Characteristics of physical properties of genetically modified potatoes : Mechanical properties of tubers

Int. Agrophysics, 2004, 18, 269-276
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Characteristics of physical properties of genetically modified potatoes.
II. Mechanical properties of tubers
J. Sadowska1*, J. Vacek2, M.C. Palacios3, and J. Fornal1
1 Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Tuwima 10, 10-747 Olsztyn, Poland
2 Potato Research Institute, 580-01 Havlickùv Brod, Czech Republic
3 Instituto de Agroquimica y Technologia de Alimentos (CSIC), Burjassot, Valencia, Spain
Received November 24, 2004; accepted January 8, 2004
A b s t r a c t. An investigation into the influence of genetic
parameters and conditions of determination are, however,
modification on potato tubers should include physical characte-
not commonly accepted. Various methods, such as uniaxial
ristics affecting their technological usability. Potato tubers of 15
compression (Thybo and van den Berg, 2002, Blahovec,
clones of cultivar Irga transformed with viral genome sequences in
2001), tensile test (Verlinden et al., 2000), penetration tests
order to improve their resistance to a necrotic strain of potato virus
(Anzaldua-Morales et al., 1992), puncture test (Ranganna et
Y (PVYN) were examined. The mechanical properties of potato
tubers were determined using a compression test and expressed by
al., 1998) and numerous variants of small deformation tests
fracture stress, F(kPa); fracture strain, D (%); and Young modulus,
(Laza et al., 2001) have been proposed for the evaluation of
E (kPa).
the mechanical/textural parameters of raw and treated potato
The variability of F, D, and E for particular clones measured
tubers.
by standard deviations was extremely high. However, the influence
During harvest and transport, potato tubers are exposed
of the modification type and breeding conditions appeared to be
to impact damage which ranges from internal black spot
statistically significant but irregular during the three-year period of
bruising through shatter bruising and finally tissue cracking
cultivation. While the effect of cultivation year was unmistakable,
(Mathew and Hyde, 1997). The extent of damage can be
the order of F, D, and E values for the particular clones was not
constant in the successive years. Results of detailed statistical
primarily attributed to physiological changes which affect
analysis (variance and discrimination analyses) confirmed also
structural components (Thybo et al., 1998), tissue turgor and
a lack of stable tendencies in average values of the mechanical
temperature affecting failure properties of tubers (Alvarez
parameters for both groups and subgroups of clones representing
and Canet, 2002; Bajema et al., 1998). Thus, the recognition
the same modification model. No repeatable and statistically
of the mechanical characteristics of potato tubers permits
significant differences in F, D, and E were found, neither for the
improvement of harvesting and handling equipment and
genetically modified nor for the control tubers. It can be concluded
operations aimed at reducing economic losses. Mechanical
that the mechanical properties of potato tubers of cultivar Irga were
properties of tubers (as a measure of texture), beside the size
not permanently affected by the type of genetic modification used.
K e y w o r d s: genetically modified potatoes, tuber,
and shape, are important factors of cultivar classification for
mechanical properties
such technological destinations as chips, French fry strips,
and cooked potato (Dale and Mackay, 1994). The
INTRODUCTION
mechanical/rheological parameters of tubers obtained using
various instrumental methods mentioned above have also
The mechanical properties and rheological behaviour of
been widely studied for development of algorithm of
raw potato tubers have been widely examined for both
instrumental methods for the prediction of sensory attributes
scientific and technological purposes. The standard
(Laza et al., 2001; Solomon and Jindal, 2003; Thybo and van
den Berg, 2002; Truong et al., 1997).
*Corresponding author’s e-mail: jaga@pan.olsztyn.pl
**This work was partly supported by the EU Centre of Excellence
© 2004 Institute of Agrophysics, Polish Academy of Sciences
CENEXFOOD (Project CA-CT-2000-70017).

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270
J. SADOWSKA et al.
On the other hand, mathematical modelling of the
et al., 1992), six tubers of similar size and weight were
mechanical properties of turgid plant tissue could enable an
selected from 1 kg sample. From each of the tubers, 3
understanding of why different fruits and vegetables have
cylindrical samples of 16 mm diameter were cut using a cork
different mechanical properties and how these properties
borer perpendicularly to the tuber length axis. Three pieces
can be changed (Blahovec, 2001; Hepworth, 2000).
of 10 mm height were cut, in the central region and close to
Then, the mechanical properties of potato tubers play an
each end of each sample. Such preparation of the samples,
important role in their physical characteristics and the
with the diameter-to-height proportion proper for uniaxial
investigation into the effect of genetic modification on
compression from all the morphological parts of tubers of
potatoes against insect pests must contain also the
different microstructure, guarantied the obtainment of
mechanical characteristics of tubers.
representative data.
The compression tests were made using the plate/anvil
MATERIALS AND METHODS
device of Instron 1011. The crosshead travel speed was 20
mm/min. The mechanical characteristics was expressed by
Material
fracture stress F, kPa, fracture strain D, %, and Young modu-
lus measured in the elastic region of compression, E, kPa.
Potato tubers of cultivar Irga were transformed with
Dry matter content of tubers was determined according
viral genome sequences in order to improve their resistance
to AOAC method No. 984.25.
to a necrotic strain of potato virus Y (PVYN). The transgenic
The statistical analysis of results was carried out with
clones were produced at the Institute of Biochemistry and
the Statistica v. 5 Software (General Convention and
Biophysics, Polish Academy of Sciences, Warsaw. The
Statistics, StatSoft, USA, 1995).
genetically modified (GM) potatoes were bred and collected
at the Plant Breeding and Acclimatization Institute,
RESULTS
M³ochów Research Centre (for details, see Sadowska et al.,
2004). Samples of all the examined potatoes were stored
Mean dry matter content (DM) of modified potatoes
under the same conditions and tested at the same time after
ranged from 19.72 to 23.02%, from 19.63 to 23.23% and
harvest.
from 20.69 to 24.38% for tubers from 2000, 2001 and 2002,
respectively (Fig. 1). In 2000 and 2001, the values of dry
Methods
matter content of tubers of the control cultivar Irga and Irga
Compression test
wt. were lower, and in 2002 almost the same as those of GM
potatoes. The lack of correlation between DM and fracture
For the elimination of possible effect of tuber size on the
stress and strain, and weak but statistically significant
mechanical characteristics of potatoes (Anzaldua-Morales
correlation between DM and elasticity modulus were found
30
Year 2000
Year 2001
Year 2002
25
] 20
[
%
t
n
t
e
n
o
c 15
r
tte
a
m
r
y 10
D
5
0
F
L
Q
T
A
Q
P
R
Y
ga
t.
R1
R1
.16
.48
.50
.27
.31
w
R1
R1
R2
ADA R2
R2
R2
R2
Ir
R1
R1
R1
R2
R2
ga
R2
NT
NT
NT
NT
NT
Ir
Fig. 1. Content of dry matter for GM potato tubers.

---

PHYSICAL PROPERTIES OF GENETICALLY MODIFIED POTATOES. PART II.
271
(R = 0.4932 at p <0.05). Though elasticity modulus is known
and R2ADA (1.40 and 1.34 MPa), R1L and R1Q (55.6 and
to be closely connected with potato tissue turgor, Alvarez
56.3%), and NTR1.16 and R1L (5.64 and 5.29 MPa),
and Canet (2002) reported quite a low total decrease of the
respectively. The lowest values of F, D, and E were deter-
Young modulus during three months. These relationships
mined for NTR1.50 and R2Y (1.13 MPa for both clones),
confirmed that irregular changes of DM were almost always
NTR2.27 and NTR2.31 (44.7 and 45.3%), and R2Y and R2Q
too small to be effective in influencing the mechanical
(4.62 and 4.77 MPa), respectively (Figs 2-4). Yet, the respecti-
properties of tubers.
ve values of the above-mentioned parameters for samples of
In 2000, the highest values of fracture stress, F, fracture
the control group ie Irga and Irga w.t. were: for F - 1.17, 1.12
strain, D, and elasticity modulus, E, were reported for NTR1.16
MPa, for D - 45.2 and 43%, and 4.66 and 4.65 MPa. Thus,
1,8
Year 2000
Year 2001
Year 2002
1,6
1,4
1,2
a
]
P
[
M
1
s
t
r
ess
0,8
r
e
u
r
act 0,6
F
0,4
0,2
0
F
L
Q
T
A
Q
P
R
Y
R1
R1
R1
R1
R2
wt.
ADA R2
R2
R2
R2
.16 .48
.50
.27 .31
Irga
R2
R1
R1
R1
R2
R2
NT
NT
NT
NT
NT
Irga
Fig. 2. Fracture stress for GM potato tubers.
70
Year 2000
Year 2001
Year 2002
60
50
] 40
[
%
i
n
r
a
st 30
r
e
u
r
act
F 20
10
0
F
L
Q
T
A
Q
P
R
Y
ga
t.
R1
R1
.16
.48
.50
.27
.31
w
R1
R1
R2
ADA R2
R2
R2
R2
Ir
R1
R1
R1
R2
R2
ga
R2
NT
NT
NT
NT
NT
Ir
Fig. 3. Fracture strain for GM potato tubers.

---

272
J. SADOWSKA et al.
7
Year 2000
Year 2001
Year 2002
6
] 5
a
P
[
M
4
odulus
m
i
t
y 3
t
i
c
s
l
a
E 2
1
0
F
L
Q
T
A
Q
P
R
Y
ga
t.
R1
R1
.16
.48
.50
.27
.31
w
R1
R1
R2
ADA R2
R2
R2
R2
Ir
R1
R1
R1
R2
R2
ga
R2
NT
NT
NT
NT
NT
Ir
Fig. 4. Elasticity modulus of GM potato tubers.
F and E values of the control tubers were clearly lower than
samples of the control group was noted, which was caused
those for modified clones, while D values were in low range of
by different manner of seed material preparation.
all presented data. It could be probably one of few exceptions
The data presented shows that the changes of
in which lower DM content resulted in lower mechanical
mechanical parameters for particular clones were found to
parameters (average DM were 19.5 and 21.5% for control and
be irregular during the three years of cultivation. The
modified tubers, respectively).
mechanical properties of tubers of the control group did not
In 2001, the highest values of fracture and strain, and
remain at a constant level, either. In 2000, the mechanical
elasticity modulus were found for R2R and NTR2.27 (1.42
properties of potatoes of the control group were lower than
for both clones), R1L and NTR1.16 and R1L (45.1 and
those of the modified clones, but in 2001 and 2002 the
45.8%), and NTR2.27 and R2Q (5.25 and 5.31 MPa),
mechanical characteristics of the control tubers were similar
respectively. The lowest values of those parameters were
to the characteristics of most of the clones. A confirmed high
determined for R2ADA and R2R (1.05 MPa for both
variability of mechanical parameters within a clone was
clones), R2R and R2Y (37.8 and 38.7%), and R2Y and
found. Thybo and van den Berg (2002) also pointed out that
R2ADA (3.8 and 3.89 MPa), respectively (Figs 2-4). In that
samples of potatoes were characterized by large variation
year, the respective values of mechanical parameters for Irga
between replications for particular cultivars and even for
and Irga w.t. were 1.21 and 1.25 MPa, 40.8 and 38.1%, and
tubers of the same cultivar. However, the obtained average
4.81 and 4.64 MPa. The F and E values for the control
data of fracture stress and strain were similar or slightly
samples were similar to mean values for Is and IIs groups of
lower than data for non-treated tubers of other cultivars
modified clones, while D values were closer rather to D
presented by Maté et al., (1998) and Alvarez and Canet
values of Ias and IIas groups.
(2000). Alvarez and Canet (2000) found also that storage
In 2002, the highest values of fracture and strain, and
time did not affect significantly fracture force and energy
elasticity modulus were found for R2P and NTR2.31 (1.4 for
from the compression test of potato tubers stored at 4oC and
both clones), R2P and NTR1.16 (44.1 and 44.6%), and R2A
85% relative humidity for even 140 days.
and R2P (5.3 and 5.35 MPa), respectively. The lowest
Despite the low differences between the maximum and
values of those parameters were determined for R2Q and
minimum mean values for the examined clones at high
NTR2.27 (1.10 and 1.14 MPa), R2A and R2R (38.8 and
values of standard deviations, the results of multifactorial
39.3%), and R2Q and NTR2.27 (4.28 and 4.36 MPa),
variance analysis, Manova, showed statistically significant
respectively (Figs 2-4). The respective values for Irga and
(at p < 0.05) influence of both the modification type and the
Irga w.t. were 1.07 and 1.34 MPa, 40.4 and 42.2%, and 4.26
year of cultivation on all the examined parameters of tuber
and 5.5 MPa. Only in that year a statistically significant
mechanical properties. Similar results of Manova (except
difference between the mechanical characteristics of both
for stress) were obtained for data from the two first years in

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PHYSICAL PROPERTIES OF GENETICALLY MODIFIED POTATOES. PART II.
273
which seed samples were prepared identically. Interactions
did not affect mechanical properties of potato tubers, although
of factors were always statistically significant, which means
it was impossible to select clones of stable distinguished
that the influence of the first factor was different at different
constant mechanical characteristics. Thus, variance analysis in
levels of the second factor, and for optimal conclusion
subgroups corresponding to the modification type was
particular results and not means of different levels should be
supplemented by Duncan multiple range test (Table 1). In
compared (Volk, 1965).
many cases, differences in the mechanical parameters of clone
Then, the influence of modification type was estimated
tubers in a subgroup were not significant. In other cases, the
for each year separately, using the Anova variance analysis.
order of clones in uniform groups of Duncan’s test was not
The results obtained again confirmed statistically significant
repeated in particular years. Such an arrangement of results of
differences for all the determined mechanical parameters at
this analysis suggested the effect of climatic and breeding
p<0.05 for each year. Also, typical correlation between
conditions to be stronger than the modification influence.
fracture stress and elasticity modulus (correlation coefficients
The purpose of the next step of calculation was to look
were 0.9283, 0.9276 and 0.9354 for 2000, 2001 and 2002
for stable tendencies in the mechanical properties for groups
years, respectively) could be accepted as the next confirmation
and subgroups of clones representing the same modification
of different mechanical characteristics of the examined clones,
model. Mean values of the mechanical parameters for
despite significant variability of collected data. Yet, the
groups and subgroups are presented in Tables 1 and 2. Mean
expected correlation between fracture stress and strain was
values of failure stress and elasticity modulus for Group II
statistically significant only for tubers from 2001. Bajema et al.
have always appeared, except for Irga w.t. in 2002, to be
(1998) found that changes in strain rate did not affect failure
higher than those for Groups I and the control (Table 2). It
stress, but failure strain was reduced dramatically with
has been also observed that tubers in both subgroups of
increasing strain rate. Then, they concluded that cell rupture
antisense position ie Ias and IIas, were more mechanically
pressure was not a function of strain rate and reduction of
resistant than tubers of the sense position subgroups ie Is and
fracture strain suggested different fracture mechanisms
IIs, respectively (Table 3). For statistical estimation of
compared with the standard viscoelastic material. Such
differences between the mentioned groups, discriminant
positive answers in Anova analysis of data from each year did
analysis was performed. However, the results of statistical
not allow a definite conclusion that genetic modifications used
analysis did not allow distinguishing subgroups of
T a b l e 1. Summary of results of Anova with Duncan’s multiple range test for evaluation of differences in mechanical parameters of clone
tubers in modification subgroups
Year
Group
2000
2001
2002
Fracture stress
1s
not significant
not significant
not significant
1as
(R2Y,R2A,R2Q) (R2P, R2R, R2ADA)* (R2Y,R2ADA,R2R) (R2P, R2Q, R2A) (R2A,R2R,R2Q)(R2ADA,R2Y,R2P)
2s
(NTR1.50, NTR.48)(NTR1.16)
not significant
not significant
2as
not significant
not significant
not significant
Control
not significant
not significant
(Irga w.t.) (Irga)
Fracture strain
1s
not significant
(R1F,R1Q,R1T)(R1L)
not significant
1as
(R2Y) (R2RR2Q) (R2A,R2P,R2ADA)
(R2R,R2Y,R2ADA)(R2Q,R2R,R2A)
(R2A,R2R,R2Q)(R2ADA,R2Y,R2P)
2s
(NTR1.50) (NTR.48,NTR1.16)
(NTR1.50)(NTR1.48,NTR1.16)
not significant
2as
not significant
not significant
not significant
Control
not significant
not significant
Elasticity modulus
1s
not significant
not significant
not significant
1as
(R2Y,R2Q,R2A)(R2P,R2ADA,R2R)
(R2Y,R2ADA,R2R)(R2Q,R2A,R2P)
not significant
2s
(NTR1.50) (NTR.48,NTR1.16)
not significant
not significant
2as
not significant
(Irga w.t.) (Irga)
not significant
Control
not significant
not significant
(Irga w.t.) (Irga)
*The uniform groups of clones are in brackets.

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274
J. SADOWSKA et al.
T a b l e 2. Characteristics of tuber mechanical resistance for modification groups
Failure stress
Failure strain
Elasticity modulus
(%)
(MPa)
Group
Year
(MPa)
Mean
St. dev.
Mean
St. dev.
Mean
St. dev.
I
2000
1.24
0.184
48.8
4.64
5.04
0.707
2001
1.20
0.221
42.1
6.38
4.61
0.823
2002
1.23
0.194
41.8
3.64
4.90
0.861
II
2000
1.25
0.210
45.7
4.94
5.04
0.925
2001
1.31
0.193
42.2
4.41
4.86
0.833
2002
1.28
0.176
42.8
3.79
5.02
0.763
Irga
2000
1.17
0.165
45.2
4.42
4.66
0.671
2001
1.21
0.176
41.2
3.32
4.71
0.725
2002
1.07
0.139
40.4
3.09
4.27
0.614
Irga w.t.
2000
1.12
0.175
43.0
5.09
4.65
0.804
2001
1.25
0.153
38.1
2.28
4.64
0.450
2002
1.34
0.159
42.2
1.42
5.49
0.805
T a b l e 3. Characteristics of tuber mechanical resistance for modification subgroups
Fracture stress
Fracture strain
Elasticity modulus
(%)
(MPa)
Group
Year
(MPa)
Mean
St. dev.
Mean
St. dev.
Mean
St. dev.
Is
2000
1.23
0.198
45.3
3.59
5.11
0.742
2001
1.20
0.199
44.2
7.46
4.60
0.761
2002
1.21
0.190
42.1
3.62
4.70
0.796
Ias
2000
1.25
0.174
51.1
4.54
5.00
0.682
2001
1.21
0.238
40.4
4.84
4.61
0.877
2002
1.24
0.199
41.6
3.67
5.02
0.887
IIs
2000
1.24
0.217
46.1
5.35
5.06
0.972
2001
1.25
0.186
42.6
4.17
4.66
0.856
2002
1.30
0.146
43.2
4.25
5.16
0.603
Iias
2000
1.26
0.202
44.9
4.17
5.02
0.857
2001
1.38
0.179
41.8
4.72
5.08
0.764
2002
1.24
0.228
41.9
2.52
4.73
0.999
statistically different mechanical properties (Fig. 5). Wilks
genetic modifications. Independently of the cultivation
coefficients ie the measure of the accuracy of group
year, the percentage of proper classification of cases in all
recognition, which ranges from 0 (ideal group discrimina-
the accepted subgroups was always very low (Table 4) and
tion) to 1 (lack of group discrimination), were 0.4318,
data for the control group were even classified as one group
0.7698 and 0.8575 for 2000, 2001 and 2002, respectively,
for the year 2000.
and confirmed non-sharp separation of groups of different

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PHYSICAL PROPERTIES OF GENETICALLY MODIFIED POTATOES. PART II.
275
3,5
3,0
2,5
2,0
1,5
Year 2000
2
1,0
0,5
Wilks ? = 0.4318
Root
0,0
Proper classification
-0,5
I/S
of cases – 68 %
-1,0
I/AS
-1,5
II/S
-2,0
II/AS
-2,5
Control
-3,0
-4
-3
-2
-1
0
1
2
3
4
5
Root 1
4
3
2
1
Year 2001
2
0
Root
Wilks ? = 0.7698
-1
I/S
Proper classification
I/AS
of cases – 35 %
-2
II/S
-3
II/AS
Control
-4
-4
-3
-2
-1
0
1
2
3
4
5
6
Root 1
5
I/S
4
I/AS
3
II/S
II/AS
2
2
Year 2002
Control
1
Root
0
Wilks ? = 0.8575
Proper classification
-1
of cases – 42 %
-2
-3
-4
-3
-2
-1
0
1
2
3
Root 1
Fig. 5. Classification of modification type subgroups in successive year of cultivation.
CONCLUSIONS
CONCLUSIONS

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276
J. SADOWSKA et al.
T a b l e 4. Proper classification of cases (%) in discriminant analysis used for the estimation of variability of mechanical resistance of the
examined GM clones
Year
Group
2000
2001
2002
Is
64
39
24
Ias
70
65
82
IIs
33
0
10
IIas
17
32
0
Control
23
0
0
Mean
51
35
42
CONCLUSIONS
General Convention and Statistics, 1995. In: Statistica for
Windows, vol. I-III, 2nd Edition, (Ed. Statsoft Inc.), Tulsa,
1. The variability of all the parameters measured ie
USA.
fracture stress and strain, and elasticity modulus for
Hepworth D.G. and Bruce D.M., 2000. Measuring of deformation
particular clones was extremely high, and the influence of
of cells within piece of compressed potato tuber tissue.
modification type and breeding conditions appeared to be
Annals of Botany, 86, 287-292.
irregular during the three-year period of cultivation.
Laza M., Scanlon M.G., and Mazza G., 2001. The effect of tuber
pre-heating temperature and storage time on mechanical
2. Stable tendencies in fracture stress and strain, and
properties of potatoes. Food Res. Int., 34, 659-667.
modulus of elasticity for groups and subgroups of clones
Maté J.I., Quartaert C., Meerdink D., and van't Riet K., 1998.
representing the same modification model were not
Effect of blanching on structural quality of dried potato
confirmed either.
slices. J. Agric. Food Chem., 46, 676-681.
3. Mechanical properties expressed by fracture stress
Mathew R. and Hyde G.M., 1997. Potato impact damage
and strain, and elasticity modulus of potato tubers of cultivar
tresholds. Transactions of the ASAE, 40, 705-709.
Irga were not permanently affected by the type of genetic
Ranganna B., Raghavan G.S.V., and Kushalappa A.C., 1998.
modification used.
Hot water dipping to enhance storability of potatoes.
Postharvest Biol. Techn., 13, 215-223.
Sadowska J., Fornal J., Vacek J., Jeliñski T., and Flis B., 2004.
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