Chapter 7 Water The Universal Solvent Images shutterstock

Chapter 7 Water: The Universal Solvent Images shutterstock. com

Objectives • Describe how the structure of a water molecule affects water’s physical characteristics. • Demonstrate a function of water in food preparation. • Explain how the water content of food affects how the food will react during preparation and storage processes. continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Objectives • Identify four functions of water in the body. • List common contaminants in water. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Water • Water is – the only substance found in abundance in the solid, liquid, and gaseous state – the main component of many foods – a nutrient necessary to sustain life • Nutritionally, water – helps control body temperature – transports nutrients and waste products – provides the solution for metabolic reactions continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Water • Water also – influences the texture, appearance, and taste of food – is an important heat medium in cooking – is an important solvent for cleaning and sanitation – is critical in food preservation – determines the likelihood of food spoilage by its presence or absence © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Types of Covalent Bonds • Water (H 2 O) has 2 hydrogen atoms and one oxygen atom – held together by covalent bonds • A nonpolar covalent bond is electrically neutral since electrons are shared equally by the atoms in the molecule • Water has a polar covalent bond, or an unequal sharing of electrons © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Hydrogen Bonds • The positive hydrogen end of one water molecule is drawn to the negative oxygen ends of other water molecules – This forms a hydrogen bond that is intermolecular, or between molecules ©Goodheart-Willcox Publisher © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Surface Tension • Hydrogen bonds in water create a greater surface tension than most compounds, allowing water to – cling to something else as well as itself – have a higher melting and boiling point than other compounds – freeze faster than it thaws – form a crystalline structure in the solid state continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Surface Tension • Hydrogen bonding helps to dissolve polar substances, making water a great solvent – Sugars, starches, and proteins form hydrogen bonds with water ©Isantilli/Shutterstock. com © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Pressure, Temperature, and Phase Changes • Atmospheric pressure impacts the boiling and freezing points – Water boils at lower temperatures at high altitudes and at higher temperatures at low altitudes – High altitude baking considerations such as increasing the amount of flour, water content, and oven temperature need to be considered © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Impact of Impurities in Water • Water is not usually found in pure form because it is such a great solvent • An impurity in water may change its – physical and chemical characteristics – flavor and color – boiling and freezing points – hydrogen bonding © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Functions of Water in Food Preparation • Water transfers heat energy into food – Water boils at a constant temperature – Steam is as hot as boiling water when not under pressure, but is hotter under pressure • Steam – leaves food more flavorful and nutritious than boiling – leavens baked goods continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Functions of Water in Food Preparation • Gas-in-water solutions – Carbon dioxide is the gas solute dissolved in water when making carbonated beverages – Oxygen also dissolves in water and is partially responsible for the taste of water • Liquid-in-water solutions – Alcoholic beverages, vinegars and fruit juice concentrates are examples continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Functions of Water in Food Preparation • Solid-in-water solutions – If a solid is dissolved in water, the chemical properties will be different than pure water – Salt and sugar lower the freezing point and increase the boiling point of water – Tea and coffee are flavor compounds dissolved in water © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Water Content in Foods • Water is a major part of most foods – Fruits and vegetables are over 70% water – Bread is 36% water – Popcorn is 4% water ©Aprilphoto/Shutterstock. com © Goodheart-Willcox Co. , Inc. continued Permission granted to reproduce for educational use only.

Water Content in Foods • Water becomes part of the structure of food in 3 ways 1. Free water – is easily separated from food tissue – often contains dissolved compounds – boils and freezes easily – readily evaporates when foods are dried continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Water Content in Foods 2. Bound water – is tied to the structure of larger molecules – does not easily freeze or boil – chemically reacts as part of the larger molecule 3. A hydrate – is any compound loosely bound with water – must be boiled to be free of water, known as anhydrous continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Water Content in Foods • The water type impacts perishability – Water bound to other compounds is not available to support food spoilage – Water in carrots is mostly bound to starch molecules, while in milk, it’s mostly free – Both are 88% water, but carrots are much less perishable ©Jozsef Szasz-Fabian/Shutterstock. com ©Dionisvera/Shutterstock. com © Goodheart-Willcox Co. , Inc. continued Permission granted to reproduce for educational use only.

Water Content in Foods • Water activity (Aw) takes into account the water available to support enzyme activity and microorganism growth – It is measured in values from 0 to 1 – The higher the number is, the more perishable the food will be – Canned foods are much more perishable than dried © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Functions of Water in the Body • The 4 main functions of water in the body are to – maintain body temperature – transport nutrients and waste products – serve as a reactant in metabolism – become part of body tissue • The water you drink and the water found in foods you eat help you stay hydrated © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

A Safe Water Supply • Rainwater that enters lakes and rivers may be filtered to become drinking water • A contaminant or pollutant is anything that makes a substance like water impure or unsafe, such as – human and animal wastes – chemicals and factory waste – garbage © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Common Pollutants • Biological contaminants – Large numbers of bacteria, protozoa, viruses, and organic waste deplete oxygen from rivers, lakes, and water supplies • Chemical contaminants – Metal ions such as calcium or magnesium cause hard water – Acid rain changes the p. H of water continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Common Pollutants • Physical contaminants – Garbage and litter such as cans, bottles, and plastics harbor bacteria, cause physical harm, and break down into toxins that enter the water supply ©Ariene Studio/Shutterstock. com © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Recap • The structure of water gives it many unique characteristics and functions in the human body and in food production • In food preparation, water acts as a – heat medium – leavening agent in baked goods when in the gaseous phase – solvent of gases, liquids, and solids continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Recap • Water becomes part of the structure of food in the form of – free water – bound water – a hydrate • Foods with higher water activity (AW) better support enzyme activity and microorganism growth continued © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Recap • Water is necessary in the body to – maintain body temperature – transport nutrients – serve as a reactant in metabolism – become part of body tissues • Common contaminants in water are – biological pollutants such as bacteria – chemical contaminants such as metal ions – physical contaminants such as litter © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.