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Water soluble interaction.pptx

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Water soluble interaction.pptx

  1. 1. Water soluble interaction G BHARATHI Assistant Professor Department of Food and Dairy Technology
  2. 2. Macroscopic Level (Water Binding, Hydration, and Water Holding Capacity)  Water binding and hydration - tendency for water to associate with hydrophilic substances, including cellular materials.  Water holding potential or capacity - The degree and tenacity of water binding or hydration depends on a number of factors including the nature of the non-aqueous constituent, salt composition, pH, and temperature.  The ability of a matrix of molecules, usually macromolecules present at low concentrations, to physically entrap large amounts of water in a manner that inhibits exudation.  Familiar food matrices that entrap water in this way include gels of pectin and starch, and cells of tissues, both plant and animal.
  3. 3. Water holding potential or capacity  Physically entrapped water does not flow from tissue foods even when they are cut or minced.  Acts as pure water during food processing  Examples: water in tissues and gels can be categorized as physically entrapped.  impairment of the entrapment capability of foods has a profound effect on food quality.  Examples of quality defects arising from impairment of water holding capacity are syneresis of gels, thaw exudate from previously frozen foods, and inferior performance of animal tissue in sausage resulting from a decline in muscle pH during normal physiological events postmortem.
  4. 4. Molecular Level Mixing of solutes and water - altered properties of both constituents. Hydrophilic solutes cause changes in the structure and mobility of adjacent water, and water causes changes in the reactivity, and sometimes structure, of hydrophilic solutes  Hydrophobic groups of added solutes interact only weakly with adjacent water, preferring a non-aqueous environment.
  5. 5. Molecular Level: Bound Water – hindered mobility
  6. 6. Interaction of Water with Ions and Ionic Groups
  7. 7. What effect does the intervening solvent have? in solution + - charge e1 charge e2 r F  e1e2 r2 Solvent Dielectric constant (D) water 78.5 methanol 32.6 acetone 20.7 benzene 2.3 As D increases, ions in solution interact more weakly with each other & more strongly with the solvent F = e1e2 Dr2 D: the dielectric constant of the solvent Ionic interactions
  8. 8. Interaction of water with ions:no naked ions Cl- Na+ Chloride anion Sodium cation + + - water Dipoles of water screen the charges of the ions so they don’t sense one another- water has a high dielectric constant Ions and ionic groups of organic molecules hinder mobility of water molecules to a greater degree than do any other types of solutes. The strength of water-ion bonds is greater than that of water- water hydrogen bonds, but is much less than that of covalent bonds.
  9. 9. Interaction of Water with Neutral Groups Possessing Hydrogen-Bonding Capabilities (Hydrophilic Solutes)  Interactions between water and non-ionic, hydrophilic solutes are weaker than water-ion interactions.  Solutes capable of hydrogen bonding does not disrupt the normal structure of pure water.  However, in some instances it is found that the distribution and orientation of the solute's hydrogen- bonding sites are geometrically incompatible with those existing in normal water.  Thus, these kinds of solutes frequently have a disruptive influence on the normal structure of water.
  10. 10. Continued…. Glucose molecules have polar hydroxyl(OH) groups in them and these attract the water to them. When sugar is in a crystal the molecules are attracted to the water and go into solution. Once in solution the molecules stay in solution at least in part because they become surrounded by water molecules. This layer of water molecules surrounding another molecule is called a hydration shell.
  11. 11. What does the strength of Hydrophilic Interactions depend on?  Inhibitory effect mainly depended on their concentration and to a lesser extent on the ion charge and hydrated ion radii.  The strength of interaction depends on the polarity parameters of solute and is independent of their chemical structure.
  12. 12. Water & polar neutral molecules: hydrogen bonding O H OH H H H H OH O H O H OH Water forms extensive H-bonds with molecules such as glucose, rendering it highly soluble
  13. 13. • Some of the common natural Hydrophobic materials are waxes, oil and fats. Hydrophobicity comes also from the greek word Hydro(water) and Phobicity (fear) it refers to the physical property of a material that repels a mass of water. Interaction of Water with Nonpolar Substances The evaluation of hydrophobicity is made through water contact angle measurements. A water droplet would be spherical so the water contact angle will be significantly high.
  14. 14. Causes of Hydrophobic Interactions • American chemist Walter Kauzmann discovered that nonpolar substances like fat molecules tend to clump up together rather that distributing itself in a water medium, because this allow the fat molecules to have minimal contact with water. Hydrophobic interactions - ChemWiki
  15. 15. • At the molecular level, the hydrophobic effect is important in driving protein folding formation of lipid bilayers and micelles, insertion of membrane proteins into the nonpolar lipid environment and protein-small molecule interactions. Substances for which this effect is observed are known as hydrophobes. HYDROPHOBIC EFFECT The hydrophobic effect represents the tendency of water to exclude non-polar molecules. The effect originates from the disruption of highly dynamic hydrogen bonds between molecules of liquid water. Continued….
  16. 16. Water & nonpolar molecules: Hydrophobic Interactions • H-bond network of water reorganizes to accommodate the nonpolar solute • This is an increase in "order" of water (a decrease in entropy) • number of ordered water molecules is minimized by herding nonpolar solutes together Yellow blob: nonpolar solute (eg oil)
  17. 17. SUMMARY Water forms H-bonds with polar solutes Ions in water are always surrounded by a hydration shell (no naked ions)  Hydrophilic (polar): water-soluble molecules Hydrophobic (nonpolar): water insoluble (greasy) Hydrophobic interaction: fewer water molecules are needed to corral one large aggregate than many small aggregates of a hydrophobic molecule
  18. 18. Water activity and relative vapor pressure
  19. 19. Water Activity • Water activity (aw) is a measure of how easy the water content may be utilized. • In 1952, Scott came to the conclusion that the storage quality of food does not depend on the water content but on water activity (Aw) Aw = P/ P0 = ERH/100 Where, ERH= Equilibrium relative humidity - RH of air and sample at equilibrium. P = Partial vapor pressure P0 = Saturation vapor pressure .
  20. 20.  In figure the desorption isotherm, indicating the course of a drying process lies slightly above the adsorption isotherm pertaining to the storage of moisture sensitive food.  Decreased water activity retards the growth of micro organisms, slow enzyme catalyzed reactions and lastly retards non enzymatic browning.  Foods with aw values between 0.6 and 0.9 are known as “Intermediate Moisture Foods” Those foods are largely protected against microbial spoilage.
  21. 21. Sorption Isotherm  The relationship between water activity and water content is indicated by sorption isotherm of food.  At low water content (<50%) even minor changes in this parameter lead to major changes in water activity.  Resorption means addition of water to the previously dried samples.
  22. 22. RELATIVE VAPOR PRESSURE AND FOOD STABILITY (a) Microbial growth vs. (p/po)T, (b) Enzymic hydrolysis vs. (p/po)T, (p/po)T FIGURE
  23. 23. (c) oxidation (nonenzymic) vs. (p/po)T (d) Maillard browning vs.(p/po)T, (p/po)T
  24. 24. (e) miscellaneous reaction rates vs.(p/po)T, (f) water content vs.(p/po)T. (p/po)T
  25. 25. THANK YOU

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