FD SC 410 Exam 1 Flashcards
(61 cards)
1
Q
- What is proximate analysis?
A
Refers to the determination of the major food components of moisture, ash, lipids, protein, and carbs.
2
Q
- What do the letters TD and TC mean on a piece of glassware?
A
- The notations TD and TC stand for the phrases “to deliver” and “to contain.”
- The TD notation, used on burettes and pipets (and some graduated cylinders), means that the apparatus is calibrated to accurately deliver or transfer the stated volume to another container.
- The TC notation, used on volumetric flasks and (most) graduated cylinders, means that the markings give an accurate measure of the volume contained, but that pouring the liquid into another container will not necessarily deliver the indicated volume
3
Q
- What are the objectives of food analysis?
A
- To assure a food/ingredient meets compositional requirements
- To assure a food/ingredient doesn’t have something it shouldn’t
- To obtain information on the status of a process
4
Q
- List at least 5 reasons for evaluating the composition of foods.
A
- Formulating and developing new products
- Evaluating new processes for making food products
- Identifying source of problem for unacceptable products
- Develop/check nutritional label (plus other government regulations)
- Check quality of raw ingredients
- Check composition during processing
5
Q
- List at least 3 types of samples that might be evaluated in a food analysis laboratory.
- Indicate why these samples would be analyzed.
A
- Raw materials (ingredients)
- Process control sample (processing)
- Final product
All would be sampled for quality control
Might also take competitor samples & complaint samples
6
Q
- What are the 3 basic steps in food analysis?
A
- Select and prepare sample
- Preform the assay
- Calculate and interpret results
7
Q
- Given a particular scenario, describe how you would choose an analytical technique.
A
8
Q
- What characteristics of a method should be considered when selecting a method to use in your laboratory?
A
- Inherent properties: specificity, precision, accuracy
- Usefulness: time required, reliability, need met
- Personnel: safety, procedures
- Applicability to laboratory: sample size required, reagents required, equipment required, cost
9
Q
- How is carbohydrate determined by “difference”?
A
100%(of the food produce) - [% moisture + % ash + % lipid + % Protein] = % Carbohydrate
To find moisture: dehydrate/dry
To find ash: burn it and measure weight b&a
To find lipid: use organic solvent to pull out lipids separate and weigh
To find protein: contains N– any assay
To find carb: must find above items and subtract from total “difference”
10
Q
- List the full name and abbreviation for at least 3 organizations that publish “official” or generally accepted methods used in food analysis.
A
- AOAC International: most products and materials
- AACC: mostly cereal products
- AOCS: mostly fat and oil analysis
- SMEDP: milk and dairy products
11
Q
- What compromises would you be willing to make when choosing a method for on-line process control when compared to methodology used to generate the data for nutrition labeling?
A
By using on-line methods of process control… you would compromise less accurate but much faster than official methods for nutritional labeling
12
Q
- Which body regulates most foods manufactured in the US?
A
FDA -Regulates most food and enforces the FD&C (1938)
-Broadest regulatory authority of most foods (except meat, poultry, eggs, water supplies, imported foods)
13
Q
- What are the two fundamental provisions of the FD&C act of 1938?
A
- To assure consumers that their food was: safe, wholesome, truthfully labeled
- Allowed for establishment of SOI (standard of Identity)
14
Q
- What is a Standard of Identity?
A
Specifies which ingredients a food must contain
- Limit the amount of water allowed in a product
- Minimum levels for expensive ingredients
- Maximum levels for inexpensive ingredients
- Kind and amount of certain vitamins and minerals if labeled “enriched”
- Might include list of optional ingredients
- Often includes recommended analytical method for determining chemical composition
15
Q
- What organization is responsible for regulating the composition of meat products in the US?
A
USDA
- Responsible for meat products
- Food safety inspection service (FSIS)
- Grade standards
16
Q
- What organization is responsible for assuring that products imported into the US are safe and not economically deceptive?
A
US Customs Service
- Ensures all imported foods are properly taxed
- All imported foods must be safe and not “economically deceptive”
- Works with FDA and USDA -Enforces duty/ tariffs
17
Q
- What is the Codex Alimentarius?
A
“Code concerned with nourishment”
- International standards and safety practices for foods and agricultural products
- Intended to protect consumers’ health, ensure fair business practices in food trade and facilitate international trade of foods
18
Q
- What organization is responsible for advertising related to food?
A
FTC (Federal Trade Commission)
- Authorized by federal trade commission act 1914
- Mission is to keep business and trade competition “free and fair”
- Authority over advertising and sales promotion, but NOT nutrition labels
19
Q
- Define the statistical term “mean”. What does the mean value tell you about the “quality” of analytical data?
A
The mean is the sum of all values of data divided by the amount of data points: resulting in the average
-The mean indicates that this is the best experimental estimate of the value–it does not say anything about how accurate or true the value is
20
Q
- Distinguish between the terms accuracy and precision.
A
Accuracy:
- How close a measurement is to the true value
- Compare mean to true value
- Assess by absolute error or relative error
Precision:
- How close are replicate measurements?
- Measure of repeatability
21
Q
- Give an example of statistical techniques for quantitatively assessing both accuracy and precision.
A
Accuracy:
- Absolute error (difference between experimental value and true value)
- Relative error (compare difference between experimental value and true value, against the true value), more useful than absolute error
22
Q
- List 5 techniques for assessing the precision of an assay.
A
- Standard deviation (SD)
- Coefficient of variation (relative Std. Dev.)
- Confidence limit (or interval)
- Standard error of the mean
- Relative deviation from the mean
23
Q
- Design an experiment to assess both the accuracy and precision of an assay. Be sure to include appropriate controls and replication.
A
—-Lab in class?
24
Q
- What is the formula for Standard Deviation?
A
-Standard deviation (SD) measures how close the values are to each other (precision)
The sum of all (experimental value-mean)^2 Divided by n-1 then take the square root
25
25. What is the formula for % Coefficient of Variation?
- Relative standard deviation
- CV \< 5% considered acceptable
Standard deviation divided by the mean, multiplied by 100 to make a percent
26
26. What fraction of a normally distributed data set can be found within 1, 2 and 3 SD of the mean value?
68% values would be w/in +/- 1 stdev
95% values would be w/in +/- 2 stdev
99.7% values would be w/in +/- 3 stdev
27
27. Which analysis is more precise? Set 1 mean = 9 grams, SD = 0.45 grams or Set 2 mean = 1.05 x 10-4, SD = 3.1 \* 10-5?
Set 1
CV%= 0.45 / 9 = 0.05
Set 2
CV%= \_\_\_\_\_\_\_\_\_blah\_\_\_\_ = 0.29
Set 1 is more precise
28
28. What is the formula for calculating a Confidence Interval?
mean +/- Zvalue (stdev/sqrt(n))
29
29. What happens to the “width” of the confidence interval as the number of samples analyzed increases?
Width decreases typically
30
30. What does the statement “this pipet delivers 1 ml with a 95% confidence interval of 0.0048” mean to you?
We are 95% confident that the true mean will fall within 1mL +/- 0.0048
31
31. List the three types of error that are common to food analysis and give an example of each type.
-Systematic error: results consistently deviate from true value
Example: pipettor calibrated incorrectly
-Random error: can fluctuate and are unavoidable
Example: differences between balances
-Blunders: big “screwup” Example: pipetting 0.5 mL instead of 1 mL
32
32. Define the term “sensitivity”
the magnitude of change in measurement with change in concentration of compound
33
33. Define the term “specificity”
-Measuring only what you’re interested in
Ex: -Crude fat determination – not very specific
-To analyze only linoleic acid, need a more specific method
34
34. Define the term “limit of detection” and describe how to calculate this value.
- The lowest possible increment that we can detect with statistical significance
- Can be calculating using X(LD) = X(Blk) + 3 \* SD(Blk)
Where:
X(LD): minimum detectable concentration
X(Blk): signal of a blank
SD(Blk): standard deviations of the blank readings
OR LOD is often reached when the signal to noise ratio is 3 or greater--when a sample gives 3times the magnitude of the noise detection--the instrument is at the lowest limit possible
35
35. Design an experiment to determine the limit of detection of a particular assay.
-------
36
36. Standard Curves.
Standard Curves
- Used to determine unknown concentrations
- Concentration of substance must be proportional to measurement
- Linear regression most often used to construct curve
37
37. Define r, which axis should it be plotted on.
Correlation coefficient (r)
-How well data fit to a straight line
(independent variable: x-axis) (dependent variable: y-axis)
38
38. Define r2, which axis should it be plotted on.
Coefficient of determination (r2) -How much of measurement is explained by regression
39
39. Describe the Q-test and how it can be used to reject analytical data.
- Significant figures (see rules)
- Reject data based on Q test
- Reject if calculated Q value is greater than Q of rejection Q = (x2-x1) / (xmax-xmin)
40
40. What are the units of “Normality”?
Normality = mole equivalents of solute / liter of solution
-For acid-base reactions normality represents moles of H+ or OH- per liter that will be exchanged in a neutralization reaction
41
41. What is the Normality of a 0.5M solution of lactic acid? Of Sulfuric acid?
- 0.5M lactic acid = 0.5N lactic acid b/c lactic acid has 1 ionizable hydrogen
- Sulfuric acid (H2SO4) has 2 equivalents of H+ per mol of acid so 0.5M = 1N
42
42. Define the term equivalent weight.
Equivalent weight = Molecular weight / number of equivalent e.g. the EqWt of H2SO4 = 98/2= 49
43
43. What is the equation for calculating %TA given grams of sample, Normality of base, predominant acid and ml of base required to reach the phenolphthalein end point?
%acid (wt/vol) = ( (normality of titrant mL)(volume of titrant mL) (eq. wt. of acid) ) / (volume of sample \* 10)
44
44. Define the terms “Titrateable Acidity “, “apparent acidity”, “fixed acidity” and “volatile acidity”.
Titratable acidity: express in terms of predominant acid; Typically 0.2 – 8%
Apparent acidity: occurs before any appeared acidity
Fixed acidity: amount remaining after boiled away, found with second titration
Volatile acidity: quality indicator for wine (acetic acid in wine) also the difference b/w fixed and total acidity. Amount boiled away/removed
Brix/acid ratio: predictor of acid flavor
45
45. Define the term predominant acid.
Titratable acidity is usually stated in terms of the predominant acid b/c food can contain several acid components
46
46. Prepare a step-by-step procedure for determining the TA of a food product.
- Know reaction stoichimetry
- Calculate the percent acid
- How many equivalents of base were used?
Eq. base=Equiv. acid
- How many g of acid were present?
- Calculate percent acidity
47
47. At what pH does the phenolphthalein indicator go from colorless to pink? Why is this value important?
-Colorless from: 0-8.2pH and greater than 12 This indicates the acid has been titrated to the endpoint when using the base--creating equivalence--should stop at just barely pink
48
48. Describe the three general types of water associated with foods in terms of the ease of removal from the food.
- Free water: retains it's physical properties and acts as the dispersing agent for colloids and the solvent for salts
- Adsorbed water: is held tightly or is occluded in cell walls or protoplasm and is held tightly by proteins
- Water of hydration: bound chemically ___ monohydrate
49
49. What factors are important when obtaining, storing and preparing a sample for moisture analysis?
- Quality factor affecting stability
- Specified in compositional standards
- Required for nutrition label calculations
- Express analytical determinations on dry weight basis, for comparison
- Representative
- Prevent moisture loss or gain
- Particle size reduction
- Container headspace
- Time to weigh
50
50. When evaluating techniques for moisture analysis, what factors should be considered and why?
- What is measured?
- How water is removed/reacted/identified?
- Assumptions?
- Sources of error?
- Applications?
51
51. A sample of food is placed into a forced draft oven at 101C. Prepare a graph showing “rate of moisture loss” as a function of time. On the graph, indicate the two regions of a typical drying curve and indicate what controls the rate of drying in each region. Indicate what factors would influence the time required to completely dry this sample during moisture analysis.
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rate of moisture loss is on the y-axis and the time it takes to dry is on the x-axis
the horizontal section "constant rate period" is the evaporation control period
the tapered decline "the falling rate period" is mass transfer control period
52
52. What is the purpose of the addition of sand during drying of some products?
- Sand pan technique
- Some food materials tend to form a semipermeable crust or lump together during drying, which will contribute to erratic and erroneos results
- The purpose of the sand is twofold: to prevent surface crust from forming and to disperse the sample so evaporation of moisture is less impeded
- Disperse the food constituents and minimize the retention of moisture in the food products
53
53. What is “case hardening” and how can it be minimized?
- A special condition related to the shrinkage and sealing of the surface of a food piece
- This can occur when there is a very high surface temperature and unbalanced drying of the piece so that a dry skin forms quickly, before most of the internal moisture has had opportunity to migrate to the surface
- The rather impermeable skin then traps much of the remaining water within the particle and the dry rate drops off severly
- The combined effects of shrinking and pore clogging from solutes contribites to casehhardening --generally this can be minimized bylower surface temperatures to promote more gradual drying throughout the food piece
54
54. A sample of food is weighed into a moisture pan. The weight of the dried pan is 3 grams and the weight of the pan + sample is 8 grams. After drying the pan is reweighed and is reweighed is weighs 6 grams. What is the percent moisture in this sample on an “as is” and on a “dry” basis?
%MC "as is basis" ((wet-dry) / (wet))\*(100) = ((5g-3g) / (5g)) \* 100 = 40%
%MC "dry basis" ((wet-dry) / (dry))\*(100) = ((5g-3g) / (3g)) \* 100 = 67%
%Total Solids ((dry) / (wet)) \*(100) = ((3g) / (5g)) \* 100 = 60%
55
55. What is the value of expressing results on a “dry basis”?
-Expresses everything in the sample besides water/moisture.
56
56. Diagram a typical vacuum oven set up for conducting moisture analysis. Describe operation of the oven during the drying phase of the analysis and give the purpose for each of the components of the system.
- The vacuum ooven dryes under reduced pressure and is able to more complely remove water and volatiles without decomposition within a 3-6h drying time
- They need a dry air purge in addition to temperature and vacuum controls
- Temp: even with reduced temp, decomposition can occur
- Heat is not conducted well in a vacuum, pans must be dirctly on metal shelves
- Evaporation is an endotheric process, pronounced cooling occurs
- Drying time is a function of total moisture present, nature of food, surface area per unit weight of sample, whether sand is used as a dispersant, and the relative concentration of sugar and other substances capable of retaining moisture or decomposing
57
57. What does Ash analysis measure?
- Inorganic residue remaining after either ignition or complete oxidation of organic matter
- Total of all inorganic elements
58
58. Select a food product and diagram a “typical” flow through the lab for conducting a proximate analysis of this product.
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59
59. What is an Operational Definition?
-A way to "define" a food product
60
60. What is attribute sampling?
- Sampling that is preformed to decided on the acceptability of a population based on whether a sample posesses a certain characteristic or not.
- Binary outcome
61
61. You are tasked with collecting samples from 50 lb. sacks of wheat flour for particle size analysis. Design an appropriate sampling process and briefly discuss what considerations / challenges you will face in obtaining truly representative samples.
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