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87
Native black Michune potato variety:
characterization, frying conditions and sensory evaluation
SUMMARY. The aim of this study was to evaluate the
chemical and nutritional composition, to establish
frying processing conditions and to determine the sensory
profile and acceptability of Black Michune (BM)
potato chips. BM had a higher protein content, half the
ether extract content and nitrogen-free extract, a lower
caloric intake (70 kcal/100g) and amylose content
(17.5%) than Desiree (DES). To set the frying conditions,
the Taguchi method was applied using a matrix
design L9 (32,22). The variables studied were: temperature,
time, potato variety (raw material) and pretreatment.
The responses evaluated were: the color
difference as well as the content of reducing sugars and
total polyphenols. The best frying conditions were BM
with a pretreatment at 160‹C for 7 min for color, DES
without pretreatment at 140‹C for 7 min for reducing
sugar content, and BM without pretreatment at 180‹C
for 4 min for polyphenol content. Then, sensory profiles
of potato chips from BM, DES and a commercial package
were determined by selecting the descriptors texture,
firmness, color, salty taste and oiliness. Significant
differences in color and oiliness were found. Finally,
the acceptability test was applied to BM potato chips
where color (64%) was the only attribute not as accepted
as texture (95%), salty taste (87%) and product
(97.3%). This study demonstrated that BM potato chips
have a satisfactory acceptability by consumers
Key words: Black Michune potato variety, frying conditions,
sensory evaluation.
RESUMEN. Papa nativa variedad Michune negra: caracterizacion,
condiciones de fritura y evaluacion sensorial..
El presente trabajo tiene por objetivo evaluar la composicion
quimica y nutricional de papa Michune negro (BM), establecer
condiciones de proceso de fritura, determinar el perfil sensorial
y aceptabilidad de papas fritas chips. BM presento un mayor
contenido proteico, la mitad de extracto etereo y extracto libre
de nitrogeno, una menor ingesta calorica (70 kcal/100g) y un
menor contenido de amilosa (17,5%) comparada con la variedad
Desiree (DES). Para establecer condiciones de fritura se
utilizo metodologia Taguchi empleando una matriz de diseno
L9 (32,22). Las variables seleccionadas fueron: temperatura,
tiempo, variedad de papa (materia prima) y pretratamiento. Las
respuestas evaluadas fueron: diferencia de color, contenido de
azucares reductores y polifenoles totales. Las mejores condiciones
de fritura fueron: BM con pretratamiento a 160oC por 7
min para color, DES sin pretratamiento a 140oC por 7 min para
azucares reductores y BM sin pretratamiento a 180oC por 4 min
para polifenoles totales. Luego, los perfiles sensoriales de las
papas chips de BM, DES y comercial fueron determinados seleccionando
los descriptores textura, firmeza, sasbor salado y
aceitoso. Se encontraron diferencias significativas en los descriptores
color y aceitoso. El color (64%) fue el unico atributo
que obtuvo un nivel de aceptacion mas bajo entre los otros
como textura (95%), sabor salado (87%) y producto (97.3%).
Este estudio demostro que los chips de BM fueron satisfactoriamente
aceptados por los consumidores.
Palabras clave: Variedad papa Michune negro, condiciones
de fritura, evaluacion sensorial.
M. Rubilar, M. Villarroel, M. Paillacar, D. Moenne-Locoz, C. Shene, E. Biolley, F. Acevedo
Center of Food Biotechnology and Bioseparations, BIOREN. Agriaquaculture Nutritional Genomic Center,
CGNA. Technology and Processes Unit. Department of Public Health. Universidad de La Frontera, Chile.
ARCHIVOS LATINOAMERICANOS DE NUTRICION
Organo Oficial de la Sociedad Latinoamericana de Nutricion
Vol. 62 No 1, 2012
INTRODUCTION
In Chile, potato is the countryfs fourth most important
crop and a dietary staple (1). The Isla Grande de
Chiloe, located in the southern part of Los Lagos Region,
is considered one of the sub-centers of origin for
potato due to the many findings of native varieties,
which were very useful for creating new potato varieties
(2). Native potato tubers show a wide variability
in tuber shape, flesh and skin color, texture, sizes, flavor,
and phenological characteristics (3). They have
recognized attributes of flavor and red/blue color due
to the presence of such antioxidants as anthocyanins,
characteristic compounds of vegetal products. Michune,
Guadacho, Lobo, Murta, Pachaconas are native
varieties, among many others. In addition, a wide variety
of potatoes cultivated in Chile such as Desiree,
Yagana, Asterix, Baraka, etc. have been introduced
from European countries or North America.
88 RUBILAR et al.
According to Miranda and Aguilera (4), potato
chips and derivatives represent 12% of the market in
the main products of potato processing. Frying is a widely
used method for cooking that creates unique textures
and flavors in foods. Among potato sub-products,
potato chips are a high consumption food for their characteristics
of flavor, aroma, crunchy texture, and increased
palatability afforded by the frying process (5).
During frying, the original structure of raw potato
undergoes transformations that will determine the quality
attributes of the final product such as oil content,
crispness, roughness, porosity. In turn, these structural
changes depend on the processing
conditions of potato prior to being
fried and on frying conditions (e.g.
pretreatment, temperature, time).
Apart from the sensory benefits
of heat treatments like potato
frying, it has been shown that
these heat processes can also induce
undesirable color changes
largely produced by the Maillard
reaction (6). In this context, it is
necessary to control the reaction factors.
Among the different physical properties of foods
and food products, color is considered an important visual
attribute in the perception quality of a product. Potato
chip color is a vital criterion for industrial potato
processing and is strictly related to consumer perception.
Among the sensory potato attributes highlighting
texture, aroma, flavor, color, texture is considered the
most important. Several methodologies been used to
describe these sensory properties, among which Quantitative
Descriptive Analysis is the best known (7, 8,
9), as it provides the sensory profile of a product, assigning
intensity values for each selected feature.
The aim of this study was to evaluate the chemical
and nutritional composition of the black Michune variety,
to establish frying process conditions, to contribute
to the knowledge of the sensory characteristics
of the black Michune variety by producing the
sensory profile, and to determine the acceptability of
potato chips.
MATERIALS AND METHODS
Sample preparation
The native Black Michune (BM) from Chiloe,
Chile (Fig 1), the white flesh potato Desiree (DES),
and commercial packaged potato chips were used as
raw material. The samples were supplied directly from
the harvest area located on Chiloe Island. Both the
black Michune and white-fleshed Desiree potatoes
were selected by discarding units with possible phytosanitary
problems. The commercial product was purchased
in the local market. Then, the selected potaoes
were hand-peeled, washed and finely cut with an electric
mill AFK Germany Model AS-150 between 2.0 to
3.0 mm thick. For the frying process, an electric fryer
fitted with a thermocouple was used.
Chemical and nutritional analysis
In order to characterize the raw material, a proximal
analysis was performed on samples of fresh native
potatoes. Moisture, ash, protein, ether extract, crude
fiber and nitrogen-free extract were measured in samples
of fresh native potato samples according to
AOAC standard procedures (10). In order to determine
the caloric intake of the black Michune potato, the percentage
of proteins, carbohydrates and ether extract
was calculated using Atwater coefficients.
Determination of amylose and total starch
To determine the amylose content in black Michune
potato, a megazyme amylose/amylopectin assay
procedure utilizing a commercial kit (Megazyme Ireland
International, Ltd., Bray, Ireland) was performed
according to the manufacturer's recommendations.
This method applies a procedure based on the specific
precipitation of amylopectin by concanavalin-A lectin.
Amylose content is expressed as a percentage of total
sample starch. The total starch was determined by measuring
the total glucose after digestion with thermostable
ƒ¿-amylase and amyloglucosidase enzymes.
FIGURE 1.
Native black Michune potato variety from the Chiloe Island.
NATIVE BLACK MICHUNE POTATO VARIETY 89
Frying process conditions
Slices of both potato varieties were subjected to an
immersion pretreatment in a 1% citric acid solution
for 40 minutes in order to reduce enzymatic browning.
An electric fryer with commercial sunflower oil was
used to perform the chip frying, with a slice:oil ratio
of 1:20. The frying temperatures ranged from 140‹C
to 180‹C for 4 and 10 min. These conditions were evaluated
applying an experimental design.
Design of experiments
The Taguchi methodology was used, as this can
work simultaneously with several control factors. This
method uses |
the so-called orthogonal arrays corresponding
to an experimental design, which allows a
mathematical evaluation independent of the effect of
each factor in the design (11). The independent variables
were temperature (T) (140, 160 and 180‹C), time
(t) (4, 7 and 10 minutes), potato variety (BM and DES)
or raw material (RM), and pretreatment (PT) (immersion
in citric acid). For this study, a matrix design L9
(32,22) was used, where the subscript 9 corresponds to
the number of experimental runs and the superscript
represents the controlling factors.
The analysis of the quality response averages for
each experimental run was carried out for studying the
"smaller is better" characteristic for a color change,
and "greater is better" for the case of reducing sugars
and total polyphenols. The average for level of each
factor and the variance analysis were then calculated
using Qualitek-4 software. The average magnitude difference
of the response for each factor level was determined
in order to calculate the inclination slope so
as to estimate the impact of each factor on the response
and determine the optimal response theoretical equation
(OTE). Finally, a confirmatory test was applied.
Color determination
To determine the potato chip color, a crushed sample
was spread evenly over a miniplate, placed to capture
the image inside a chamber isolated from natural
light and analyzed using Adobe Photoshop software
to determine the parameters L*=L/255, a*=(240a/255)
- 120, b*= (240b/255) - 120, where L: gives a luminance
or brightness value of the sample, a: shows the
variation area between red and green of the spectrum,
b: refers to the variation area between yellow and blue
of the spectrum (12).
The color change ĢE was determined from the values
of L *, a * and b *:
Determination of reducing sugars
An aqueous extract was obtained using a 2 g sample,
which was centrifuged by removing the supernatant
containing reducing sugars. A calibration curve
was prepared using 20 mg/L glucose as standard. An
aliquot of the sample (1 mL) was added to 1 mL of
2,5-dinitrosalicylic acid (DNS) and boiled for 5 min
(13). Then the sample was diluted with 5 mL of distilled
water and measured in a spectrophotometer
(Thermo Genesys model 6) at 540 nm. The samples
were run in triplicate.
Determination of total polyphenols
Total phenolic content was determined by its reaction
with Folin.Ciocalteu (FC) reagent (Fluka, Japan),
according to the method reported by Velioglu et al. (14).
Briefly, 200 microliters from the methanolic extract
were mixed with 1 mL of Folin-Ciocalteu reagent and
0.8 mL of Na2CO3 (60 g/L) (Sigma-Aldrich, Germany)
solution was added to the mixture. After heating for 15
min at 45 ‹C in a water bath (MSH-10 Daih Scientific),
the absorbance of samples was measured at 765 nm
(Genesys 6, Thermo Scientific, USA). Results were expressed
as gallic acid (Sigma-Aldrich, Germany) equivalent
per gram of dry matter (mg GAE/g d.m.). The
measurement was carried out three times.
Sensory profile
For the sensory sample evaluation, the Quantitative
Descriptive Analysis (QDA) was measured using unstructured
descriptive analytical scales 85 mm long.
The generation of descriptors (texture, firmness, color,
salty and oily taste) as well as the manner for evaluating
them took place in open panel sessions during the
training panel. At the same time, discriminatory capacity
was found by assessing their reproducibility. In
particular, firmness was determined by manipulating
the sample to evaluate whether it maintained its structure
or disintegrated easily. With respect to the oily
characteristic, the remaining oil residue on the hand
was determined.
Consumer acceptability test
To perform the acceptability test, four parameters
90 RUBILAR et al.
were selected: salty taste, color, crunchy texture and
product. The acceptability of each parameter was measured
by means of the hedonic test (7) using a five-point
scale with ends: I dislike it very much and I like it very
much. In this trial, eighty-five consumers participated.
Statistical data analysis
The data were analyzed using analysis of variance
(ANOVA) and the significant mean difference was
determined with Duncanfs multiple comparison test
(p . 0.05).
RESULTS
Characterization of black Michune potato
The chemical and nutritional composition of the native
BM variety was compared with the standard whitefleshed
DES potato variety, as shown in Table 1.
From these values, the protein content of the BM
(6.8%) highlights that this doubles the protein content
of a standard potato, whereas the nitrogen-free extract
(NFE) in BM is 10%. This value is less than the standard
potato content corresponding to 16% (15). According
to these results, the variety from Chiloe Island
presented a lower carbohydrate content than the standard
potato. In addition, the amylose percentage in
BM was slightly lower, reaching 17.5% compared
with 22.0% of the DES. The value obtained for energy
intake (70 kcal/100g) was lower than the value for a
standard potato.
Effect of frying conditions on color change in
potato chips
For color, the criterion "less is better" was used, i.e.
less color change is the best response. BM with a pretreatment
at 160‹C for 7 min of frying (design point
5) presented the best frying conditions obtained with
a ĢE of 8.18 (Table 2). ANOVA showed that the factors
T, t and RM were significant (p<0.05), contributing
87.41% of the variation, where the temperature
conditioned the response robustness of 56.26%.
Effect of frying conditions on the reducing sugar
content in potato chips
For reducing sugar content, the criterion "more is
better" was used. The best frying conditions were obtained
using a standard potato without pretreatment at
140‹C for 7 min (design point 2) reaching 0.97 mg of
glucose/g d.m. (Table 2). The variables T, t and RM
significantly affected the response (p<0.05), providing
together 95.79% and conditioning the response robustness
of 89.65%.
Effect of frying conditions on the polyphenol
content in potato chips
For the evaluation of the effect of frying conditions
on the polyphenol content in BM and DES potato
chips, the criterion "more is better" was used, i.e. higher
polyphenol content after the frying process is better.
Thus, the best combination of design factors were
found in the BM variety without pretreatment at 180‹C
for 4 min of frying and reached 2.57 mg GAE/g d.m.
(design point 7) (Table 2).
ANOVA showed that the RM, T and PT variables
were significant (p<0.05) providing together 85.75%.
These variables determined a response robustness of
84.61%.
Sensory Profile
In texture and firmness, the samples showed a similar
intensity degree without significant differences
(p . 0.05) among the samples (Table 3).
On the subject of firmness, a similarity was observed
in results cataloging samples as resistant to manipulation
without presenting signs of fragility. The salty taste
perception was similar in BM samples and in the commercial
product with an appropriate degree of intensity,
which differed significantly from the DES variety.
As for the color, values obtained in DES and commercial
samples were significantly higher than those
found in the BM as both were characterized by a yellow
color.
TABLE 1.
Chemical and nutritional composition of black Michune
and white-fleshed Desiree potatoes.
Parameter (g/100 g)
Black
Michune
potato
White-fleshed
Desiree
potato
Moisture 77.12 75.33
Ash 4.77 1.10
Proteins 6.86 2.53
Crude fiber 0.68 0.26
Ether extract 0.03 0.06
Nitrogen-free extract 10.54 20.72
Amylose 17.5 22.0
Energy (Kcal/100g) 69.86 93.54
NATIVE BLACK MICHUNE POTATO VARIETY 91
The perception of oily potato chips was evident in
the three samples, with the presence of residual oil in
products of BM and DES varieties being more marked
than in the commercial sample.
Acceptability Test
To find out if the variety of BM potato chips gratifies
consumer expectations or not, an acceptability test
was performed separately analyzing color, texture,
salty taste and the product (Fig. 2).
a) Color
The result of the consumer survey was 64%
for the sum of the scores: I like it a lot, I like it and I
am indifferent, compared with 36% of the ratings
made by: I dislike it, I dislike it a lot. This attribute
must be taken into account because color is one of the
most important quality parameters valued by consumers
in this type of product.
b) Texture
In connection with this descriptor, the results
were significantly better for BM potato chips as the
acceptability reached 95%.
c) Salty taste
A low percentage of consumers (13%) rejected
the product for its salt content, while 87% of consumers
accepted it.
d) Product
The BM potato chip was very well accepted
by consumers based on several characteristics. Only
2.7% of consumers said they disliked the product
compared with 97.3% of favorable responses.
TABLE 2
Orthogonal arrays L9 (32, 22) and responses of Color, Reducing Sugar Content and Total
Polyphenols obtained for frying processing conditions
Design
Point
Independent variables Color (ĢE) RSC
(mg glucose/g d.m.)
TP
(mg GAE/g d.m.)
T t RM PT
1 1 1 1 1 9.35}0.12 0.71}0.09 2.15 |
}0.05
2 1 2 2 2 10.36}2.85 0.97}0.01 1.54}0.13
3 1 3 1 1 8.91}1.26 0.64}0.02 1.85}0.05
4 2 1 2 1 13.32}0.91 0.7}0.01 0.61}0.02
5 2 2 1 1 8.18}0.30 0.54}0.01 1.37}0.71
6 2 3 1 2 14.91}2.26 0.27}0.05 2.42}0.17
7 3 1 1 2 13.87}1.06 0.43}0.003 2.57}0.14
8 3 2 1 1 15.65}3.95 0.41}0.02 2.52}0.01
9 3 3 2 1 29.38}1.58 0.42}0.001 1.93}0.09
T: temperature, t: time, RM: Raw Material, PT: Pretreatment RSC: Reducing Sugar Content
TABLE 3
Value averages (mm) of descriptors per
sample. Means with different letter (a, b)
indicate significant differences between
potato varieties, according to the Duncanfs
test at 0.05 significance.
Descriptor
Black
Michune
variety
Desiree
variety
Commercial
potato
Texture 78(a) 78(a) 81(a)
Firmness 81(a) 74(a) 72(a)
Salty 69(b) 62(b) 77(a)
Color 22(b) 66(a) 74(a)
Oiliness 12(b) 16(b) 40(a)
FIGURE 2
Acceptability results of the studied
characteristics in black Michune potato chip variety.
DISCUSSION
The results of the amylose percentage found in BM
(17.5%) and DES (22.0%) are similar to those reported
in the literature. (16, 17). A high amylose content is
supposed to be favorable in foods such as potatoes.
The presence of high levels of amylose may enhance
the functionality of starch, e.g. its film-forming ability
(18, 19). In addition, Hu et al. (20) reported that the
amylose/amylopectin ratio is generally 20/80. However,
an increased amylose content also increases the
resistant starch content, as amylose is not completely
digested by digestive enzymes. Therefore, not all carbohydrates
rich in amylose are used by the organism.
Consequently, an increase in amylose content could
contribute to a reduction in the glycemic index.
The value obtained for energy intake was 25% less
for BM than for DES. Considering that one of the greatest
public health problems nowadays is the obesity
caused by an inappropriate diet with an increased intake
of high-calorie foods, BM represents a nutritious
and healthy alternative that could be incorporated into
everyday foods.
The evaluation of the effect of frying conditions on
the color change in BM and DES potato chips variety
made it possible to obtain the best combination of
frying conditions.
The fried potato chip color is an important parameter
to be controlled during the transformation process. Fried
potatoes with a noticeable color change are the result of
the Maillard reaction, which depends on the content of
reducing sugars, amino acids or proteins in the surface,
on the temperature and on the frying time (21).
The DES potato chip obtained the best response
with regard to the effect of frying conditions on the reducing
sugar content. This fact should be explained
because the black Michune potato has a lower initial
reducing sugar content and it is therefore also lower
after frying.
The reducing sugar content is an important parameter
to measure, since this is a precursor to the formation
of the Maillard reaction, and a substantive
change in the reducing sugars would indicate that the
reaction had occurred. A higher content of reducing
sugars remaining after frying is better as this indicates
that this precursor has not been used during the Maillard
reaction.
Polyphenols are secondary metabolites widely
known to have antioxidant activity. Polyphenols processed
at high temperatures tend to decrease because
some of them are thermolabile. For this reason, it was
important in this study to evaluate the total polyphenol
content in native potatoes after a frying process. When
comparing the total polyphenol content in both potato
varieties after the frying process, BM showed the highest
value. Vattem and Shetty (22) observed the increasing
polyphenol content in potato chips after the
frying process. These authors explained that the polyphenol
content increase may be because a high temperature
would lead to a pyrolysis of phenolic
compounds present in the vegetable cell wall.
The lower values obtained in color of the BM compared
with DES and commercial samples could be explained
by the chemical composition of potato from
Chiloe Island, which has a blue/reddish color due to
the polyphenol presence in this variety.
The presence of increased residual oil in BM and
DES products compared with the commercial sample
may be attributed to the non-commercial frying process
for BM and DES. According to the results of the
acceptability test, BM was properly accepted by consumers,
and color was the only attribute that produced
a certain level of rejection.
CONCLUSIONS
Chemical analysis in native BM potato showed differences
to standard white-fleshed potato DES, mainly
in the protein content and NFE. In the blue BM variety,
potato chips were obtained with less of a color
change, a lower reducing sugar content and a higher
polyphenol content, where the potato variety, temperature
and frying time significantly influenced the responses
(p<0.05).
The sensory profile was determined for BM potato
chips using QDA, and an analysis of variance was carried
out. Significant differences in color and oily descriptors
were found, and the results of this study
demonstrated that BM potato chips have a satisfactory
acceptability, with color being the only descriptor that
causes a certain rejection due to the presence of reddish
blue shades.
ACKNOWLEDGEMENTS
Authors acknowledge the financial support given
92 RUBILAR et al.
NATIVE BLACK MICHUNE POTATO VARIETY 93
by Project DI08-0032 and GAP 2009, Direccion de Investigacion
at Universidad de La Frontera.
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Recibido: 21-07-2011
Aceptado: 08-01-2012 |
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