moisture analysis

Question 1

Physically bonded water

Answer 1

 in molecular contact with other food constituent e.g. protein, carbohydrate or minerals.
 bonds significantly different from normal water
 different physico-chemical properties than bulk water

Question 2

Chemically bonded water

Answer 2

 chemically bonded to other molecules
 lactose monohydrate, or salt e.g. NaS04.10H20.
 stronger bond than the normal water
 different physico-chemical properties to bulk water

Question 3

DRYING DEVICES Convection oven heat source

Answer 3

stationary, w/o fan

Question 4

convection oven, air movement is

Answer 4

obstructed further by pans

Question 5

Forced oven draft

Answer 5

circulating hot air

Question 6

Forced oven draft more unifrom

Answer 6

temperature distribution

Question 7

Vacuum oven

Answer 7

Drying under reduced pressure

Question 8

vacuum oven good in complete

Answer 8

removal of water and
volatiles without decomposition

Question 9

• Air inlet and outlet for vacuum oven?

Answer 9

to carry the moisture lost from the sample
out of the vacuum oven, which prevents the accumulation of moisture within the oven.

Question 10

Microwave oven

Answer 10

Water molecules microwave energy;
them to become absorb causes thermally excited

Question 11

Microwave oven need to standardized

Answer 11

method
and ensure uniform
heating

Question 12

nfrared lamp drying uses what principle

Answer 12

Thermogravimetric principle

Question 13

Thermogravimetric principle

Answer 13

The test sample is placed on an aluminium pan
* Sample’s start weight is recorded, then a radiator dries it while an integrated balance
continually records the sample weigh

Question 14

Water molecules absorb infrared energy in infrared lamp drying,

Answer 14

become thermally excited

Question 15

Important to (infrared lamp)

Answer 15

control the distance between the
sample and the IR lamp and the dimensions of the sample

Question 16

Halogen moisture analyser

Answer 16

Heating element consists
of glass pipe filled with
halogen gas

Question 17

principle of distillation method

Answer 17

• Direct measurements of water removed from a food sample by evaporation
• Involve heating of a weighed food sample in the presence of an organic solvent that is immiscible with water
• Water in the sample evaporates and later collected in a graduated glass tube where its mass is determined
• Used for very low moisture samples

Question 18

TOLUENE DISTILLATION

Answer 18

 Distillation of sample with excess organic
solvent (toluene) and condensation of
vapour (water and solvent) in a suitable
trap: Bidwell-Sterling moisture trap

Question 19

) DEAN AND STARK

Answer 19

Known weight of sample is placed
in flask with organic solvent, such
as xylene or toluene

Question 20

Problems with distillation method

Answer 20

• formation of emulsion between water and solvent; difficult to separate
• Water droplets can adhere to the inside of the glassware
• Decomposition of thermally labile samples (high temperature used)

Question 21

CHEMICAL METHODS

Answer 21

chemical reagents is added to the food that reacts specifically with water to produce a measureable change in the properties of the system

Question 22

KARL FISHER

Answer 22

reaction of elemental iodine with water in
the presence of sulfur dioxide

Question 23

the water reacts with iodine. The endpoint of the titration is reached when all
the water is consumed

Answer 23

I2​+SO2​+H2O→2HI+HSO4−

Question 24

There are two possibilities to add the iodide to the sample:

Answer 24

volumetric abd coulometric

Question 25

Volumetric Karl Fischer Titration

Answer 25

a solution with an exactly known concentration of iodine is added to sample by means of an electric burette. The amount of iodine added to the sample is calculated from the volume of iodine solution used

Question 26

Coulometric Karl Fischer Titration

Answer 26

the iodine is electrolytically generated. The amount of iodine added to the sample is determined by measuring the current needed for the electrochemical generation of the iodine. When reacting with water, the brown iodine is reduced to the colourless iodide

Question 27

SOURCE OF ERROR FOR KF

Answer 27

* Incomplete water extraction (* use smaller particle size) * Moisture from surrounding (* external air must not be allowed to infiltrate reaction chamber) * Water droplets at the walls of apparatus (* all glassware and utensils must be carefully dried) * Interference from certain food constituents * Ascorbic acid is oxidized by KF reagents (higher reading) * Carbonyl compound reacts with methanol to form acetal and release water * Unsaturated fatty acid reacts with iodine

Question 28

Physical method: infrared analysis

Answer 28

* Measure absorption of radiation by molecules in foods

Question 29

Physical method: refractometry

Answer 29

Based on how water in a sample has an effect on light reflection. when a beam of light is passed from one medium to another and the density differs, the beam is bent or refracted

Question 30

WATER ACTIVITY

Answer 30

Ratio of the water vapor pressure of food (P) to that of vapor pressure of pure water (P0) at the same temperature