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Chapter 4

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University of Guelph
Food Science
FOOD 2010
Massimo Marcone

CHAPTER 4 4.4 - THE CHEMICAL AND FUNCTIONAL PROPERTIES OF WATER  Functional Properties: physical and chemical properties of food molecules that affect their behavior in foods during formulation, processing and storage  Can include things such as sensory and mechanical properties of foods, texture, effects on water, and on physical condition  The functional properties are determined by functional groups  Functional properties of water in foods: Component of colloidal dispersions, fat-replacer ingredient, heat transfer, medium for chemical reactions, medium for microbial growth, plasticizer (a substance that, when added to a food system, makes it softer), product moisture, solvent Water Molecule Structure  H2O, the two hydrogen atoms bonded to oxygen  The oxygen atoms are partially negative, and the hydrogen atoms are partially positive, making it a dipole  The dipole nature affects physical characteristics like the boiling point, freezing point, and vapor pressure Solvation and Dispersing Action  Foods can form bonds with water, making them able to be dispersed or dissolved termed solubility  Compounds that easier bind to water are termed hydrophilic compounds  Water dissolves minerals, salts, some vitamins, sugars, complex carbohydrates, amino acids, and proteins  Hydration is the process by which water surrounds and interacts with solutes by acting as a solvent  Water disperses amphiphilic molecules, ones that have a both a hydrophilic and hydrophobic component  Dispersion of amphiphilic molecules requires micelles, molecules that group to form pockets to prevent exposure of the hydrophobic sections to the water  Interactions between water and food molecules are called noncovalent interactions Water Activity and Moisture  The presences of water in foods is called the moisture content or water activity of the food  Moisture is the amount of water present in a food, as a component, relative to all the solid constitute, such as proteins, carbohydrates, and any nonwater liquid  Free water is the most common form of water; it is lightly entrapped and therefore easily pressed from food matter  Absorbed water associates in ayers through hydrogen bonds around hydrophilic food molecules, also called structural water  Bound water or water of hydration exists in tight chemically bound situations such as in a crystalline structure  Water activity (awor A w is a measure of the availability of water molecules to enter into microbial, enzymatic, or chemical reactions  Water activity determines the shelf life of a food, it is temperature dependant Water as a Component of Emulsions  Emulsions are types of colloidal dispersions of liquids, or phases, which normally do not mix; dispersed phase and a continuous phase  Water can function as a dispersed or continuous phase; the presence of water is a prerequisite for an emulsion Water and Heat Transfer  Important vehicle for heat transfer during food processing and preperation  Water molecules always posses kinetic energy provided they have a temperature greater than 0 degrees Kelvin  Adding heat increases thermal energy  Water is available to act as a conductor of thermal energy to food molecules called heat transfer Water as an Ingredient  Water is used often in processing foods, it is often used in lower calorie foods  Water changed the state due to the freezing thawing temperature Water as a Plasticizer  Water acts as a plasticizer in low moisture and frozen foods  Plasticizers lower the glass transition temperature, which refers to the temperature at which a change in the physiochemical state and the mobility of the water and polymer molecule constituents of the food occurs  Water activity and glass transition temperature show a steady relationship  Plasticizer acts as a food system softener, increasing food polymer molecular volume as well as mobility 4.5 - THE CHEMICAL AND FUNCTIONAL PROPERTIES OF FOOD ACIDS  Acids are important in food  Acids come in many varieties; proteins contain amino acids that are important for shape, function, and nutrition, fats are made of fatty acids.  Tartaric acid functions as a leavening agent in baked products  The taste or citrus fruits comes from citric acid  Phosphoric acid is an important component in cola drinks Food Acid Structure  Typically food acids are carboxylic acids, a carboxylic acid group attached to the remainder of the molecule  Where the group is located differs, contributing to physical and chemical properties  Acids containing carboxylic acid groups are organic, ones missing it are considered to be inorganic  Food acid function ranges from influencing flavour to acting as a antimicrobial agents  Some foods use acids to sweeten flavour or to give a desired sour flavour  Certain foods require an acid to exhibit hygroscopicity, a low attraction to water, to prevent clumping of the ingredients  Functions of food acids is related to size and structure Acid Strength  Food acids donate (lose) protons, all considered weak acids  Weak acids are ones mainly in COOH form, with some H+ separated and some COO-, the have small ionization constants, strong acids are found mostly in the disassociated form  The amount of H+ ions determines the food pH, affecting sweetness, sourness, flavour, mouth feel, and appearance  Higher K aeans stronger acid, lower pK means stronger acid Fumaric Acid and Dough Softening  Some acids, fumaric included can soften flour dough  Dough’s contain the amino acid cysteine which forms disulfide bonds which make dough very tough and difficult to manipulate, fumaric can break these bonds, creating softer, easily manipulated dough Salts of Organic Acids  Organic salts are formed from organic acids where the hydrogen is replaced by a metal ion, sodium, calcium, or potassium is common ones  They are formed of base cations and acid anions Buffers  Buffers are solutions of weak acids and its salts at a pH where the solution has the ability to maintain that pH when quantities of the base are added  Milk acid (lactic acid) forms a buffer with lactate, the anionic conjugate  Buffering range is limited to a pH range extending one-half pH unit on either side of the pK a of an acid Leavening  Leavening refers to the production of gas by yeast fermentation, by the reaction of an acid with baking soda in batter and dough products, or by the heating of salts  Fermentation occurs when carbohydrates are converted to carbon dioxide gas and ethanol  Leavening occurs due to the production of gases expanding the product  Carbon dioxide, water vapour, air, ammonia, and ethanol are examples of gases, which cause leavening  Leavening acids are useful; they generate hydrogen ions that facilitate the release of carbon dioxide from baking soda  Gas release causes expansion of a baking bough or batter product because of increased nuclei pressure  Important properties of leavening acids are neutralizing value (NV) and dough reaction rate  NV is
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