Food Engineering

Food Engineering

1. 8 Characteristics of Temperature and Heat

   • Temperature scales (Celsius, Fahrenheit, Kelvin)
     • Thermal Equilibrium: state of equalized temperature achieved between food and surrounding
   • Molecular motion and temperature
   • Measuring heat
     • Calories (Cal): amount of heat necessary to raise temperature of 1 g of water by 1 degrees Celsius
   • Heat Transfer: Conduction; Convection; Radiation
   • Microwave Energy: Dipolar particles twisted back and forth, rubbing between molecules => cause heating
   • Thermal Conductivity (k): rate of heat conducted through a unit thickness of material
     • K = 0.6W (water) + 0.2P (proteins) + 0.18F (fats) + 0.2C (carbohydrates) + 0.14A (ash)
   • Conservation of mass: mass is neither created nor destroyed
   • Thermodynamics: study of how natural processes are affected by changes in temperature
     • 1st law: conservation of energy
     • 2nd law: transfers energy from high to low environment

2. Physicochemical approach

   • 4 physicochemical states
     • Crystalline: lowest mobility
     • Glassy: high polymer viscosity, low polymer mobility
       • Decreased potential for microbial growth; increased ingredient stability => increased shelf stability
     • Rubbery: low polymer viscosity, high polymer mobility
       • Increased potential for microbial growth; decreased ingredient stability => decreased shelf stability
     • Liquid: highest mobility
   • Glass Transition (Tg): change in state from solid glass to liquid or rubbery
     • helps predict storage life and stability
     • determined by glass transition temperature (Tg')

3. Rheology: concerned with the flow and deformation characteristics of food materials

   • affected by stress, strain, and shear forces
   • Viscosity: tendency of a fluid to resist any internal action
     • Absolute viscosity (mPa.sec) = shear stress / shear rate
   • Newtonian (no change in viscosity as shear rate increased) vs Non-Newtonian (change in viscosity as shear rate increased) foods

4. Psychrometric charts

   • graph that represents eight physical properties of air
   • 8 physical properties of air
     • Dry bulb temperature (db)
     • Wet bulb temperature
     • Relative humidity (RH)
     • Moisture content (specific humidity)
     • Dew point (Dpt)
     • Total heat content (enthalpy)
     • Specific volume
     • Vapor pressure (kPa, mb, psi)
     • State point: junction between any 2 properties