Unit 8: How Energy Fuels Your Body & Cooks Your Food CH. 5

Energy Energy – the ability to do work Food Scientist examine How heat is transferred How energy affects the structure of food during processing

2 Types of Energy Potential Energy – Energy that is stored or the energy of work done Example: Rock at the edge of a cliff. Lifting the rock to the edge stored the work done in the lifting.

2 Types of Energy Continued… 2. Kinetic Energy – Energy of motion. The faster an object moves the more kinetic energy it has. Energy can switch between Kinetic Energy and Potential energy. Example) child on a swing.

External vs. Internal Energy Kinetic and Potential energy can be described as external or internal. External Energy – Energy applied to an object by another source. Example) Sitting still= external potential energy. Friend pulls you out of chair= external kinetic energy Internal Energy – Energy within an object. Example) Your body doing work= internal kinetic energy. Fat in the body= internal potential energy.

5 Forms of Energy in the UNIVERSE! Mechanical Chemical Electrical Nuclear Radiant

1. Mechanical Energy Mechanical energy – total kinetic and potential energy of a system. Energy acquired by the objects upon which work is done. Importance to food science – machinery must be able to convert energy to a usable form without damaging the food product

2. Chemical Energy Chemical Energy – Energy created from forming and breaking bonds between atoms. Breaking chemical bonds of food (carbohydrates, proteins, & fats) creates chemical energy to fuel bodily functions. Importance: Chemical energy is involved in all processes from food preparation through digestion.

Endothermic vs. Exothermic Reactions Can be physical or chemical reactions Endothermic – absorbs or stores energy. Result= lower temperature after the reaction. Example) Salt + Ice = lower temperature. Therefore, you can make homemade ice cream.

Endothermic vs. Exothermic Continued… Exothermic – energy is released during the reaction. Result= higher temperature after the reaction. Example 1) Sodium Hydroxide + water = higher temperature. Drain cleaner heats up water to remove fats and unclog drains. Ex 2) Digestion – Break down food. Heat released.

Endothermic vs. Exothermic Continued…

3. Electrical Energy Electrical Energy – Energy produced by the movement of electrons. Transported through conductors & easily transformed into other forms of energy

Electrical Energy Continued… Examples) Hydroelectric Dams: Falling water (mechanical energy) transported through wires as electric energy Appliances: Lamps= electrical energy into light. Toasters= electrical energy into heat.

4. Nuclear Energy Nuclear Energy – result of splitting or combining atoms of certain elements, which then give off radiation Radiation can be used for X-rays Food preservation (irradiation) Generate electricity (nuclear power plants)

5. Radiant Energy Radiant Energy – transmitted in the form of waves through space or some medium. AKA the electromagnetic spectrum. Examples: Light (visible radiant energy) Radio waves Ultraviolet waves Microwaves

Radiant Energy - Microwave Ovens Convert electrical energy into radiant energy to cook food Interior surfaces designed to reflect waves towards food Causes polar substances (like water) to vibrate, which heats the food faster. Foods high in fats and sugars conduct heat away from other compounds in food; therefore, will also heat rapidly in the microwave

Radiant Energy - Induction Cooktops Use electromagnetic waves to generate heat in foods. Special, flat bottomed pans are needed to conduct the energy. Alternating currents create a magnetic field that excites electrons and produces a low electric current in the pan. Can boil water in ½ the time of gas and electric stoves

2 Main Energy Measurements in Food Science 2 main energy measurements in F.S. – Heat & Temperature Heat – Energy transfer from one body to another caused by a temperature difference between the two bodies.

Energy Measurements Continued… Food scientists most often measure food energy in terms of the capacity to produce heat. Units of measurement = joule (metric system) and Calorie. Calorie – (aka kcal or kilocalorie) heat required to raise the temperature of one kilogram of water one degree Celsius.

Energy Measurements Continued… Heat Capacity – ability of a substance to absorb heat. Water content of a food determines the food’s heat capacity, since water has the ability to rapidly absorb heat and transfer it. Food with high water content = high heat capacity

Energy Measurements Continued… Specific heat – the amount of energy needed to raise the temperature of 1 gram of that substance 1 degree Celsius Specific heat (a physical property) is important in food storage

Energy Measurements Continued… Cooling foods with low specific heats will require less heat energy to be removed than cooling foods with high specific heats. Knowing specific heat of food helps in predicting how a food will react during processing Researchers also evaluate the heat produced or released by machinery in food processing to become the most energy efficient (more work for less money)

Energy Measurements Continued… Temperature – the measure of the average kinetic energy of a group of individual molecules. Types of thermometers needed in food prep & storage: Candy Deep-fat Freezer Meat Oven

Energy Measurements Continued… Food companies use precision equipment to carefully monitor temperature during each step of production Especially important to monitor temperature in pasteurization, fermentation, bread production, etc. Changes in only a few degrees can make a huge difference in product quality

Heat Transfer Heat always flows from hot objects to cooler ones 3 basic methods of heat transfer Conduction Convection Radiation Responsible for cooking the inside of foods. Outside of foods (browning).

1. Conduction Conduction – transfer of heat through matter from particle to particle collisions.

1. Conduction Continued… Heat source has rapidly moving particles that collide with the pan. The particles of the heated pan then collide with the food and heat it up until the source, pan and food are all the same temperature. Metals are the best conductors because they use electron conduction. Also, metals are durable so commonly used in cookware.

2. Convection Convection - Transfer of heat by the motion of molecules within a liquid or gas Faster than conduction As the fluid heats the cooler molecules sink until they come into contact with the heat source – convection currents.

2. Convection Continued… Convection ovens cook faster than regular ovens because fans move the hot air more rapidly (forced convection) around the food being cooked.

3. Radiation Radiation – transfer of heat by electromagnetic waves. Does not require the presence of matter. Allows the sun to travel through the vacuum of space Examples) Solar oven, broiling & rotisserie cooking

Energy Flow in Phase Changes Flow of energy to a substance can cause phase changes Fusion (melting) – solid to liquid. Energy added. Crystallization (freezing) – liquid to solid. Energy removed. Energy needed to melt or freeze a substance is called the latent heat of fusion.

Energy Flow in Phase Changes Continued… Vaporization (evaporation) – liquid to gas. Energy added. Condensation (liquefaction) – gas to liquid. Energy removed. Amount of heat needed to either evaporate or condense a substance is called the latent heat of vaporization.

Energy Flow in Phase Changes Continued… Temperature remains constant during the phase change. Gives time for the molecules to all arrange in the new form.

Energy Flow in Phase Changes Continued… Sublimation – solid to gas. Energy added. Example) Dry ice (solid CO2) & gas rising (gaseous CO2). Deposition – gas to solid. Energy removed. Example) Frost on window on cold morning. The water vapor in the air changed directly to a solid state. Food examples) Sublimation – freeze dried coffee and instant tea.

Energy Flow in Phase Changes Continued…

Energy Flow in Phase Changes Continued…

Latent Heat Latent heat - energy needed to rearrange molecules Substance being cooled= Energy being released Occurs during freezing, condensing, and deposition. Substance being heated= Energy (heat) being used or absorbed. Occurs during melting, vaporization, and sublimation.

Latent Heat Continued…

Factors That Affect Food Preparation Rates Temperature Surface Area Thickness Which one of these factors would slow food preparation rates? Which would speed up? Slow: thick, low temps Fast: thin, more surface area, high temp, enzymes

1. Temperature of Reactants Rate of a reaction doubles for every 10 degrees Celsius increase in temperature. More temperature= more molecular motion & collisions. Example) Roast cooks faster in an oven than in a slow cooker (which uses lower temperatures)

2. Amount of Surface Area Greater the surface area= faster the reaction Heat mainly transfers through conduction; therefore, more surface area gives larger areas of contact for heat transfer. Example) 4 lb. roast in slow cooker will take 7-8 hours to cook. Chopping the same roast into cubes and cooking in the slow cooker will only take 3-5 hours.

3. Thickness of Food Farther the center is from the surface= longer cooking time. Decreasing the distance from the center decreases the cooking time.

3. Thickness of Food Continued… Microwaves can speed up cooking time because the radiation can penetrate food up to a depth of 5 to 7.5 cm. Allows cooking to begin below the surface, instead of having to travel from the outside to the inside. Foods that are thicker than 10-15 cm should be cooked at lower power levels to allow heat to move to the center without overcooking the outside.