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Unit 9

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University of Guelph
Food Science
FOOD 2010
Massimo Marcone

Unit 9 Notes P.356-370; P.374-390 Chapter 13: food engineering -A food engineer focuses on the physical makeup of foods and how to measure the effect of processing on foods physical properties. -also encompasses the design and operation of food processing, storage and analytical equipment Food engineering—basic terms and principles -food engineering is the application of engineering principles to the manufacture of foods. Some important topics it covers include; heat transfer, mass and energy conservation, matter flow, and mechanical food properties -temperature scales—3 temperature scales measure and record temp: Celsius, Fahrenheit, and Kelvin -Tf = Fahrenheit temp -Tc = Celsius temp Tc = 5/9 (Tf-32) Tc = (Tf-32) / 1.8 Tf = 9/5 (Tc + 32) Tf = (Tc * 1.8) +32 -2 basic concepts related to temp are thermal contact (contact with surrounding air) and thermal equilibrium (food having same temp as environment due to thermal contact) Molecular motion and temp -absolute zero temp (-273 celsius or 0 degrees Fahrenheit) is the temp in which all molecular motion stops. Thus, no heat energy -In a solid, the only molecular motion they have is rotational and vibrational. Measuring heat -calorie—amount of heat necessary to raise the temp of 1g of water by 1 Celsius degree -Kilocalorie—heat needed to raise the temp of 1 kg of water by 1 celsius degree -joule and Btu are other heat units used to measure heat Conduction, convection, and radiation -heat is transferred by Conduction, convection, and radiation -conduction—occurs at molecular level. Heat transfer is directed from the high temp region to the lower temp region -convection—when heat is transferred between either liquid or gas and solid surfaces -type of convection called forces convection can be used in food processing. Involves the use of fan or pump to create movement of the fluid material -Radiaton—part of the electromagnetic spectrum. It refers to transfer of heat between 2 surfaces. -depends on 2 factors; the emissivity of radiation surface and the absorbativity of the other surface. Microwave energy -microwaves are long in wavelength, high in frequency, and low in energy -in a microwave oven heat is generated internally within the food as a result of friction between molecules -thermal conductivity—refers to the rate of heat that will be conducted through a unit thickness of material, such as any food material. Dielectric properties -reflects the ability of a material to store and to dissipate electrical current. This differs for each food material Conservation of mass -mass—a measure of the amount of matter in an object and the property that makes an object “reluctant” to change its state of motion (or nonmotion, if at rest) -law of conservation for mass states that 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 are accompanied by flow of energy -steady state—material input through the system equals the material output through the system. System properties do not change with time -in transient heat transfer-which means that the temp of a heating or cooling material is defferent at a different time. system properties do change with time Thermodynamics -system—object or set of objects (such as food) that we are studying. 2 types; open system and closed system. -environment—everything that does not fit in with the definition of a system -open systems—are alive and exchanging nutrients -closed system—achieve constant mass (hence, no longer grow, respire etc) -thermodynamics—is the study of how natural processes are affected by changes in temp. Involves heat work and energy -heat-transfer of energy due to difference in temp. Involves motion that are at molecular level -work—transfer of energy not due to difference in temp. Macroscopic level -First law of thermodynamics states that a change in the internal energy of a system is = to the heat added to the system minus work done by the system -Second law of thermodynamics states that heat will spontaneously flow from a hot object to a cold one, but not the reverse, and that natural process tent to move towards greater state of disorder rather than order. -entropy—quantitative measure of disorder in a system -2 types of thermodynamic processes: -isothermal processes is one carried out by constant temp -adiabatic process is one in which no heat is exchanged -heat transfer-manner in which heat is transferred from foods surrounding to the surface and interior of the food -surface area, foods thermal properties, rheological properties, product density and thickness all effect heat transfer -heat capacity—amt of heat necessary to speed up its molecules enough to raid the temp of a unit of a material by 1 degree Celsius -specific heat—ratio of the heat capacity of a material to that of water. Depends on percent composition of carbs, proteins, fat, and water -thermal conductivity of high moisture foods tend to be similar to that af water -heat energy can cause chemical, physical, sensory, and nutritional changes in foods Heat exchanger -It is a specialized peice of equipment that is used in food processing and storage to either add or remove heat from food Deep-fat frying –an illustration of heat transfer, mass transfer, and boundary layers -in deep-fat frying, conduction occurs within a solid food material -boundary layers—dividing lines or fronts as two dissimilar materials , the heating oil and the food material , come in contact with each other. This is where heat transfer and mass transfer occurs -mass transfer—movement or migration of a liquid (such as frying oil) or a food component, either within one phase or between different phases, which is caused by physical conditions (ie, concentration gradient) present in the liquid oil/food system. Food material science—a physiochemical approach -this approach enables food scientists to construct a 3-D model of food system structures Physicochemical states, glass transitions, and water mobility -4 pshysicochemical staes characterize the movement of water ingredient molecules in food: Crystalline 2. Liquid 3. Amprphous rubbery and 4. Amorphous glassy -glass—any material that has solidified and become a rigid material without forming a regular crystal structure. Are unstable. Ex. Dry sugar candy -glass transition—change in the physicochemical of amorphous food materials between the solid glass and the liquid of rubbery state -the temp range over at which this transformation occurs is called glass transition temp -water acts as plasticizer in low moisture and frozen foods Mobility of food molecules and ingrediants -foods can become immobilized within chrystaline structures -in amorphous rubbery and glassy states ingredient molecules retian mobility -small molecules posses mobility -molecular entanglement and aggregation is what leads to an amorphous rubbery or glassy state -the closer a food is to the glassy state transition temp, the less likely it is to undergo dynamic phase shifts Food microstructure –Influencing physical and sensory qualities -food microstructure—refers to the organization of food structures at the microscopic level and their interactions to produce a food product’s physical and sensory characteristics Food product engineers are food scientists especially trained to understand the connection between food structure and food properties Psychrometrics –looking at air and food processing -the filed of psychometrics is concerned with evaluating the thermodynamic properties of the mixed gases present in air. -air is a mixture of N, O, CO2 and water vapour -ideal gas law relates the pressure, volume, temp, and amount of any gas under set conditions Latent and sensible heating and cooling -Sensible heat—heat energy in an air stream due to temp of the air -Latent heat—heat energy in an air stream due to the moisture of the air Psychometric charts -graphic method of displaying the properties of the various mixtures of air and water vapour -chart describes all the drying apparatus Adiabatic saturation process: heated air flows past a moist food product in a drying operation, with the air supplying the heat of evaporation to dry the product, with no change in enthalpy. Sensible air heat is converted to laten heat, with the uptake of water in the vapor state Psychometric charts can be useful in solving problems related to increasing the efficiency or energy conservation of food processing equipment such as food dryers. 13.6 Rheology-studying flow and deformation Structured fluids : another term used to describe semisolids. Examples of structured fluids include suspensions, emulsions, gels and foams. Structured fluid is a low modulus material having a solid-like and liquid-like properties simultaneously due to its three- dimensional inner structure Brittle gels exhibit high stress and low strain A mushy gel material would exhibit low stress and low strain, while a very strong tough gel would demonstrate both high stress and stain at the point of structural failure Texture: represents both a physical property and a mechanical behaviour of food that takes into account a foods size and shape dimension’s, its density and weather it has a porous or nonporous surface. is related to food mechanics, a branch of mechanics that, for the food engineer, studies the flow characteristics of liquid and semisolids food Viscosity is the principal parameter that characterizes the flow properties of foods where’s rheology is the science that is concerned with the flow and deformation characteristics of food materials. Thus viscosity is a type of rheological measurements, where’s rheology itself is the area of scientific study involved in understand such a measurements Mechanical and rheological measurements Mechanics is the study of motion of objects. Rheological measurements include measures of viscosity, fluidity, elasticity and plasticity of nonsolid. Stresses, elastic solids, and plastic solids A stress can be considered a force per unit area of food materials. Strain is a result of a stress, and may take the form of deformation in the case of a solid material Fluids do not recover after a stress is removed. Instead, fluids response to stresses by changing shape, which means movement or flow away from the stress. Solids response to stress by exhibiting strain, deformation, or rupture. Shear refers to the relative motion of one surface with respect to another surface in parallel to it, which creates a zone of shearing action on any substance (fluids or solid) located between the moving surfaces. -elasticity is equated to springiness a term that is used to calculate the distance that a food recovers after being initially compressed. -viscoelastic food behaviour means that some foods are composed of both visous and elastic materials. They exhibit both flow and deformation Newtonian and non-Newtonian foods -Newtonian foods are homogenous mixtures that exhibit no change in viscosity as the rate of shear is increased -Newtonian fluid is one in which the viscosity is independent of the shear rate Food packaging -primary functions of food packaging include; 1) preservation, 2)protection against physical demage, 3)protection against chemicals, dirt and biological contamination 4)easing the distribution of from manufacturer to vendor and on to the consumer 5) to create or enhance visual appeal -primary packaging—is the packaging material that comes into direct contact with the food product it is surrounding -secondary package—cardboard box with all of the brand graphics and nutritious info -tertiary and quaternary have to do with food shipping and distribution activities -there are 10 golden rules for food processing Container types -cans—all food cans are hermetically sealed by fusion, which means that they are completely sealed so that no gas can enter or escape -flexible pouches—often made of composite material for eliminating light and setting up a barrier to gas entry -glass containers—permit product visibility, does not affect product taste , and offers non-corrosive containment -Microwavable containers—withstands microwave energy, is lightweight, unbreakable, easy to open, and able to be closed -edible films—can be fabricated into small packets to hold food ingredients, provide moisture and gas barrier, provide extended handling and shelf life, also serve as glazes to improve product appearance. Packaging approach -Controlled atmosphere storage-- involves controlling the amount of gases in the foods environment -modified atmosphere packaging—refers to the exchange of air in a processed food product package with a gas or gas mixture to exclude oxygen -oxygen scavenging—reduces Oxygen levels to the vanishing point, and extends product shelf life -vacuum packaging—refers to the removal of air from a packaged food -Aseptic packaging –designed to make the product free from pathogenic or spoilage microorganisms Chapter 11 • Food Safety deals with disease-producing or toxic hazards that are accidentally introduced into the food supply • Food security is planned contamination of food with these substances as a result of malicious and criminal intent. 11.1 What is Foodborne Illness? • Foodborne illness: any illness resulting from ingestion of food. • Three times of foodborne illness: biological, chemical, and physical • Biological hazards: include bacteria, molds, viruses, and parasites such as protozoa, flatworms and round worms. • Chemical Hazards: chemical substances that occur naturally in food such as plant toxins and those that are added to food. • Physical Hazards: Bone, metal, plastic and other foreign matter that can damage the consumer if ingested 11.2 Types of Biological Hazards in Food • Bacteria can cause diseases in human by the classifications of: infection, intoxication and intoxification. • Foodborne l Infection: bacteria are those who invade intestinal tract. Step 1. Make their way to intestinal tract and colonize. Step 2. Epithelial cells linings get damaged which causes water to be secreted from the tissues back into the intestinal tract which causes diarrhea. You can also vomit. • Foodborne Intoxication: Bacteria that cause
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