Methods of Food Analysis Flashcards
(119 cards)
1
Q
Principle
Forced draft oven
A
- H2O evaporates when it boils at 100C
2
Q
Principle
Vacuum oven
A
- H2O evaporates at reduced pressure, ~70C
3
Q
Principle
Microwave drying oven
A
- H2O evaporates by microwave energy
4
Q
Principle
Rapid moisture analyzer
A
- H2O evaporates at 100C w/ halogens as heating elements
5
Q
Principle
Reflux distillation
A
- H2O co-distills from sample w/ toluene
6
Q
Principle
Karl fischer
A
- H2O reacts w/ SO2 to cause reduction of iodine
7
Q
Advantages & Disadavantages
Forced draft oven
A
A: Easy to handle many samples at a time
DA: Causes loss of volatiles, lipid oxidation, & browning
8
Q
Advantages & Disadavantages
Vacuum oven
A
A: Low temperature reduces problems w/** high sugar problems**
DA: More expensive than forced draft oven
9
Q
Advantages & Disadavantages
Microwave drying oven
A
A: Rapid (4-8 mins/sample)
DA: More expensive; One sample at a time
10
Q
Advantages & Disadavantages
Rapid moisture analyzer
A
A: Rapid
DA: Expensive; One sample at a time
11
Q
Advantages & Disadavantages
Reflux distillation
A
A: Less thermal decomposition; Solvent protects volatiles
DA: Solvent is flammable & toxic; Less accurate reading
12
Q
Advantages & Disadavantages
Karl fisher
A
A: No thermal decomposition; Higher accuracy than other methods for low moisture foods
DA: One sample at a time; expensive if automated
13
Q
AOAC Method for chocolate, dried vegetables, dried milk, and oils & fats
A
Reflux Distillation
14
Q
Direct moisture analysis method for low-moisture foods
A
Karl Fischer Method
15
Q
Indirect moisture analysis methods
A
- Hydrometer
- Refractometer
- Infrared analyzer
16
Q
Principle
Infrared analyzer
A
Molecular vibration of OH group of H2O determines absorption
17
Q
Principle
Dry Ashing
A
Incineration at high temperatures (500-600C) w/ a muffle furnace
18
Q
Principle
Wet Ashing
A
Oxidation using acids & oxidizing agents
19
Q
Commonly used acids for Wet Ashing
A
- Hydrochloric acid
- Sulfuric acid
- Nitric acid
- Perchloric acid
20
Q
Applications of Dry Ashing
A
Total ash content for proximate analysis
21
Q
Applications of Wet Ashing
A
Ashing of samples prior to official mineral analyses
22
Q
Advantages & Disadvantages
Dry Ashing
A
A: Many samples at a time; little technician time
DA: Slow; Minerals volatilized; Difficult to resolubilize
23
Q
Advantages & Disadvantages
Wet Ashing
A
A: Little to no volatilization; Faster
DA: Sample loss due to spattering; Lower sample throughput
24
Q
Principles
EDTA Titration
A
EDTA complexes Ca & Mg
25
# **Principles**
Mohr Titration
* Direct argenometric titration for anions such as Cl
* volume & molar concentration of AgNO3 are used
26
# **Principles**
Volhard Titration
* Direct argenometric titration for anions such as Cl
* Excess AgNO3 is back-titrated w/ KSCN
27
# **Principles**
Colorimetric methods
Chromogen in reagent reacts w/ mineral & forms colored compound
28
# **Principles**
Ion-selective electrode
Composition of glass in sensing electrode is senstive to a specific mineral
29
# **Principles**
Atomic Absorbance Spectroscopy (AAS)
| *Mineral Analysis*
* Flame converts molecules to atoms & energy, excites atoms
* Light is absorbed & decrease in light intensity is measured
30
# **Principles**
Inductively couple plasma optical emission (ICP-OES)
* Plasma converts molecules to atoms & ions, excites atoms
* Emitted energy is measured while returning to ground state
31
# **Method**
* Testing water hardness
* Calcium in ash of fruits & vegetables
EDTA Titration
32
# **Method**
* Salt content of variety of foods
* Strip versions & automated instruments
Mohr Titration
33
# **Methods**
Salt content of variety of foods
Volhard Titration
34
# **Method**
Low cost method for analyzing single element
Colorimetric methods
35
# **Method**
Quality control especially Na or K
Ion-selective electrode
36
# **Methods**
Single element analysis in a given food
Atomic Absorbance Spectroscopy (AAS)
37
# **Method**
Multiple elements in a large number of samples
(ICP-OES)
Inductively coupled plasma optical emission spectrometry
38
# **Method**
Mineral analysis method for nutritional labeling
(ICP-OES)
Inductively coupled plasma optical emission spectrometry
39
Mineral analysis methods for determining salt content in foods
* Mohr Titration
* Volhard Titration
40
Organic Solvent Extraction methods for Fat Analysis
* Soxhlet (Semi-continuous)
* Goldfish (Continuous)
* Mojonnier
* Gas Chromatography
41
Nonsolvent Wet Extraction methods for Fat Anaysis
* Babcock
* Gerber
* Instrumental: IR, NMR, ASE
42
Methods used for TOTAL LIPID CONTENT
Organic Solvent Extraction method
43
Methods that may be necessary prior to Fat Analysis
* Pre-drying of sample
* Particle size reduction
* Acid hydrolysis
44
Nitrogen-based Protein Analysis methods
* Kjeldahl method
* Dumas method
45
Colorimetric methods in Protein Analysis
* Anionic dye-binding
* Biuret method
* Lowry method
* Bicinchoninic acid (BCA)
46
AOAC official method for Crude Protein Analysis
Kjeldahl method
47
# **Principles**
Kjeldahl method
Involves neutralization, distillation, & titration
48
# **Principles**
Dumas method
* Combustion at 1000C
* Reduction of nitrogen oxides w/ Cu to form elemental N
* Quantification of total nitrogen by gas chromatography using a thermal conductivity detector
49
# **Principles**
Infrared spectroscopy
Peptide bonds absorbs radiation at specific wavelength in mid or near IR region
50
# **Principles**
Anionic dye-binding
**Proteins + excess anionic dye → Protein—dye insoluble complex + unbound dye**
Absorbance of unbound soluble dye is measured
↓ unbound dye, ↑ protein content
51
# **Principles**
Biuret method
**Peptide bonds complexes w/ Cu producing a violet-purplish color**
↑ absorbance (color intensity), ↑ protein content [proportional]
52
# **Principles**
Lowry method
Biuret reaction w/ reduction of Folin-Ciocalteau phenol reagent by Tyr & Trp residues
*Yellow to Blue color complex*
53
# **Principles**
Bicinchoninic acid (BCA)
**Peptide bonds & proteins is complexed w/ Cu, Cu is chelated by BCA and forms color complex**
Protein + Cu[2+] → Cu[+] + BCA → [Cu+ — 2BCA]
*Green to Purple color complex*
54
# **Principles**
UV absorption
Amino acids Trp & Tyr in proteins shows strong absorbance at UV 280 nm
55
# **Applications**
Kjeldahl method
* Applicable to all foods
* Limited applications due to automated Dumas systems
56
# **Applications**
Dumas method
* Applicable to all foods
* Now widely used for official & quality control analysis
57
# **Methods**
Rapid quality control method for Protein Analysis
Infrared spectroscopy
58
# **Applications**
Infrared spectroscopy
* Used in infrared milk analyzers
* Applicable to wide variety of foods (grains, cereals, meat, & dairy products)
59
# Protein Analysis methods
Widely used in protein biochemistry due to simplicity & sensitivity
Lowry method
60
# **Applications**
Anionic dye-binding method
* Milk, wheat flour, soy products, & meat
* Automated version used for quality control
* Compare results against N-based method
61
# **Protein analysis method**
* Cereal, meat, soybean proteins
* Qualitative test for animal feed
Biuret method
62
# **Protein analysis method**
* Used in protein isolation & purification
* Largely replaced other quantitative colorimetric methods
Bicinchoninic acid (BCA) method
63
# **Protein Analysis Method**
* Milk & meat products
* Not widely used in food systems
* Best used w/ purified, hydrolyzed protein systems
UV Absorption
64
# **Principles**
Total Carbohydrate for **Nutrition Labeling**
g carbohydrate = total g - [g moisture + g protein + g lipid + g ash]
65
# **Description**
Phenol-sulfuric acid method
TOTAL CARBOHYDRATE
* spectrophotometric method
* measures all carbohydrates except sugar alcohols
66
# **Desciption**
Somoygi-Nelson method
TOTAL REDUCING SUGAR
* spectrophotometric method
* measures glucose/dextrose & other low MW oligosaccharides
67
# **Description**
Enzymatic Assay
| *Carbohydrate Analysis*
GLUCOSE/DEXTROSE
* determines amount of glucose in a mixture of sugars
68
# **Description**
High Performance Liquid Chromatography
| *Carbohydrate Analysis*
FRUCTOSE
* specific determination of fructose
69
# **Principles**
Hydrometer/Refractometer
CONCENTRATION OF SYRUPS
* measures specific gravity, refractive index to determine concentration of solids in the solution
70
# **Principles**
Hydrolysis of Starch
| *2 Carbohydrate Analysis Methods*
STARCHES (exc. Resistant Starch)
* hydrolysis of starch using mixture of amylases & determination of glucose
* hydrolysis of starch w/ glucoamylase & determination of glucose w/ glucose oxidase
71
# **Description**
m-hydroxiphenyl-sulfuric acid method
PECTIN
* spectrophotometric method
* for uronic acids
72
# **Principles**
Gravimetric method
| *Carbohydrate Analysis*
TOTAL DIETARY FIBER
* residue after removal of lipids, digestive starch, proteins, & subtraction of ash content
73
Dietary Fiber Analysis Methods
* Hydrometer (specific gravity)
* Refractometer (refractive index)
* Polarimeter (specific optical rotation)
74
# **Method & Principle**
Total Reducing Sugar
Somogyi-Nelson method
* based on reduction of Cu and formation of **arsenomolybdate complex (BLUE)**
Cu+ + ammonium molybdate + sodium aresenate (H2SO4) → arsenomolybdate complex (BLUE)
75
# **Method & Principle**
Total Carbohydrate
Phenol-Sulfuric acid
* Carbohydrates + Sulfuric acid → Furan derivatives + Phenolic compounds → **Yellow-gold color**
76
# **Applications & Limits**
Enzymatic Assay
* Great specificity for target carbohydrate
* Low detection limit, inexpensive
* Requires only a pure enzyme to be used
77
Similarities of Soxhlet & Goldfish
| *Fat Analysis*
* Tedious methods
* For dry/low moisture samples
* Uses cellulose thimble to hold sample during extraction
* Same applications
78
Similarities of Mojonnier & Gas Chromatography
| *Fat Analysis*
* GC commonly uses Mojonnier flask for initial fat extraction
79
Similarities of Babcock & Gerber
| *Fat Analysis*
* For same applications
* Uses volumetric measurements
80
Similarities of Mojonnier & Soxhlet
| *Fat Analysis*
* Uses gravimetric methods
* For same applications
81
Similarities of Babcock & Mojonnier
| *Fat Analysis*
* Uses liquid/solid sample
* Originally for dairy
82
# **Descriptions**
Soxhlet VS Goldfish
| Soxhlet method
* Semi-continuous
* Sample stays cool
* No channeling
* With soaking effect
* Slow (4-16h)
| Channeling may result in incomplete extraction
## Footnote
Soaking effect refers to the process where the solid sample is repeatedly contacted with fresh solvent, allowing for efficient and complete extraction of the desired compounds.
83
# **Descriptions**
Soxhlet VS Goldfish
| Goldfish method
* Continuous
* Sample gets heated
* Channeling is likely
* No soaking effect
* Faster (4h)
| Channeling may result in incomplete extraction
## Footnote
Soaking effect refers to the process where the solid sample is repeatedly contacted with fresh solvent, allowing for efficient and complete extraction of the desired compounds.
84
# **Descriptions**
Mojonnier VS GC
| Mojonnier method
* Measures weigh of fat
* Component of GC method
85
# **Descriptions**
Mojonnier VS GC
| Gas Chromatography
* Requires hydrolysis
* Extraction done w/ mojonnier flasks
* Measure fat as sum of fatty acids
* Nutrition labeling
86
# **Descriptions**
Babcock VS Gerber
| Babcock method
* H2SO4 only
* Charring occurs in high sugar foods
* More complex & slower
87
# **Descriptions**
Babcock VS Gerber
| Gerber method
* H2SO4 + Isoamyl Alcohol
* Charring does not occur
* Simple & Faster
88
# **Descriptions**
Mojonnier VS Soxhlet
| Mojonnier method
* Multiple solvent
* Solid/liquid samples
* Discontinuous
89
# **Descriptions**
Mojonnier VS Soxhlet
| Soxhlet method
* Single solvent
* Solid sample only
* Semi-continuous
90
# **Descriptions**
Babcock VS Mojonnier
| Babcock method
* Uses H2SO4
* Dairy products only
* Measures fat volume
91
# **Descriptions**
Babcock VS Mojonnier
| Mojonnier method
* Multiple solvents
* Any food product
* Measures fat weight
92
Physical Analysis methods
| Filth Analysis
* Sedimentation
* Floating in Oil
* Sieve mesh sizes
93
# **Filth Determination method**
Separation of heavy filth based on density
Separation of heavy filth based on density
94
# **Filth Determination method**
Aqeuous liquid mixture for separation of oleophilic light filth
Floating in Oil
95
# **Filth Determination method**
Quantitative separation of Sieved Filth
Sieve mesh sizes
96
# **Method & Principle**
Color Analysis method
MUNSELL SYSTEM
designates color in terms of hue, value, chroma
97
# Rheological Testing Method
Instruments to measure viscosity
* Brookfield Viscometer
* Bostwick Consistometer
98
Thermal Analysis Methods
* Thermogravimetric Analysis (TGA)
* Differential Scanning Colorimetry (DSC)
* Thermomechanical Analysis (TMA)
* Dynamic Mechanical Analysis (DMA)
* Moisture Sorption Analysis (MSA)
99
# **Thermal Analysis Methods**
* Measures weight change
* For monitoring processes that involves changes in mass
Thermogravimetric Analysis (TGA)
100
# **Thermal Analysis Methods**
* Measures heat flow
* For studying melting, crystallization, & protein denaturation
Differential Scanning Calorimetry
101
# **Thermal Analysis Methods**
* Measures dimensional change
* Concerned w/ expansion, contraction, penetration as function of temperature
Thermomechanical analysis (TMA)
102
# **Thermal Analysis Methods**
* Stiffness & Energy dissipation
* For studying different viscoelastic properties
* Applying oscillating stress + measuring response (texture)
Dynamic Mechanical Analysis (DMA)
103
# **Thermal Analysis Methods**
* Moisture sorption
* For stability & shelf-life determination
Moisture Sorption Analysis (MSA)
104
Chromatographic Methods
* Gas Chromatography (GC)
* High Performance Liquid Chromatography (HPLC)
105
Phases in Gas Chromatrography
* Mobile phase: Gas
* Stationary phase: Immobilized liquid on inert solid support (Packed/Capillary Type column)
106
Phases in Liquid Chromatrography
* Mobile phase: Liquid
* Stationary phase: Solid/Liquid
107
# **Applications**
Gas Chromatography
Limited to **semi-volative**, **volatile**, **thermally stable** compounds
108
# **Applications**
HPLC
Suitable for separating **nonvolatile** species
109
Spectroscopic Methods in Food Analysis
* UV-Vis Spectrophotometry
* Fluorescence Spectrophotometry
* Infrared Spectrophotometry
* Atomic Absorption Spectrophotometry
* Atomic Emission Spectrophotometry
110
# **Principles**
UV Vis Spectrophotometry
* Based on absorption by analyte of radiant energy
* Absorption ⇄ Concentration of Analyte
111
# **Principles**
Fluorescence Spectrophotometry
* Based on emission by analyte of radiant energy
* Emitted energy ⇄ Concentration of Analyte
112
# **Principles**
Infrared Spectrophotometry
Based on absorption by analyte of radiant energy from a mid-IR source
113
# **Principles**
Atomic Absorption Spectroscopy
* Flame converts molecules to atoms
* Atoms are activated by the hollow cathode lamp
114
# **Principles**
Atomic Emission Spectroscopy
* Plasma converts molecules to atoms
* Plasma activates atoms from ground state
115
# **Applications**
UV Vis Spectrophotometry
Measurement of concentration of analyte
116
# Principles
Fluorescence Spectrophotometry
Measurement of concentration of analyte that will emit energy in UV or Vis region
117
# **Applications**
Infrared Spectrophotometry
Qualitateive & quantitative analysis of sample
118
Quantative Analysis of Minerals
| *Spectrophotometric method*
* Atomic absorption
* Atomic emission
119
