There are two parts to this paper: Exam 3 (100 points) is material from
the last exam to the end of the semester and Comprehensive (50 points),
which is as the name suggests. Answer all questions and try to divide
your time according to the points available. This exam will end at 4:45
PM.
Question
Points
available
Points
gained
1
8
2
8
3
4
4
6
5
2
6
6
7
4
8
4
9
16
10
6
11
6
12
4
13
2
14
4
15
6
16
4
17
4
18
6
Name: _____________________
FDSC 400: Exam 3
1. The following is an intermediate from lipid oxidation. Draw the two additional
radical compounds formed by radical migration. Include the mechanism for the
formation of one of these compounds.
(8 points)
2. What is the biological source of: (8 points)
 Gelatin

Carageenan gum

Xanthan gum

Pectin
3. What does it mean when a flavor has a “character impact compound”?
(4 points)
4. What is polymorphism in fats?
(6 points)
5. Give an example of a bitter-tasting chemical
(2 points)
Perceived Rancidity
6. The figure shows the development of a rancid flavor in potato chips over time.
Add a curve to the figure showing the expected kinetics if a primary (radical
scavenging) antioxidant was added. (6 points)
120
100
80
60
40
20
0
0
10
20
30
40
50
Time /months
7. Briefly describe how pregelatinized starch is manufactured?
(4 points)
Red Color Intensity
8. The following graph shows the intensity of the red color in cranberries as a
function of pH. What is the pK of the important pigment in cranberries?
(4 points)
9. Chocolate is tempered by heating to about 50°C, cooling to about 25°C and
holding, reheating to about 32°C then pouring into a mold and allowing to set. In
the following table describe how the total amount of fat crystals changes with
each temperature change and also how the balance of polymorphic forms alters.
(You may, if you prefer, confine your discussion of polymorphic forms to more or
less of the “more stable” or “less stable” types. (16 points)
Change in total amount of
solid fat
Heat to 50°C
Cool to 25°C and hold
Reheat to 32°C
Pour into a mold and cool
to room temperature
Change in distribution of
crystal polymorphs
10. Vacuum-packed meat is a dull purple color but when the package is opened and
the meat exposed to the air takes on a bright-red color. Why?
(6 points)
11. Some types of pectin can be gelled with calcium ions while another requires high
sugar and low pH. What is the chemical difference between these types of
pectin? (4 points)
Viscosity
12. Sketch a graph showing how the viscosity of a xanthan gum solution increases
with concentration (6 points)
[xanthan]
13. Are most polyunsaturated fatty acids cis or trans? (2 points)
14. The freezing point of a fat is typically lower than its melting point. Why?(4
points)
15. List two defects common in poorly tempered chocolate (6 points)


16. Give an example of a radical scavenging antioxidant (4 points)
17. What are the two glucose polymers in starch? (4 points)


18. What is a “sniff-port” on a gas chromatograph and why is it a useful in flavor
chemistry? (6 points)
Name: _____________________
FDSC 400: Comprehensive
Question
Points available
Points gained
1
2
6
3
5
4
8
5
5
6
8
18
1. You want to conduct an accelerated shelf life test to determine how long a cookie
will last. You store samples of products at a series of elevated temperatures,
measure the reaction kinetics and calculate a rate constant at each temperature.
Sketch a graph to illustrate how you would estimate the rate constant at lower
temperatures.
(6 points)
2. When milk is poured onto a breakfast cereal the cereal goes from crunchy to soft.
Mark what is happening on the following state diagram and explain what is
happening (5 points)
3. Milk fat can be separated into high melting and low melting fractions by cooling
so the high melting crystallizes then centrifuging it out to separate. The goal is to
make large crystals. Why is the fat typically cooled fast, and why are the large
crystals more easily centrifuged out? (8 points)
4. Milk coagulates to form a yogurt-like gel when the pH is lowered to 4.6. The
following diagram shows a suspension of casein micelles in milk. Draw a similar
sketch of the coagulated milk gel (5 points)


1. Casein micelles in milk (pH 7).
Typical micelle diameter ~ 1 mm.)
2. Casein micelles in coagulated milk
gel (pH 4.6)
5. Lipoxygenase is added to bread dough to increase the number of inter-protein
disulfide bonds present. The effect of the additive is tested in a creep test where a
force is applied to a sample of dough, held then released and the deformation
measured as a function of time.
 What is the reaction catalyzed by lipoxygenase? (2 points)
On the following axes, sketch the creep curves (deformation as a function
of time after the applied force is removed) for the original recipe and for
the modified dough. (6 points)
deformation

time
6. Briefly define/explain the meaning of the following terms and provide a food
example of each
(2 points for each definition, 1 for each example)
Definition
Retrogradation
Tempering
Metal chelator
Foam
Enzymatic browning
Maillard reaction
Example