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FD SC 410 > Exam Two - New > Flashcards

Exam Two - New Flashcards

1
Q

Select a food product and diagram a typical flow through the lab for conducting proximate analysis.

A
  1. Remove moisture
    1a. Remove proteins (wet basis) - optional
  2. Remove fat
    2a. Remove proteins (dry basis) - optional
  3. Remove proteins - better to do on a dry basis
  4. Ash analysis
  5. Calculate carbohydrate percentage
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2
Q

Describe the structure of a typical triglyceride.

A

A typical triglyceride consists of a glycerol head and three fatty acid chains of varying lengths and saturation

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3
Q

What is an operational definition?

A

An operational definition is a result of the process of operationalization and is used to define something in terms of a process needed to determine its existence, duration, and quantity. It is a clear and concise and detailed definition of a measure

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4
Q

What is a compound lipid? Give some examples.

A

A compound lipid contains an ester of a fatty acid with an alcohol. It is not composed of only a glycerol head and fatty acid chains. Some examples are phospholipids, cerebrosides, and sphingolipids

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5
Q

What is a derived lipid? Give some examples.

A

A derived lipid is a substance derived from neutral lipids or compounds lipids with the general properties of lipids. Some examples are fatty acids, long chain alcohols, sterols, fat soluble vitamins, and hydrocarbons

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6
Q

Why is it important to predry samples before lipid analysis?

A

Predrying samples is important because water acts as a diluent to the solvent. It creates a barrier between the solvent and the sample. Removing water before analysis will lead to better extraction and more accurate results

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7
Q

Why is it important to reduce particle size of a sample prior to lipid analysis?

A

Reducing particle size increases surface area. An increase in surface area leads to more interaction between the sample and the solvent and results in overall better extractability and more accurate results

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8
Q

Compare and contrast petroleum ether and ethyl ether.

A

Petroleum ether is cheaper. less hygroscopic, and flammable compared to ethyl ether. Ethyl ether is more expensive, explosive, and partially hygroscopic

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9
Q

Solvent extractions can be performed in a soaking or rinsing mode. What are the advantages or limitations of each approach?

A

Soaking:
A: a lot of sample/solvent interactions
L: decrease in extractability over time (solvent can become saturated)
Rinsing:
A: fresh solvent treats the sample at all times
D: channeling can occur and it doesn’t give a large amount of solvent/sample interaction

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10
Q

What are the advantages of a Soxhlet type fat extraction approach?

A

A Soxhlet extraction is a combination of soaking and rinsing. It is the most accurate method for lipid analysis but soaking and rinsing doesn’t occur at the same time

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11
Q

What is the principle of the Babcock method?

A

The Babcock method is based on sulfuric acid and how it digests proteins, releases fat, and generates heat. The release of fat and then centrifugation leads to possible determination of fat content using a Babcock bottle and the density differences between fat and water

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12
Q

What would happen if the Babcock analysis was done at a lower than recommended temperature?

A

The fat could solidify which would skew results

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13
Q

How does the Mojonnier test work?

A

It measures the amount of fat in a sample. Fat is extracted with petroleum or ethyl ether in a Mojonnier flask. The extracted fat is then dried, weighed, and expressed as the total fat percentage of the sample

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14
Q

How does the Creamery measure fat content?

A

The Creamery uses a combination of rapid drying and nuclear magnetic resonance to calculate fat content. NMR is a instrumental method which analyzes the nuclei of the sample. It is then exposed to pulse energy and releases a specific signal which can be measured. It is fast, accurate, and reproducible

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15
Q

How is the melting point of a fat assessed?

A

Melting point can be defined using a variety of ways such as the dropping melting point

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16
Q

Define the terms smoke point, flash point, and fire point. What is the significance of these characteristics? What factors will alter these characteristics?

A

Smoke point: the point at which a fat smokes
Flash point: the point at which a fat flashes
Fire point: the point at which a fat becomes inflamed
The amount of free fatty aids affects these characteristics. As free fatty acids increase all three points decrease. They are important for safety while cooking

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17
Q

What do the cold test and the cloud point asses?

A

The cold test assess the winterization of the oil by holding the sample at 0C for 5.5 hours and looking for crystallization. The cloud point measures when the oil clouds. Both measure the degree of saturation

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18
Q

What does the iodine value measure? How is it determined?

A

The iodine value is a measure of the degree of unsaturation. It is defined at the grams of iodine absorbed per 100g of sample. The higher the amount of unsaturation the more iodine is absorbed which leads to a higher iodine value

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19
Q

What does the saponification value measure? How is it determined?

A

It is the amount of alkali necessary to saponify a given quantity of fat. It is expressed as the mg of KOH required to saponify 1 g of sample. It is the mean molecular weight of triglycerides in the sample. The smaller the saponification value the longer the average fatty acid chain length

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20
Q

How is the saponification value calculated?

A

((volume of titrant for blank (mL)-volume of titrant for sample (mL)) x normality of HCl (mmol/mL) x 56.1 (MWof KOH (mg/mmol))/sample mass (g)

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21
Q

What does the acid value mean? How is it determined?

A

The acid value is the amount of mg of KOH needed to neutralize all of the free fatty acids present in 1 g of fat. It is used as a quality indicator for frying oils. It is determined by multiplying the percentage of free fatty acids by 1.99

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22
Q

What does the peroxide value measure? How is it determined?

A

The peroxide value measures the primary oxidation products. It is the milliequivalents of peroxide per kilogram of sample. It is a redox titrimetric determination. The assumption is made that the compounds reacting under the conditions of the test are peroxides

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23
Q

What is a TBARS test?

A

A TBARS test measures secondary oxidation products of lipid oxidation. It involves reaction of malonaldehyde or similar products with TBA to yield a colored compound that is measured spectrophotometrically

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24
Q

Give an example of a conjugated protein.

A

An example of a conjugated protein contains non amino acid components such as carbohydrates or lipids. Some examples are lipoprotein, glycoprotein, and phosphoprotein

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25
Q

What are three unique protein characteristics? List one analytical technique based on each one.

A

Proteins contain nitrogen, have peptide bonds, and are charged at various pH levels. Nitrogen: Kjeldahl/Dumas
Peptide: infrared spectroscopy/Biuret
Charge: Bradford

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26
Q

What is a peptide bond?

A

A peptide bond is a bond between a carbonyl group and an amine group

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27
Q

What is non protein nitrogen? Give examples.

A

They are nitrogen containing compounds that are not protein. Some examples are caffeine, nitrates/nitrites, theobromine, ammonia, and phospholipids

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28
Q

How do you calculate the amount of protein in a sample based on the Kjeldahl analysis?

A

First calculate the amount of nitrogen by multiplying the normality of HCl by ((mL standard acid for sample-mL standard acid for blank)/g of sample), convert liters to milliliters, (14 g N/equivalent), and 100. Then convert the percentage of nitrogen by the Kjeldahl factor: % nitrogen x 6.25 is the percentage of protein.

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29
Q

Explain the derivation of the Kjeldahl factor for the average protein.

A

The Kjeldahl factor is based on the fact that most proteins contain 16% nitrogen. This means that per 100 g of sample 16 g of nitrogen or that approximately nitrogen is 6.25% of the total protein

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30
Q

Explain the basis of the Dumas analysis. What are the advantages/disadvantages.

A

The Dumas method is based on the principle of combustion. It requires putting the sample in an incinerator and the amount of nitrogen containing compounds is calculated by using gas chromatography.
A: automated, quick, user friendly, handle many samples at once, no sample prep
D: must be calibrated within the range you’re looking for, requires Kjeldahl factor, and can be dangerous

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31
Q

What is the basis of the Bradford method?

A

The Bradford method focuses on a protein’s amphoteric nature. A protein’s charge depends on the pH of the environment. During the Bradford method the environment is acidic so the proteins are positively charged. A negatively charged dye is then added and binding occurs. The binding results in a switch of a max absorption from 495 nm to 595 nm. The protein content then can be measured using a spectrophotometer with Beer’s law and a standard

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32
Q

What are some advantages and disadvantages to the Bradford method?

A

A: quick, accepted, reproducible, sensitive
D: sample must be in liquid form, standard curve must be made, compounds may affect results, and it only measures protein within a certain range

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33
Q

How does measuring absorbance at 280 nm estimate protein? What are the advantages and limitations of this method.

A

Measuring absorbance at 280 nm is also called the ultraviolet method. Tryptophan and tyrosine especially show a strong absorbance value in this region. Because the tryptophan and tyrosine percentage is somewhat constant the absorbance at 280 nm can be used to calculate protein concentration using Beer’s law.
A: rapid, sensitive, non destructive
D: nucleic acids also absorb light at 280 nm, aromatic amino acids are not picked up, the solution must be clear and odorless, and the sample must be pure

34
Q

Define immunoassay.

A

A test that measures the presence or concentration of an antigen in a solution through the use of an antibody

35
Q

Define antigen.

A

A substance usually a protein that induces antibody formation when introduced into the body

36
Q

Define antibody.

A

A protein that is produced as a response to the presence of an antigen that can specifically bond to that antigen

37
Q

Define epitope.

A

The part of the antigen that binds to the antibody

38
Q

Define polyclonal.

A

The ability to recognize multiple epitopes on any one antigen

39
Q

Define monoclonal.

A

The ability to detect only one epitope on the antigen - higher specificity

40
Q

Define FAB.

A

The head region of the antibody that is called the fragment antigen binding region

41
Q

Define FC.

A

The tail region of the antibody that is called the fragment crystallizable region

42
Q

Define conformational epitope.

A

An epitope that is recognized by antibodies in its non linear 3D structure

43
Q

Define linear epitope.

A

An epitope that is recognized by antibodies by its linear sequence of amino acids - primary structure

44
Q

Define competitive ELISA.

A

Occurs when you add a purified antigen that will compete with a possible antigen in the sample

45
Q

Define reporter antibody.

A

A secondary antibody for the sandwich ELISA that also is connected to an enzyme

46
Q

Define Western blot.

A

The technique which involves a general PAGE gel, transferral to a cellulose membrane, covering of the proteins of un-interest, addition of antibodies with enzyme and substrate, and possible color change

47
Q

Define 2D PAGE.

A

The technique that involves isoelectric focusing and then SDS PAGE

48
Q

Define lateral flow strip assay.

A

An assay which tests for the presence of certain antigens. Antibodies are bound to the paper and form a visible strip if the antigens’ epitope matches the antibodies

49
Q

Describe how to produce an antibody for a specific allergen.

A
  1. Inject the antigen into an animal so antibodies are produced
  2. Mix antibody producing animal cells with cancerous cell to form hybridome cells to help instigate growth
  3. Purify so only antibodies are remaining
    Needs to be done at least twice for a sandwich ELISA
50
Q

Describe the sandwich ELISA test.

A

Connect the primary antibody to the well. Add substrate, allow time for incubation, wash several times. Add the conjugate and the substrate. Wait for color change or another form of detection

51
Q

Define SDS PAGE.

A

SDS PAGE is separating the proteins by size

52
Q

Define native PAGE.

A

Native PAGE separates proteins by size, shape, and charge

53
Q

Define isoelectric focusing.

A

Isoelectric focusing separates proteins by their isoelectric points

54
Q

Describe the factors that affect mobility of a protein in an electric field.

A

The factors that affect the mobility of a protein in an electric field are size, weight, charge, shape, pore size (% of acrylamide), buffer, and voltage of electric field

55
Q

Define isoelectric point.

A

The isoelectric point of a protein is the pH level at which the protein has a net neutral charge

56
Q

How can relative mobility be calculated?

A

Relative mobility can be calculated by dividing the distance the band traveled by the distance of the dye front

57
Q

Why are bromophenol blue, b-mercaptoethanol, and SDS added to a protein sample for SDS PAGE?

A

Bromophenol blue is a tracking dye that allows you to visually observe the movements of the bands across the gel. B-mercaptoethanol breaks the covalent disulfide bonds. Sodium dodecyl sulfate bonds with the proteins to make them all negatively charged

58
Q

Why is a protein sample boiled prior to loading onto an SDS PAGE gel?

A

Boiling the proteins allow for further denaturation - makes it easier to differentiate

59
Q

Which direction do proteins migrate in SDS PAGE?

A

Proteins migrate run from negative (cathode) to the positive (anode)

60
Q

List the commonly used stains or ways to detect protein bands.

A

Some commonly used stainds are coomassie brilliant blue (high abundance proteins), amido black (low abundance proteins), silver staind (100x more sensitive than coomassie, low abundance), and Western blot

61
Q

Identify a few major proteins found in whey protein isolate.

A

A few proteins found in whey protein isolate are immunoglobulins, bovine serum albumin, alpha lactalbumin, and beta lactoglobulin

62
Q

What is the difference between one and two dimensional gel electrophoresis?

A

One dimensional gels separate proteins by only one characteristic. Two dimensional gels separate by two characteristics such as size and charge

63
Q

What is the difference between a stacking gel and a resolving gel? Why do we use both in one gel?

A

The stacking gel contains chloride ions the leading ions which migrate more quickly through the gel than the protein sample while the buffer contains glycine ions are the trailing ions which travel more slowly. The protein molecules are trapped in a sharp band between these ions. As the protein enters the separating gel which has a smaller pore size a higher pH and a higher salt concentration the glycine is ionized, the voltage gradient is dissipated, and the protein is separated based on size

64
Q

How does acrylamide percentage affect mobility of proteins of various sizes?

A

Acrylamide percentage affects pore size. The greater the percentage the smaller the pore size which allows smaller proteins to travel faster than the larger proteins

65
Q

Describe the role of pH in SDS PAGE. What about the role of pH in isoelectric focusing?

A

The pH in SDS PAGE is used to help the proteins move through the gel with a lower pH in the middle than the two ends while in isoelectric focusing there is a pH gradient which helps move the protein through the gel as well but once it reaches its isoelectric point it stops

66
Q

What is the relationship between energy and wavelength?

A

Energy and wavelength have a negative correlation.

67
Q

In an atom, what kind of energy transitions are allowed? What about in a molecule?

A

Atoms can go from an excited energy state to a lower state while molecules can absorb energy and go into an excited state that can be maintained or reduced

68
Q

What is the difference between absorbance and fluorescence?

A

The difference between absorbance and fluorescence is that absorbance is how much energy is absorbed from the sample (lower to higher energy state) while fluorescence is lower energy light is emitted as the electrons move from a higher to lower energy state after excitation by a higher energy wavelength

69
Q

What are some examples absorbance spectroscopy methods are commonly used for analyzing macro or micro food components?

A

The phenol sulfuric acid assay for carbohydrates, Bradford assay for proteins and the Lowry method for proteins are all used for macro food components. The peroxide value assay and the TBARS test check for primary and secondary oxidation products which are micro food components

70
Q

Why does more molecular conjugation lead to absorbance at higher wavelengths (lower energy)?

A

Conjugated pi bonds delocalize electrons which mean it takes a smaller amount of energy to excite electrons from a lower to higher energy state

71
Q

What kind of useful information is attained from an absorbance spectrum?

A

You can learn the absorbance of a compound at that particular wavelength and the maximum absorbance

72
Q

Why do we use absorbance and not percent transmittance in quantitative absorbance spectroscopy?

A

Absorbance is better than transmittance because it has a linear relationship with concentration while percent transmittance does not

73
Q

What are the reasons for using a reference cell in absorbance spectroscopy?

A

The reference accounts for any interference that may be caused by other components in the sample

74
Q

What is the equation for Beer’s law?

A

Absorbance = molar absorptivity/extinction coefficient multiplied by the path length of light and the concentration

75
Q

What are some reasons why Beer’s law can fail?

A

Beer’s law is only followed in dilute solutions since at higher concentrations the distance between neighboring molecules decreases to the point where it can change the charge distribution throughout the sample

76
Q

Define extinction coefficient. How can sample conditions affect the EC of a molecule?

A

The extinction coefficient is the measure of how strong a molecule can absorb light. It is dependent on the molecular properties

77
Q

What is the difference between a phototube and a photomultiplier?

A

A phototube converts lights signals to electronic signals while a photomultiplier increases the number of electrons generated by the photons. A photomultiplier is used to generate more current from less radiation to result in a more sensitive method for analysis

78
Q

List the different types of commonly used cuvettes.

A

Some types of cuvettes are plastic, quartz, silica, and fused silica. Plastic is cheap and used with visible light along with silica. Fused silica and quartz are the most expensive and are used for the UV range of light

79
Q

Describe the major components of an absorbance spectrophotometer. What are the major components of a fluorescence spectrophotometer?

A

The major components of an absorbance spectrophotometer are the light source, monochrometer, sample, and detector. For a fluorescence spectrophotometer the arrangement is changed. The detector is moved 90 degrees so the light source doesn’t interfere with the fluorescence

80
Q

Describe how to prepare standards and perform analyte concentration calculations using the standard addition calibration. Why is this method useful for determining concentrations of some analytes in complex matrices?

A

One example could be to add vitamin C into OJ. Put standard in increasing increments and make a linear plot. Solve for the x intercept to get the initial vitamin C concentration

81
Q

What types of food components can be quantified using atomic absorbance spectroscopy and atomic emission spectroscopy? What are the fundamental differences between the two techniques?

A

Some types of food components that can be quantified are trace metals which can act as an oxidation catalyst. The difference is that absorbance is based on absorbance while emission is based on emission making it more sensitive

82
Q

Why does ionization need to be suppressed in atomic absorbance spectroscopy and atomic emission spectroscopy?

A

Ionization needs to be suppressed in order to ensure that the electron distribution throughout the analyte of interest is maintained. This is affected by the ionization because it changes the localization of charges and therefore affects their ability to absorb or emit a given wavelength

FD SC 410 (11 decks)

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