EFFECT OF POST-DRYING METHOD ON SELECTED PROPERTIES OF POTATO CHIPS

Acta Agrophysica, 2008, 11(1), 91-100
EFFECT OF POST-DRYING METHOD ON SELECTED PROPERTIES
OF POTATO CHIPS
Agnieszka Kita1, Adam Figiel2
1Department of Food Storage and Technology,
Wroc?aw University of Environmental and Life Sciences
ul. Norwida 25, 53-375 Wroc?aw
e-mail: Agnieszka.Kita@wnoz.up.wroc.pl
2Institute of Agricultural Engineering,
Wroc?aw University of Environmental and Life Sciences
ul. Che?mo?skiego 37/41, 51-630 Wroc?aw
A b s t r a c t . The aim of the investigation conducted was determination of the effect of different
drying methods (in hot air flow, vacuum and vacuum-microwave dryers) on fat content, texture,
colour and sensory properties of potato chips. The material for our investigation were potato chips
fried in palm oil at the temperature of 175°C to range 20%, 15% and 5% of moisture and then post-
dried using different methods to moisture level below 2%. Control sample were potato chips fried to
less than 2% moisture. The following parameters were the subject of determination: moisture, fat
content, texture – using Instron 5544 device, colour – by Minolta CR-200 colorimeter, and sensory
properties (like colour, flavour, taste and texture – according to 1-5 point scale). Investigations
proved that shortening frying time and then post-drying decreases fat content in chips product and
increases chips hardness, as well as results in chips lighter colour. It was suggested that post-drying
applied at lowered pressure requires assorting appropriate parameters of the process.
K e y w o r d s : Potato chips, post-drying, fat content, texture, colour, sensory assessment
INTRODUCTION
Potato chips are known as one of the most popular kinds of fried snacks made
from potatoes. For 150 years they have enjoyed high popularity both in the USA
and in the European countries, which they owe to their specific sensory properties
– characteristic colour, taste and flavour (due to the combination of features of
raw materials used: potato, oil and spices), but, first of all, to their crispy texture.
Obtained through frying thin potato slices in hot oil, chips are characterised by
relatively high content of fat (30-35%) and low amount of water (<2%) (Lisi?ska
and Leszczy?ski, 1989).

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A. KITA, A. FIGIEL

In recent years more and more attention has been paid to health aspects of
food. Therefore, there have been undertaken trials to modify technology in view
of lowering the fat content without worsening the quality of the final product. To
this end there are used different kinds of blanching solutions, slice drying prior to
their frying, as well as combinations of appropriate frying parameters (time and
temperature) (Mellema 2003). It is also possible to manipulate the kind of frying
oil, although nowadays, on an industrial scale, palm oil and its fractions is
a dominant one and it successfully eliminates other, often less hydrogenised vege-
table oils (Kita et al. 2007).
The presence of acrylamide has turned out to be not of the least importance.
This is a substance featuring potentially cancerogenous effects for people and it
can be found in carbohydrate products undergoing thermal processing. Especially
high quantity of this undesired compound, many times exceeding the norms in
force, have been detected in potato chips, therefore, in the last years numerous
investigations were undertaken, aiming at limiting or complete elimination of
acrylamide from this popular product (Claeys et al. 2005). One of the first modi-
fications introduced in technology was lowering of chips frying temperature
(from 185°C to 175°C or lower) (Gertz and Klosterman, 2002). Another proposal
involved, among others, shorter frying period and then post-drying chips until
they reach moisture levels below 2% (Kita et al. 2004).
Such modifications not only result in decreased content of acrylamide, but
also affect other quality properties. In connection with the mentioned fact the aim
of this investigation was determination of the degree of chips frying at the tem-
perature of 175°C to different moisture levels and then post-drying effects on the
properties of the final product. Also, a comparison was made of different methods
of post-drying – in a convectional dryer, vacuum, or in a vacuum-microwave
dryer in view of the resulting quality of potato chips.
MATERIALS AND METHODS
Potato variety Eldena was used for laboratory potato chips production. After
washing and trimming (carborundum peeler, Sirman, Italy), the potatoes were cut
into slices of 1.8±0.1 mm in thickness (slicing machine, Brown, Germany),
washed in cold water, superficially dried (paper towels) and fried in a fryer
(Beckers, Italy) until the moisture content was 20%, 15%, 5% and below 2%. The
potato chips were fried in palm oil heated to 175oC. After discharging of the oil
and cooling, potato chips with moisture content higher than 2% were post-dried
using convectional dryer, vacuum dryer (SPT-200, Poland) and vacuum-micro-
wave dryer (Plazmatronika, Poland) – Table 1. Next, 100 g samples of potato
chips were packed in aluminium foil packages and taken for laboratory analysis.

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EFFECT OF POST-DRYING METHOD ON SELECTED PROPERTIES OF POTATO CHIPS
93

All experiments were performed in triplicates and the results shown in the present
paper are the mean values obtained in the investigation.

Table 1. Parameters of post-drying of potato chips fried at different moisture levels


Type of post-drying

Moisture content
of potato chips
convection
vacuum
vacuum-microwave
after frying (%)
(50 oC)
(50oC/1kPa)
(480W/4-6kPa)
5
2 h
1 h 15 min
2-3 min
15
2 h 30 min
1 h 30 min
3.5-6 min
20
2 h 45 min
1 h 30 min
4.5-8.5 min

Moisture content in potato chips was determined by drying 2 g homogenized
samples in hot air oven at 105oC for 2h (AOAC). Fat content of potato chips was
estimated using the Soxhlet procedure (AOAC). Fat was extracted applying a Büchi
B-811 Universal extraction system (Büchi Labortechnic AG, Flawil, Switzerland).
A 2g sample was extracted for 180 min with diethyl ether used as a solvent.
The texture of potato chips was determined using an Instron 5544 connected
to a computer, equipped with a “share blade” rectangular attachment for cutting
(70 mm x 3 mm). The velocity of the head with the attachment was 250 mm min-1
with a 100 kG load cell. The measurements were taken to determine the maxi-
mum shear force (Ftmax) necessary to cut one slice of potato crisp. Each measure-
ment was conducted on 30 potato chips (Kita et al. 2007).
The colour of potato chips was assessed with the use of a Minolta Chroma
Meter CR-200 Reflectance system. The device is a tristimulus colorimeter which
measures four specific wavelengths in visible range, specified by the Comission
Internationale de l’Esclairage (CIE). Tristimulus data supply a three-dimensional
value to equal perceived colour differences. The L, a, and b values are three dimen-
sions of a measured colour which gives specific colour value of the material. The L
value represents light-dark spectrum with a range from 0 (black) to 100 (white). The a
value represents green-red spectrum with the range from –60 (green) to +60 (red).
The b value represents blue-yellow spectrum with the range from –60 (blue) to
+60 (yellow). The measurements were conducted after milling potato crisps to
unified grind size on 10 g crisps samples from all frying and post-drying condi-
tions (Papadakis et al., 2000).
The sensory qualities – colour, flavour, odour and texture were assessed ac-
cording to the five-grade scale (5 points – the best, 1 point – the worst).

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A. KITA, A. FIGIEL

One-way analysis of variance was used for comparison of the results obtained for
the fat content and texture of potato chips. Homogenous groups were determined us-
ing the Duncan test (p?0.05). The data were analysed using Statistica 6.0 program.
RESULTS AND DISCUSSION
Figure 1 shows moisture and fat content alterations in potato chips fried in
palm oil heated to 175°C. The longer the frying time the lower the water content
in chips recorded, and the alterations mentioned were described using a sigmoidal
curve. The highest water loss took place between 2 and 3 minutes of frying. After
that time chip moisture values reached a similar level (<2%). Water loss, depend-
ing on frying temperature as well as on other parameters, in the course of chips
frying was the subject of investigation by other authors (Gamble et al. 1987,
Moyano et al. 2006). They observed increasing pace of water evaporation as the
temperature was going up.
50
fat
)
moisture
40

(
%

M
r
e
t
u
i
s 30
o
T=45.77- 44.15/t
)
,

M
R2=0.99

(
%

T 20
e
k
t
a
p
M=2.71+40.98/(1+EXP((t-2.43)/0.241))
t

u
a 10
F
R2=0.99
0
1
2
3
4
5
Frying time t (min)

Fig. 1. Moisture and fat content of potato chips fried in palm oil at 175°C

In the process of frying the space once occupied by evaporated water be-
comes filled with frying fat. The pace of fat absorption in the experiment con-
ducted was described by a hyperbolic curve. As frying time prolonged fat content
in chips increased and after 4.5 minutes it ranged at 35%. Similar relations were

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EFFECT OF POST-DRYING METHOD ON SELECTED PROPERTIES OF POTATO CHIPS
95

recorded by other authors who compared the amount of fat absorbed, both during
classical frying and in a vacuum process (Gamble and Rice 1987, Garayro and
Moreira 2002, Pedreschi and Moyano 2005b).
The relation between chips moisture and their fat content when fried at tem-
perature 175° C is shown in Figure 2. Slight changes of the moisture were ob-
served when fat content did not exceed 25%, and when it exceeded 30%. The in-
crease in fat content within the range from 25 to 30% was accompanied by the
decrease in chips moisture from 35 to 10%.
50
40
)

(
%
t

M 30
n
t
e
n

co
r
e 20
t
u
i
s
o
M
M=1.72+40.03/(1+EXP((T-27.52)/1.84))
10
R2=0.99
0
15
20
25
30
35
40
Fat uptake T (%)

Fig. 2. Relationship between moisture and fat content of potato chips fried in palm oil at 175°C

Potato chips obtained featured different fat content (Fig. 3). The longer the frying
time of potato slices in oil the higher the fat content charactering ready products.
Therefore, introduction of shorter frying and then post-frying chips to appropriate
moisture level significantly lowered the content of the component in ready products.
However, different fat contents were recorded between the chips post-dried according
to different methods. Post-drying performed both in a vacuum dryer and in a vacuum-
microwave one caused fat loses as fat remained on the surface of glass containers
where the drying took place. Probably the applied parameters resulted in too intensive
fat vaporisation from the surface of the product. Therefore, considering the methods
of drying a product previously subjected to frying, there is a need to determine the
parameters which would not allow loses of that component. The effect of different
technological treatments on fat content in potato chips was the subject to examination
of many researchers. Gamble et al. (1987), comparing fat content in chips obtained

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96
A. KITA, A. FIGIEL

from pre-dried potato slices, noticed that both pre-drying in hot air and with the use of
microwaves resulted in lower fat content in final product. Pedreschi and Moyano
(2005a) also came to the same conclusions as the recorded lowered fat content in pre-
dried blanched potato slices.

38
e
36
34
d
) 32

(
%
e 30
c
k
c
c
c
t
a
p 28
t

u
a
b
F 26
ab
ab
a
24
22
20
2
5
15
20
Moisture of potato slices after frying (%)
covection
vacuum
vacuum-microw ave

Fig. 3. Fat content of potato chips fried at different moisture levels and next post-dried

Fat content and moisture are directly related to chips texture. The results of
texture measurements regarding chips hardness are shown in Figure 4. The most
delicate texture was featured by chips fried in a traditional way – directly to their
moisture level below 2%.
Introduction of shorter frying and then post-drying according to conventional
method affected chips increased hardness: by 1 N – when slice moisture amounted to
5% and by 4 N – at slice moisture of 15 and 20%. Chips post-dried in vacuum and
vacuum-microwave dryer were characterised by harder texture (1-1.5 N) in compari-
son to chips dried using the conventional method.
Another investigation involving the texture of chips featuring different fat
content proved a similar relation – the lower the fat content the harder the chips
(Kita et al. 2007). Pedreschi and Moyano (2005a), comparing the texture of chips

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EFFECT OF POST-DRYING METHOD ON SELECTED PROPERTIES OF POTATO CHIPS
97

subjected to blanching and pre-drying, recorded the fact that those treatments did
significantly increase crispiness of potato chips.

36
b
b
b
b
35
b
b
34
33
ab
ab
)

(
N 32
e
a
r
c 31
o
a
F 30
29
28
27
2
5
15
20
Moisture of potato slices after frying (%)
covection
vacuum
vacuum-microw ave

Fig. 4. Texture of potato chips fried at different moisture levels and next post-dried
An equally considerable chips quality parameter is their colour. The results of
colour assessment of ready products based on Chroma Minolta CR-200 colorime-
ter indications are presented in Table 2. Applied post-drying resulted in lighter
colour of the final product (higher values of L* parameter) and decreased values
of a* and b* parameters. There were recorded different colour intensities of L*
and in contribution of red colour a* in chips obtained from slices post-dried to 5%
moisture and to higher moisture values. The method of post-drying did not signi-
Table 2. Colour (L,a,b) of potato chips fried in different oils and post-dried using air-dryer, vac-
uum-dryer and vacuum-microwave dryer
Type of post-drying
Without

convection
vacuum
vacuum-microwave

2%
5%
15%
20%
5%
15%
20%
5%
15%
20%
L
53.35
59.22
63.46
59.75
57.3
61.26
61.44
60.34
63.64
60.28
a
1.63
0.24
–2.86
–2.16
–1.45
–2.63
–0.97
–0.45
–3.1
–2.32
b
30.02
26.09
26.04
24.18
25.14
27.85
25.36
25.17
27.75
23.26

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98
A. KITA, A. FIGIEL

ficantly affect this quality parameter. Alterations in chips colour according to fry-
ing parameters were also investigated by other authors. Gökmen and ?enyuva
(2006) stated that regardless of the temperature applied, as frying time prolonged
L* and b* parameters decreased, while a* reached higher values. Pedreschi et al.
(2007), comparing the colour of chips obtained from pre-dried potato slices, no-
ticed distinctly lighter colour of the resulting product.
The results of general sensory assessment of potato chips are shown in Figure 5.
The chips to reach the highest assessment note were those traditionally fried, as well
as the ones made of potato slices initially dried to 5% moisture level and then
post-dried according to the conventional method. Comparing the properties of
chips post-dried using different methods, chips conventionally post-dried proved
to be the best (although the time consumed by this process was the longest), while
the worst assessment was given to vacuum post-drying. Worse assessment of
chips dried at lowered pressure was connected with the leakage of fat whose boil-
ing point underwent considerable lowering in those conditions.
6
c
5
bc
b
4
b
-
5
a
a

1
b
a
t
s 3
a
a
i
n
o
a
P
2
1
0
2
5
15
20
Moisture of potato slices after frying (%)
covection
vacuum
vacuum-microwave

Fig. 5. Total sensory assessment of potato chips fried at different moisture levels and next post-dried
CONCLUSIONS
1. Application of shorter frying time followed by post-drying considerably
decreased fat content in finally produced chips.

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EFFECT OF POST-DRYING METHOD ON SELECTED PROPERTIES OF POTATO CHIPS
99

2. Potato slices post-dried with the use of vacuum and microwave dryers
featured fat losses in ready product.
3. Chips obtained using post-drying process were characterized by harder
texture as compared to the ones dried in the traditional way.
4. Post-drying affected chips colour which was lighter than that of classi-
cally dried ones.
5. Among chips obtained using post-drying, chips conventionally post-dried
featured the best sensory properties. Application of other, quicker post-drying meth-
ods requires the selection of appropriate parameters of the process.
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100
A. KITA, A. FIGIEL

WP?YW RÓ?NYCH METOD DOSUSZANIA NA WYBRANE
W?A?CIWO?CI CZIPSÓW ZIEMNIACZANYCH
Agnieszka Kita1, Adam Figiel2
1Katedra Technologii Rolnej i Przechowalnictwa, Uniwersytet Przyrodniczy we Wroc?awiu
ul. Norwida 25, 50-375 Wroc?aw
e-mail: Agnieszka.Kita@wnoz.up.wroc.pl
2Instytut In?ynierii Rolniczej, Uniwersytet Przyrodniczy we Wroc?awiu
ul. Che?mo?skiego 37/41, 51-630 Wroc?aw


S t r e s z c z e n i e . Celem przeprowadzonych bada? by?o wyznaczenie wp?ywu ró?nych metod
dosuszania (w przep?ywie ciep?ego powietrza, pró?niowo i mikrofalowo-pró?niowo) na zawarto??
t?uszczu, konsystencj?, barw? i cechy organoleptyczne czipsów ziemniaczanych. Materia?em u?y-
tym do bada? by?y czipsy ziemniaczane sma?one w oleju palmowym o temperaturze 175oC do wil-
gotno?ci 20%, 15%, i 5%, a nast?pnie dosuszane ró?nymi metodami do wilgotno?ci poni?ej 2%.
Prób? kontroln? stanowi?y czipsy ziemniaczane usma?one do wilgotno?ci poni?ej 2%. W czipsach
oznaczano: wilgotno??, zawarto?? t?uszczu, konsystencj? – przy u?yciu aparatu typu Instron 5544,
barw? – przy u?yciu kolorymetru Minolta CR-200 oraz cechy organoleptyczne: barw?, smak, zapach i
konsystencj? – wed?ug skali punktowej (1-5 pkt.) Stwierdzono, ?e skrócenie czasu sma?enia a nast?p-
nie dosuszanie czipsów obni?a zawarto?? t?uszczu w produkcie, zwi?ksza jego twardo?? i rozja?nia
barw?. Zasugerowano, ?e stosowanie dosuszania przy obni?onym ci?nieniu wymaga dobrania odpo-
wiednich parametrów procesu.
S ? o w a k l u c z o w e : czipsy ziemniaczane, dosuszanie, zawarto?? t?uszczu, tekstura, barwa,
ocena sensoryczna

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