Lecture 4 - Moisture Analysis Flashcards
list the 5 main food components used in proximate analysis?
- moisture
- ash
- protein
- fiber
- fat
how do you measure carbohydrate?
100-everything else
draw the proximate analysis tree
ok
what does water contribute to a food matrix?
- structure
- standard of identity
- cheap filler
- undesired in dry products
what does dry matter contribute to in a food matrix?
- economic value
- nutrition
- easy transport
significance of moisture?
- food safety
- shelf-life/stability
- food quality
- economic consideration
- govt regulation
what are the 3 common moisture levels in food?
- high moisture
- intermediate moisture
- low moisture
what forms of water are there? (4)
- free/bulk
- capillary/trapped
- physically bound
- chemically bound
type of water in food free from any other constituents, surrounded only by other water molecules with the same physicochemical properties as pure water
free
type of water held in narrow channels formed by physical barriers by capillary forces; has similar properties to pure water
- capillary/trapped water
type of water that is bound with other molecules; different physicochemical properties than pure water
- physically bound water
type of water that is bound in the form of hydrates; different physicochemical properties than bulk water
- chemically bound water
what types of methods are there for moisture determination?
- drying
- distillation
- chemical methods
- physical methods
describe dry methods of MD
remove water in the form of weight; lost weight is taken as the measure of moisture content
list some drying methods
oven - convection oven - forced air oven - microwave oven - vacuum oven freeze, infrared
what happens to the boiling point as the food dries?
the BP continuously elevates as solute concentration increases
list some relationships between moisture and temperature
- higher temp leads to more moisture loss
- after 185C decomp of proteins occur
- CHO releases water at higher temps
- oxidation of FA could increase weight of sample
heating takes place in a chamber (105-110C for 22-24h); moisture remains in chamber
convection oven
disadvantages of convection oven?
- long time
- loss of volatile components other than water
- larger temp gradient
- air circulated by fan
- T can be higher and time is shorter (135C for 4h)
- temp differential not greater than 1C
- no condensation of vapour due to fan
- forced air oven
disadvantages of forced air oven?
- possibility of lipid oxidation
chamber that has a built in balance to monitor weight as the sample is treated with specified microwave energy and time
microwave oven
chamber that adjusts pressure surrounding liquid to equal the vapor pressure of the liquid; temp rang (95-102C or 60-70C for high sugar)
vacuum oven
what are the 3 components of a vacuum oven?
vacuum oven, drying agents, vacuum pump
list 4 common drying agents for vacuum oven
- anhydrous CaCl2 (safest)
- anhydrous SO3
- phosphorus pentoxide P2O5
- concentrated H2SO4 (most effective)
advantages of vacuum oven?
- reduction in lost volatiles
- less effect on degradation
- faster
factors affecting oven drying methods:
- temp
- time
- particle size
describe IR drying
- not approved by AOAC
- IR rays dry sample
- short drying time (10-25 min)
- heat of lamp is 1730-2230C
describe rapid moisture analyzer tech
- uses halogen or ceramic heater
- detects moisture levels from 50ppm to 99% using sample weights of 150mg-40mg
- usual temp 25-275C
- instrument equipped with digital abalance
describe thermogravimetric analysis
- mass continuously measured as heated at controlled rate/CA
- N used to avoid oxidation and mass gain
- can use higher temps so can measure decomposition, weight %ash
