Effective Ways of Decreasing Acrylamide Content in Potato Crisps during Processing

Abstract

The aim of this work was to examine the effect of blanching or soaking in different acid solutions on the acrylamide content in potato crisps. Furthermore, the effects of a shorter frying time and a lower frying temperature combined with a postdrying were investigated. Soaking or blanching of potato slices in acidic solutions decreased the pH of potato juice and increased the extraction of amino acids and sugars. Potato crisps obtained after such pretreatments were characterized by lower acrylamide content. The most effective extraction of free amino acids and sugars as well as the largest decrease of acrylamide content (90%) in crisps was obtained when potato slices were soaked in acetic acid solution for 60 min at 20 degrees C. Shorter frying time followed by postdrying resulted in low-moisture potato crisps. Furthermore, the postdrying treatment gave a decreases in acrylamide content of approximately 70% when potato slices were fried at 185 degrees C and approximately 80% when potato slices were fried at 160 degrees C. Effective ways of decreasing acrylamide content in crisps production have been found. Crisps with low acrylamide content and good sensory quality can be obtained either by blanching in acetic acid as pretreatment or by a short frying followed by postdrying.

Full text

Effective Ways of Decreasing Acrylamide Content in Potato
Crisps during Processing
AGNIESZKA KITA,*,† ERLAND BRA°THEN,‡SVEIN HALVOR KNUTSEN,‡AND
TRUDE WICKLUND§
Department of Food Storage and Technology, Faculty of Food Sciences,
Agricultural University of Wroclaw, ul. C.K. Norwida 25, 50-375 Wroclaw, Poland;
Matforsk, Norwegian Food Research Institute, Osloveien 1, N-1430 A°s, Norway; and
Department of Chemistry, Biotechnology and Food Science, Agricultural University of Norway,
P.O. Box 5036, N-1432 A°s, Norway
The aim of this work was to examine the effect of blanching or soaking in different acid solutions on
the acrylamide content in potato crisps. Furthermore, the effects of a shorter frying time and a lower
frying temperature combined with a postdrying were investigated. Soaking or blanching of potato
slices in acidic solutions decreased the pH of potato juice and increased the extraction of amino
acids and sugars. Potato crisps obtained after such pretreatments were characterized by lower
acrylamide content. The most effective extraction of free amino acids and sugars as well as the
largest decrease of acrylamide content (90%) in crisps was obtained when potato slices were soaked
in acetic acid solution for 60 min at 20 °C. Shorter frying time followed by postdrying resulted in
low-moisture potato crisps. Furthermore, the postdrying treatment gave a decreases in acrylamide
content of ∼70% when potato slices were fried at 185 °C and ∼80% when potato slices were fried
at 160 °C. Effective ways of decreasing acrylamide content in crisps production have been found.
Crisps with low acrylamide content and good sensory quality can be obtained either by blanching in
acetic acid as pretreatment or by a short frying followed by postdrying.
KEYWORDS: Acrylamide; potato crips; soaking; blanching; postdrying
INTRODUCTION
Potato crisps are one of the most popular snack products in
the world. They are also among the products that have been
reported to have the highest levels of acrylamide. Because
acrylamide is a potential carcinogen, several works have been
devoted to the study of the mechanism of its formation and the
factors influencing its formation (1-12). Still, there are few
solutions on how to decrease acrylamide creation during
processing (13,14). One of the possibilities could be decreasing
the content of acrylamide precursors: reducing sugars and
asparagine by soaking or blanching of potato slices. When water
has been used for that kind of pretreatment, the results have
been inconclusive, having no, very little, or a significant effect
on the amount of acrylamide formed during frying (13,15).It
has been suggested that lowering the pH during processing limits
acrylamide formation. Jung et al. (14) found that blanching or
soaking in a citric acid solution before baking or frying greatly
reduced acrylamide formation in corn chips and French fries.
It is possible that such treatment could also be introduced in
crisps production.
The critical point when acrylamide is formed during crisps
processing is frying. It has been shown that the most important
factors influencing acrylamide formation are temperature and
time of frying (5,8,13). It is suggested that frying temperature
should be below 175 °C and time of frying should be no longer
than necessary to obtain the right quality parameters of fried
products. However, a lower frying temperature will influence
the fat content and the moisture of crisps (16,17).The moisture
is one of the critical quality factors of potato crisps because it
affects the texture, which should be crispy not only after frying
but also during several months of storage (18). In general, the
moisture of crisps should be very low, not higher than 2%. This
is easy to obtain when crisps are fried in hot oil (usually at
185-190 °C). Decreasing the frying temperature necessitates
increasing the frying time, which could affect the acrylamide
content. To limit acrylamide formation during relatively long
frying times, we introduced a new step in crisps processings
postdrying (Figure 1).
The aim of this work was to examine the effect of blanching
or soaking in different acid solutions. In addition, the effects
of a reduced time and temperature during frying combined with
* Author to whom correspondence should be addressed (telephone +48-
71-3205239; fax +48-71-3205221; e-mail kita@wnoz.ar.wroc.pl).
†Agricultural University of Wroclaw.
‡Matforsk.
§Agricultural University of Norway.
J. Agric. Food Chem.
2004,
52,
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−
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Published on Web 10/15/2004

a postdrying step on the acrylamide content in potato crisps
were investigated.
MATERIALS AND METHODS
Chemicals. Citric acid, acetic acid (98%), NaOH, glucose, fructose,
sucrose, and mannitol were obtained from Merck (Darmstadt, Ger-
many). Acrylamide was supplied by Sigma (Deisenhoffen, Germany)
and deuterium-labeled d3-acrylamide by CIL (Cambridge Isotope
Laboratories Inc., Andover, MA). All other solvents and chemicals used
were of analytical grade.
Raw Material. For crisps production three different potato varieties
were used: Tivoli and Saturna, stored for 1-2 months at 8 °C, and
Asterix, stored at 4 °C for 1 month. All potatoes came from specialized
farms in Norway. Storage was conducted in a storage room with
monitored temperature and moisture.
Soaking or Blanching in Acid Solutions. Potato tubers of the
varieties Tivoli and Asterix were washed, peeled, and sliced (1 mm)
(slicer machine Crypto Peerless Ltd.). After a rinse in water, 500 g of
potato slices was soaked (1 min at 20 °C or 60 min at 20 °C) or
blanched (1 min at 70 °C or 3 min at 70 °C) in water, 0.05 M citric
acid solution, and 0.15 M acetic acid solution (both acid solutions
having the same concentration of acidic protons) (all experiments with
solution/potato )20:1). In addition, soaking in a 1% NaOH solution
was used. The slices were dried using paper towels, and 100 g samples
were fried for 4 min in 10 L of palm oil heated at 175 °C in an electric
frying pan (Masterline). After soaking or blanching, the pH in potato
juice and sugars and amino acids contents in freeze-dried material were
measured. In crisps, acrylamide content was measured. All experiments
were run in duplicates.
Postdrying of Potato Crisps. Potato tubers of the variety Saturna
were washed, peeled (carborundum peeler, Millert B.V., Ulft, Holland),
and sliced (1.5 mm) (slicing machine, Brown). After rinsing in water
and drying (paper towels), 100 g of potato slices was fried in a 10 L
electric frying pan (Elframo) for 3-7 min in palm oil at 160 °C and
for 2-5 min in palm oil at 185 °C. After frying, potato slices were
dried in a hot air oven (105 °C) (WTB Binder) for 30-120 min. After
frying and postdrying, the moisture and acrylamide contents were
measured. The experiment was conducted according to a central
composite design.
Sugars Analysis. The concentrations of sucrose, fructose, and
glucose in potatoes were quantified using an HPLC technique based
on that of Coop et al. (19) with a few modifications.A5gsample of
freeze-dried potato tubers was shaken with 25 mL of 50% methanol
with 1.5 mg/mL mannitol as an internal standard. Activated carbon
(2.5 g) was added, and the suspension was shaken for 100 min at room
temperature. The samples were filtered by paper filters, and the filtrate
was collected. Five milliliters of the filtrates was incubated at 35 °C
for 16 h, and precipitates were removed by centrifugation. One milliliter
of filtrate was evaporated by vacuum centrifugation (ISS110 SpeedVac,
Termo Savant) and redissolved in 1 mL of distilled water. After filtration
through Millex-HV (0.45 µm, 13 mm), the samples were analyzed by
HPLC on a Shimadzu pump (LC-10AD) controlled by Class VP
software. Twenty microliters of sample was injected with an SIL-10
autoinjector into a Varian Carbohydrate PB column (300 ×7.8 mm)
eluted with water (0.4 mL/min) at 80 °C and equipped with a refractive
detector (RID-6A). The sugars were quantified on the basis of their
areas relative to the internal standard, corrected for their individual
response factors. All samples were analyzed in duplicates.
Amino Acids Analysis. Amino acids were analyzed using an HPLC
(series 410) pump, an ISS 200 autoinjector (series 200) column oven,
an LC240 fluorescence detector, a Turbochrom version 4.1 LC terminal,
and a 900 series interface (Perkin-Elmer, Norwalk, CT) equipped with
a Hypersil ODS 4 ×4 mm precolumn and a 250 ×4 mm column,
both with a particle size of 5.0 µm (Agilent, Wilmington, DE). The
precolumn derivatization method of Bu¨tikofer and Ardo¨(20) with
O-phthaldialdehyde (OPA) and fluorenylmethyl chloroformate (FMOC)
was used, but the internal standard contained 0.5 µmol/mL L-norvalin
and 0.5 µmol/mL piperidine-4-carboxylic acid (PICA) (Merck). Extrac-
tion, deproteination, and derivatization of the amino acids were made
by dispersing1goffreeze-dried potatoes in 10 mL of 0.1 M HCl
containing the internal standards mentioned above, according to the
method of Ardo¨ and Polychroniadou (21). The amino acid standards
were delivered by Pierce (Erembodegem, Aalst, Belgium), the L-amino
acid kit was from Sigma (St. Louis, MO), OPA, FMOC, and borate
buffer were from Agilent, and sodium acetate trihydrate, tritriplex III,
and tetrahydrofuran were from Merck.
Acrylamide Analysis. Crisps were ground by a c-mill electrical
coffee grinder (Bodum, Switzerland) and stored at -20 °C until
Figure 1.
Potato crisp processing steps
s
possibilities of decreasing
acrylamide formation.
Table 1.
Sugars and Amino Acids Contents in Potato Tubers
potato variety
Tivoli
a
(mg/kg) Asterix
a
(mg/kg)
sucrose 1405 a 1440 a
glucose 270 a 2040 b
fructose 79 a 1200 b
aspargine 3168 b 2661 a
glutamine 4423 b 3115 a
a
Different letters in the same row indicate significant differences (
P
e
0.05).
Table 2.
Effect of Soaking or Blanching in Acid Solutions on pH of
Potato Juice
pH
a
soaking/
blanching
solution
soaking/
blanching
temp (
°
C)
soaking/
blanching
time (min) Tivoli Asterix
raw material 6.05 c 6.10 c
water 20 1 6.05 c 6.10 c
60 5.95 c 6.10 c
70 1 6.05 c 6.10 c
3 6.00 c 5.95 c
citric acid 20 1 4.95 b
60 4.15 a
70 1 4.60 ab
3 3.85 a
acetic acid 20 1 4.95 b 4.90 b
60 3.70 a 3.85 a
70 1 4.25 ab 4.60 ab
3 4.00 a 4.20 a
NaOH 20 1 11.40 d
60 12.00 d
a
Different letters indicate significant differences (
P
e
0.05).
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Vol. 52, No. 23, 2004 Kita et al.

analysis. Two grams of the homogenized sample was defatted with 80
mL of n-hexane. To the residue were added and mixed 20 mL of water,
200 µL of internal standard, d3-acrylamide (10 µg/mL). Acrylamide
was extracted by sonication for 30 min. The sample was purified by
adding 500 µL of Carrez I and Carrez II, respectively. The samples
was centrifuged at 4000 rpm for 10 min, and the supernatant (3 mL)
was filtered through SPE columns Isolute Multimode 300 mg (ITS,
Hengoed, U.K.) pretreated with acetonitrile (1 mL) and water (2 ×2
mL). The first portion (1 mL) was discarded, and the remaining portion
was collected and passed through a 0.22 µm syringe filter Millex-GS
(Millipore, Bedford, MA). The filtrate was frozen and stored for later
analysis. Five hundred microliters of filtrate was passed through a
centrifuge spin filter, Microcon YM-3 (Millipore) (13000 rpm, 10-20
min) until a sufficient volume had been obtained for analysis with LC-
MS-MS.
The analysis of acrylamide was done by the Norwegian Air Research
Institute (NILU), using a method similar to that of Rose´n and Hellena¨s
(7), using high-resolution time-of-flight mass spectrometry instead of
tandem mass spectrometry. Acrylamide was separated from the sample
matrix by using a high-performance liquid chromatography (HPLC)
Agilent HP-1100 system. The chromatographic separation was per-
formed with a Waters Atlantis precolumn in front of an analytical
column (3.9 mm ×20 mm, 3 µm, no. 186001313, and 3.9 ×150 mm,
3µm, no. 186001317, respectively). The injection volume was 100
µL, and the mobile phase was 100% water at a flow rate of 0.8 mL/
min up to 6 min with a subsequent column flushing (100% acetonitrile).
The detector was a Micromass LCT orthogonal time-of-flight (TOF)
mass spectrometer equipped with a Z-spray ion source operated in the
atmospheric pressure chemical ionization positive mode APCI(+). The
cone voltage was 15 V, and the monitoring ions were m/z72 and 75
for acrylamide and the internal standard, respectively, with a signal
peak width of typically 30 mDA. The limit of detection (signal-to-
noise ratio of 3) depends on instrument tuning and ion source
contamination and corresponds typically to 10-30 µg/kg acrylamide
in the sample.
Statistical Analysis. Statistical analysis of the data was performed
using Minitab, version 14. Tukey’s multiple-range tests were performed
to determine significant differences (Pe0.05) among treatment means.
RESULTS AND DISCUSSION
Soaking or Blanching in Acid Solutions. The potato
varieties used for crisps production varied in sugars and amino
acids contents (Table 1). In the first experiment only Tivoli
was used. Soaking in acid decreased the pH of the potato juice
(Table 2). However, due to the low reducing sugars contents
in Tivoli, soaking and blanching were repeated with the potato
variety Asterix. Only water and acetic acid were used in this
case because acetic acid was more effective in reducing the pH
in the first experiment.
As shown in Table 2 there were no changes in the pH of
potato juice when water was used for soaking or blanching.
Most effective in decreasing pH was soaking for1hat20°C
in acetic acid solution (pH <4). Quite satisfactory results (pH
<4.2) were also obtained after blanching for 3 min at 70 °Cin
both acids. Soaking or blanching changed the chemical com-
position of the potato slices by removing reducing sugars as
well as amino acids (Table 3). When pure water was used, the
most efficient extraction of reducing sugars was observed after
3 min of blanching at 70 °C.
Table 3.
Extraction of Asparagine and Sugars from Potato Slices: Percentages Related to the Initial Content
extraction (%)
asparagine sucrose glucose fructose
soaking/blanching
solution soaking/blanching
temp (
°
C) soaking/blanching
time (min) Tivoli Asterix Tivoli Asterix Asterix Asterix
water 20 1 6 7 14 5 2 5
60 9401617 22 17
70 1 4 16 7 8 17 15
3 11341518 35 32
citric acid 20 1 8 8
60 18 13
70 1 26 25
331 42
acetic acid 20 1 22 30 14 0 19 9
60 83 76 83 78 65 63
70 1 19223114 21 20
3 38364138 48 46
NaOH 20 1 38 78 99 99
60 89 80 99 99
Table 4.
Acrylamide Content in Potato Crisps after Soaking or
Blanching Potato Slices in Acid Solutions
acrylamide
soaking/
blanching
solution
soaking/
blanching
temp (
°
C)
soaking/
blanching
time (min) content
a
(
µ
g/kg) reduction
(%)
water 20 1 550 d 10
60 438 c 24
70 1 472 c 19
3 428 c 26
citric acid 20 1 399 b 31
60 289 b 50
70 1 438 c 24
3 293 b 49
acetic acid 20 1 329 b 43
60 60 a 90
70 1 336 b 42
3 293 b 49
a
Different letters indicate significant differences (
P
e
0.05).
Table 5.
Most Effective Ways of Decreasing Acrylamide Content in
Potato Crisps during Processing
treatment decrease
(%)
soaking in citric acid solution (60 min/20
°
C) 50
soaking in acetic acid solution (60 min/20
°
C) 90
blanching in citric acid solution (3 min/70
°
C) 49
blanching in acetic acid solution (3 min/70
°
C) 49
frying for 2 min/185
°
C and postdrying for 75 min/105
°
C69
frying for 3 min/160
°
C and postdrying for 75 min/105
°
C83
Decreasing Acrylamide Content in Potato Crisps
J. Agric. Food Chem.,
Vol. 52, No. 23, 2004 7013

Similar results have been obtained by other authors (13,15)
after soaking or blanching potato slices for different periods of
time at different temperatures.
Much more interesting results were observed when acids or
bases were used for pretreatment. The most efficient extraction
of sugars (60-80%) as well as of asparagine (80%) was
observed after soaking of potato slices in acetic acid or NaOH
solutions for 60 min at 20 °C. Citric acid reduced the content
of these components by <20%. However, in citric acid efficient
extraction of sugars and asparagine (∼40%) was obtained after
blanching for 3 min at 70 °C.
The different treatments of potato slices before frying
influenced acrylamide content in crisps (Table 4). Soaking or
blanching of potato slices in all solutions used decreased the
acrylamide content. The highest decrease (90%) was observed
after soaking of potato slices in acetic acid solution (60 min/20
°C). Furthermore, a 50% decrease of acrylamide content in
crisps was obtained after only 3 min of blanching at 70 °Cin
both acid solutions. Due to variability known to be present
between potato tubers, exact reductions are impossible to give,
but on the basis of our results the reduction should be in the
range of 40-60% in a real situation. Such results suggest that
it is possible in an easy way to decrease acrylamide creation
during crisps production.
However, a sour taste was detected with the citric and acetic
acid when slices were soaked in those solutions for 60 min (data
not presented). A slight sour taste was detected also in crisps
blanched for 1 or 3 min at 70 °C in citric acid solution, but no
detectable taste differences were observed when acetic acid was
used. This suggests that acetic acid could be a better acidulant
for the pretreatment for potato crisps.
A large decrease of acrylamide content (74%) was also
observed after soaking of potato slices in 1% NaOH solution
(results not shown), but the base solution influenced the
appearance as well as the taste and flavor of crisps, which were
not sensorially acceptable. The results show that it is possible
to decrease acrylamide content also with an increase of pH, most
probably due to the removal of sugars and amino acids.
However, more investigations with respect to which actual base
or its concentration are needed to define a process.
Postdrying of Potato Crisps. The moisture content of crisps
depended on frying temperature as well as on frying time
Figure 2.
Effect of frying time on moisture of potato crisps.
Figure 3.
Response surface plot of moisture in potato crisps after frying at 160
°
C(a) and at 185
°
C(b) followed by postdrying: (
b
) measured values.
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J. Agric. Food Chem.,
Vol. 52, No. 23, 2004 Kita et al.

(Figure 2). It was possible to obtain a low-moisture product
after frying at 185 °C for 4.5 min, whereas when the frying
temperature was lower (160 °C), the minimum frying time was
2.5 min longer. After a longer or shorter postdrying step, there
was no problem in obtaining low moisture in the final product
(Figure 3). The apparent increase in dry matter at long frying
and drying times probably is a result of the second-order
regression and is probably not real.
At both frying temperatures decreased frying times followed
by postdrying resulted in a decrease in acrylamide content in
the crisps (Figure 4). When crisps were fried in oil at 185 °C,
it was possible to obtain a 70% decrease of acrylamide content
after 2 min of frying and 75 min of postdrying. An even larger
decrease was observed after frying at 160 °C. In this case it
was possible to decrease acrylamide content in crisps by >80%
if, after 3 min of frying, the crisps were dried for 75 min (Figure
5). This shows that it is possible to decrease acrylamide content
by postdrying during crisps prodution.
The products had taste and mechanical properties (data not
presented) comparable to those of regular processed products.
A full sensory evaluation will be performed after a pilot-scale
processing, taking advantage of the findings obtained by the
postdrying procedure in the present work.
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JF049269I
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J. Agric. Food Chem.,
Vol. 52, No. 23, 2004 Kita et al.