FOOD 2400 Study Guide - Summer 2018, Comprehensive Midterm Notes - Vegetable Oil, University Of Guelph, Singlet Oxygen
12 Oct 2018
School
Department
Course
Professor
FOOD 2400
MIDTERM EXAM
STUDY GUIDE
Fall 2018
Unit 1 Learning Outcomes
1. List some unique chemical and physical properties of water and ice
Physical properties:
• Water has relatively high melting and boiling temperatures.
• It has large values for surface tension, dielectric constant, heat capacity
and heats of phase transitions (heats of fusion, vaporization and
sublimation).
• Water has a moderately low density
• Water exhibits an unusual attribute of expanding upon solidification.
• The thermal conductivity of water is relatively large compared to that of
other liquids
• The thermal conductivity of ice is moderately large compared to that of
other non-metallic solids.
• The thermal conductivity of ice at 0°C is approximately four times that of
water at the same temperature, indicating that ice will conduct heat
energy at a much faster rate than immobilized water.
• Ice has a thermal diffusivity approximately nine times greater than that of
water, indicating that ice, in a given environment, will undergo a
temperature change at a greater rate than water.
• Vapor pressure: Ice < water
• Density: Ice > water
• Specific heat: Ice > water
• Heat of vaporization: Ice > water
• Thermal conductivity: Ice < water
• Surface tension: Ice > water
• Viscosity: Ice > water
• Refractive index: Ice > water
• Dielectric constant: Ice > water
Chemical properties:
2. Describe some interaction of water with other molecules
• It is able to influence non-covalent bonds (including hydrogen, ionic, and
polar) that stabilize large molecules.
• The tendency of water to associate with hydrophilic substances to
varying degrees depends on the nature of the non-aqueous constituents,
salt, composition, pH, and temperature.
• The addition of various substances to water results in altered properties
for the added substance, and for the water itself.
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• Hydrophilic substances interact strongly with water by ion-dipole and
dipole-dipole interactions, causing changes in water structures and
mobility.
3. Define what is meant by water activity
Water activity is the water available to participate in reactions and for microbial
growth
4. Explain the 3 regions represented in a sorption isotherm
Table in notes
5. Explain the importance of sorption isotherms to food stability
6. Define what is meant by hysteresis
The effect on which the adsorption and desorption curves on a sorption
isotherm are not always superimposable; it depends on the nature if the food,
physical changes such as the addition or removal of water, temperature, rate of
deposition, and the degree of water removed during desorption
7. Explain the differences between bound water and free water in food systems
Bound water:
• Is the water that remains unfrozen at some prescribed temperature
below 0°C, usually at -20°C.
• Is the amount of water in a system that is unavailable as a solvent.
• It exhibits reduced molecular mobility and possesses other significantly
altered properties as compared with bulk water in the same system
• It cannot act as a solvent and does not freeze at -40°C.
Free water:
• Water that can be extracted easily from food by squeezing or cutting or
pressing
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Unit 1 learning outcomes: list some unique chemical and physical properties of water and ice. Physical properties: water has relatively high melting and boiling temperatures. Chemical properties: describe some interaction of water with other molecules. Water activity is the water available to participate in reactions and for microbial growth: explain the 3 regions represented in a sorption isotherm. Table in notes: explain the importance of sorption isotherms to food stability, define what is meant by hysteresis. Is the water that remains unfrozen at some prescribed temperature below 0 c, usually at -20 c. Is the amount of water in a system that is unavailable as a solvent. It exhibits reduced molecular mobility and possesses other significantly altered properties as compared with bulk water in the same system. It cannot act as a solvent and does not freeze at -40 c. Free water: water that can be extracted easily from food by squeezing or cutting or pressing.
