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Intro to food science- Chapter 13 - chapter summary.docx

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University of Guelph
Food Science
FOOD 2010
New Prof

CHAPTER 13FOOD ENGINEERING A food engineer focuses on the physical makeup of foods and how to measure the effect of processing on foods physical propertiesFood engineering also encompasses the design and operation of food processing storage and analytical equipment131 FOOD ENGINEERINGBASIC TERMS AND PRINCIPLESfood engineering is the application of engineering principles to the manufacture of foodsCharacteristics of temperature and heat Temperature scales3 temperature scales Celsius Fahrenheit and Kelvin or absolute see page 357 for conversionsTwo concepts related to temperature are thermal contact and thermal equilibrium Ex If a carton of milk is removed from the refrigerator and placed on a counter at room temperature it comes in thermal contact with the counter the counter and the milk achieve the same temperature as the environment and are at thermal equilibriumMolecular motion and temperatureAbsolute zero temperature 273 Celsius or 0 Kelvin is the temperature at which all molecular motion stops At absolute zero matter does not possess heat energy in gases molecules travel at high speeds and are relatively unrestricted to move aboutthere is much space between them and gas molecules exert little selfattraction in liquids molecular motion is more restricted because the molecules are closer togetherthey may touch and tumble over each other and exhibit selfattraction which contributes to a definite shape in a solid molecular motion is the most restrictedmolecules are locked into a specific location and shape and the only kind of motion they have is rotational and vibrational each state of matter will respond identically with the addition of heat energymolecular motion increases Measuring heatcalorie amount of heat necessary to raise the temperature of 1 gram of water by 1 c degree one joule equals 0239 calories Btu is another heat termOne Btu amount of heat that will raise or lower the temperature of one pound of liquid water 1 degree FOne btu252 calories1055 JoulesConduction Convection and Radiation Conduction occurs at the molecular levelConvection heat is exchanged between either liquid or gas and solid surfaces The warmed mass of air that rises above a fire is due to natural convection A form of convection called forced convection can be used in food processing Forced convection involves the use of a fan or pump to create movement of the fluid material Radiation offers another form of heat transfer Microwave Energy They are effective in heating foods because foods contain water Microwaves are long in wavelength high in frequency and low in energy An electronically charged particle inside the oven such as water will be twisted back and forth 245 billion times a secondThe intense twisting causes adjacent individual water molecules to rub back and forth against each otherThe rubbing causes thermal friction and the molecules heat up Heated water molecules in turn pass heat energy along to other molecules in the food such as proteins carbs and fats Thermal conductivity k refers to the rate of heat that will be conducted through a unit of thickness of material such as any food material see page 361 for formulaDielectric properties Foods in the microwave oven convert the energy to heat Foods with high loss heat quickly and conveniently in a microwave while low loss do not Dielectric properties reflect the ability to of a material to store and to dissipate electrical energy The amount of microwave energy a food material can absorb is termed absorptivity o The more polar a molecule the greater its absorptivity the higher the dielectric propertyFood mechanical factors such as product density and viscosity as well as dielectric properties and the thermal heat capacity each affect how rapidly a food heats up once microwaves are deposited in it Conservation of mass Mass I a measure of the amount of matter in an object and is the property that makes an object reluctant to change its state of motion or nonmotion if at restThe law of conservation of mass says 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 All changes in matter are accompanied by a flow of energy
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