Chapter Images shutterstock.com 7 Water: The Universal Solvent

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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 continued ©Aprilphoto/Shutterstock.com

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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 continued ©Dionisvera/Shutterstock.com ©Jozsef Szasz-Fabian/Shutterstock.com

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Water Content in Foods Water activity (A w ) 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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 pH of water continued

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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 Recap continued

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

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. 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 Recap