The Effect of Emulsifiers and Stabilizers in Oil and Vinegar Salad Dressing
November 20, 2005
Matt Thornton
F&N 453: Food Chemistry
Abstract: Emulsifiers and stabilizers are known to be effective agents of emulsification. When used in an
oil and vinegar salad dressing, they contribute to significant changes in density, viscosity, and color when
compared to the control which contains no emulsifiers or stabilizers. The stabilizer used was xanthan
gum and the emulsifier used was lecithin. It was found that the control remained the densest, followed by
the stabilizer-sample, then the emulsifier-sample. This is potentially due to the fact that air remains
emulsified in the emulsifier- and stabilizer-samples. The xanthan gum sample was demonstrated to be by
far the most viscous due to its action as a thickener as well as an emulsifier. Finally, color was very
clearly affected by the additives. The samples containing the additives were most similar to each other
and undertook a much lighter, creamier color than the control. Overall, addition of even a very small
amount of emulsifier/stabilizer to an emulsion results in significant characteristic changes of the salad
dressing, besides simply promoting and maintaining the emulsion.
I. Introduction:
Generally speaking, homemade recipes for salad dressings do not contain any emulsifiers or stabilizers,
and hence rely on a very slow and steady addition of oil during preparation to ensure that an emulsion is
being properly formed. Furthermore, after being allowed to set for even a relatively short period of time,
the oil and vinegar constituents will fall out of emulsion and separate to opposite ends of the container.
At this point, a thorough and extensive shaking is required to return the dressing back to its original state
of emulsion. Even a heavy shaking still cannot completely return the dressing back into the emulsion that
it was just after being prepared. Thus forms the basis of this project. Compared to a salad dressing
control sample with no additives, to what degree will a stabilizer or an emulsifier in the recipe of a
homemade salad dressing affect the color and textural qualities of the product. In this paper, the effect of
emulsifiers and stabilizers in an oil and vinegar salad dressing will be quantified, analyzed, and discussed.
The stabilizer used is xanthan gum and the emulsifier is lecithin. It has been exhaustively established in
the literature that both lecithin xanthan gum are effective emulsifiers that are used commonly in
commercial industry. Xanthan gum is the result of the fermentation of corn sugar using Xanthomonas
campestris bacteria. These bacteria produce Xanthan as part of their cell wall, meaning it is indigestible
and is a highly effective emulsifier in pharmaceuticals, cosmetics, and foods (Kim and Yoo 2005).
However, lecithin and xanthan gum are generally used only in industry and not in homemade recipes.
Study of how these two emulsifiers, when added to a homemade recipe, change the quality characteristcs
of the resulting product may be useful for homemade recipes, especially ones that are made to be stored
for extended periods of time. In a previous study concerning the use of xanthan gum compared to
propylene glycol alginate, it is concluded that since a medium viscosity product is preferred in salad
dressings, xanthan gum is a better choice than the alginate (Paraskevopoulou et al. 2005). Furthermore,
xanthan gum is one of the most widely known emulsifers in industry. Quantification of the effects of
these two additives on the dressing was done objectively, using a colorimeter and a hydrometer, and
subjectively, using taste panel of peers. The independent variable, then, becomes the presence (or
absence) of a stabilizer or emulsifier in the dressing.
II. Methods:
The procedure for each trial begins with acquiring all necessary ingredients and supplies. The ingredients
are listed by amount required below:
Oil and vinegar dressing:
250 mL safflower oil
125 mL olive oil
125 mL cider vinegar
0.5 g salt
0.5 g pepper
0.5 g emulsifier (xanthan gum or lecithin)
1. Preparation
A medium-sized bowl is used to combine the ingredients. First the vinegar, salt, and pepper are measured
out and mixed together. The lecithin or xanthan gum, if called for, are also added at this stage. It is vital
that the lecithin or xanthan gum is measured accurately since the addition of these ingredients forms the
basis of this experiment. Furthermore, when adding them to the vinegar, salt, and pepper mixture, care
should be taken that they are added slowly enough so that they can be dispersed immediately. To do this,
a hand-mixer should be used simultaneously as the xanthan gum or lecithin is slowly poured in. The
reason for this is that if they are added too quickly or all at once, they will clump together. Once xanthan
gum or lecithin has clumped together in the vinegar mixture, it is virtually impossible to get them to
disperse. At this point, the oil is added. The oil should be measured out in beakers before beginning the
experiment. This way, the oil can be added as soon as possible after the emulsifier or stabilizer is mixed
in with the vinegar. The safflower and olive oils are added very slowly while still using the hand mixer to
ensure that the oil droplets are small and become well-dispersed throughout the vinegar mixture. The
salad dressings are then mixed until thoroughly emulsified.
2. Subjective Testing
A small amount of each sample is poured into each of three custard dishes for the taste panel. The taste
panel is presented by placing the samples on a tray with their randomly-assigned numbers in front of
them. Carrots are served with the dressings to make trying the dressing samples easier and more
appealling. The taste panel cards are placed by the tray for panelists to fill out while tasting the samples.
Which sample (496 or 327) has better mouthfeel? Texture?
Mouthfeel:
Texture:
Which sample (237 or 897) has better mouthfeel? Texture?
Mouthfeel:
Texture:
Which sample (193 or 547) has better mouthfeel? Texture?
Mouthfeel:
Texture:
Rate the three samples in terms of mouthfeel and texture*.
*(the actual taste is not as important)
Figure 1: Taste Panel Evaluation Trial 1: The format from trial 1
is a pair-preference format but was determined to be not specific enough.
After analyzing the results using this evaluation format, it was decided that using a more “user-friendly”
format would also achieve more specific and useful results. This format shown below was used for trials
2 and 3.
Color:
Rank the following samples from most appealing color to least appealing color.
______Sample 191
______Sample 630
______Sample 309
Viscosity:
Rank the following samples from thickest to thinnest.
______Sample 191
______Sample 630
______Sample 309
Figure 2: Revised Format Trials 2 and 3: The revised format is a ranking which
allows for paired comparisons still while understanding the overall preference. This
version was used to replace the original format in trial 1.
All the numbers used were obtained using a random three-digit number chart. Also, to prevent any order
bias, the samples were presented in different order for each trial.
3. Objective Testing:
Then the rest of the samples are tested for specific gravity (density) and color. To test the specific
gravity, some of the salad dressing is poured into a graduated cylinder and a hydrometer is dropped into
the salad dressing sample. Once the hydrometer comes to rest, a measurement can be read by eye. The
reading will be given in units of specific gravity, which is a unitless quantity obtained from dividing the
product density by the density of water (1g/mL). Finally, the rest of the sample is put into a 500 mL
beaker to be tested for color. A Hunter colorimeter is used. First, it must be calibrated using standarized
white and black tiles. Then the sample is placed over the “eye” to be read; results are given as L, a, and b
values. Once all measurements have been made and panelists are done tasting the samples, the
equipment, supplies, and work are cleaned and put away.
IV. Results:
Measurements of the three different salad dressing samples are taken for three specific characteristics,
namely specific gravity, viscosity, and color. Density measurements, as discussed previously, showed the
following trend:
1
Specific gravity (unitless)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Control
Xanthan Gum
Lecithin
Figure 3: Average density comparisons by sample: Specific gravity measurements using a hydrometer
showed that the control sample had the highest average specific gravity (0.9049), followed by the sample
containing xanthan gum (0.9260), and lastly the sample containing lecithin (0.9049). It is interesting to
note that the difference between each successive sample shows a more or less linear relationship.
The viscosities of each of the salad dressings are compared by results obtained from the taste panels. The
xanthan gum sample was preferred more than the control and lecithin sample combined, as shown
graphically in Figure 2.
Times Chosen for Thickness
35
30
25
20
15
10
5
0
Xanthan Gum
Control
Lecithin
Figure 4: Comparison of perceived viscosities of each sample: The sample with xanthan gum added
was clearly perceived as the most viscous sample. It was preferred in terms of thickness more often than
the control and lecithin-added samples combined. This is likely due to its effect of thickening the
continuous phase of the emulsion.
Table 1: Taste Panel Preferences: The preferences of comparisons between samples obtained in Trials 2
and 3, show that the control was much favored in terms of color and the xanthan gum sample was
overwhelmingly the perceived-thickest of the three samples
Xanthan Gum
COLOR
VISCOSITY
Control
17
31
Lecithin
25
15
12
8
30
Times Preferred
25
20
15
10
5
0
Xanthan Gum
Control
Lecithin
Figure 5: Overall color preference by sample: These values are based on preference of color by taste
panelists. The control is most preferred but followed by the xanthan gum sample.
Color changes were the most unexpected changes in this experiment. Visually, it is easy to tell that
samples are different, but it is hard to identify exactly how and to what magnitude. Fortunately, color of
samples can be compared qualitatively using values obtained from the Hunter colorimeter. The color is
described by three values: L, a, and b. The L-value designates the lightness of the sample, the a-value
describes the redness-greenness of the sample, and the b-value describes the yellowish-bluish aspects of
the sample.
3
2.5
a-value
2
1.5
1
0.5
0
Control
Xanthan Gum
Lecithin
Figure 6: Color comparisons of a-values: The
graph above suggests that the lecithin and control
samples have much more red-green color than the
xanthan gum, which is very creamy white.
14
12
b-value
10
8
6
4
2
0
Control
Xanthan Gum
Lecithin
Figure 7: Color comparisons of a-values: The
graph above suggests that the three samples are
fairly close in terms of yellow-blue color.
50
45
40
L-value
35
30
25
20
15
10
5
0
Control
Xanthan Gum
Lecithin
Figure 8: Color comparisons of L-values:
The graph above suggests that the two variable
samples are generally lighter in color than the control.
The chart of L-values confirms what can be observed visually: that the samples with the additives are
lighter in color and closer in value to each other than either is to the control. The charts comparing the aand b- values show that the xanthan gum sample has the lowest redness-greenness and the highest
yellowness-blueness. The control has the lowest yellowness-blueness and middle redness-greenness, and
the lecithin sample has the highest redness-greenness and middle yellowness-blueness. The following
equation obtained from Billmeyer 1969 is used to determine the Hunter unit of color difference and can
be used to compare color differences:
ΔE = ( L1 − L2 ) + (a1 − a2 ) + (b1 − b2 ) ,
where
ΔL – designates lightness difference
Δa – designates redness-greenness
Δb – designates yellowness-blueness
ΔE – a unit of color difference. It is the total difference in hue, saturation, lightness
Using this equation to compare the samples two at a time can be used to show which samples are most
similar in color.
Table 2: Comparison of Sample Colors: The two-pair comparisons show that the xanthan gum and
lecithin were most similar in color, with a unit of color difference of 3.
Color difference
ΔL
Δa
Δb
ΔE
Control and Xanthan Gum
21.73 -0.79
4.73
5.07
Control and Lecithin
13.16 0.65
2.71
4.06
Xanthan Gum and Lecithin
8.57 -1.44
2.02
3.02
Table 1 shows that based on the ΔE-values, the xanthan gum- and lecithin- containing samples are the
most similar in color, followed by the control and lecithin samples, and lastly the control and xanthan
gum samples. Visually, the control has a light golden yellow color, with a hint of green. It should also be
noted that in the control sample, the pepper settled to the bottom, which could potentially skew the color
results of the control sample due to the fact that the colorimeter reads through the bottom of the beaker.
The xanthan gum sample can be described as a creamy white color with the pepper well-disseminated.
The lecithin sample is a duller and slightly darker creamy white than the xanthan gum sample.
III. Discussion:
1. Preface:
The hypothesis of this experiment was shown to be true. The addition of an emulsifier or a stabilizer to
an oil and vinegar salad dressing did in fact result in noticeably better emulsions, as was expected. It also
changed the color and textural characteristics, as expected, but on average, the changes in color, density,
and viscosity were more significant that expected. Before proceeding, it should be understood that
stabilizers and an emulsifiers are the same in one sense and different in another. That is, both an
emulsifier and a stabilizer serve to create and maintain emulsions, but the difference is that each does so
by a different mechanism. In general, stabilizers work by thickening the continuous phase so that the
dispersed phase is unable to coalesce. Emulsifiers work by being surface active and forming protective
coatings around the droplets in the discontinuous phase, which prevents them from coalescing. (Wendin
and Hall, 2001) Xanthan gum, the stabilizer additive used in this experiment, is a commercially produced
biopolymer used to thicken and stabilize emulsions. It serves to stabilize by thickening the continuous
phase of the emulsion with weak gel-like structures. The structures formed by the xanthan gum
molecules in the continuous phase have a greater yield stress than the gravitational lift acting on the
droplets (Kiosseoglou et al. 2003). As a result, interfacial tension is lowered, leading to an increase in
emulsion stability. Xanthan gum is one of the main stabilizers used in industry; others include intact or
modified starches, galactomannans, and pectin. (Paraskevopoulou et al. 2005) Lecithin is the emulsifier
used in the experiment. Since each molecule of an emulsifier contains a hydrophilic portion and a
lypophilic portion (Kong et al. 2003), they prefer to position themselves at the interface between fat (olive
and safflower oil) and water (vinegar). As a result they act to reduce the interfacial tension, the force
which exists between the two phases of the emulsion.
2. Density:
The density of each of the salad dressings was different from each other, but more or less the same
between the same recipe in each trial. That is, the sample containing no additives (the control) was the
most dense, then the sample with the stabilizer additive, and lastly the sample with the emulsifier
additive. All density measurements throughout all three trials gave a specific gravity of less than one,
reflecting the fact that oil, the major constituent in salad dressing, is less dense than water. The fact that
each sample gave approximately the same density measurements and each was the same relative to the
other samples shows that the emulsifier and stabilizer had a certain effect on the recipe. To understand
why the dressings with additives added were less dense than the dressing, consider the process by which
they are made. As the salad dressing ingredients are whipped together, air is also incorporated into the
dressing. After the final product is done and allowed to sit, the portions of different densities have the
tendency to separate, unless there is an emulsifier or stabilizer preventing or slowing this from happening.
When portions do separate, they separate by density, that is, the vinegar falls to the bottom since it is most
dense, and the oil moves to the top. But there is another layer, the air that was beat into the product rises
to the top and leaves the product since it is by far the lightest constituent. However, in the case that an
emulsifier is used (whether xanthan gum or lecithin), some of the air remains trapped in the emulsion by
the action of the emulsifiers. This accounts for the lowering in the density of the stabilizer- and
emulsifier-containing samples. Moreover, the sample containing a stabilizer has a density which is less
than that of the control but greater than that of the lecithin-emulsified dressing. This is due to the fact that
xanthan gum emulsifies by thickening the aqueous phase. So on one hand the xanthan gum serves to thin
or decrease the density since air has a much lower density than that of oil or vinegar. On the other hand,
the xanthan gum thickens by controlling the water activity in the product.
3. Viscosity:
Salad dressing emulsions are similar to mayonnaise emulsions in the sense that they are both still oil in
water solutions despite the very high oil to water ratios. The result of this is very closely packed oil
droplets that sometimes must be deformed to fit together causing the product to be rather viscous, more
than that of oil or water alone (Depree and Savage 2001). The viscosity of each sample is different due to
the emulsifier, stabilizer, or lack thereof. As previously discussed xanthan gum acts as an emulsifier by
causing the aqueous phase to be thicker. Since the gel-like structures attract water, the overall water
activity is reduced. This is the main reason that the xanthan gum solution is shown in the results to be by
far the thickest of the three samples. The control and lecithin sample are closer to each in terms of
perceived viscosity due to the fact that the aqueous phase in both is left unaffected by experimental
variables. The fact that the lecithin sample contains more air might hint to that sample being more
viscous, but the results do not show this to be true. For potential future work, it might be interesting to
understand more in depth the effect that emulsified air bubbles have on the viscosity of the emulsion.
Furthermore, understanding of why the air bubbles do or do not affect the viscosity could have
applications in food processing or areas where products (food, water, sewage, etc) are made to flow
through pipes.
4. Color:
In perusing the literature, there are many theories and ideas about how to best compare colors. The
purpose of this research is not as much concerned with quantifying the changes caused by additives in the
salad dressing as demonstrating that there are in fact noticeable changes in color. Both the subjective
visual preferences and the objective Hunter colorimeter analysis show that there is indeed a change. The
subjective results showed that the control is by far the most preferred in terms of color, perhaps due to the
fact that it is a golden color that is more reminiscent of a salad dressing that the other samples.
Furthermore, the two samples containing the additives were most similar in color based on objective
measurements and analyses based on the Hunter unit of color difference. Perhaps the fact that they
contain more air is directly related to the fact that they are generally lighter than the control sample.
Nonetheless, this too, would perhaps be an interesting area to further study; that is, the relationship
between emulsifiers and stabilizers on product color. An understanding of why this happens would be
very applicable and beneficial to any industry that uses emulsified products (paint, dressings/spreads, etc.)
5. Error Discussion:
There are a number of areas that could account for inaccuracies may have arisen throughout this project.
In general, there was a general progression from the first trial to the third trial of how smoothly and
quickly the experiments and subsequent measurements went. More efficient and more precise methods
are learned and applied, meaning, for example, that results from the first trial may not be as reliable in
terms of accuracy as the third trial. Nonetheless, compiled results from all three trials of the project tend
to point to the same findings. One of the major difficulties encountered in all three experiments dealt
with dispersing the emulsifier throughout the vinegar before the oil was added. The lecithin and the
xanthan gum had to be added in very small portions and each portion had to immediately and thoroughly
dispersed; otherwise, it would clump together and at that point was very difficult or impossible to break
up. This was an area for concern throughout the project because if the emulsifiers were not aptly
dispersed, the results would be skewed. Other instances where the human factor may have been a cause
for errors are: correctly reading the hydrometer, correctly measuring ingredients for the samples, mixing
long and thoroughly enough, and adding ingredients gradually enough. On the other hand, mechanical
error may account for just as much inaccuracy as human error. The colorimeter gave somewhat erratic
results. For example, one sample could give different color value results on two separate tests. The
values given were proximate however and therefore do not detract from the value of the measurements.
Also, in the control sample, due to the lack of emulsifiers, the pepper sinks to the bottom. This would be
expected to skew the colorimeter readings due to the black specks of pepper. Using the hydrometer also
gave somewhat erratic values. In some cases, the instrument would bob or start to rise or sink slowly if
the sample was disturbed even slightly. Therefore, very precise measurements were not plausible, but
estimates by eye were more or less reliable. Overall, measurements taken in this project serve more to
determine tendencies and less to obtain exact values. With that being said, the averages of the
measurements can and should be considered reliable indications of the true values.
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