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Chapter 4

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Food Science
FOOD 2010
Massimo Marcone

Chapter4 4.4TheChemicalandFunctionalProperties FunctionalProperties:physical and chemical properties of food molecules that affect their behaviour in foods during formulation, processing, and storage -includes sensory and mechanical properties of foods flavour, texture, effects on water, and physical condition of final product) -determined by functional groups -Functional properties of water in foods: - acting as a diluent and carrier of hydrophilic food ingredients - provide a medium for chemical and enzymatic reactions - dispersing and solvent action -serves as a fat replaced and zero-calorie ingredient -acts as a medium for heat transfer -functions as a plasticizer -accounts for food moisture -reactant in chemical reactions WaterMoleculeStructure -2 hydrogen atoms bonded to 1 oxygen -each H shares electron pair with oxygen atom -charge separation results, n which oxygen partly negative and hydrogen partly positive SolvingandDispersingAction - compounds that hydrogen bond easily to water to form solutions called Hydrophilic compounds -water dissolves substances by hydrating them Hydration:process by which water molecules surround and interact with solutes by acting as a solvent (considered salvation event) Micelles:clusters of molecules in which the hydrophobic groups are directed away from the water while the polar groups are exposed on the eternal surface. -non-polar hydrophobic groups form a stable inner core due to forces called hydrophobic interaction Non-covalentInteractions:between water molecules and between water and food molecules -important in food chemistry, include hydrogen bonding, ionic interactions, and hydrophobic interactions WaterActivityandMoisture -presence of water described as moisture content or water activity -Moisture refers to absolute amount of water present in a food -water activity has to do with the form in which the water exists in the food Moisture:amount water present, as a component, relative to all the solid constituents, such as proteins, carbs, and any non water liquid most water in foods called freewater(lightly entrapped and easily pressed from food matter) AbsorbedWater-associates in layers via intermolecular hydrogen bonds around hydrophilic food molecules BoundWater-exists in a tight chemically bound stations, such as within a crystalline structure, via water-ion and water-dipole interactions. Won't freeze at 09 or act as a solvent WaterActivity:(aw or Aw), measure of the availability of water molecules to enter microbial, enzymatic, or chemical reactions. Availability determines the shelf life of a food. Inversely related to bound water. & of bound water in a food increases, water activity decreases aw - P/Po P = vapour pressure of the food Po = vapour pressure of the pure water at same temp aw = water activity RH(relative humidity)(%) = aw x 100 MoistureSorptionisotherms:-graphs of data that interrelate the water contents of a food with its water activity at a constant temperature increase in temp = increase in water activity WaterasaComponentofEmulsion Emulsion: type of a colloidal dispersion, a system containing two liquids or phases that normally do not mix; a dispersed phase and a continuous phase -Water (aqueous component of an emulsion) either dispersed or a continuous phase WaterandHeatTransfer -important vehicle for heat transfer in foods during food processing operations and food preparation -with heat added, kinetic energy of water molecules increases(proportional) -Water conductor of thermal energy to food molecules, product called heat transfer WaterasanIngredient -common in processed foods, increasing amount of water can have quality repercussions because can act as solvent, change state with temperature, and exhibit motion within a food system WaterasaPlasticizer -acts as plasticizer especially in low moisture and frozen foods -plasticizer, when added to a polymer food system, lowers the glass transition temptation (temp at which a change in the physiochemical state and mobility of the water and polymer molecule constituents of a food occurs) -water activity and glass transition steady relationship T decreases with increased water activity 4.5TheChemicalandFunctionalPropertiesofFoodAcids FoodAcidStructure -typically carboxylic or organic acid (contains COOH) Hygroscopicity:low attraction for moisture AcidStrength -food acids donate protons Food acids are weak -weak acid is mainly in the form of COOD, but a small amount of H+ separated or dissociated, to form COO- + H+ -strong acids have large amount of dissociated ions ionizationconstant:-low in weak acids-pK measure of acids strength
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