Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

FDSC 300 > Lecture 5 - Moisture pt 2 > Flashcards

Lecture 5 - Moisture pt 2 Flashcards

1
Q

how is H2O removed via distillation method?

A
  • with distillation solvents (toluene or mineral oil)

- vapor is cooled and water collected and measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

distillation solvents should be chemically (stable/unstable) at distillation temps.

A

stable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the 2 versions of distillation solvents?

A

immiscible

  • volatile (toluene)
  • nonvolatile (mineral oil)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

distillation is a (direct/indirect) method of moisture determination

A

direct

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

is the distillation technique AOAC approved?

A

yep

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

distillation is more effective with (volatile/non-volatile liquid)

A

volatile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

which distillation solvent is more effective?

A

toluene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

when distilling with toluene, which layer does the water go to?

A

bottom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

disadvantages of distillation methods

A
  • difficult to read meniscus
  • toluene can be a health/env hazard
  • toluene is flammable
  • not adaptable to routine, fast testing
  • possibility of decomposing CHO or inducing Maillard rxns
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the karl fischer method?

A

titration method - adaptable to products that show erratic results when heated or subjected to vacuum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

can the KF method determine bound water?

A

yeah

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

when is the KF method used?

A

for low and very low moisture foods (dried veggies, spices, chocolate)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

reagents in KF titration method?

A
  • iodine
  • sulfur dioxide
  • pyridine
  • methanol
    supplied as 2 solutions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

describe the KF titration

A
  • Iodine and SO2 are added by a buret to the sample in a closed chamber
  • excess I2 not reacted with water produces dark red-brown color
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what’s the role of iodine in the KF titration?

A

reacts with water. it gets converted to iodide.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what’s the role of sulfur dioxide in KF titration?

A

produces sulfuric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what’s the role of pyridine in KF titration?

A

acts as base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what’s the role of methanol in KF titration?

A

solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what do you do if your food sample is solid but you wanna use KF titration?

A
  • moisture must be made accessible by extracting with an appropriate solvent (methanol) after powdering the sample
  • methanolic extract is used for titration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what compound is used as a primary standard during KF titration? why?

A

sodium tartrate dihydrate

it’s very stable and contains 15.66% water under all lab conditions

21
Q

true or false: particle size of sample is not an issue with KF titration

A

false - fineness of grind is important for penetration of solvent

22
Q

true or false: atmospheric moisture is problematic during KF titration

A

true

23
Q

true or false: moisture can adhere to glassware

A

true - equipment should be carefully dried prior to analysis

24
Q

what food constituents can potentially interfere with KF titration?

A
  • ascorbic acid: overestimate
  • acetal formation releases water: overestimation
  • unsaturated fatty acids react with iodine: overestimation
25
Q

describe coulometric KF titration

A
  • iodine is generated electrochemically during titration to titrate water in sample
  • amount of I required to titrate is determined by current needed to generate iodine
26
Q

which is more sensitive: volumetric or coulometric KF titration?

A

coulometric

27
Q

what are the physical methods of determining moisture?

A
  • electrical method (measures conductance and capacitance)
  • hydrometer
  • pycnometer
28
Q

what is conductance?

A

reciprocal of resistance (1/R)

29
Q

what is capacitance

A

related to dielectric constant

30
Q

electrical methods require _____ against samples of known moisture content as determined by standard methods

A

calibration

31
Q

the dielectric method is widely used for what kind of food commodity?

A

cereal grains

32
Q

what does IR analysis do?

A

measures abs of IR radiation by molecules in food

33
Q

what’s the method of choice for the grain research laboratories for testing canadian wheat?

A

IR analysis

34
Q

are IR analysis, NMR, and chromatography techniques official methods?

A

no, they must be calibrated against a reference method

35
Q

rate of water loss is related to ______

A

RH

36
Q

how much moisture is lost at 50% RH

A

0.01% in 5 s

37
Q

how much moisture is lost at 70% RH?

A

0.01% in 10 s

38
Q

what aw is the cutoff point for pathogenic microbial growth in canned food?

A

0.85

39
Q

true or false: the relationship between moisture content and aw is linear

A

false

40
Q

how do you measure water activity?

A

measure vapor pressure of headspace after a closed system attains equilibrium (aw and RH will be equal)

41
Q

dry and dense samples require (longer/shorter) time to attain equilibrium in a closed system

A

longer

42
Q

what are some detectors for measuring vapor pressure of headspace?

A
  • dewpoint
  • electric hygrometer sensors
  • direct measurement of manometric pressure
  • tunable diode laser sensor
  • freezing point determination
43
Q

what components does a dew point analyzer have?

A
  • fan for air circulation in headspace
  • IR thermometer to measure sample temp
  • temp-controlled mirror
  • sensor that detects condensation on mirror
44
Q

dew point measures RH in the (matrix/headspace)

A

headspace

45
Q

what data is recorded in the dew point analyzer

A
  • temp of sample and mirror
  • temp of sample is used to determine waver vapor pressure (po)
  • temp of mirror is used to determine vapor pressure of headspace (p)

aw = p/po

46
Q

higher temps lead to (higher/lower) aw readings

A

higher

47
Q

temperature differences between sample and containers could cause ______

A

condensation

48
Q

at what temp are Aws mostly measured?

A

25C

FDSC 300 (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions