partially successful. Ample justification exists,therefore, to study water and ice with considerable care2.2Physical Properties of Water and IceAs a first step in becoming familiar with water, it is appropriate to consider its physical properties as shown in Table 2. Bycomparing water's properties with those of molecules of similar molecular weight and atomic composition (CH, NHs, HF, HSHSe, HaTe) it is possible to determine if water behaves in a normal fashion. Based on this comparison, water is found to meltand boil at unusually high temperatures; to exhibit unusually large values for surface tension, permittivity (dielectric constant), heatcapacity, and heats of phase transition (heats of fusion, vaporization, and sublimation), to have a moderately low value fordensity, to exhibit an unusual attribute of expanding upon solidification; and to possess a viscosity that in light of the foregoingoddities,issurprisinglynormal.In addition, the thermal conductivity of water is large compared to those ofother liquids, and the themal conductivity ofice ismoderatelylargecomparedtothoseofothernonmetallic
Pag e 19 TABLE 1 W ater Contents of Various Foods Food W ater content (%) Meat Pork, raw, composite of lean cuts 53–60 Beef, raw, retail cuts 50–70 Chicken, all classes, raw meat without skin 74 Fish, muscle proteins 65–81 Fruit Berries, cherries, pears 80–85 Apples, peaches, orang es, g rapefruit 90–90 Rhubarb, strawberries, tomatos 90–95 Veg etables Avocado, bananas, peas (g reen) 74–80 Beets, broccoli, carrots, potatoes 85–90 Asparag us, beans (g reen), cabbag e, cauliflower, lettuce 90–95 somewhere in the atmosphere as suspended ice particles, or on the earth's surface as various types of snow and ice. It is essential to life: as an important governor of body temperature, as a solvent, as a carrier of nutrients and waste products, as a reactant and reaction medium, as a lubricant and plasticizer, as a stabilizer of biopolymer conformation, as a likely facilitator of the dynamic behavior of macromolecules, including their catalytic (enzymatic) properties, and in other ways yet unknown. It is truly remarkable that organic life should depend so heavily on this small inorganic molecule, and, perhaps even more remarkable, that so few scientists are aware of this fact. Water is the major component of many foods, each having its own characteristic allotment of this component (Table 1). Water in the proper amount, location, and orientation profoundly influences the structure, appearance, and taste of foods and their susceptibility to spoilage. Because most kinds of fresh foods contain large amounts of water, effective forms of preservation are needed if long-term storage is desired. Removal of water, either by conventional dehydration or by separation locally in the form of pure ice crystals (freezing), greatly alters the native properties of foods and biological matter. Furthermore, all attempts (rehydration, thawing) to return water to its original status are never more than partially successful. Ample justification exists, therefore, to study water and ice with considerable care. 2.2 Physical Properties of Water and Ice As a first step in becoming familiar with water, it is appropriate to consider its physical properties as shown in Table 2. By comparing water's properties with those of molecules of similar molecular weight and atomic composition (CH4, NH3, HF, H2S, H2Se, H2Te) it is possible to determine if water behaves in a normal fashion. Based on this comparison, water is found to melt and boil at unusually high temperatures; to exhibit unusually large values for surface tension, permittivity (dielectric constant), heat capacity, and heats of phase transition (heats of fusion, vaporization, and sublimation); to have a moderately low value for density; to exhibit an unusual attribute of expanding upon solidification; and to possess a viscosity that in light of the foregoing oddities, is surprisingly normal. In addition, the thermal conductivity of water is large compared to those of other liquids, and the thermal conductivity of ice is moderately large compared to those of other nonmetallic