Moisture Content & Aw

Question 1

MCWb

Answer 1

G water / g total sample
MCdb / (1 + MCdb)

Question 2

MCdb

Answer 2

G water / g solids
MCwb / (1 - MCwb)

Question 3

Oven Drying Methods

Answer 3

Sample heated under certain conditions
Loss of weight used to calculate MC
Know mass of wet food + dry solids

Question 4

Oven Drying Cons

Answer 4

Decomposition of samples
Loss of volatiles

Question 5

Oven Drying Types

Answer 5

Convection, forced draft, vacuum

Question 6

Vacuum Drying

Answer 6

Reduced pressure
Remove water w/o decomposition
High sugar products

Question 7

Rapid Moisture Analyzer

Answer 7

Based on infrared or microwave drying
Digital balance
Constant heating system
Not good for high sugar, fat, heterogenous

Question 8

Distillation

Answer 8

Codistillation of moisture with a high boiling solvent
Separate by density

Nuts, oils, soaps, waxes
Less thermal decomposition

Question 9

Distillation issues

Answer 9

Toxic solvents
Time consuming
Sources of error
Volume not mass
Form emulsions
Incomplete extraction
Decomposition creates water
Less accurate than weight measurements

Question 10

Karl Fischer

Answer 10

Water interacts with iodine at a 1:1 mol ratio
Excess iodine is detected by indicator electrode
Anion product has specific current

Question 11

Karl Fischer foods

Answer 11

Low moisture foods
High in sugar or protein

Dried fruit/veg, chocolate, candies, roasted coffee, oils

Question 12

Dielectric method

Answer 12

Change in resistance to electric current
Requires calibration
30-35% moisture foods

Cereal grains

Question 13

Hydrometry

Answer 13

Specific gravity → density
For milk, salt, sugar, alcohol beverages

Question 14

Pycnometer

Answer 14

Measure specific gravity

Alcohol content, solids in sugar syrup, solids in milk

Question 15

Refractometer

Answer 15

Different densities between 2 media → light is refracted
RI = ratio of the angles (dimensionless)

Question 16

Brix

Answer 16

% soluble solids w/w

Question 17

IR

Answer 17

Instantaneous method
Non-contact, non destructive
Almost any liquid/solid
Measure fat, protein, sugar, fiber

Question 18

IR issues

Answer 18

Needs to be calibrated
Surface measurement only

Question 19

Water activity estimated by

Answer 19

Measuring vapor pressure (Manometer)
Heating sample above BP of water
Using freezing pt depression
Measure mass changes in a controlled atmosphere

Question 20

Aw meter

Answer 20

Standard salt solutions are used to calibrate
Sample of known mass is stored in a closed chamber and allowed to equilibrate with atmosphere

Question 21

Aw meter sensors

Answer 21

Relative humidity sensor
Chill mirror dew point
Dielectric humidity sensor

Question 22

Karl Fischer issues

Answer 22

Incomplete moisture extraction
Atmospheric moisture
Moisture adhering to walls of unit
Interferences

Question 23

IR foods

Answer 23

Cereal
Cheese
Coffee
Dairy powder
Flour
Snacks
Pet food