Sweet Potato as a Fat Replacer in Oatmeal Raisin Cookies

Sweet Potato as a Fat Replacer
in Oatmeal Raisin Cookies
Final Written Presentation
Rachel Bredeweg
Michele Lawler
Rachael Smith
Kimberly Ziarko
November 21, 2011

Abstract
Creating healthier desserts and snacks is in high demand from consumers as obesity rates in the
United States are on the rise. Substituting sweet potato for butter into oatmeal raisin cookies was
studied to see how replacing butter in the recipe affected the color, texture, and taste of the cookies
compared to the normal oatmeal raisin cookie recipe. Variations of half‐fat replacement (50% fat
replaced) and full‐fat replacement (100% fat replaced) were tested against the control to determine
which variable consumers would like most. Objective measures from the Hunter Colorimeter, Water
Activity System, and Texture Analyzer were recorded as well as sensory measures from 30 panelists
using a Hedonic scale. It was found that the most preferred variable was the cookie with half‐fat
replacement.
Introduction
In the past decade, creating overall healthier desserts and snacks has been a high consumer
demand as the nation has become more aware of our growing health issues. An estimated 32% of
children and 66% of adults are overweight and obese, which has been steadily increasing over the last
thirty years (Lloyd‐Jones, 2010). This increase in obesity has also led to a higher prevalence in heart
disease, diabetes, and other correlated health problems in recent years. For this reason, producing more
heart‐healthy food items has been a major target in the food industry. One way to decrease the dietary
fat in foods is to substitute fat with a fat replacer to lower the amounts of saturated fats and trans‐fat
that can lead to the growing obesity and health issues. One possible substitute that was tested was the
use of sweet potatoes as a fat replacer.
Sweet potatoes are not only a healthier option than butter in cookies but they also provide
additional vitamin and mineral benefits. They are an excellent source of vitamin A, which is converted
into beta‐carotene, and are a good source of vitamins B, C, and E and the minerals manganese and
potassium. It is also a decent source of dietary fiber. These nutritional advantages can help consumers

eat preferred foods, such as cookies and sweets, while maintaining their daily vitamin and mineral
values. These nutrients may help prevent against cancer and heart disease and contribute to boosting
the immune system, healing wounds, and preventing blindness (Palmer, 2009).
In order to help control fat intake in a consumer accepted product, such as oatmeal raisin
cookies, the fat (butter) in the cookies was replaced with sweet potatoes that had been softened in
boiling water and mashed. The idea behind this was to produce an oatmeal raisin cookie that is similar in
consumer acceptance to the original, while containing half the amount of calories from fat and no
saturated fat or trans‐fat. Three trials each of full replacement of fat, half replacement of fat, and no
replacement of fat (the control group), were tested to see which looked the most similar to the control,
while tasting similar in flavor and texture. It has been proven that consumers accept fat replacements in
food products with up to 25‐50% fat replacement (Wekwete, 2008). From this, it can be deduced that
the half‐replaced cookie would be the one that is both healthier and accepted by the public.
Changing the fat in an already acceptable food product can affect the flavor, texture, and color
of the cookie. The raisins in the oatmeal raisin cookie were used to mask the bland flavor that the
mashed sweet potatoes would give over the butter, which had a sweeter flavor. Also, because sweet
potatoes are a deep orange color, their appearance had a slightly different color than the original
cookie. Oatmeal has a distinct brown color and since it was the major ingredient, it hopefully distracted
from the orange tint that was contained in the cookies made using sweet potatoes.
This orange tint could have also been disguised by the Maillard Browning effect. The Maillard
Reaction is a chemical reaction that takes place in the presence of an amino acid and a reducing sugar,
typically using heat application. This leads to the product browning, which can be acceptable in baked
goods to a certain degree. For the oatmeal raisin cookies, a small amount of Maillard Browning is
wanted and produced under normal baking conditions. According to research on the browning effects of
sweet potato content, a higher percentage of sweet potato in the product could lead to a faster and

higher rate of Maillard Browning (Iwe, 2003). This possible effect was analyzed and determined as to
whether it contributed to the overall appearance and acceptance of the oatmeal raisin cookies. The
Maillard Browning Reaction overview can be viewed in Appendix I.
The texture and moisture content of the cookie was affected from the fat replacement of the
sweet potatoes as well. According to research on this topic, adding mashed sweet potato increases the
moisture of food products while keeping the same stabilizing properties of the food (Bhosale, 2011).
This demonstrated that using a fat replacement in the oatmeal raisin cookies helped to provide a softer
and possibly even more acceptable cookie, based on palate and texture.
Because color and texture are important in comparison and approval against the original cookie,
the machines that were used to compare the fat‐replaced cookies from the control were the Hunter
Colorimeter, Water Activity System, and Texture Analyzer to test for any significant changes that could
affect how consumers view the modified oatmeal raisin cookie. To subjectively test and evaluate the
acceptance levels between the three cookie groups, a hedonic rating scale was also used. Fat affects the
stability, texture, and taste of the cookie.
This confirmed that our independent variables of half‐replaced and full‐replaced fat in the
cookie were critical in the outcome of the experiment’s physical properties of the cookies. In this
experiment, the independent variable was the sweet potato as a fat replacement to butter in the
oatmeal raisin cookies. The dependent variables were the physical properties of the cookies, like its
appearance, taste, and texture, and the consumer acceptance and approval of the cookies. Using all of
this information, it was hoped that the newly modified cookies would be both softer, yet similar in taste
and appearance to the original cookie control group.

Methods
Preparation
Using a regular oatmeal raisin cookie recipe, boiled and mashed sweet potatoes were
substituted as a fat replacer for the butter. The three cookie recipes made include the control, which is
the regular oatmeal raisin cookie, half‐replaced fat with half butter and half sweet potatoes, and full‐
replaced fat with all sweet potatoes. Cookies will be made in 600 gram batches each. Three trials of the
experiment were executed on Wednesday, October 12, 2011, and objective and subjective testing was
completed the next day in the laboratory. The directions used follow the recipes below.
Recipes
Control Variable 1 Variable 2
(Regular) (Half‐Fat Replaced) (Full‐Fat Replaced)
100 g butter, softened 50 g butter, softened 120 g boiled sweet potatoes
100 g sugar 60 g boiled sweet potatoes 100 g sugar
110 g packed brown sugar 100 g sugar 110 g packed brown sugar
1 egg 110 g packed brown sugar 1 egg
3 ml vanilla extract 1 egg 3 ml vanilla extract
120 g old‐fashioned oats 3 ml vanilla extract 120 g old‐fashioned oats
95 g all‐purpose flour 120 g old‐fashioned oats 95 g all‐purpose flour
2 g baking soda 95 g all‐purpose flour 2 g baking soda
3 g salt 2 g baking soda 3 g salt
30 g chopped walnuts 3 g salt 30 g chopped walnuts
35 g raisins 30 g chopped walnuts 35 g raisins
35 g raisins
(All conversions were made using http://www.gourmetsleuth.com)
Directions
1. Preheat oven to 190 degrees Celsius (375 degrees Fahrenheit).
2. Peel and dice sweet potatoes, making sure they are all similar in size. Add potatoes to boiling
water and cook until they fall apart when poked with a fork.
3. In a medium bowl, mix together the fat (butter and/or sweet potatoes) with brown sugar and
regular sugar. Beat in the egg and vanilla extract into the mixture.
4. In a separate bowl, mix the dry ingredients containing oats, flour, baking soda, and salt until all
incorporated.

5. Slowly add the dry ingredients to the wet ingredients, making sure everything is well combined.
6. Stir in walnuts and raisins.
7. Scoop 40 g (2 tablespoons) of the cookie dough and place it on an ungreased cookie tray.
8. Bake for 10 minutes. After baked, allow to cool for 15 minutes.
There were three trials performed with the variation of the three fat replacement choices. Each
trial took about 25‐30 minutes. After the cookies cooled, they were separated into three bags, each
containing ten cookies for the objective and subjective testing. Before the cookies were analyzed in lab,
they were cut into quarters.
To make sure that the three recipes and trials for the cookies were prepared the same way, each
variable was consistently measured and weighed before continuing with the above directions. The only
ingredient that was not controlled the same was the fat due to the different recipe variations using the
sweet potatoes. Same ingredients, ovens, and people were used to make the oatmeal cookies.
To prevent external variables, measurement of ingredients were precise, cookies were all measured out
to 40 grams (2 tablespoons) to make sure they would be equal in mass, clean utensils were used, and
the temperature of the ingredients were the same. To minimize confounding variables, three trials were
ran and tested. Photos of the final products from Trial 3 are shown in Appendix II.
Objective testing
The objective testing performed was to measure texture, water activity, and color and see how
substituting sweet potatoes for fat will affect the cookies and differ from the control. The Stable Micro
Systems Texture Analyzer was used to measure the force (in grams) needed to record the action
between the probe and density of the cookie. The results show the strength of the sample. A quarter of
the oatmeal cookie from each trial was tested using the cone probe for hardness and penetration
(Weaver and Daniel) and “cookie” was the setting used. Recorded was the average of each of the three
trial measurements. The Water Activity System used a thermocouple to identify how much moisture is
in the cookie by the condensation temperature (Weaver and Daniel). The Hunter Colorimeter measured

the color difference of the three variables. The machine can provide the color of the cookies using the L,
a, b Hunter parameters (Weaver and Daniel, 2003).
Subjective testing
Sensory testing that was analyzed included the Hedonic scale to evaluate the taste of the
cookie. Each variation of cookie was assigned a random number to reduce bias. The full fat control
cookie received number 736, half sweet potato and half fat‐replaced number 542, and full fat‐replaced
sweet potato number 387. Each three‐digit number was matched to the sensory evaluation scorecard.
Thirty subjects completed the sensory analysis. All cookies were cut into ¼ pieces to keep the sample
size the same and then placed on white plates with the correct number labeling. Cookies were tasted by
other FN 453 students as well as some faculty members during lab on October 13, 2011. The samples
were tested on the same day to prevent any staling issues that may result after several days. The testers
used the scorecard below to rate their preferences among the samples:
Please rate each sample based on overall appearance, texture, and flavor.
Degree of Preference Sample #387 Sample #542 Sample #736
Like Extremely
Like Very Much
Like Moderately
Like Slightly
Neither Like Nor Dislike
Dislike Slightly
Dislike Moderately
Dislike Very Much
Dislike Extremely
Please Circle Your Preference
Sample #387 Sample #542 Sample #736
Results
Each trial was tested both objectively and subjectively. For the objective testing, the Hunter
Colorimeter, Water Activity System, and Texture Analyzer were used. To test the samples using sensory

testing, a Hedonic scale was used to gather information from consumers about which sample was
preferred. Table 1 shows the results from the objective testing using the Texture Analyzer, Hunter
Colorimeter, and Water Activity System. Table 2 shows the average for each of the variables.
Table 1: Objective Testing Results and Standard Deviations
Texture
Analyzer (g)
Hunter
Colorimeter
Water Activity
System Standard Deviations
L,a,b
Trial 1 Control 297.1 51.4,5.49,2.74 0.57 27.33461237
50% 302.1 41.37,9.30,12.17 0.613 17.74524255
100% 146.2 47.19,6.05,3.03 0.706 24.67024388
Trial 2 Control 654.4 39.79,7.35,7.03 0.542 18.82229883
50% 93.9 46.96,7.64,6.55 0.7 23.02252013
100% 153.9 41.22,7.86,7.30 0.749 19.42408127
Trial 3 Control 206.4 47.47,5.15,2.12 0.561 25.35345407
50% 217.7 41.62,8.44,13.41 0.727 17.89514552
100% 117.9 41.88,7.28,8.93 0.756 19.51744946
Table 2: Average Values
Variable
Average
Texture
Analyzer
Values (g)
Average Water
Activity Values
Average Hunter
Colorimeter Values
L,a,b
Average L,a,b
values
Control 385.967 0.557 46.22,5.99,3.96 L: 44.32
50% 204.567 0.68 43.32,8.46,10.71 a: 7.17
100% 139.333 0.737 43.43,7.06,6.42 b: 7.03
Figure 1, Figure 2, and Figure 3 show the results from Trial 1, 2, and 3 respectively using the
Hunter Colorimeter to find the values of L, a, and b. The error bars indicate the standard deviations for
each trial. Figure 4 shows the average Hunter Colorimeter values for the combined trials.

Figure 1: Hunter Colorimeter Trial 1
Hunter parameter value
60
50
40
30
20
10
0
Figure 2: Hunter Colorimeter Trial 2
Hunter parameter value
60
50
40
30
20
10
0
L a b
Hunter parameter
Figure 1: Hunter Colorimeter for Trial 1
L a b
Hunter parameter
Figure 2: Hunter Colorimeter for Trial 2
Control
50%
100%
Control
50%
100%

Figure 3: Hunter Colorimeter Trial 3
Hunter parameter value
Figure 4: Average Hunter Colorimeter Values
Hunter parameter value
60
50
40
30
20
10
0
50
45
40
35
30
25
20
15
10
5
0
L a b
Hunter parameter
Figure 3: Hunter Colorimeter for Trial 3
L a b
Hunter parameter
Figure 4: Average Hunter Colorimeter
Figure 5, below, shows the force (in grams) it took the Texture Analyzer to penetrate a sample in
each trial. Measurements were taken once for each trial to be compared against one another. Figure 6
shows the average values obtained from the Texture Analyzer over the three trials.
Control
50%
100%

Figure 5: Texture Analyzer Values for Each Variable
Texture Analyzer Values (grams)
Figure 6: Average of Texture Analyzer Values
Average Texture Analyzer Values (grams)
700
600
500
400
300
200
100
0
450
400
350
300
250
200
150
100
50
0
Control 50% 100%
Variable
Figure 5: Texture Analyzer Values for Each
Variable
Variables
Figure 6: Average Texture Analyzer Values
Using the Water Activity System, the water activity of each sample was obtained as shown in
Figure 7. Figure 8 below shows the average water activity values for each variable.
Trial 1
Trial 2
Trial 3
Control
50%
100%

Figure 7: Water Activity Values
Water activity value
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Figure 8: Average Water Activity Values
Average Water Activity Value
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Trial 1 Trial 2 Trial 3
Trial #
Figure 7: Water Activity Values
Variable
Figure 8: Average Water Activity Values
Control
50%
100%
Control
50%
100%

Figure 9 shows the results of the panelists over all three trials combined. 50% of the panelists
preferred the 50% fat replaced cookies, 30% enjoyed the control best, and 20% found the 100% fat
replaced cookies to be the best.
Figure 9: Sensory Sample Preference
Table 3 shows the results of the ANOVA testing as obtained after ANOVA experimentation. The
result when using the Tukey‐Kramer Multiple Comparisons Test shows that if the value of q is greater
than 3.773, then the p‐value is less than 0.05. Table 4 shows the values used in the ANOVA testing and
as the results from the p‐value significance shows, the control and the 100% fat replaced cookie are not
significantly different while the 50% fat replaced cookie is significantly different.
Table 3: ANOVA Testing
100% Replacement:
20% Preferred
50% Replacement:
50% Preferred
Control:
30% Preferred
Mean
Comparison Difference q P value
================================================
Variable 1 vs Variable 2 171.55 3.202 ns P>0.05
Variable 1 vs Variable 3 240.90 4.497 * P0.05

Mean 95% Confidence Interval
Difference Difference From To
================================================
Variable 1 ‐ Variable 2 171.55 30.586 373.68
Variable 1 ‐ Variable 3 240.90 38.766 443.03
Variable 2 ‐ Variable 3 69.353 132.78 271.49
Table 4: Results of ANOVA Testing Significance
Discussion
The goal of the project was to find what effect fat replacement had on the overall palatability,
appearance, and consumer acceptability of the cookie. In the experimental trials, it was found that the
more fat a cookie contained, the less water activity, and therefore moisture, the product had after being
baked. As expected from literature findings, adding mashed sweet potato increases the moisture of food
products (Bhosale, 2011).
It was found that replacing butter with mashed sweet potato in oatmeal raisin cookies produced
a cookie that was more desirable when half of the fat was replaced. However, when all of the fat was
replaced, the cookies became less desirable to consumers. One reason why is because the cookie stayed
in the same shape as when it was put in the oven instead of thinning out while baking, making it look
less like a cookie and more like a granola bar. Therefore, the appearance of the cookie was less desirable
to consumers. From the Hunter Colorimeter figures, it is noted that for the cookies with fat
replacement, the L, a, and b values from the Hunter Colorimeter were less than those values from the
control. Consumers may have preferred the half‐fat replaced cookie because it had the lightest color.

The panelists also preferred the overall mouth feel of the half‐fat replaced cookie, saying it had a more
smooth texture than both the control and the full‐fat replaced cookie. The Water Activity System results
showed that the more fat replaced by sweet potato, the more moisture that was held/retained in the
cookie. The average Texture Analyzer values show that as the fat was replaced, the cookie required less
force to penetrate, following the same trends as found by the Water Activity System. This is also
consistent with the findings in the lecture notes about the experiment ran with avocado and Oatrim as
fat replacers in oatmeal cookies. Each of the cookies that contained 50% of either Oatrim or avocado
instead of butter was found to have a smaller force required to penetrate the cookie using the Texture
Analyzer (Daniel, 2011).
The overall conclusion from the experiments was that it is desirable to replace half of the fat in
the cookies to produce a healthier product and provide additional vitamin and minerals. Doing so
resulted in a cookie that was softer than the control because of the added moisture content but still
similar in taste and appearance to the control. The ANOVA testing showed that there was no significant
difference in the control and full‐fat replaced cookie, whereas the half‐fat replaced cookie was found to
be significantly different.
If the experiment were to be performed in the future, it would be desirable to test a larger
population on each of the trials. In theory, the larger population that is sampled, the smaller the
standard deviation. It may also be pertinent to see what effect replacing 75% of the fat had on the
acceptability and approval of the consumers. This data could be used to find the highest percentage of
fat that can be replaced while still meeting the criteria set by consumers for a desirable product.
Another experiment that could be ran in the future would be to test different fat replacers in oatmeal
raisin cookies against the half‐fat and full‐fat replacements using sweet potato to see which fat replacer
is most acceptable to consumers. According to the lecture notes, other carbohydrate based fat
substitutes in cookies are Oatrim, Beta‐glucan, and Inulin that simulate the mouth feel of fats by

interacting well with water to control both the structure and mobility of the water. The fiber sources
increase the viscosity and lubricity of the product which helps to simulate the mouth feel of fat and oils
(Daniel, 2011).

References
Bhosale S.S., Biswas A.K., Sahoo J., Chatli M.K., Sharma D.K., Sikka S.S. 2011. Quality evaluation of
functional chicken nuggets incorporated with ground carrot and mashed sweet potato. Food
Science and Technology International. 17: 233‐239.
Daniel, J.R. 2011. FN 45300 Food Chemistry Lecture Notes‐ Fat Replacers.
Iwe M.O., Van Zuilichem D.J., Stolp W., Ngoddy P.O. 2003. Effect of extrusion cooking of soy‐sweet
potato mixtures on available lysine content and browning index of extrudates. Journal of
Food Engineering. 62: 143‐150.
Lloyd‐Jones D., Adams R.J., Brown T.M., Carnethon M., Dai S., De Simone G., . . . Wylie‐Rosett J. 2010.
Executive summary: Heart disease and stroke statistics‐2010 update. Circulation Journal of
the American Heart Association. 121: 948‐954.
Palmer S. 2009. Sweet potatoes glow with health and flavor. Environmental Nutrition. 8.
The Gourmet Food and Cooking Resource. “Conversions.” 28 September 2011.
Weaver, Connie and Daniel, James. The Food Chemistry Laboratory‐a manual for Experimental Foods,
Dietetics, and Food Scientists. 2003. CRC Press (2 nd edition); pgs 43‐47.
Wekwete B., Navder K.P. 2008. Effects of avocado fruit puree and Oatrim as fat replacers on the
physical, textural and sensory properties on oatmeal cookies. Journal of Food Quality. 31:
131‐141.

Appendix
I. Maillard Browning Chemistry (Weaver and Daniel, 2003).

II. Photographs of the Control, Variable A, and Variable B
Control:
Variable A (Half‐Fat Replaced):

Variable B (Full Replaced):

III. Raw Data for Trials 1, 2, and 3
Objective
Texture
Analyzer Hunter Colorimeter Water Activity System
L,a,b
Trial 1: Control 297.1 51.4,5.49,2.74 0.57
50% 302.1 41.37,9.30,12.17 0.613
100% 146.2 47.19,6.05,3.03 0.706
Trial 2: Control 654.4 39.79,7.35,7.03 0.542
50% 93.9 46.96,7.64,6.55 0.7
100% 153.9 41.22,7.86,7.30 0.749
Trial 3: Control 2006.4 47.47,5.15,2.12 0.561
50% 217.7 41.62,8.44,13.41 0.727
100% 117.9 41.88,7.28,8.93 0.756
Average of T.A. Control: 985.967g
50%: 204.567g
100%: 139.333g
Water Activity Temperature of Machine:
Trial 1: Control 23.7 C
50% 23.5 C
100% 23.6 C
Trial 2: Control 23.3 C
50% 23.1 C
100% 23.5 C
Trial 3: Control 23.8 C
50% 23.7 C
100% 23.7 C
Subjective
Average Texture Analyzer:
Cookie: 736=Control 542= Half‐Fat Replaced 387= Full‐Fat Replaced
Preference: 9/30 liked it best 15/30 liked it best 6/30 liked it best
% Preference: 30 50 20
Hedonic Test
Control Half‐Fat Replaced Full‐Fat Replaced
Most selected "Dislike Slightly" Most selected "Like Moderately" Most Selected "Dislike Moderately"

Standard Deviations
Trial 1: Control 51.4 5.49 2.74
Standard
Deviation
27.33461237
50% 41.37 9.3 12.17 17.74524255
100% 47.19 6.05 3.03 24.67024388
Trial 2: Control 39.79 7.35 7.03 18.82229883
50% 46.96 7.64 6.55 23.02252013
100% 41.22 7.86 7.3 19.42408127
Trial 3: Control 47.47 5.15 2.12 25.35345407
50% 41.62 8.44 13.41 17.89514552
100% 41.88 7.28 8.93 19.51744946
One‐way Analysis of Variance (ANOVA)
The P value is 0.0217, considered significant.
Variation among column means is significantly greater than expected
by chance.
Tukey‐Kramer Multiple Comparisons Test
If the value of q is greater than 3.773 then the P value is less
than 0.05.
Mean
Comparison Difference q P value
================================== ========== ======= ===========
Variable 1 vs Variable 2 171.55 3.202 ns P>0.05
Variable 1 vs Variable 3 240.90 4.497 * P0.05
Mean 95% Confidence Interval
Difference Difference From To
================================== ========== ======= =======
Variable 1 ‐ Variable 2 171.55 ‐30.586 373.68
Variable 1 ‐ Variable 3 240.90 38.766 443.03
Variable 2 ‐ Variable 3 69.353 ‐132.78 271.49