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131 Cards in this Set
- Front
- Back
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Carbohydrate Analysis importance
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Nutrition facts-total carb, dietary fiber, sugars
Ingredient list-abundance in food Quality tests-water, sugar added in fruit juice |
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Determining total carbs
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Calculated
Total weight - (protein, total fat, moisture, ash) |
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Determining other carbs
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Total carbs - (dietary fiber, sugars, sugar alcohols)
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Carb sample prep
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Dry in vacuum oven
Grind Lipid extraction Extraction with ethanol Ion exchange Evaporate ethanol with rotary evaporator |
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Total carb method
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Phenol sulfuric acid method
Phenol to solution Sulfuric acid-Monosaccharides decompose Condense with phenol |
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Reducing sugars
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Free carbonyl group, act as reducing agent
Cu2+ to Cu+ by reducing sugars Glucose, maltose |
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Fructose alkaline conditions
Fructose neutral conditions Fructose acidic conditions |
Reducing sugar
Nonreducing Nonreducing |
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Nonreducing sugars
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No carbonyl group
Sucrose, raffinose |
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Measurement of individual mono- and oligosaccharides
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HPLC or GC
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Starch measurement
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Starch to D-glucose with enzymes
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Starch measurement
Adv: |
Very specific, useful for complex foods
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Starch measurement
Disadv: |
Pure enzymes needed
Not for high amylose starch Resistant starch may not be measured |
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Resistant starch
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Starch, starch degradation products that escape digestion in small intestine
Trapped in food matrix Retrograded starch |
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Retrograded starch
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Starch polymers that recystallized after gelatinization of granules
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Food gums (hydrocolloids)
measurement why |
Polysaccharides other than starch
To determine purity of gum Label declarations of processors are correct Monitor that gums aren't added when not allowed Amount in a given compound |
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Physical methods carb measurement
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Microscopy
NIR spectroscopy Specific gravity (only pure solutions) Refractive index (pure solutions)-sugar concentration in liquids Polarimetry |
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Dietary Fiber
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Non-digestible components of food
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Components of dietary fiber
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Cell wall: Cellulose, hemicellulose, pectin,
Non cell wall polysaccharides: hydrocolloids lignin |
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Insoluble fiber
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Cellulose
Lignin Hemicellulose Resistant starch |
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middle cerebral artery
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trunk, arm, face
brocas wernickes usu site for atherosclerotic stroke |
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Dietary Fiber sample prep
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Needs to be low in fat
Dry Finely ground |
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Gravimetric methods dietary fiber
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Crude fiber-older
Acid and neutral detergent fiber-older Insoluble fiber-caught by filter Soluble fiber-in filtrate and washings |
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Insoluble fiber gravimetric methods
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=residue wt - (wt of protein + wt of ash)
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Soluble fiber gravimetrhic methods
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=residue wt - (wt of protein + wt of ash)
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Total fiber calculations
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=soluble fiber + insoluble fiber
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Fat soluble vitamins
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A, D, E, K
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Causes vitamins to deteriorate
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pH, heat, air, light, temperature
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Prevent vitamin loss in measurement
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Limit exposure to bad conditions
Extract in dark Antioxidants |
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Vitamin analysis extraction methods
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One or several of:
Heat, acid, alkali, solvents, enzymes |
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Water soluble vitamins extraction
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Boiling or autoclaving in acid
Vitamin C- cold extraction with metaphosphoric acid/acetic Niacin-autoclaving in acid (noncereal products) or alkali (cereal products) |
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Fat soluble vitamins extraction
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Organic solvent extraction
Saponification Re-extraction with organic solvents |
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Vitamin analysis 3 methods
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Bioassays
Microbiological Physiochemical |
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Bioassays
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Humans, animals
Vitamins B, D |
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Microbiological assays
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Protozoa, bacteria, yeast
Time consuming Extraction Water soluble vitamins Growth of microbe proportional to requirement of niacin/folate |
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Physiochemical assays
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Easiest
Extraction Vitamins A, E, C, thiamin, riboflavin |
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Line test
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Vitamin D assay
Extract with organic solvent, saponify fats, reextract with organic solvent, feed to rats Feed known, unknown amounts Sacrifice rats, calcification of bones-staining bone; score-darkness |
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Vitamin A, E analysis
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HPLC
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Vitamin C analysis
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2, 6-Dichloroindophenol titration
Fluorometric method |
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Thiamin, riboflavin analysis
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Fluorometric method
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Bioassays vs. microbiolocial and chemical vitamin methods
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Bioassays-Time consuming
More info Less undesirable changes in extraction Micro/chem-easier Vitamin extraction Not bioavailability to humans |
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HPLC physiochemical vitamin method
adv, disadv |
Adv: applicable to most vitamins
Simple, accurate, precise Simultaneous analysis of multiple vitamins Currently being developed for many vitamin analyses Disadv: separation not identification High capital expense |
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Name 3 preparation steps for carbohydrate analysis in a solid food.
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Dry Sample
Grind Remove fat |
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What technique/method is used to measure total starch in a food?
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Conversion of starch to glucose by enzymes
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What carbohydrate analysis method was performed in lab?
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Phenol-Sulfuric Acid Method
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How is the %DV calculated?
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Amount of nutrient
--------------------------- X 100 DRV or RDI |
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Name 2 ways to obtain data for a nutrition facts label
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Nutrient Database
Measure nutrients in a lab |
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Name a vitamin that would be extracted from a food using the following technique:
Organic solvent extraction, saponification, and reextraction with organic solvents |
Vitamins A, E, D, K
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Why is metaphosphoric acid/acetic acid used in extraction of Vitamin C?
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To stabilize the vitamin C
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Give an advantage of
ICP-AES over AAS |
Can measure multiple elements at once
More sensitive for some elements Better for compounds stable at high temperatures Fewer interferences Larger linear working range |
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Which instrument uses a plasma?
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ICP-AES
Plasma Polychromator Detector Readout device |
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What mineral analysis technique measures in mV?
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Ion Selective Electrodes
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Name an advantage of ISE
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Advantages
Can measure many anions and cations directly (in contrast to measuring complexes they form with other compounds) Analyses are independent of sample volume, turbidity, color, and viscosity Simple (only requires electrodes and a pH meter) |
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Name a disadvantage of ISE
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Disadvantages
Limit of detection is usually 2-3 ppm Slow electrode response time at low levels of measurement (below 10-4 M) Some electrodes have short operating life |
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What color system uses an atlas of color chips?
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The Munsell System
Value: lightness or darkness Hue: red, green, blue, yellow, etc. Chroma: intensity |
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What government agency has developed color grading standards for a variety of products?
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USDA
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Advantages, disadvantages of USDA grading standards
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Advantages:
easy to understand Disadvantages: Visual standards do not provide all possible colors Munsell chips can be tiring and tedious; fragile Colors may change with use, time |
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What values may be obtained from a colorimeter?
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XYZ
Lab L*a*b* |
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What colors occur at the endpoints of the following titrations:
1) EDTA complexometric method (for hard water) 2) 2,6-dichloroindophenol method (for vitamin C) |
Blue for
EDTA complexometric method 2) Rose pink for 2,6-dichloroindophenol method (for vitamin C) |
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Beer's law
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Linear relationship between absorbance and analyte concentration
Absorbance=absorbtivity constant X path length X concentration of species |
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How is fluorescence spectroscopy better than UV-Vis?
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1 to 3 orders of magnitude more sensitive than UV-Vis
Unfortunately, most molecules don’t fluoresce (this technique won’t work) Thiamine is convterted to thiochrome which fluoresces |
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In mid-IR spectroscopy, how is a dispersive instrument different from a Fourier-transform instrument?
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Mid-IR Spectroscopy: Dispersive
Similar to a double beam UV-Vis Has a monochromator Mid-IR Spectroscopy: Fourier Transform Instrument uses an interferometer instead of a monochromator Beam split and then recombined All wavelengths arrive at the detector simultaneously Advantage: FT can acquire spectra more rapidly, with greatly improved signal-to-noise ratio. |
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How is MS different from other types of spectroscopy?
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Molecules are ionized and broken into fragments
Mass/charge ratio measured Used to identify compounds |
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If a sample being analyzed for a mycotoxin was diluted 1:10 prior to analysis, what is the original concentration if the test result is 1 ppb?
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10 ppb
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What is the purpose of chromatography?
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To separate a mixture of compound into individual components
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What is the difference between the stationary and the mobile phase?
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Mobile phase moves sample through the stationary phase
Stationary phase helps separate the components based on differing levels of attraction |
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List all of the uses you can think of for chromatography in food analysis
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To measure:
Proteins Fats Carbohydrates Vitamins Colorants Pesticides Bioactive compounds Flavor compounds Etc. |
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UV-Vis Spectroscopy
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Quantification of macrocomponents, microcomponents
Estimates of rancidity Surveillance testing |
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UV-Vis Spectroscopy 2 types
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absorbance
fluorescence |
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UV-Vis Spectroscopy
Absorption spectroscopy |
Concentration of analyte
Amount of light absorbed from reference beam as it passes through sample |
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Absorption spectroscopy varies with
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Wavelength
Chemical environment: pH, solvent Reflection Scattering |
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UV-Vis Spectroscopy
Sample prep |
Homogenize
Clarification-Solutions can't be cloudy Modification-modify to absorb in range |
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UV-Vis Spectroscopy
Parts of instrument |
Light source
Monochromator Sample/reference holder Radiation detector Readout device |
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UV-Vis Spectroscopy
Types of spectrophotometers |
Single, dual beam
Array detector |
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UV-Vis Spectroscopy
Fluorescence spectroscopy |
Concentration of analyte
Measured signal is radiation emitted 2 wavelength selectors-excitation, emission More sensitive than UV-Vis Most don't fluoresce |
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UV-Vis Spectroscopy
Application |
Ripeness of fruit
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IR Spectroscopy
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Vibrational energy-stretching, bending
Vibration allows absorption of IR radiation |
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IR Spectroscopy
2 instruments |
Dispersive
Fourier Transform |
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Fourier Transform
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All wavelengths simultaneous at detector
Interferometer not monochromator Spectra more rapidly |
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Mid IR applications
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Milk analyzers
Fat in emulsified meat Unsaturation and cis/trans of fats, oils Specific functional groups in unknown substance Indentify unknown substance |
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Near IR
Mid IR type of analysis |
Near-quantitative analysis--composition of solid food products
Mid-qualitative analysis |
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Overtones
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Absorption that moves molecule to higher excited state
Low intensity absorption |
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NIR adv/disadv
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Adv-bands are common groups in food
Disadv-weaker in intensity, overtones |
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NIR applications
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Grain, cereal products, oilseeds
Meats, dairy eggs Can monitor changes during processing |
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NMR
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nuclear spins oriented in magnetic field
orientation=energy level |
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NMR Application
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Determine water, solid fat content
Temperature dependant |
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General principles of AAS, AES
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Separated into individual atoms
Atomization-flame, electrothermal-graphite furnace (AAS), or argon plasma (ICP-AES) |
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AAS
Cathode |
Specific for each element
Made of element |
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AAS
Chopper |
detector to subtract continuous signal from flame
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AES
Flame/plasma |
Atomizes analyte
Emission of photons measured after heat excites atoms Flame good for elements with low excitation energies |
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AES
Monochromator |
Selects emission wavelength of compound of interest
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Spectrometry:
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technique used to measure concentration of a particular species
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Spectrophotometer:
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measures in visible region
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Mass spec used for
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Detect, identify compounds
Pesticide residues Contaminants in drinking water Flavor compounds in food |
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GC used for
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Separating compounds
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MS
Most popular mass analyzer |
Quadrupoles
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Chromatography
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Paper
Thin layer Column GC HPLC |
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Chromatography
Applications |
Analysis of proteins, fats, carbs, vitamins, etc
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Chromatography
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Partitioning of a sample between mobile and stationary phase
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Mobile phase
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gas (GC)
liquid (LC) supercritical fluid (SFC) |
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Stationary phase
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liquid
solid (more common) |
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Chromatography
Adsorption |
Used to remove impurities before other analyses
Based on polarity For: lipids, fat soluble pigments, fat soluble vitamins |
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Chromatography
Partition |
Separation based on polarity
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Chromatography
Ion exchange |
Charged molecules: amino acids, proteins, sugars, acids
Charge + or - |
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Cation exchange
Anion exchange |
- Charge attracts cations
+ charge attracts anions |
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Chromatography
Size exclusion |
Molecules of various molecular weights (proteins, polysaccharides)
Size, smaller molecules trapped along way through column |
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Chromatography
Affinity |
Biomolecules
Separation based on binding to ligand (puzzle piece) |
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Chromatography
Quantitative analysis |
Concentration based on peak height/area/mass (cut and weight)
Integration or area-computer |
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Chromatography
Internal standard |
add to every sample
unique to sample ratio to estimate concentration |
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Applications of HPLC
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Analysis of carbs, lipids, proteins, caffeine, food dyes, vitamins etc
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HPLC Preparative
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Separate, collect purified compounds
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HPLC
Analytical |
Separate, detect compounds
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Isocratic elution
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Solvent proportions constant
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Gradient elution
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Solvent proportions change over run (increase strength)
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Guard column
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protects analytical column
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Fraction collector
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Collects separated components for future use
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HPLC
Normal phase |
Stationary phase polar
Mobile phase nonpolar Separating nonpolar compounds |
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HPLC
Reversed phase |
Stationary phase nonpolar
Mobile phase polar Separating proteins, vitamins, caffeine etc |
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HPLC
RI Detector |
Change in RI of mobile phase due to solutes
Universal |
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HPLC
UV diode |
3-D plot of absorbances
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Sample prep GC
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Prevent sample degradation-inactivate enzymes
Reduce particle size-dry, grind Isolate solutes from food-headspace, distillation, solvent extraction Sample derivatization |
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GC
Distillation |
SDE-Simultaneous distillation extraction
Extract volatiles Boiling temp Vacuum to prevent artifact formation |
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GCSolid Phase Microextraction
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SPME
Easy prep-sample in vial, add standard SPME fiber exposed to sample while heating; volatile adsorb to fiber Inject into GC Not reproducible |
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GC
derivatization |
Non-volatile or too polar for good separation without derivatization
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GC
Fatty acid analysis |
Extract lipids
Hydrolyze fatty acids, esterify |
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GC columns
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Packed
Capillary |
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Packed columns
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Stainless steel or glass
Stationary phase on solid support |
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GC capillary columns
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Hollow fused or silica glass
Stationary phase on walls More efficient |
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Reduced
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25% less than reference
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Value
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lightness or darkness
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Hue
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red, green, blue, yellow
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USDA Grading standards
Adv/disadv |
Adv: Easy to understand
Disadv: not all possible colors Munsell chips tiring, tedious Colors change with time/use |
