Assay of reproducible methods for crispiness evaluation of potato by pptfiles


									Assay of reproducible methods for crispiness
         evaluation of potato chips


                 Akhilesh Pandey


                   Guidance of

                 Dr. Elena Castell

                Dr. Rosana Moreira


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.


        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

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


        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.

                                  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).

       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

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.

                                      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
                                                                   Fig 2.The Ball probe setup
    review (C. Granda, R. Moreira 2005)
                                                                    Source(Texture tech Inc.).

     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.

           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.

       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


                           [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.


                                 h           F                D

                      rectangular                         circular
                            3         3                       3        3
                   E = Fa /(4dbh )                 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.

                                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.

      Table 1: Descriptive analysis through statistical method by SPSS software

               Type of Probe
                  setup                                                  Statistic   Std. Error
10 Replications Ball Probe                         Mean                  20.7503      1.75611
                                    95% Confidence        Lower Bound
                                   Interval for Mean
                                                           Upper Bound
                                             5% Trimmed Mean              10.4711
                                                   Median                  .2000
                                                  Variance               3370.725
                                                Std. Deviation           58.05794
                                                  Minimum                   -6.80
                                                  Maximum                  298.30
                                                    Range                  305.10
                                             Interquartile Range             1.30
                                                  Skewness                 2.970       .074
                                                   Kurtosis                8.166       .148
     10       Guillotine probe                       Mean
               with altered to
                                                                          4.0670      .21775
 Replications emulate three
               point bending
                                    95% Confidence        Lower Bound
                                   Interval for Mean
                                                           Upper Bound
                                             5% Trimmed Mean              3.3911
                                                   Median                 1.2313
                                                  Variance                29.114
                                                Std. Deviation           5.39571
                                                  Minimum                  -1.13
                                                  Maximum                 22.81
                                                    Range                 23.94
                                             Interquartile Range            4.44
                                                  Skewness                1.872        .099
                                                   Kurtosis               2.540        .197
     10         Guillotine Probe                     Mean
                                                                          2.0907      .41270
                                    95% Confidence        Lower Bound
                                   Interval for Mean
                                                           Upper Bound
                                             5% Trimmed Mean              .8162
                                                   Median                 .3131
                                                  Variance                38.833
                                                Std. Deviation           6.23158
                                                  Minimum                  -.72
                                                  Maximum                 38.01
                                                    Range                 38.74
                                             Interquartile Range            .05
                                                  Skewness                3.971        .161
                                                   Kurtosis               15.538       .321

                                                Average Force vs. Distance Graph for Ball probe




  Average Force (N)




                            0        2      4        6         8            10             12   14   16   18   20

                                                                   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.

                                           Average Force vs. Distance Graph for Guillotine Probe



  Average Force(N)



                     -15             -10            -5                   0              5          10    15

                                                             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.

                                        Average Force vs. Distance graph for Guillotine probe









                  0        0.5      1         1.5        2         2.5         3        3.5     4   4.5    5


                      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.


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.

roperties of potato chips.


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