WATER AND WATER ACTIVITY OBJECTIVES 1 To understand

WATER AND WATER ACTIVITY OBJECTIVES 1. To understand what is bound water; 2. To learn what is water activity; 3. Importance of water activity for food chemistry and food technology; 4. Influence of water activity on major processes in foodstuffs.

WATER AND WATER ACTIVITY WATER – a matter of life and death Essential for the life on Earth: - as medium for development of organisms - as solvent - as regent in chemical and biochemical reactions - as cooling substance - as carrier of nutrients and wastes - as lubricant and plasticizer - as stabilizer of biopolymer conformation 1

WATER AND WATER ACTIVITY Product 2 WATER, % Meat - pork 53 - 60 - beef 50 - 70 - chicken ~ 74 - fish 65 - 81 Fruits - strawberry, cherry, pear, banana 80 - 85 - apple, peach 85 - 90 - orange, grapefruit 90 - 95 Vegetable - green pea 74 - 80 - potato, carrot, red beet, broccoli 80 - 90 - cabbage, tomato, lettuce, green bean, spinach 90 - 95 Beverages - beer 90 - juices 87 - whiskey, ouzo 58 - 60 - milk 85 - 88 Others - cheese 37 - white bread 35 - salami 30 - honey 20 - dry fruits 18 - butter, shortening (margarine) 16 - flour 12 - dry milk 4

WATER AND WATER ACTIVITY Structure and physical properties Hydrogen bonds formation with neighbors water molecules (or other subst. ) Н-bond energy – 13 -25 k. J/mol 3

WATER AND WATER ACTIVITY 4 Structure and physical properties Extended structure of ice – hexagonal lattice Ice density at 0 о. С (0, 9168 g/cm-3) and density of the liquid water in it - (0, 9998 g/cm-3) The highest density water has at 3, 98 о. С.

! WATER AND WATER ACTIVITY 5 Interactions of water with solutes 1. Macroscopic level (hydration, water-binding capacity) 2. Molecular level (bound water) - Bound water is that which does not freeze at some arbitrary low temperature (usually -40°C or lower). - Bound water is that which is unavailable as a solvent for additional solutes. - Bound water is that which moves with a macromolecule in experiments involving sedimentation rates, viscosity, or diffusion. - Bound water is that which exists in the vicinity of solutes and other nonaqueous substances and has properties differing significantly from those of “bulk” water in the same system.

WATER AND WATER ACTIVITY ! 6 Interactions of water with solutes Type Example Strength of interaction compared to water-water hydrogen bonda Dipole-ion Water-free ion Water-charged group on organic molecule Greaterb Dipole-dipole Water-protein NH Water-protein CO Water-sidechain OH Approx. equal Hydrophobic hydration Water + Rc - R(hydrated) Much less a About 12 -25 k. J/mol. b But much weaker than strength of single covalent bond. c R is alkyl group.

WATER AND WATER ACTIVITY Interactions of water with solutes 1. Interaction with ions and ionic groups Ion – ion (charged groups); Ion – dipole; H-bonds between water molecules Likely arrangement of water molecules adjacent to sodium chloride. Only water molecules in plane of paper are shown 7

WATER AND WATER ACTIVITY 8 Interactions of water with solutes 2. Interaction with neutral groups (having Hbonding capabilities Hydrogen bonding (dotted lines) of water to two kinds of functional groups occurring in proteins. dipole – dipole interactions Examples of a three-molecule water bridge in papain; 23, 24, and 25 - water molecules. (From Berendsen, H. J. C. (1975). Specific interactions of water with biopolymers, in Water—A Comprehensive Treatise, vol. 5 (F. Franks, ed. ), Plenum Press, New York, pp. 293– 349. )

WATER AND WATER ACTIVITY 9 Interactions of water with solutes 3. Interaction with nonpolar substances Proposed water orientation at a hydrophobic surface. (Adapted from Lewin, S. (1974). Displacement of Water and Its Control of Biochemical Reactions, Academic Press, London. ) Schematic depiction of a globular protein undergoing hydrophobic interaction. Open circles are hydrophobic groups, “L-shaped” entities around circles are water molecules oriented in accordance with a hydrophobic surface, and dots represent water molecules associated with polar groups.

! WATER AND WATER ACTIVITY Water activity (RVP) aw = Pw / Pºw where Pw – partial pressure of water vapors above solution or product Pºw – partial pressure of water vapors above pure water at the same temperature 10

WATER AND WATER ACTIVITY 11 Water activity (RVP) aw % water 1 100 meat 0. 97 - 0. 99 53 -75 milk 0. 97 85 Fruit juice 0. 95 – 0. 97 87 Cheese 0. 93 - 0. 96 35 -37 Bacon < 0. 85 - 0. 82 – 0. 94 - 0. 75 - room air 0. 5 - 0. 7 - honey 0. 5 - 0. 7 20 dry fruits 0. 5 - 0. 6 18 Product jam saturated solution of Na. Cl

! WATER AND WATER ACTIVITY Water activity (RVP) Moisture sorption isotherm (according to Labuza, T. P. , Kinetics of lipidoxidation in foods. Crit. Rev. Food Technol. 2, 355 (1971)). a Food with high moisture content; b Food with low moisture content 12

WATER AND WATER ACTIVITY 13 Water activity (RVP) – moisture sorption isotherms Information derived from MSIs are useful : 1). for concentration and dehydration processes, because the ease or difficulty of water removal is related to aw; 2) formulating food mixtures so as to avoid moisture transfer among the Ingredients; 4) to determine what moisture content will curtail growth of microorganisms of interest; 5) to predict the chemical and physical stability of food as a function of water content.

! WATER AND WATER ACTIVITY 14 Water activity (RVP) – moisture sorption isotherms Values of monomolecular layer of water for different dehydrated products – bound water (inaccessible microorganisms) Product g water/ 100 g product Dehydrated potatoes 5 -8 Dehydrated green been 4 -6 Dehydrated onion 4 Dehydrated biscuits 4 Dehydrated milk powder 2 Dehydrated beef 4 -6 Generalized moisture sorption isotherm for the low-moisture segment of a food Layers of water on food surface

WATER AND WATER ACTIVITY 14 a Water activity (RVP) Values of water BET monolayer value of a food provides a good first estimate of the water content providing maximum stability of a dry product BET equation p/p 0 of 0. 2 BET plot for native potato starch (resorption data, 20°C). Layers of water on food surface

WATER AND WATER ACTIVITY ! 15 Water activity (RVP) – moisture sorption isotherms Product water 1 meet 0. 97 - 0. 99 milk 0. 97 juice 0. 97 cheeses 0. 93 - 0. 96 bacon < 0. 85 jams 0. 82 – 0. 94 saturated solution of Na. Cl microorganism aw 0. 75 room air 0. 5 - 0. 7 honey 0. 5 - 0. 7 dry fruits 0. 5 - 0. 6 aw Clostridium botulinum 0. 97 Pseudomonas fluorescens 0. 97 Escherichia coli 0. 95 Clostridium perfringens 0. 95 Salmonella 0. 95 Vibrio cholerae 0. 95 Clostridium botulinum A, B 0. 97 Bacillus cereus 0. 93 Listeria monocytogenes 0. 92 Bacillus subtilis 0. 91 Staphylococcus aureus 0. 87 Most of the molds (fungi) 0. 70 No development 0. 60

WATER AND WATER ACTIVITY 16 Relative Vapor Pressure and Growth of Microorganisms in Food Microorganisms generally Range of inhibited by lowest p/p 0 in this aw range Foods generally within this range 1. 00– 0. 95 Pseudomonas, Escherichia, Proteus, Shigella, Klebsiella, Bacillus, Clostridium perfringens, some yeasts Highly perishable (fresh) foods and canned fruits, vegetables, meat, fish and milk; cooked sausages and breads; foods containing up to approximately 40% (w/w) sucrose or 7% sodium chloride 0. 95– 0. 91 Salmonella, Vibrio parahaemolyticus, C. botulinum, Serratia, Lactobacillus, Pediococcus, some molds, yeasts (Rhodotorula, Pichia) Some cheeses (Cheddar, Swiss, Muenster, Provolone), cured meat (ham), some fruit juice concentrates; foods containing up to 55% (w/w) sucrose or 12% Na. Cl Many yeasts( Candida, Torulopsis, Hansenula), Micrococcus Fermented sausage(salami), sponge cakes, dry cheeses, margarine; foods containing up to 65% (w/w) sucrose (saturated) or 15% Na. Cl 0. 91– 0. 87– 0. 80 Most molds (mycotoxigenic penicillia), Staphylococcus aureus, most Saccharomyces (bailii spp. ), Debaryomyces Most fruit juice concentrates, sweetened condensed milk, chocolate syrup, maple and fruit syrups; flour, rice, pulses containing 15– 17% moisture; fruit cake; country-style ham, fondants, high-ratio cakes

WATER AND WATER ACTIVITY 17 Relative Vapor Pressure and Growth of Microorganisms in Food Microorganisms generally Range of inhibited by lowest p/p 0 in this aw range Foods generally within this range 0. 80– 0. 75 Most halophilic bacteria, mycotoxigenic asperg illi Jam, marmalade, marzipan, glacé fruits, some marshmallows 0. 75– 0. 65 Xerophilic molds( Aspergillus chevalieri, A. candidus, Wallemia sebi), Saccharomyces bisporus Rolled oats containing approximately 10% moisture; grained nougats, fudge, marshmallows, jelly, molasses, raw cane sugar, some dried fruits, nuts 0. 65– 0. 60 Osmophilic yeasts( Saccharomyces rouxii) , few molds( Aspergillus echinulatus, Monascus bisporus) Dried fruits containing 15– 20% moisture; some toffees and caramels; honey 0. 50 No microbial proliferation Pasta containing approximately 12% moisture; spices (10% moisture) 0. 40 No microbial proliferation Whole egg powder (5% moisture) 0. 30 No microbial proliferation Cookies, crackers, bread crusts(3– 5% moist. ) No microbial proliferation Whole milk powder containing 2– 3% moisture; dried vegetables app. 5% moisture; corn flakes containing approximately 5% moisture; country style cookies, crackers 0. 20

! WATER AND WATER ACTIVITY Water activity (RVP) – moisture sorption isotherms Speed of deterioration of foods and speed of some important reactions depending of water activity (according to T. P. Labuza, Sorption phenomena in foods: Theoretical and practical aspects. In “Theory, determination and control of physical properties of food materials”, C. K. RHA ed. , p. 197, Riedel, Dordreht, 1975) 18

WATER AND WATER ACTIVITY 19 Water activity (RVP) – influence of the physical state MSI of sucrose – amorphous and crystalline state Transition from amorphous to crystalline – release of solvent and volatiles

WATER AND WATER ACTIVITY Water activity (RVP) – influence of the physical state In addition to chemical reactions and microbial growth, p/p 0 also influences the texture of dry and semidry foods. For example, suitably low RVPs are necessary if crispness of crackers, popped corn, and potato chips is to be retained; if caking of granulated sugar, dry milk, and instant coffee is to be avoided; and if stickiness of hard candy is to be prevented [*]. The maximum p/p 0 that can be tolerated in dry materials without incurring loss of desirable properties ranges from 0. 35 to 0. 5, depending on the product. Furthermore, suitably high water activities of soft-textured foods are needed to avoid undesirable hardness. * Labuza, T. P. , and R. Contreras-Medellin (1981). Prediction of moisture protection requirements for foods. Cereal Foods World 26(7): 335– 344. 19 a

WATER AND WATER ACTIVITY 20 Molecular mobility and food stability. Glass transition temperature State diagram of a binary system. Assumptions: maximal freeze concentration, no solute crystallization, constant pressure, no time dependence. Tmɤ is the melting point curve, TE is the eutectic point, Tms is the solubility curve Tg is the glass transition curve, and Tg’ is the solute-specific glass transition temperature of a maximally freeze concentrated solution. Heavy dashed lines represent conditions of metastable equilibrium.

WATER AND WATER ACTIVITY 21 Molecular mobility and food stability. Glass transition temperature State diagram of a binary system showing stabilities of diffusion-dependent properties of food. It is assumed that the “Tg’ zone” is the appropriate Tg for frozen foods, but this is still a matter of some disagreement.

WATER AND WATER ACTIVITY Molecular mobility and food stability. Glass transition temperature State diag ram of a binary system showing possible paths for freezing (unstable sequence ABCDE; stable sequence ABCDETg’F, drying (unstable sequence AHIJK; stable sequence AHIJLG) and freeze drying (unstable sequence ABCDEG; stable sequence ABCDETg’FG. 22

WATER AND WATER ACTIVITY 23 Combined methods approach to food stability and safety