Lecture 3 HN 300-3 - Water and The Physical Aspects of Food...

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Water and The Physical Aspects of Food Preparation Lecture 3 HN 300
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Water Often taken for granted Its abundance and unique characteristics make it an invaluable substance especially when it comes to food and cooking.
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Water and Food It is a principal constituent of foods, with most foods containing over 50% water. The water content of food changes with cooking. It is a solvent in many foods and also a dispersing medium. Promotes chemical reactions via H bonding. Water content can also affects food spoilage.
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Water: The Internal Sea Functions of water in the body Solvent Reactant Lubricator and protector Transporter Regulator of temperature and pH
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Chemical Structure of Water
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Functions of Water: An Example
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Functions of Water: Another Example Important for maintaining the proper pH , a measure of the level of acidity or alkalinity of a solution
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Distribution of Body Water Intracellular fluid: ~2/3 water is inside cells In adults, ~ 60% of total body weight Blood ~90%, muscle ~75%, bone ~25%, and adipose tissue ~10% Extracellular fluid: ~1/3 water is outside cells Blood plasma and lymph Interstitial fluid Other type of fluid
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Why does water behave the way it does? Because of its polarity Polarity = refers to the dipole-dipole intermolecular forces between the slightly positively-charged end of one molecule to the negative end of another or the same molecule.
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Water is a Dipole This means that it is electrically asymmetrical—that is, one side is slightly negative and another side of the molecule is slightly positive
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Water’s Structure The electrons of water's hydrogen atoms are strongly attracted to the oxygen atom, and are actually closer to oxygen's nucleus than to the hydrogen nuclei; thus, water has a relatively strong negative charge in the middle, and a positive charge at the ends
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Structure of Water 105° Angle - + +
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This promotes the formation of hydrogen bonds between water molecules:
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Hydrogen bonds: An attractive interaction that exists between an electronegative atom and a hydrogen atom bonded to another electronegative atom Enable water to be in liquid form over a relatively wide temperature range They are relatively weak bonds (secondary bonds), but are sufficiently strong to hold water molecules in close proximity unless a lot of energy in introduced into the system
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States of Water: Solid (a.k.a ice) Gas Liquid Each of these reflect varying energy states
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Changes in the state of water:
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Heat of Fusion Heat released when a liquid is transformed into a solid (ex: liquid water to ice) This is 80 calories per gram with water Also called the heat of solidification Removal of 80 kcals per gram results in a change of state, without a change in temp.
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Ice: As water cools molecules separate Causes an increase in volume, hence ice is less dense than liquid water Bonding in ice leads to hexagonal openings, or an organized lattice
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Melting of ice: It takes 79.7 kcals per gram of water for ice
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