NDFS 350 Test 2
State the two governmental agencies primarily responsible for nutrition labeling.
USDA and FDA
The term gas chromatography usually refers to gas-liquid chromatography where the stationary phase is in a closed tube or column. What is the mobile phase (gas or liquid)?
gas
State three attributes samples must have before being analyzed for fiber, i.e., three preparation steps.
dry, defat and grind
***Distinguish between the terms DV, RDI and DRV.
dv-daily value (shown as %DV on label), a generic term used to describe the other two RDI-reference daily intake--used for essential vit&mins DRV-daily reference value--used for the other food components (based on 2000-2500 reference calorie intake)
***Explain why each element can be measured using atomic spectroscopy.
each element has a unique emission and absorption spectrum
****Define dietary fiber.
edible parts of plants and similar carbs that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine
Briefly explain the use of a) equivalence point of the titration and b) standard addition in ISE methodology.
eq pt- once reach a jump in the graph, shows added enough that endpt has been reached -measure initial electrode pot. then an aliquot with a known conc of the measured species is added and the potential is again measured, helps to eliminate background effects from actual sample
****State the purpose of performing a test for oxygen demand.
evaluate the potential effect of organic pollutants on either a wastewater treatment process or a receiving water body
State the full name of the FSIS and the agency in which it is located.
food safety inspection service, in the USDA
"Proximate composition" refers to analysis for moisture, ash, fat, protein, and carbohydrate. Identify which of these components of "proximate composition" are actually required on a nutrition label. Also, explain why it is important to measure the nonrequired components quantitatively if one if developing a nutrition label.
for label: fat, protein, and carbs -moisture and ash are needed to calc %carbs -ash needed to calc some vitamins and minerals
In the quantitation of Na by atomic absorption, KCl or LiCl was not added to the sample. Would you likely over- or underestimate the true Na content? Explain why either KCl or LiCl is necessary to obtain accurate results.
underestimate without the addition of these, sodium would be ionized before it can be read -NA is an easily ionized element, when it ionizes, it increases the conc of electrons and shifts the equilibrium of (M --arrows-- M+ + e-) to the left, thus making the amount seem less than actually is. -these reagents would react with Na, and prevent it from ionizing
****The standard by which all chemical methods to measure vitamin D content are compared is a bioassay method. Describe this bioassay method.
"line test" feed animals, after depletion phase, feed known and unknown amounts of Vit D. then kill them. then measure bone calcification
Using a diagram, explain the instrumental components (and their arrangement) of a single beam atomic absorption spectrometer.
(draw picture, in notes) -radiation source (can be hollow cathode lamp or electrode-less discharge lamp -atomizer (can be flame or furnace) -detector (can be photomultiplier tube or solid state detector) -(electronics and readout make up computer)
****Using a diagram, state the instrumental components (and show arrangement) of a GC system.
(see notes)
You applied a mixture of proteins, in a buffer at pH 8.0, to an anion-exchange column. On the basis of some assays you performed, you know that the protein of interest adsorbed to the column. a. Does the anion-exchange stationary phase have a positive or negative charge? b. What is the overall charge of the protein of interest that adsorbed to the stationary phase? c. Is the isoelectric point of the protein of interest (adsorbed to the column) higher or lower than pH 8.0? d. What are the two most common methods you could use to elute the protein of interest from the anion-exchange column? Explain how each method works. (See also Chapter 15)
+ - lower d. changing pH and changing ionic strength
The FDA and FSIS of the USDA have very similar regulations for nutrition labeling, with differences due primarily to the inherent difference in the food products they regulate. Identify the differences in regulations between FDA and FSIS regarding nutrient content claims that support this generalization.
-'enriched' and 'fortified' are not defined in FSI -lean and extra lean are defined and approved for use on all USDA-regulated products but only for FDA-reg products of seafood, game meat, and meal products -__%lean is approved for USDA but not FDA
There are two commonly used AOAC methods to measure the vitamin C content of foods. Identify these two methods; then compare and contrast them with regard to the principles involved.
-2-6 dichloroindophenol method and microfluorometric method -both oxidize L ascorbic acid -indophenol uses titration while micro uses flourescence -indophenol measures only L-ascorbic acid while micro measure both forms of ascorbic acid
What kind of final data does one obtain with an MRI? List two applications of MRI.
-2D or 3D image of the sample --analysis of cooked products --comp of pastes and sauces
For most types of food samples other than clear liquids, what type of sample preparation and treatment is generally required before using ICP-AES, AES, or AAS for analysis?
-ash -solubilize ash in dilute acid -dilute to volume
****Explain the principles of using an ISE to measure the concentration of a particular inorganic element in food.
-both electrodes are in the solution. -measure the electric potential by comparing to the reference electrode, which has a fixed potential -the diff. in potential is related to activity, which relates to conc thru A=gamma(C) the gamma is a function of ionic strength; ionic strength must be adjusted to a nearly constant, high level then the nernst eq relates electrode response to conc
Sometimes a food label is abbreviated and does not contain all of the required information. State the rule that allows for the use of a simplified label.
-can use simplified if 7 or more of the required 13 nutrients are present in only insignificant amounts
****What are the principles behind total carbohydrate determination using the phenol-sulfuric acid method? Give an example of another assay procedure based on the same principle.
-carbs are heated in the presence of acid to produce furan derivatives, that condense with phenol, to form compounds that can be quantitated spectrophotometrically -thiamin extraction
What is gradient elution from a column, and why is it often advantageous over isocratic elution?
-changing the nature of the mobile phase useful when components range widely in polarity; enhances resolution and decreases analysis time
The detection limit for calcium is lower for ICP emission spectroscopy than it is for flame AAS. How is the detection limit determined, and what does it mean?
-determined by the analysis of samples with known conc. of analyte and by establishing the min. level at which the analyte can be reliably detected. -lowest conc. of the element that can be distinguished from the blank at a given level of confidence, usually 98%
State 3 methods of isolating solutes from food in preparation for GC analysis
-distillation; solvent extraction; solid-phase extraction
Give three general requirements for HPLC column packing materials
-good chem stability -sufficient mechanical strength to withstand pressure -well-defined particle size
****To be quantitated by most methods, vitamins must be extracted from foods. What treatments are commonly used to extract the vitamins? For one fat-soluble vitamin and one water-soluble vitamin, give an appropriate extraction procedure.
-heat, acid, alkali, solvent, enzymes, saponification -fat: extract with organic solvent, saponify, reextract with organic solvent, use antioxidants -water: ex. Vit C: cold extraction with acid
Explain the purpose(s) of each of the steps in the AOAC Method 994.13 for total dietary fiber listed below as applied to determination of the dietary fiber content of a high-fiber snack food: a. Heating sample and treating with α-amylase c. Treating sample with protease b. Treating sample with glucoamylase d. Adding four volumes of 95% ethanol to sample after treatment with glucoamylase and protease e. After drying and weighing the filtered and washed residue, heating one duplicate final product to 525°C in a muffle furnace, and analyzing the other duplicate sample for protein
-heating: allows enzymes to get in, removes starch sections randomly, prepares for glucoamylases protease: gets ride of protein gluco: cuts each section down to glucose (completing amylase's work) adding: seperates soluble from insoluble fiber after: some ash gets through, so have to subract this amount out of total fiber amt; some protein gets through as well, so have to subtract it out
Ion chromatography has recently become a widely promoted chromatographic technique in food analysis. Describe ion chromatography and give at least two example of its use.
-high-performance ion-exchange chromatography using low-capacity stationary phase with conductivity detector -sugars, phenols
State the light source for AAS; explain how it works, including why a different lamp must be used for each element. (similar to Study Question 6, part a)
-hollow cathode lamp -hollow tube filled with argon or neon, an anode made of tungsten, and a cathode made of the metallic form of the element being measured -it emits radiation of exactly the right energy to excite the element of interest -when voltage applied across the electrodes, the lamp emits radiation that is characteristic of the metal on the cathode. when this rad. passes thru the flame containing the sample, the metal of interest in the flame will absorb some of the rad. because the rad. has the exact amount of energy to excite the metal of interest.
What is solid-phase extraction and why is it advantageous over traditional lliquid-liuid extractions?
-liquid sample passed through cartridge containing a chromatographic column. solutes with affinity are retained on stationary phase. stat phase rinsed with water or weak solvent, then with stronger solvent to elute the solutes of interest adv: less solvent req, speed, less glassware needed, better precision/accuracy; minimal solvent evaporation for further analysis; readily automated
What are the advantages of ICP-AES over AAS?
-multiple elements in a single sample -better for refractory compounds -fewer interferences -much wider linear range -detection limits lower for some elements
Give five potential sources of error in sample preparation prior to atomic absorption analysis
-not using distilled and/or deionized water -not using reagent grade chemicals -not using sufficiently clean glassware -using glass rather than plastic labware -not diluting sample properly
List the factors to control, consider, or eliminate for an accurate measure of concentration by the ISE method.
-operate at a constant temp -adjust pH and ionic strength to high, constant level -remove electrode interferences -selectivity -detection limit -sensitivity -response time
The term chromatography applies to a wide variety of separation techniques. Explain how a sample is separated into its component parts, using terms that apply to all the techniques (i.e., do not explain a specific type of chromatography or one of the principles of separation)
-partitioning of sample/solute between moving phase and a fixed (stationary) phase. -series of equilibrations between mobile and stat phase -relative interaction of solute with the 2 phases is the partition coeff, K. (=sol conc in stat/solute conc in mobile)
You want to develop macaroni and cheese product that can be labeled reduced sodium. The first step is to identify a reference food that you will use for comparison. What are some potential reference foods you could use and how would you select one?
-pick a different company's mac and cheese -use one that has a high sodium amount, so that there is a big enough difference to make label claim
List the components of the NMR spectrometer and their functions.
-powerful cryomagnet- supplies external magnetic field and is the probe into which the sample is placed -electronics console-for transmitting and receiving the radio signals -data/work station provides computer control, collects and processes data
Describe the interaction of the net magnetization with the RF pulse (90º) and the subsequent NMR signals.
-the RF pulse energy tilts the net magnetization from the z plane into the xy plane -the net magnitude evolves in the xy plane and seperates into component vectors (unique for each proton) -each emits a signal into the receiver coil as they decay back to the z axis -this is the NMR signal which is then converted to a spectrum
Define what is meant by "extraction" and recognize how it applies to more than chromatography
-transfer of a solute from one liquid phase to another -used as actual means of analysis; prelim sample clean up; conc of the component of interest
Write the general scheme for sample preparation and extraction of mono- and disaccharides.
1. dry sample 2. grind to fine powder 3. extract lipids out 4. extract with 80% hot ethanol
***Explain the sample preparation required before injecting a sample into a GC.
1. prevent sample degredation 2. reduce particle size 3. isolate solute from food and conc them 4. sample derivitivzation
***List the 3 general types of food applications of NMR and give an example of each.
13C-can analyze adulterated olive oil 1H NMR monitors oxidation of cooking oiil low resolution NMR determines solid/fat content of an oil or fat
Describe the principle behind each step in Fig. 10-11. What is the reason for each step?
?? didnt think was important
State the methods most commonly used in mineral analysis.
AAS ICP-AES
Explain how AAS and AES spectra are produced.
AAS uses a flame, and ground state atoms or ions absorb energy from the flame, amt of energy absorbed gives a spectra AES-can use plasma or flame, excite atoms/ions, then the atoms/ions emit energy when they return to a lower or ground energy state both aas and aes are related to concentration
Define the abbreviations AAS, ICP-AES and ICP-MS.
AAS-atomic absorption spectroscopy ICP-AES- inductively coupled plasma atomic emission spectroscopy ICP-MS- inductively coupled plasma mass spectrometry
***State the two references containing approved methods of analysis required by the two agencies responsible for nutrition labeling.
AOAC methods (for FDA) "USDA analytic chemistry lab. guidebook" (FSIS)
State the two main methods used to determine oxygen demand. Define their abbreviations.
BOD (biochem oxygen demand) and COD (chemical oxy)
In your new job as supervisor of a lab that has previously been using the BOD method to determine oxygen demand of wastewater, you have decided to change to the COD method. a. Differentiate the basic principle and procedure of the BOD and COD methods for your lab technicians. BOD Principle - BOD Procedure- COD Principle - COD Procedure -
BOD princ: measure amt of oxygen required by microorg to oxidize the biodegradable organic constituents present in water and wastewater proced: put "seeded" waterr in BOD bottle, measure initial dissolved oxygen; incubate for 5 days and measure final dissolved O2 COD princ: organic comp. are destroyed by refluxing in strong acid solution with known quantity of an oxid agent (amount of oxid agent consumed is directly proportiona lto amount of organic matter) proced: heat with sulfuric acid and known quantity of potassium dichromate for about 2 hours; titrate to determine excess potassium dichromate
Which 3 techniques are most widely used in food analysis? (State their name and abbreviation.)
Thermogravimetric analysis (TGA) differential scanning calorimetry (DSC) modulated temperature DSC (MDSC)
What kinds of samples are analyzed by a) liquids NMR and b) solid-state NMR?
a) relatively pure and things that readily go into solution in any of the many solvents available b) powders, fresh tissue, cheese and intact food samples
Briefly explain a method that could be used for each of the following: a. To prevent hydrolysis of sucrose when sugars are extracted from fruits via a hot alcohol extraction b. To remove proteins from solution for an enzymatic analysis c. To measure total carbohydrate d. To measure total reducing sugars e. To measure the sucrose concentration in a pure sucrose solution by a physical method f. To measure glucose enzymically g. To measure simultaneously the concentrations of individual free sugars
a-include Ca carbonate b-Carrez treatment c-Phenol-Sulfuric acid Method d-munson-walker method e-spec gravity f-use glucose oxidase and peroxidase g-HPLC
Regarding TGA: a. What information about a material does TGA provide? b. What property does it measure? c. State 3 common measurements made with TGA.
a. composition and thermal or oxidative stability b. weight change as sample is heated c. temperature of weight change; composition; decomp temp
Using the Van Deemter equation, HETP, and N, as appropriate, explain why the following changes may increase the efficiency of separation in column chromatography: a. Changing the flow rate of the mobile phase b. Increasing the length of the column c. Reducing the inner diameter of the column
a. reduces the HETP when optomized b. N would go up, more theoretical plates so more seperation c. reduces eddy diffusion, so bands more narrow
Regarding DSC: a. What information about a material does DSC provide? b. What property does it measure? c. State 5 common measurements made with DSC.
a. universal detector for measuring structure b. heat flow c. glass transition temp of amorphous structure -crysallization of amorphous material -denaturation of proeins -gelatinization of starch -oxidative stablility of fats and oils
****Using diagrams, explain each of the 5 physicochemical principles of separation as shown in Fig. 27-3.
adsorption: solute adsorbed onto surface of stat phase partition: solute dissolved in liq phase coated on solid support ion exchange- mobile anions held near cations that are covalently attached to stat. phase; small molecules pentrate pores of particles; there is anion-exchange resin so anions can be attached molecular exclusion: large molecules excluded affinity: one kind of molecule in a complex mix becomes attached to molecule that is covalently bonded to stat phase; all other molecules pass thru
You have decided to purchase an ISE to monitor the sodium content of foods produced by your plant. List the advantages this would have over the Mohr/Volhard titration method. List the problems and disadvantages of ISE that you should anticipate. Advantages -Disadvantages -
adv-can measure many cations and anions directly -analysis independent of sample voume, turbidity, color, and viscosity -simple dis-limit of detection usually 2-3 ppm -slow electrode response time at low levels of measurement -some electrodes have a high rate of premature failure or short operating life
c. You realize there are advantages and disadvantages of the two potential methods, BOD and COD. Give two advantages and two disadvantages for the BOD method (as compared to the COD method).
adv: less expensive truly measures dissolved oxygen lost dis: slower; lower precision
What are the advantages and disadvantages of using HPLC for vitamin analysis?
adv: simple, accurat, precise, applicable to most vitamins, sometimes allows simultaneous analysis of vitamins or isomers dis: peak identity and purity must be determined, high capital outlay initially
Describe the FID and the NMR spectrum, including the concepts of time domain, frequency domain, and data transformation.
as the instrument detects a quickly decaying series of signals, it yields the FID (a time domain graph), which is processed by fourier transformation to make peaks on the NMR (frequency on x axis)
The Munson-Walker, Lane-Eynon, and Somogyl-Nelson methods can be used to measure reducing sugars. Explain the similarities and differences among these methods with regard to the principles involved and the procedures used.
based on reduction of cupric ions in alkaline solution to cuprous ions by reducing sugars; amt of cuprous ions generated is measured to quantify reducing sugars diff: how cuprous ions generated are measured
Why are external standards commonly used for HPLC (unlike in GC, for which internal standards are more commonly used)?
bc it is easier; the injection technique has a syringe inject the sample and spins it around in a loop so you cant mess it up the sample loop is very repeatable, makes it not as variable
Why must sugars and fatty acids be derivatized before GC analysis, while pesticides and aroma compounds need not be derivatized?
bc they are thermally unstable, not volatile enough, have poor chromatopgraphy sep due to polarity so need to de deriv. to be seperated properly
Why has HPLC largely replaced GC for analysis of carbohydrates?
because liq chromatography does not require derivitization
Though official methods (e.g., from AOAC International, the European committee for Standardization, US Pharmacopeial Convention or AACC International ) are well accepted, they are often limited in what way?
because they cannot be applied to other matricies
In GC, explain why a balance has to be maintained between efficiency and capacity. Also, give an example situation in which you would sacrifice capacity for efficiency.
cant get 100% of both --if sample has numerous compounds that dont need to be collected
List the major constituents of dietary fiber.
cellulose, hemicellulose, lignin, pectin (and other non-starch plant polysacchs), other nondigestible polysacch
How can chromatographic data be used to quantify sample components?
data analysis software; measures area under the peak to get the concentration
Describe two methods for determination of pectin.
gravimetric-precipitate adn weigh pectin as calcium pectate spectrophotometric: carbazole or m-hydroxydiphenyl methods measure pectin based on galacturonic acid content
Explain how measurement of dietary fiber relates to calculating the caloric content of a food product.
have to subtract this amount from the total carb count, before multiplying the total carb by 4 in order to the caloric content (bc its not digested or absorbed)
HETP - N - L -
height equiv to a theoretical plate N=number of theoretical plates L-column length
State the factors and conditions that lead to poor resolution of two peaks.
high temperature high mobile phase flow rate Large HETP, low N, short column lot of Column selectivity - decrease capacity column efficiency
***The analytical laboratory in your company plans to purchase an inductively coupled plasma-atomic emission spectrometer. a. Explain the instrumentation and principle of its operation to analyze foods for specific minerals.
instrumentation: argon plasma torch, monochromator or polychromator (transmits the wavelengths from the emission), detectors (convert into signal), computer principle- -sample is volatized, then atomized and excited by plasma -atoms or ions in an excited state emit energy (of specific wavelength for each element being measured) when they return to a lower or ground energy state -amount of radiation emitted is related to conc. over 4 orders of magnitude
****Why would you choose to use an internal standard rather than an external standard? Describe how you would select an internal standard for use.
it minimizes errors due to sample prep, apparatus, and operator technique select: strucurally related to comp of interest; elutes at diff time; not naturally present in sample
What is the primary use of relaxometry in food analysis?
it yields info about the interaction of water with the macromolecules in the sample (like powders--protein mixes ex--dissolving in water)
The term liquid chromatography refers to several techniques including paper and thin-layer chromatography (both planar), and column liquid chromatography. In all cases, what is the mobile phase?
liquid
Describe the principle behind separation and analysis of water-soluble gums.
measurement is a challenge bc of diversity of structures. methods depend on extraction of the gums followed by fractionation of the extract to remove free sugars and other water-soluble polysacchs. the isolated gum is acid hydrolyzed and its constituent sugars are quantitated by HPLC or GC
What factors should be considered in selecting the assay for a particular vitamin?
method accuracy and precision -need for bioavailability info -time and instrument requirements -personnel requirement -type of biological matrix to be analyzed -# of samples to be analyzed -regulatory requirements
Explain how SFC differs from LC and GC, including the advantages of SFC.
mobile phase usually uses liquid CO2; supercritical fluids have high diffusivity and low viscosity so better resolution and less time
Discuss why mono- and oligosaccharides are extracted with 80% ethanol rather than with water. What is the principle involved?
mono and oligo are soluble in ethanol, while polysacch and proteins are not soluble in it
You are performing HPLC using a stationary phase that contains a polar nonionic functional group. What type of chromatography is this, and what could you do to increase the retention time of an analyte?
normal phase --decrease polarity of mobile phase
You are performing LC using a stationary phase that contains a polar nonionic functional group. What type of chromatography is this, and what could you do to increase the retention time of an analyte?
normal phase chromotography -decrease the polarity
****Explain the basic principles associated with NMR spectroscopy, including the function of the magnet and the concept of nuclear spin.
nuclei are placed in a magnetic field, and spin either aligned with or against the field -the spin has a slight excess in the parallel (with the field) orientation, giving a net mag vector, which has a precessional orbit and specific frequency
Give three reasons why carbohydrate analysis is important
nutrition label, measure adulteration, to analyze any given amount of a constituent (like red sugar)
Explain the operating principle of the Flame Ionization Detector (FID).
organic compounds burned in hydrogen flame, which creates ions that change the potential applied across flame
What types of chromatography does GC rely upon for separation of compounds?
partition chromatography and bp
***Thermal analysis refers to a broad range of analytical techniques. What do they measure?
physical and chem properties as a function of time, temp and atmosphere
You are training a new technician in your laboratory on mineral analysis by AAS and ICP-AES. Briefly describe the purpose of each of the following items associated with those instruments/analysis. b. Plasma in ICP-AES c. Monochromator in ICP-AES d. Nebulizer in AAS and ICP-AES
plasma-used as the atomization and excitation source mono-selects the wavelengths of light that are being emitted by atoms coming back to ground state nebulizer- converts solution to fine mist
What is the advantage of bonded supports over coated supports for partition chromatography?
prevent liq stat phase from being stripped off bc covalently bonded to a support
What is the primary function of an HPLC detector (regardless of type)? What factors would you consider in choosing an HPLC detector? Describe three different types of detectors and explain the principles of operation for each. Primary function of detector Factors to consider in selecting detector Types of detectors
primary: translates conc changes in HPLC column effluent into electrical signals factors: solute type and conc sensitivity linear range selectivity compatibility with solvent effect of temp or flow rate changes possibility of use with gradient elution initial and operating costs types: variable-wavelength and PDA (photodiode array)
Describe the principles behind the enzymic determination of starch. What are the advantages of this method? What are potential problems?
principles: gelatinized starch is converted totally into D-glucose by enzymes specific for starch, and D-glucose is quantified enzymatically adv: very specific, commercial kits available potential probl: amylases might not be pure; may not be quantitative for samples high in resistant starch or amylose starch
Define reducing sugar. Classify each of the following as a reducing or nonreducing carbohydrate: D-glucose - D-fructose - (describe conditions. why?) sorbitol - sucrose - maltose - raffinose - maltotriose - cellulose - amylopectin - κ-carrageenan -
red sugar: mono and oligosacch that contain a free carbonyl group that can act as red agents glucose: yes fructose: yes, reducing under alkaline cond and nonred under neutral or acid conditions sorbitol: non sucrose: non malt: yes raff: non malto: yes cellulose and amylopectin: non (bc polymers are nonred) k-carrageenan: non
A sample containing compounds A, B, and C is analyzed via LC using a column packed with a silica-based C18 bonded phase. A 1:5 solution of ethanol and H2O was used as the mobile phase. The following chromatogram was obtained. (peak A at 2 min, peak B at 4 min, peak C at 14 min) Assuming that the separation of compounds is based on their polarity, a. Is this normal- or reversed-phase chromatography? Explain your answer. b. Which compound is the most polar? c. How would you change the mobile phase so Compound C would elute sooner, without changing the relative positions of Compounds A and B? Explain why this would work. d. What could possibly happen if you maintained an isocratic elution mode at low solvent strength?
reversed bc C18 (the stat phase) is nonpolar b. A b/c the stat phase is nonpolar so polar comes off 1st c. after 6 min, make mobile phase less polar so that C wants to move down the column d. C may never come off
****Using a diagram, explain the instrumental components (and their arrangement) of a system for HPLC.
see paper
Explain the concept of shielding and chemical shift.
shielding: an electron cloud creates a secondary, induced mag. field around the nucleus that acts in opposition to the external, applied magnetic field (the more dense the field, the more shielded from external mag field) chem shift: the freq differences that result from the diff. in the electronic environments
What is a guard column and why is it used?
small column identical to analytical but product goes through it first, so if something gets stuck, it will get stuck on this -protects lg column from being damaged
Would the vitamin C content as determined by the 2,6-dichloroindophenol method be underestimated or overestimated in the case of heat processed juice samples? Explain your answer.
some is converted during heat proccessing (before testing) so underest bc need reducing agent to push the final product back to the beginning so that the final amount can be fully measured
Describe the principles behind and the limitations of determining sugar (sucrose) concentrations by : Specific gravity - Principles - Refractive index - Principles - Limitations of both-
spec gravity: use of hydrometer calibrated in degrees Brix or Baurne Modulus RI: use refractive index to determine total solids in solution limitations of both: only useful with clear liquid samples; accurate only for pure solutions
Why might you choose to use HPLC rather than traditional low-pressure column chromatography?
speed wide variety of stat. phases improved resolution greater sensitivity easy sample recovery
What is the physiological definition and the chemical nature of resistant starch? What types of foods have relatively high levels of resistant starch?
starch and starch degredation products that escape digestion in the small intestine; physically inaccesible to amylases, trapped in food matrix -banana and potato
In GC, compounds are separated on the basis of which physicochemical properties?
stationary phase (liq vs solid)
You are doing GC with a packed column and notice that the baseline rises from the beginning to the end of each run. Explain a likely cause for this increase.
stationary phase is coming off the column
The ingredient list for a cooking spray is canola oil, grain alcohol, and lecithin. The label states that the product is for fat-free cooking. How is this possible when the first ingredient is oil?
the serving size is so small, that the amount of fat is so small it can be rounded to zero, stating its fat free, even though if you made the serving size a lot larger, the product would not be fat free
State the purpose of "preparative" chromatography.
to get large quantities of pure compounds
Why is the injection port of a GC at a higher temperature than the oven temperature?
to rapidly vaporize the sample
***State how to determine the amount of "total carbohydrate" and "other carbohydrate" shown on nutrition labeling of packaged food.
total carb=100% -(%moisture+ash+lipid+protein) other carb=total carb- (dietary fiber+sugars)
Every vitamin can be measured in several ways. Vitamins are measured using a bioassay, microbiological assay or a chemical method (commonly HPLC.) For the following vitamins, state the common method of analysis and explain the principle upon which it is based: Vitamin A Thiamin Riboflavin Niacin Folate Vitamin B12 Vitamin C Vitamin D Vitamin E
vit A: chem; saponify and extract with organic solvents; HPLC with UV detection vit E: chem; saponify and extract with organic solvents; HPLC with fluorescence detection thiamin and riboflavin- chemical; extract with heat and acid; enzymatic hydrolysis, chromatographic cleanup, oxidize to thiochrome, measure flourescence niacin- micro; autoclave in acid (cereal) or alkali (non cereal) then measure turbidity folate- microbiological; enzyme treatments and measure turbidity vitamin C- chemical assay, either use titration and use vol dye to measure amt vit C or react with flourescent compound and measure flourescence vitamin D-bioassay; feed animals amounts of vit D then measure bone calcification vitamin B12- bioassay; feed animals to figure out
State what is plotted (and the units used) on the x- and y-axis of the semi-log paper used to plot the results of ISE data. State which axis contains the logarithmic data. What type of calibration curve is expected (linear or nonlinear, positive or negative slope)?
x- log concentration (M) y- electrode potential (mV) x contains log -linear -positive or negative slope depending on mineral (positive if like K+ but negative if like Cl-)
You want to label 1% fat milk as "99% fat free". Can you do this?
yes, bc you can say __%fat free if the product is low fat (<3g/serving)
