Assay of reproducible methods for crispiness
evaluation of potato chips
By
Akhilesh Pandey
In
Guidance of
Dr. Elena Castell
Dr. Rosana Moreira
1
Abstract
The reproducible method to analyze textural properties of potato chips was done by
comparing ball probe results with two settings of guillotine probe. The results were
obtained from texture analysis of Frito-Lays® brand potato chips through TA-XT2i
texture analyzer. These results were interpreted by SPSS software to check the
variability in data. The results showed high difference from each other due to testing
methods. These differences were plotted in form of Force-Distance graph for further
analysis. The best method was found by changing the gap between the guillotine probe
to emulate it with the three point bend rig. The gap was set with the help of trial and
error method to obtain the minimal difference between any two replications. This led
to better results than any other methods lessening the variability in each replication.
The numbers of multiple peaks due to high variability in ball probe were highly
reduced in this method. Therefore the three-point bend rig emulation by guillotine
probe was verified as the most suitable method for textural analysis of potato chips.
2
Introduction
During the recent few decades numerous evaluation methods and
instrumentation has been developed for analysis of mechanical properties of biological
materials. Numerous researches have been conducted to produce better quality and to
perform quantification of properties like crispiness, hardness, fracturability etc. These
basic properties were being related with the processing parameters such as color,
moisture content and various unit operations such as blanching, steeping, slicing,
frying time. The prior need was to correlate the various quality attributes to the
mechanical properties of the food products in order to evaluate the shelf life,
stackability, mouthfeel; which serve as major factors in overall product quality. The
basic concept behind all these parameters is very vast and difficult to quantify as well
to evaluate it.
Current researchers continuously thrive for achieving consistency in there data
to make superior reproducibility of there results. Many methods have been evolved for
qualitative analysis of potato chips lately, with the help of R&D carried out by
universities and companies like Frito-Lays®. These methods emphasize on use of a
reproducible technique to give consistency in results for evaluation of quality
attributes of the final product. In the following experimental analysis of crispiness of
potato chips the results were dually analyzed with the use of rupture test with the help
of guillotine and ball probe. The basic objective was to achieve reliability and
consistency in the results obtained. The principle of the test was to calculate the force
required to fracture and break the potato chips as the measure of crispiness and
brittleness. The surface irregularity of the chips inhibited the similarity in results of
3
two different samples of chips. This is the major problem in evaluation of the potato
chips and to obtain reproducibility in the acquired results. Since potato chips also
contain blisters due to frying operations thus making it have higher variability in the
texture analysis results. This is due to the fact that no two potato chips are similar to
each other in shape and size.
The second objective of the experimental analysis was to determine the best
method for evaluation of crispiness and brittleness in potato chips. The analysis was to
be done by use of two different probes namely Guillotine and Ball probe to see the
least variations in the results. Altogether a statistical analysis of the data was required
to help in elucidating the results obtained and to provide a result with minimum
variability.
The method evolved slowly and was practiced as three point bending method
that is generally used for evaluation of a sample through snapping test. This method
had been used recently in fewer researches for textural analysis of processed food
materials. Recently the method has been utilized for testing shelf-life, crispiness and
staling of potato chips.
4
Literature Review
The work carried out in the texture analysis of the potato chips is at its
primitive level and more is to be achieved in this area to find better alternatives for
measuring crispiness, hardness like variables of the complex shaped objects like
potato chips. The major problem with reproducibility of the results obtained from
texture analysis of potato chips is due to the shape irregularity of the chips. Therefore
a method must be devised to ensure consistency in the results. In last few decades very
few research papers have been published correlating various qualitative properties of
potato chips to textural properties of the chips. In this paper they are being listed in a
chronological order as published in different Journals.
A very basic level of rupture testing of potato chips for textural analysis using
a ball probe was also done by (C.Granda, R.Moreira 2005) in her thesis Acrylamide
content of potato chips. The work carried out was similar to other cylindrical probe of
0.203 cm in diameter and a cylindrical base with an outside diameter of 25.5 cm and a
hole of 19 mm was used in a bite compression test with a probe velocity of 10 mm/s.
Kawas (2000) used a similar procedure to measure texture of tortilla chips: a ¼ inch
ball probe traveled at a downward velocity of 0.1 mm/s until it broke the sample; the
sample was located on an 18 mm diameter hollow cylindrical base. Fracturability was
determined as the first peak of the force vs. distance curve. Garayo (2001) used a
rupture test on fried potato chips. He used the same approach used by Kawas (2000);
hardness of the chips was determined by finding the maximum force at compression
(Steffe, 1996).
5
One of the most important researches was carried out named Mechanical
properties of fried crust (Isabel Lima, R. Paul Singh ; 2001) at UC Davis; used both
ball probe for the puncture testing of potato chips and guillotine type three point
bending probe for snapping test. In this paper restructured potato model system was
fried in canola oil for 5, 10, or 15 min at 170, 180, or 190oC and tested in a Dynamic
Mechanical Analyzer. Selected mechanical properties were measured using puncture
and three-point bending cells. Forces involved in puncture were a combination of
tension, compression, and shear, while the three-point bend test studied the crust
flexural properties. Therefore evaluating, the effect of frying time and multiple
temperatures on the textural properties of the potato chips.
In other researches various quality attributes such as effect of time and storage
condition on Rheological properties of Masa for corn tortillas( Rosana Moreira, Elena
Castell, Bootsrapa Limanond 1999) conducted test for evaluating the textural
properties of corn masa. A similar research paper named Textural properties of Baked
tortilla chips (Ahmed Kayacier, Rakesh Singh, 1999) was conducted to analyze
changes in texture with multiple baking temperatures). The conclusion of this paper
said that the force required to break the sample was higher for samples with higher
work values.
Three point bending using Instron punch was utilized for comparing the textural
properties of potato chips by assay of changes in moisture content and sorption/
desorption, Thickness of potato chips, position of slice within potato tuber, frying
time, temperature and potato specific gravity effects were deeply studied in the paper
6
named reproducible texture analysis of potato chips (S. Segnini, P. Dejmek and R
Oste, 1999).
Materials and Methods
Sample Procurement
The sample used was Frito Lays® brand classic potato chips procured at a rate
of $3.50 per bag cost. These were the biggest possible bags of basic potato chips
available by the company. The biggest bag was utilized due to the fact that more
number of chips had shape irregularity. Only the samples with even and desired shape
were presorted for the test to minimize variability in the results. The nominal thickness
of the chips was around 1.6 mm. During every change in measurement or other day of
test a new bag of potato chips was utilized so as to minimize variability in results due
to moisture absorption. The chips were claimed to have no trans fats and fried in 100%
sunflower oil. The seasoning on the chips was salt as claimed by company.
Sample Preparation
Once the potato chips bag was opened the chips were sorted out according to the
shape and size. The check was done for any irregularities and to utilize the chips with
very less blisters in the surface due to frying operation. Normally any brokens and
cracked or fissured chips were discarded. The sample was ensured to have a straighter
shape rather than a curved one. Also the thickness was checked to match the nominal
thickness of other samples. This was done to provide consistency in the results and
minimize the variability.
7
Instrument and its setup
The apparatus utilized was:

TA-XT2i Texture Analyzer
Texture Technologies Corp, NY
This equipment basically detects the force
applied on its arm when a probe is used to
compress/extend or rupture a product. In
this project it was the main unit for
determining the textural properties of
potato chips under various settings.
Fig 1.TA-XT2i Equipment Source:
(Texture Tech. Inc)
The main methodology was to use two different settings in the primary calculation by
using the following probes:

TA- 8 1/4“ diameter ball, stainless steel
This probe was previously utilized in various other
researches of textural analysis of various materials.
It has been used for rupture test in which a ball
shaped dong ruptures the potato chips surface by
compressive force placed over a cylindrical cavity.
One of similar analysis is presented in the literature
review (C. Granda, R. Moreira 2005)
Fig 2.The Ball probe setup
Source(Texture tech Inc.).
8

TA-7K Guillotine block (for TA-90) for
snapping test.
This probe was used for snapping test to
determine crispiness and hardness of the chips
through rupture test. Later on it was altered to
emulate the three point bending probe. This was
done by changing the gap width of the base.
Fig 3. The Guillotine
probe setup.
Source(Texture Tech.
Inc.)
The instrument is setup according to the setup in Thesis report of Acrylamide
in potato chips (Granda 2005) for the setup of ball probe for texture analysis. The
guillotine probe was primarily utilized for normal rupturing of the sample. Later on
due to inconsistency of the results and by study of more methods guillotine blade was
emulated as three point bending test to snap the potato chips. This led to better results
with low variability and high consistency. The setting of ball probe was similar to
others, in which a spherical probe of ¼ inch in diameter and a cylindrical base with a
hole of 19 mm was used in a rupture test with a probe velocity of 10 mm/sec with a
total distance of 18 mm for the arm and return distance of 4mm for the ball probe.
While similar method parameters were utilized for guillotine probe except the total
distance traveled by the probe was 15 mm with same return distance due to bigger size
of the probe.
9
The potato chips were kept in a manner such that a plain uniform cross-section
part of the chips surface was facing the probe without any blisters. This was ensured
for every sample chips tested. There were 10 replications made for each type of the
probe setting.
Later on the guillotine probe was adjusted in a manner to maximize the gap of
the base plate to emulate the three point bend snap test. The formula used for this was
taken from (Bruns and Bourne, 1975):
[F = (2/3) σ b h2/ L]
(1)
The flexural strength of the potato chips is the resistance it offers to the probe
on bending. The maximum stress caused by bending is calculated by following
formula:
[σ = 3 F L/b d2]
(2)
Where, F is snapping force or the maximum force at yield or break (N), σ is
the flexural strength (N/m2), b is the width of the sample, h is the height of the sample
and L is the length between two supports.
10
d
b
F
h
rectangular
3
D
circular
3
E = Fa /(4dbh )
3
3
E = 4Fa /(3dpD )
Fig.4 Calculation of Young modulus for various shaped object in Three point bending
test.( Texture profile analysis lecture slide; BAEN 620,spring 2007)
The three point bending is basically the method developed for evaluation of
crispiness and hardness of a potato chip. The length between two supports was set by
trial and error method to find out the minimal difference in the force values of two
replications. The trial and error method was practiced because of the lack of
calculating method of flexural strength of potato chips in the given time. Therefore
this work was recommended in the future researches in the conclusion of the report.
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Results and Discussion
The results were interpreted through the average of all the force and distance
obtained in the experiment and the plots were obtained from the test. Further on the
statistical analysis was done to determine the variance and the mean force values. The
results with the ball probe had very high variability in the results. Similarly difference
between the guillotine probe with normal gap and changed gap width were having a
difference in its values of force. While the guillotine probe when emulated as a three
point bending snap test equipment resulted in least variability of results. Therefore the
three point bend test was the best testing method available for the texture analysis of
the potato chips.
The plots of the three different testing conditions are shown in the next page
which is average of 10 replications by using ball probe, Guillotine probe with no
alterations and Guillotine probe with changed gap width of the base plate to emulate
the three point bending system. A statistical analysis was done with the help of SPSS
software to determine the mean, variance and distribution of the force with distance to
find out the best method with higher consistency in results. The statistical analysis was
cross checked with the graphs obtained by the results in force and distance by texture
analysis of potato chips. This was to verify and quantify the variability in the results
obtained through by checking the variance with the graphs. A Table was copied from
the SPSS results to show the variability and distribution of force in the whole testing
procedure as Table 1 on the next page. It was noticed that the mean value had a high
difference in the values.
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Table 1: Descriptive analysis through statistical method by SPSS software
Type of Probe
setup
10 Replications Ball Probe
Statistic
20.7503
Mean
95% Confidence
Interval for Mean
Lower Bound
Upper Bound
10
Guillotine probe
with altered to
Replications emulate three
point bending
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
Mean
95% Confidence
Interval for Mean
Lower Bound
Upper Bound
10
Guillotine Probe
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
Mean
Std. Error
1.75611
17.3046
24.1961
10.4711
.2000
3370.725
58.05794
-6.80
298.30
305.10
1.30
2.970
8.166
.074
.148
4.0670
.21775
3.6394
4.4947
3.3911
1.2313
29.114
5.39571
-1.13
22.81
23.94
4.44
1.872
2.540
.099
.197
2.0907
.41270
Replications
95% Confidence
Interval for Mean
Lower Bound
Upper Bound
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
1.2775
2.9039
.8162
.3131
38.833
6.23158
-.72
38.01
38.74
.05
3.971
15.538
.161
.321
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Average Force vs. Distance Graph for Ball probe
350
300
Average Force (N)
250
200
150
100
50
0
0
2
4
6
8
10
12
14
16
18
20
-50
Average Distance (mm)
In the graph above between average force and distance we can notice the
multiple peaks formed by the forces acquired from different replications. This resulted
in very high inconsistency of the results. Therefore assumption was made that the
results cannot be reproduced with higher accuracy. As per the industrial level
measurement criteria the results obtained must be reproducible and comparable with
other results in such a manner that the value of force show least variability. Therefore
in context of Frito-Lays® like chips making company this method will be highly
unreliable. In the statistical analysis the variance in the values as seen in table 1 is very
high in comparison to the variance in the results of the guillotine probe. Thus dually
proving the inconsistency of results obtained from the rupture test conducted through
ball probe.
14
Average Force vs. Distance Graph for Guillotine Probe
25
20
Average Force(N)
15
10
5
0
-15
-10
-5
0
5
10
15
-5
Avergage Distance (mm)
In the above graph the average values of force are very much consistent and do
not show as high variability as the ball probe results. This shows that the results
obtained have higher reproducibility between multiple numbers of samples. Similarly
in the statistical results the variability in the results is very much lower than that
obtained from the ball probe. Thus guillotine blade may serve better in obtaining
replicable and consistent results for industrial use.
15
Average Force vs. Distance graph for Guillotine probe
40
35
30
Force(N)
25
20
15
10
5
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
-5
Distance(mm)
In the graph above the there are very less number of peaks for fracturability
and crispiness making it the best result overall. In the statistical analysis the variance
in the values is also minimum. Therefore we can say that; when the guillotine probe
was emulated to do the three-point bending test the results were highly consistent.
Therefore this method provided very good reproducibility for the potato chips.
Normally most of the literature also covers the three point bend test of snapability for
various food products to check crispiness and other properties. Thus, making it the
most prospective method for use at industrial level to get consistency in results.
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Conclusion
The whole work carried out for devising of best reproducible method was done
without any idea of methods used at industrial level for texture analysis of potato
chips. During the work it was discovered that the certain way of using the guillotine
blade by changing the gap between the base-plate would provide consistent results.
Later on to be found as the emulation of Three-point bend rig generally used for
checking crispness, fracturability, hardness for industrial use. Therefore it can be said
assuredly that the method used by Frito-Lays® involving guillotine like blade probe is
the typical three point bending probe setup. This setup was enquired for procurement
from Food Technology Corporation as Part number 423-027 and was priced around
$ 975 with 10% discount on academic purchases.
Future Recommendations
The future work must be carried out for:
Procurement of correct three-point bend apparatus to get better results.

The flexural strength of the potato chips must be calculated by the equation 1
and 2 for further in-depth analysis of the textural properties of potato chips.
17