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Chapter 13

Chapter 13 - Food Engineering.docx

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Food Science
FOOD 2010
Massimo Marcone

Chapter 13 : Food Engineering 13.1 Food Engineering - Basic Terms and Principles -food engineering = application of engineering principles to the manufacture of foods -characteristics of temperature and heat -temperature scale -mostly Celsius is used -two basic concepts related to temperature -thermal contact (when product taken from fridge and put out) -thermal equilibrium (when its the same temp as the enviro) -molecular motion and temperature -molecular motion depends upon temp and phase of food material -absolute zero = O K -temperature at which all molecular motion stops -measuring heat -calorie = amount of heat necessary to raise the temp of 1g of water by 1 C -conduction, convection, and radiation -conduction = occurs at molecular level -temperature gradient causes the heat transfer to be directed from the high region to the lower temperature region -convection = heat exchanged between liquid or gas, and solid -ie think of a fire -radiation -depends on emissivity (of emitting source) and absorptivity (of other surface) -microwave energy -effective because food contains water -create fluctuating electrical field changes 2.45 billion times a second -causes friction between water molecules, thus heating -heat water passes heat energy to other molecules in food -thermal conductivity = rate of heat that will be conducted through a unit thickness of material -dielectric properties -dielectric constant (K') ability to store electrical energy -dielectric loss factor (K") ability to dissipate electrical energy -relates to the ability to act as a insulator -differs because of chemical composition, physical structure, temperature -conservation of mass -when a reaction takes place, the total mass of reactants is equal to the total mass of products formed plus the mass of reactant remaining -changes in matter are accompanied by flow of energy steady state = no accumulation of mass within system -has to due with nature of heat transfer and refers to system properties that do not change with time Chapter 13 : Food Engineering -transient heat transfer -system properties change with time -"unsteady state" characterized by temperature changes with time -thermodynamics -study of natural processes are affected by changes in temperature -1st law = change in internal energy is equal to heat added to the system minus work done by system -2nd law = heat will spontaneously flow from a hot object to a cold one -entropy = quantitative measure of disorder in a system -isothermal = process carried out at constant temp -adiabatic = process in which no heat is exchanged -heat transfer -refers to manner in which heat energy is transported from a food's surroundings to the surface and interior of the food -driving force is temp diff -greater the surface area, the quicker the transfer - q = Q/A = delta t / R -where A = area, Q = heat transfer in watts, q = heat transfer per unit area, R = thermal resistance of material, t = temp -heat capacity and specific heat -heat capacity = amount of heat energy necessary to speed up its molecules to raise the temp of a unit mass by 1 C -specific heat = ratio of the heat capacity of a material to that of water -thermal conductivity -rate that heat will be conducted through a unit thickness of material -heating and chemical changes -rate of a chemical reaction doubles for every 10 C increase in temp -heat exchangers -heat exchanger = specialized piece of equipment used in food processing and storage to either add or remove heat from food -different types -scraped surface heat exchanger (SSHE) -double-pipe heat exchanger -plate heat exchanger -canned veg and meats, fluid dairy, dried fruit and grains go through process 13.2 Deep-Fat Frying - An Illusion of Heat Transfer, Mass Transfer, and Boundary Layers -boundary layers = dividing lines as two dissimilar materials, the heating oil and the food material, come in contact with each other -changes to frying food and frying oil -viscosity changes and lipid oxidation can occur, as well as thermal breakdown of the oil -mass transfer Chapter 13 : Food Engineering -movement or migration of a liquid or a food component, either within one phase or between different phases, which is caused by physical conditions present in the liquid oil/food system -similarities and differences between heat and mass transfer might become apparent 13.3 Food Materials Science - A Physiochemcial Approach -physiochemcial states, glass transition, and water mobility -4 physiochemical states 1 - Crystalline 2 - Liquid 3 - Amorphous Rubbery 4 - Amorphous Glassy -most foods are multiphasic meaning they have 3, 4 and water -glass is defined as any material that has solidified and become
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