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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
water content direct measurement methods (& how its done)
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
26
water content indirect measurement methods (& how its done)
BASED ON A PROPERTY OF FOOD RELATED TO PRESENCE OF WATER -dielectric capacitance -hydrometer -refractometer -NIR spectroscopy -freezing point, cryoscope -microwave absorption -conductivity
27
what do you need to consider when regarding methods?
-how should samples be handled -what is measured? -how is water removed/reacted/identified? -assumptions? and sources of error? -applications? -official method requirements
28
oven drying method principle
-sample is heated to evaporate off water -weight loss equals moisture content
29
oven drying method calculation
-% moisture (wt./wt.) = (wet wt. - dry wt. / wet wt.) x 100
30
oven drying method sources of error
-particle size -volatile compounds present -lipid oxidation -sample very hygroscopic -alteration of carbohydrates -surface crust formation -splattering -improper storage in dessicator
31
what does the red box indicate in moisture content by drying oven graph
-indicates the break points at which there is sample break down
32
microwave drying analyzers characteristics
-greatly reduces analyses time -allows for in-process analyses & process adjustment -variables: time and power
33
infrared drying characteristics
-involves heat penetration directly into the sample (vs. heat conductivity & convection with conventional oven)
34
Karl Fischer method principle
-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
35
Karl Fischer Coulometric method
-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
36
how can standardization of the Karl Fischer be done?
-pure water, water-in-methanol standard -sodium tartrate dehydrate (commonly used)
37
Dielectric method principle
-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
what is capacitance
-ability of material object/device to store electrical charge
39
Freezing point measurement
-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
importance of water activity
-affects important quality and safety factors -> growth of spoilage and pathogenic microorganisms -can be a critical control point in HACCP plans
41
what does the water activity of 0 vs. 1 mean
-aw of 0 = absolutely no water -aw of 1 = pure water
42
water activity methods
-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
rheology
science devoted to the deformation and flow of all materials
44
rheological properties
-subset of mechanical properties of food -determined by applying and measuring forces and flows or deformations as a function of time
45
what do rheological method measure
force, deformation, flow
46
stress vs. strain definition
-stress: force per area -strain: relative deformation
47
how are stress and strain linked
by constant of proportionality (moduli)
48
what do ideal solids and ideal fluids obey
-ideal solids: obey Hooke's Law -ideal fluids: obey Newtonian principle
49
viscosity
internal resistance to flow
50
stress
-fundamental measurement of force -stress = force/ area -expressed in Pascals (Pa) for low pressure and Bars (1 bar = 100 kPa) for high pressure
51
normal stress
force is perpendicular to surface ex: chewing piece of gum
52
shear stress
force is parallel to surface ex: spreading butter on toast
53
strain
dimensionless quantity representing relative deformation of material
54
normal strain
-ɛ̝ (epsilon) -applied stress is perpendicular to surface -ex: large deformation such as in texture testing
55
shear strain
-γ (gamma) -applied stress is parallel to sample -ex: pumping tomato paste through pipe
56
shear (strain) rate
-degree of deformation with respect to time
57
simple shear
-laminar (layered) deformation in a plane parallel with an applied force
58
Hooke's Law
-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
elastic modulus (E)
proportionality constant when normal stress is applied to sample
60
shear modulus (G)
proportionality constant when shear stress is applied to sample
61
relationship of viscosity to temp
viscosity dec as temp inc
62
apparent viscosity
-shear-dependent viscosity -shear stress divided by corresponding shear rate -what the viscosity "appears to be" under shear stress
63
newton's postulate
doubling shear stress doubles shear rate within fluid
64
Newtonian fluids (ideal fluids)
-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
Non-Newtonian fluids
-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
shear thinning (pseudoplastic) fluids
-viscosity decreases as shear rate increases, and is independent of time -ex: applesauce, pie fillings
67
shear thickening (dilatant) fluids
-viscosity increases as shear rate increases, and is independent of time -ex: corn starch slurries
68
thixotropic fluids
-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
antithixotropic (rheopectic) fluids
-viscosity increases with time -ex: some clay mixtures
70
thinning (time dep vs. time indep)
-time dep: thixotropic -time indep: pseudoplastic
71
thickening (time dep vs. time indep)
-time dep: anti-thixotropic -time indep: dilatant
72
yield stress
-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
rheometers
-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
what do rheometers use based on if they are testing a solid vs. liquid sample
-solid samples: use compression, extension, and torsion (shear) analysis -liquid samples: use rotational viscometry
75
rotational viscometry
-viscosity will determine the torque needed to rotate the bob at a constant rate -bob: hanging ball or weight
76
zahn cup
-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
bostwick consistometer
-measures distance sample flows in given time interval -only measures how far the sample will flow under its own weight
78
what are viscoelastic materials
-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
oscillatory rheometry
-characterize viscoelastic properties of a material under small stresses and strains
80
TA
-measure the total acid concentration -affects flavor -an indicator of maturity
81
pH
-measure of the free hydrogen ion -measure of active acidity -affects certain reactions in foods
82
acids vs. conjugate base examples
EX 1 -> acid: H+ -> conjugate base: Cl- EX 2 -> acid: H+ -> base: CH3COO-
83
molarity vs normality
-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
equivalent weight
-molecular weight / number of equivalent -ex: H2SO4 -> molar mass = 98g -> 2 H -> 98 / 2 = 49 g (Et wt)
85
percent concentration
ratio of weight or volume of solute to weight or volume of solute plus solvent x 100
86
when do you use ppm
when concentration is < 1%
87
what is the titratable acidity a measure of
-dissociated and undissociated acids in sample
88
what is pH only a measure of
dissociated acids
89
equivalence point in titration
number of acid equivalence equals the number of base equivalence & total acid neutralization is achieved
90
potentiometric method
-using pH meter to identify endpoint -advantage: precise equivalence point identified -disadvantage: slow response
91
colorimetric method
-using a phenolphthalein indicator to identify endpoint -phenolphthalein endpoint = phenolphthalein changes from clear -> red in pH range of 8 - 9.6
92
when is it better to use a pH endpoint vs a colorimetric one?
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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