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Food Analysis > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

what is the mean and how do you calculate it

A

-mean = average
-sum of values/ number of values

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2
Q

accuracy

A

-how close a measurement is to the true value
-compare mean to true value
-assess by absolute error or relative error

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3
Q

absolute error

A

diff btwn experimental value and true vlaue (Eabs = x - T)

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4
Q

relative error

A

-compare diff btwn experimental value and true value, against the true value
-(Erel = (x-T)/T

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5
Q

precision

A

-how close are replicate measurements to each other
-measure of repeatability
-assess by:
stdev
CV
CI
std error of the mean
relative deviation from the mean

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6
Q

standard deviation

A

-measures precision: how close vlaues are to each other
-use n in denominator for 30 + samples, otherwise use n-1
-SD = square root (sum (xi - mean)^2 / n-1)

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7
Q

sources of error with evaluation of analytical data

A

-systematic error
-random error
-blunders

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8
Q

systematic error

A

-results consistently deviate from true value
ex: pipette not calibrated correctly

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9
Q

random error

A

-can fluctuate and are unavoidable
-ex: differences btwn balances (drafts in the room)

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10
Q

blunders

A

-big “screw ups”
-ex: pipetting 0.5 ml instead of 1 ml

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11
Q

what is the reliability of analysis?

A

sensitivity vs. limit of detection

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12
Q

sensitivity

A

-magnitude of change in measurement with change in conc. of compound
-ex: how great is the change on y-axis relative to change on x-axis

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13
Q

limit of detection (LOD) & values similar to LOD

A

-lowest possible amount that we can detect with statistical significance
-values similar:
method detection limit
limit of quantitation

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14
Q

what is regression analysis & how is it used

A

-standard curves: estimates the linear relationship btwn a scalar response and one or more explanatory variables (dep. and indep.)
-used to determine unknown concentrations
->only if conc of substance is
proportional to measurement

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15
Q

what is linear regression most often used to construct?

A

curves

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16
Q

what is the importance of moisture content

A

-preservation and stability
-quality factor
-convenience in packaging or shipping
-meeting compositional standards and Standards of Identity
-required for nutrition label calculations
-express results of other analytical determinations on a dry weight basis, for comparison

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17
Q

what are total solids

A

dry matter that remains after moisture removal

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18
Q

how are challenges created in moisture and water activity analysis

A

-struct. of water molecules and its moving to and from the environment during sample handling
-measuring water in all its common states
-water interacts with food components

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19
Q

what are water’s common states

A

solid, liquid, gas

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20
Q

what do you need to do prior to moisture analysis?

A

minimize moisture losses and gains in sample collection and sampling

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21
Q

how do water molecules interact with each other

A

-hydrogen bonding

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22
Q

hydrogen bond characteristics

A

-relatively weak and short-lived
-ex: picoseconds for forming, breaking, and reforming
-stable enough overall for good interactions

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23
Q

dynamic equilibrium

A

-exists once reversible reaction occurs
-substances transition btwn states at equal rates, no net change
-there is a steady state

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24
Q

steady state

A

conc. of reactants and products form at such a rate that neither changes

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25
Q

water content direct measurement methods (& how its done)

A

DONE BY REMOVING WATER
-forced draft oven drying
-vacuum oven drying
-microwave analyzer
-rapid moisture analyzer technology
-thermogravimetric analyzer
-lyophilization
-chemical desiccation
-Karl Fischer titration

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26
Q

water content indirect measurement methods (& how its done)

A

BASED ON A PROPERTY OF FOOD RELATED TO PRESENCE OF WATER
-dielectric capacitance
-hydrometer
-refractometer
-NIR spectroscopy
-freezing point, cryoscope
-microwave absorption
-conductivity

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27
Q

what do you need to consider when regarding methods?

A

-how should samples be handled
-what is measured?
-how is water removed/reacted/identified?
-assumptions? and sources of error?
-applications?
-official method requirements

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28
Q

oven drying method principle

A

-sample is heated to evaporate off water
-weight loss equals moisture content

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29
Q

oven drying method calculation

A

-% moisture (wt./wt.) = (wet wt. - dry wt. / wet wt.) x 100

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30
Q

oven drying method sources of error

A

-particle size
-volatile compounds present
-lipid oxidation
-sample very hygroscopic
-alteration of carbohydrates
-surface crust formation
-splattering
-improper storage in dessicator

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31
Q

what does the red box indicate in moisture content by drying oven graph

A

-indicates the break points at which there is sample break down

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32
Q

microwave drying analyzers characteristics

A

-greatly reduces analyses time
-allows for in-process analyses & process adjustment
-variables: time and power

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33
Q

infrared drying characteristics

A

-involves heat penetration directly into the sample (vs. heat conductivity & convection with conventional oven)

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34
Q

Karl Fischer method principle

A

-volumetric titration of sample with Karl Fischer reagent (KFR), involving reduction of I2 (molecular iodine) by SO2 (sulfur dioxide) in the presence of water
-reach the endpoint of titration when excess I2 present that cannot react with water (measure by visual (color), potentiometric, or conductometric endpoint)
-volume of titrant (KFR) consumed is used to calculate % moisture

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35
Q

Karl Fischer Coulometric method

A

-Karl Fischer reagent (KFR) must be titrated with a standard to determine KFR water (moisture) equivalence (i.e. how much water reacts with 1 ml KFR)
-water content can be determined immediately from the coulombs required for electrolytic oxidation

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36
Q

how can standardization of the Karl Fischer be done?

A

-pure water, water-in-methanol standard
-sodium tartrate dehydrate (commonly used)

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37
Q

Dielectric method principle

A

-based on electrical properties of water
-measure change in capacitance or resistance to an electric current passed through sample
-can assess consistency in processing
-dielectric constant (permittivity) is measured as an index of capacitance

38
Q

what is capacitance

A

-ability of material object/device to store electrical charge

39
Q

Freezing point measurement

A

-use cryoscope to measure freezing point
-used to test for added water in milk
-if freezing point is above -0.507 C then there is too much water

40
Q

importance of water activity

A

-affects important quality and safety factors
-> growth of spoilage and pathogenic
microorganisms
-can be a critical control point in HACCP plans

41
Q

what does the water activity of 0 vs. 1 mean

A

-aw of 0 = absolutely no water
-aw of 1 = pure water

42
Q

water activity methods

A

-dew-point measurement (chilled mirror)
-electric hygrometer sensors
-direct measurement of manometric pressure
-inc. in sorbent mass (isopiestic method)
-thermocouple psychrometry
-freezing point determination

43
Q

rheology

A

science devoted to the deformation and flow of all materials

44
Q

rheological properties

A

-subset of mechanical properties of food
-determined by applying and measuring forces and flows or deformations as a function of time

45
Q

what do rheological method measure

A

force, deformation, flow

46
Q

stress vs. strain definition

A

-stress: force per area
-strain: relative deformation

47
Q

how are stress and strain linked

A

by constant of proportionality (moduli)

48
Q

what do ideal solids and ideal fluids obey

A

-ideal solids: obey Hooke’s Law
-ideal fluids: obey Newtonian principle

49
Q

viscosity

A

internal resistance to flow

50
Q

stress

A

-fundamental measurement of force
-stress = force/ area
-expressed in Pascals (Pa) for low pressure and Bars (1 bar = 100 kPa) for high pressure

51
Q

normal stress

A

force is perpendicular to surface
ex: chewing piece of gum

52
Q

shear stress

A

force is parallel to surface
ex: spreading butter on toast

53
Q

strain

A

dimensionless quantity representing relative deformation of material

54
Q

normal strain

A

-ɛ̝ (epsilon)
-applied stress is perpendicular to surface
-ex: large deformation such as in texture testing

55
Q

shear strain

A

-γ (gamma)
-applied stress is parallel to sample
-ex: pumping tomato paste through pipe

56
Q

shear (strain) rate

A

-degree of deformation with respect to time

57
Q

simple shear

A

-laminar (layered) deformation in a plane parallel with an applied force

58
Q

Hooke’s Law

A

-when solid materials are exposed to stress, the resulting deformation or strain is proportional to the magnitude of the stress
-so, stress = modulus x strain

59
Q

elastic modulus (E)

A

proportionality constant when normal stress is applied to sample

60
Q

shear modulus (G)

A

proportionality constant when shear stress is applied to sample

61
Q

relationship of viscosity to temp

A

viscosity dec as temp inc

62
Q

apparent viscosity

A

-shear-dependent viscosity
-shear stress divided by corresponding shear rate
-what the viscosity “appears to be” under shear stress

63
Q

newton’s postulate

A

doubling shear stress doubles shear rate within fluid

64
Q

Newtonian fluids (ideal fluids)

A

-viscosity is constant for all shear rates; follows Newtonian principles
-ex: water, oil, honey
-there is a constant viscosity independent of stress (doesn’t matter what you do to it)

65
Q

Non-Newtonian fluids

A

-viscosity is not constant and is function of shear rate
-xanthan gum solution, butter, cheese
-viscosity changes with force to either more liquid or more solid

66
Q

shear thinning (pseudoplastic) fluids

A

-viscosity decreases as shear rate increases, and is independent of time
-ex: applesauce, pie fillings

67
Q

shear thickening (dilatant) fluids

A

-viscosity increases as shear rate increases, and is independent of time
-ex: corn starch slurries

68
Q

thixotropic fluids

A

-viscosity decreases over time with agitation
-ex: ketchup, pumpkin pie filling
-ex: shaking bottle of ketchup actually thins the contents, which then quickly return to gel-like state

69
Q

antithixotropic (rheopectic) fluids

A

-viscosity increases with time
-ex: some clay mixtures

70
Q

thinning (time dep vs. time indep)

A

-time dep: thixotropic
-time indep: pseudoplastic

71
Q

thickening (time dep vs. time indep)

A

-time dep: anti-thixotropic
-time indep: dilatant

72
Q

yield stress

A

-minimum force (stress) required to initiate flow (strain)
-fluids that do not flow at low magnitudes of stresses:
-> exhibit yield stress
-> are non-newtonian
-> ex: ketchup, yogurt, mayo, salad
dressing

73
Q

rheometers

A

-designed to determine viscosity, elasticity, and other rheological properties of materials
-physical values (ex: pressures, flow rates) are used to determine relationships btwn stress and strain/ stress and strain rates

74
Q

what do rheometers use based on if they are testing a solid vs. liquid sample

A

-solid samples: use compression, extension, and torsion (shear) analysis
-liquid samples: use rotational viscometry

75
Q

rotational viscometry

A

-viscosity will determine the torque needed to rotate the bob at a constant rate
-bob: hanging ball or weight

76
Q

zahn cup

A

-determines viscosity
-cup is dipped and completely filled with a substance, after lifting the cup out of substance, you measure time until liquid stops dripping out of it

77
Q

bostwick consistometer

A

-measures distance sample flows in given time interval
-only measures how far the sample will flow under its own weight

78
Q

what are viscoelastic materials

A

-materials that exhibit both viscous and elastic characteristics
-viscous (water): resist shear flow and strain linearly with time when stress is applied
-elastic: exhibit strain when stress is applied and quickly return to their original state once stress is removed

79
Q

oscillatory rheometry

A

-characterize viscoelastic properties of a material under small stresses and strains

80
Q

TA

A

-measure the total acid concentration
-affects flavor
-an indicator of maturity

81
Q

pH

A

-measure of the free hydrogen ion
-measure of active acidity
-affects certain reactions in foods

82
Q

acids vs. conjugate base examples

A

EX 1
-> acid: H+
-> conjugate base: Cl-
EX 2
-> acid: H+
-> base: CH3COO-

83
Q

molarity vs normality

A

-molarity: moles of solute / liter of solution
-normality: number of mole equivalent of solute / liter of solution (1 M H2SO4 = 2 N H2SO4 bc 2 H)

84
Q

equivalent weight

A

-molecular weight / number of equivalent
-ex: H2SO4
-> molar mass = 98g
-> 2 H
-> 98 / 2 = 49 g (Et wt)

85
Q

percent concentration

A

ratio of weight or volume of solute to weight or volume of solute plus solvent x 100

86
Q

when do you use ppm

A

when concentration is < 1%

87
Q

what is the titratable acidity a measure of

A

-dissociated and undissociated acids in sample

88
Q

what is pH only a measure of

A

dissociated acids

89
Q

equivalence point in titration

A

number of acid equivalence equals the number of base equivalence & total acid neutralization is achieved

90
Q

potentiometric method

A

-using pH meter to identify endpoint
-advantage: precise equivalence point identified
-disadvantage: slow response

91
Q

colorimetric method

A

-using a phenolphthalein indicator to identify endpoint
-phenolphthalein endpoint = phenolphthalein changes from clear -> red in pH range of 8 - 9.6

92
Q

when is it better to use a pH endpoint vs a colorimetric one?

A

when phosphoric or carbonic acid are present since they buffer at pH of 8.2 but food acids DO NOT

Food Analysis (4 decks)

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