Vol.5 (2015) No. 1
ISSN: 2088-5334
Physical and Chemical Properties of Restructured Sweet Potato
Stick from Three Sweet Potato Cultivars
Joko Susilo Utomo#, Russly Abdul Rahman*
#
Indonesian Citrus and Subtropical Fruits Research Institute (ICSFRI) No. 1 Raya Tlekung, Junrejo, East Java, Indonesia
E-mail: jokosut@yahoo.com
*Department of Food Technology, Faculty of Food science and Technology, University Putra Malaysia, Selangor DE, Malaysia
Abstract— Restructured Sweetpotato Stick (RSS) was developed in attempt to overcome the lack of sweetpotato availability during off
season. Moreover, RSS was produced aimed to control of the adequate qualities caused by the variation characteristics of
sweetpotato. The making of RSS from 3 sweetpotato varieties was to study physicochemical and sensory attributes of the final
product. RSS was produced using three sweetpotato (SP) varieties with different flesh colour namely White, Yellow and Orange.
Samples, including raw materials, intermediate and final products were analyzed for physicochemical attributes. White and Orange
cultivars judged generated the good quality RSS. A similar hardness and shearing force of RSS made of White and Orange was
found. Proximate compositions on dry base (db) were: protein 3.59 and 2.74%, fat 21.44 and 35.91%, carbohydrate 71.83 and
59.19%; and ash 3.13 and 2.17%, respectively. White cultivar produced the RSS having yellow bright colour, high firmness and low
fat content, whereas Orange cultivar generated RSS with bright orange colour, medium firmness but high fat content. RSS made
from White and Orange cultivars were preferred with sensory score above the average. Result from this study illustrates that White
and Orange sweetpotato cultivars can be used to make a convenient restructured product (RSS).
Keywords—RSS, texture, physicochemical, sensory
affect colour, texture and flavour of the finished product and
must be controlled. Controlling of the adequate qualities can
be made by prepared “fabricated” French fries or sticks from
restructured SP roots [18],[19],[25],[22]. Sweet potato
French fries or sticks from restructured SP roots known as
Restructured Sweet potato Stick (RSS). Therefore, the
development of RSS was studied in an effort to overcome
these problems.
The objectives of this study are to determine the physical
and chemical properties and sensory characteristics of
restructured sweet potato stick (RSS) made from three sweet
potato cultivars; and selecting the suitable cultivars based on
chemical and physical characteristics of raw material is a
key to produce the desirable RSS.
I. INTRODUCTION
Sweet potato is a nutritious vegetable with a good
complement of energy, vitamin and minerals. The
intervention of humans by domestication and artificial
selection of the sweet potato has resulted in the existence of
a large number of cultivars. Cultivars differ from one to
another in the physical properties and chemical composition
[9], [12], [17]. Starch is the major component of SP, can
comprise from 50-70% of total dry matter [28]. It was noted
that the variation in starch content depends on variety. Other
important physical characteristic is flesh colour that may be
exploited to introduce an attractive colour into food made of
sweet potato.
The popular frying products of SP are French fried-type
products or sticks and chips. Sweet potato French fries and
chips were judged to be of a good quality and acceptability
by a consumer panel [25],[11], [16]. Conventional processes
for preparing French fries from potato fresh roots have
several drawbacks. The quality of fried product varies
among varieties. Further difficulties arise due to physical
and chemical characteristics of the raw materials such as size,
shape, sugar content, solid content, etc. All these variations
II. MATERIALS AND METHODS
A. Materials Preparation
Three sweet potato (SP) cultivars consist of White and
Yellow was collected from farmer field in Sepang and Ipoh
Malaysia, respectively, while Orange cultivar was bought
from Bukittinggi, Indonesia. Refined bleached and
deodorized (RBD) palm olein was obtained from a local
store. Carboxymethylcelullose (CMC) and Sodium
16
tripolyphosphate (STP) were of food grade. All chemicals
and solvents used were of analytical grade unless otherwise
specified. Sweetpotato-flour (SP flour) was prepared in Food
engineering laboratory, Faculty of Food Science and
Technology, UPM. SP tubers were peeled and shredded
manually. Drying was conducted using a cabinet drier at
55 °C for 24 hours. Dried material was then milled and
sifted through a 70 mesh. RSS was made using the method
in previous study [21].
students and staff of Faculty of Food Science and
Technology, UPM, Malaysia. A 7-point hedonic scale is
used for scoring the samples (1=dislike extremely; 2=dislike
moderately; 3=dislike slightly; 4=neither like nor dislike;
5=like slightly; 6=like moderately; 7=like extremely).
Samples are coded with 3 digits in a randomized
arrangement to equalize the effect of samples sequence food
preference.
C. Statistical Analysis
The experiment is arranged with a randomized complete
block design with 3 replications. The data collected were
analysed by the analysis of variance (ANOVA) and the
significant differences among means were determined by
Duncan’s multiple range test (DMRT) using MSTAT-C
statistical software.
B. Characterizations
Textural characteristics of SP tubers and RSS were
evaluated. Hardness, adhesiveness, springiness and
chewiness were quantified by Texture Profile Analysis (TPA)
method [4]. Texture analyzer (TA.TX2i) was fitted with a 25
Kg load cell with a probe having 50 mm diameter
compression plate (P/50). Each sample was compressed
longitudinal for two cycles. The test condition was: pre-test
speed, 2 mm/s; test speed, 1 mm/s; post-test speed, 2 mm/s;
time between two cycles, 5 second; and degree of
compression, 35 % of its initial height. The measurement
was subjected into cylindrical sample of cooked tubers and
RSS. TPA curves were obtained for 15 replicates per
samples. Firmness of dough was recorded as a force needed
during extruding the dough into sticks. Texture of fried stick
was determined using two methods i.e. puncture and cuttingshear test. Firmness was expressed as force needed of the
P/2 probe puncturing the samples. Texture of fried stick was
determined using two methods i.e. puncture and cuttingshear test. Firmness was expressed as force needed of the
P/2 probe puncturing the samples. Shearing force was a
force required shearing and cutting the samples by the single
downward action of the shear blade (HDP/BS). The test
speed, both puncture and shearing was 1 mm/s until it
reached 110 % distance. Firmness of dough and hardness of
fried stick were expressed in Newton (N). Data collection
and analysis were accomplished by the EXTRAD
Dimension Software of the texture analyser.
The colour of fried stick was determined by the Hunter
Colour Instrument (Hunter Lab, Reston, Virginia, USA) and
values (L, a, b) were collected. L describes Lightness (0 =
black, 100 = white), a intensity in red (a > 0) and b intensity
in Yellow (b > 0). Three pieces of RSS covered with plastic
sheet were then used to determine the colour value through
the reading hole. Ten replication of reading per sample were
done.
Moisture content of root, blanched chip and dough before
extrusion, frozen stick and fried stick was determined by an
oven drying method [2]. Dry matter content of dough was
calculated by subtracting 100 with moisture content.
Proximate analysis was determined on the final product.
Moisture, protein, fat, and ash were determined by the
AOAC method [2]. Protein was calculated as nitrogen
(Kjeldahl) x 6.25. Starch content of SP tubers was
determined by acid-hydrolysis method and total sugars
produced were calculated quantitatively by Nelson-somogyi
method [3].
Amylose content was determined using
colorimetric iodine binding procedure [1].
Sensory evaluations were performed on all fried samples
includes colour, texture, flavour and overall acceptability.
Forty untrained panellists evaluated the products consist of
III. RESULTS AND DISCUSSION
A. Physicochemical characteristics of 3 raw sweet potato
cultivars
A characteristic of raw material is an important in
producing a certain product, such as moisture content,
texture and chemical composition. Table 1 exhibits moisture
content of 3 commercial cultivars. Moisture content of fresh
or steamed tubers was different within the 3 cultivars.
Moisture content of White and Yellow increased during
steaming, but Orange decreased. Moisture content of
samples was slightly changed after steaming in 100 °C for
20 min in the range of 1 to 4% and it is in agreement with
the result of Bradbury & Holloway [6]. The increase of
White and Yellow was 2.14 and 2.01% respectively, whereas
the decrease of Orange was 1.04%. The fluctuation of
moisture content after cooking occurred due to the stages of
gelatinization process that were initiated by absorption of
water by starch grain until maximum swelling; the
increasing volume of starch grain in between 55 to 65 °C
[27], by the increasing temperature, disorganizing of starch
polymer occurred to form gel. Generally, steaming would
increase the moisture content, but the decrease which
happened to the Orange cultivar that might be caused by the
evaporation after the gelatinization was complete.
TABLE I.
MOISTURE CONTENT OF 3 SWEETPOTATO COMMERCIAL CULTIVARS
Cultivar
Fresh (%)
Steamed (%)
73.82 c
75.96 b
Yellow
78.53
a
80.54 a
Orange
76.48 b
75.44 c
White
a – c
Means within column followed by different superscripts letters are
significantly different at P < 0.05
TPA data are shown in Table 2 for the texture profile
characteristics of the 3 sweet potato cultivars. White has the
highest hardness followed by Orange, however they not
significant different (P>0.05). Yellow had the lowest
hardness and showed significant difference (P<0.05) with
White and Orange. White cultivar has the lowest
adhesiveness value followed by Orange and Yellow.
17
Springiness of White was the highest compared with the two
other cultivars. It shows that the sample was able to recover
it’s the initial form. Chewiness is an important character that
is expressed as the force needed to masticate the material.
White and Orange showed insignificant chewiness.
and Yellow. Also, Orange contained the highest amylose
(27.15%) followed by White (25.54%), and lowest being
Yellow (24.84%). This proved that White having the highest
hardness was due to the highest starch content. Other texture
profile attributes affected by starch and amylose content was
springiness. Springiness of tubers was positively correlated
with starch content (r = 0.74, P<0.01) (Figure 1b) but
negatively with amylose content (r = 0.79, P<0.01) show in
(Figure 1c).
TABLE II
TEXTURE PROFILE CHARACTERISTICS OF 3 SP COMMERCIAL CULTIVARS
Cultivar
White
Hardness
(N)
Adhesiveness
(Ns)
6.73 a
0.18 b
Springiness Chewiness
(%)
(N)
92.57
a
2.73 a
hardness
10
Yellow
4.95 b
0.23 a
84.81 b
1.93 b
Orange
5.94 a
0.21 ab
86.63 ab
2.53 a
a
8
6
4
a–c
Means within column followed by different superscripts letters are
significantly different at P < 0.05
N = Newton ; Ns = Newton second
2
y = 0.2477x + 2.0678
r = 0.92
0
1
Starch content of White was the highest and followed by
Orange and Yellow. The amylose content of starch from
three cultivar was significantly different. Orange contained
the highest amylose content and followed by White and
Yellow (Table 3).
TPA attributes of sweet potato commonly are affected by
the chemical component of the tuber, such as moisture,
starch and amylose content. Several studies reported that
amylose-amylopectin ratio was responsible for the textural
characteristics of sweet potato [28], [29], however Noda [13]
explained in term of the molecular architecture of
amylopectin. Besides that, the variation of TPA attributes
could be explained by the varietal differences in the
magnitude of degradation of starch and cell wall substances
during cooking. From 3 cultivars studied showed that
moisture content of steamed specimen affected the TPA
attributes, especially hardness; the higher the moisture
content, the lower the hardness.
b
12
14
16
starch (%)
18
2
2
s pringiness
(%)
100
95
90
85
y = 1.0416x + 72.007
r = 0.74
80
10
12
14
16
18
20
22
starch (%)
100
s pringine s s
(N)
c
y = -1.6217x + 159.42
r = -0.79
95
90
85
80
40
42
44
46
amylose (%)
48
50
TABLE III
STARCH CONTENT OF FRESH TUBER AND AMYLOSE CONTENT
OF STARCH 3 CULTIVARS
Cultivar
Starch
(%,fwb)
Amylose
(%,fwb in starch)
White
19.30 a
25.54 b
c
24.83 c
Yellow
12.34
Fig 1. a. Correlation between hardness and starch content for combination
of 3 commercial cultivars. b. Correlation between springiness
and starch content for combination of 3 commercial cultivars. c.
Correlation between springiness and amylose content for
combination of 3 commercial cultivars.
Previous study found that not only starch and amylose
content influenced the springiness value, but also the
cooking process, including the conversion of starch into
simple sugars and dextrin by amylase enzymes [24] and the
interaction of pectic compounds with sugars or dextrin
which generate certain textural characteristics [23].
Chewiness was measured in term of the energy to masticate
a solid food involving compressing, shearing, piercing,
grinding, tearing and cutting. In the three cultivars,
chewiness was positively affected by the starch content (r =
0.87, P<0.01).
27.15 a
14.43 b
Orange
a–c
Means within columns followed by different superscripts letters
are significantly different at P < 0.05
Also it was found that, hardness of sweet potato tubers
was high positively correlated with starch content of fresh
tubers (r = 0.92, P<0.01) (Figure 1a), but was not affected by
the amylose content. Starch content of SP tubers was
reported to be varied depending on the varieties. Onwueme
[14] reported 8-29% starch in fresh tubers. Den [7] stated
that varietal variation of starch content ranged from 11 to
25%. Whereas Bradbury & Holloway [6] and Paul &
Southgate [15] reported that the starch content of selected
fresh SP tuber was 20.1 and 11.8% respectively. Starch
content of the 3 commercial cultivars varied from 12.34 to
19.30 %, with White was the highest, followed by Orange
B. Moisture content changes
A moisture content change during process of food
production is an important factor regarding the texture of the
product. Figure 2 shows the changes of moisture content
during preparing the RSS.
18
relationship between oil uptake and moisture content of final
product [8], [22].
M oisture (%)
90
White
Yellow
Orange
80
70
C. Physicochemical characteristics of RSS
Texture of dough was measured by reason of the relation
between its characters and the quality of product. Table 4
exhibits the physical characteristics of dough. Dry matter
content of dough generated from White and Orange was not
significant different (P>0.05), and considered higher than
Yellow. Although the dry matter content of Yellow dough did
not meet the requirement of Gutcho [10], the deformation of
stick during first frying did not occur. According to Gutcho
[10], products containing more than 73 % by weight of water
tend to puff undesirably during frying. There was no
significant different (P>0.05) on firmness and work extrude
of SP mashed during extrusion process. Although the dry
matter content of dough showed sign of difference, firmness
and work of extrusion exhibited insignificant difference
(P>0.05). It seems that the texture of SP mashed was not
only influenced by moisture but also by other factors such as
starch, amylose and amylopectin content. It was proved that
the work of extrusion was correlated with starch and
amylose content of tubers i.e. r = 0.71, P<0.05; and r = -0.67,
P<0.05 respectively. Amylose content of Orange was higher
than White and Yellow cultivars [20].
60
50
40
30
20
10
0
Tuber
Blanche d chip
Mashed
Frozen stick
Frie d s tick
Processing preparation
Fig 2. Moisture content changes during RSS processing for White, Yellow
and Orange varieties.
Slight increase of moisture content was occurred in
blanched chip. In the next stage, the moisture content of
mashed or dough decreased. The decrease of moisture
content continued until the final product which in this case
was caused by frying. First frying of the raw sticks was
conducted at about 163 °C for 1 min, then packaged in
plastic bags and frozen at -20 °C, whereas the second frying
was done by deep frying in 175 °C for 2 minutes as a final
preparation.
TABLE IV
PHYSICAL CHARACTERISTICS OF DOUGH MADE OF 3 CULTIVARS
Cultivars
White
Dry matter
(%)
27.68 a
Firmness
(N)
112.3 a ns
Work of extrusion
(Ns)
4,513 a ns
Yellow
24.79 b
125.1 a
3,063 a
Orange
29.29 a
116.1 a
3,926 a
TABLE V
PHYSICAL CHARACTERISTICS OF RSS MADE OF 3 CULTIVARS
Physical
characteristics
a – b
Means within columns followed by different superscripts letters are
significantly different at P < 0.05
N = Newton ; Ns = Newton second
The fluctuation of moisture content of the three cultivars
was monitored during production of RSS Based on cultivars,
the fluctuation of moisture content followed similar pattern.
Increase of moisture content occurred during blanching due
to gelatinized of the starch; however small decrease occurred
in Yellow cultivar. Addition of SP flour caused reduction in
dough moisture content; however the decrease of moisture
content in the 3 cultivars followed similar leaning. In this
stage, addition of 5% SP flour was generated significant
(P<0.05) dry mater content of dough. White and Orange
contained 27.68 and 29.29% dry matter or 72.32 and 70.71%
moisture content, respectively; whereas Yellow cultivar had
24.79% dry mater or 75.21% moisture content. Nonetheless,
the different dry mater contents did not provide any effect on
firmness or work during extrusion of dough (Table 4). The
decrease of moisture content for White, Orange and Yellow
was 5.29; 4.69; and 5.12% respectively. The different
tendency of declining moisture occurred during frying
process.
White and Yellow had similar tendency of
decreasing moisture content, whereas Orange declined
sharply. The difference of this occurrence might be due to
the amylose content. Orange contained the highest amylose
compared with White and Yellow. The water trapped in
dough was easily removed by the frying temperature. The
decrease of moisture content from dough to final product
was 19.87; 21.29 and 31.1% respectively for White, Yellow
and Orange. Removing water from the food during frying
affected the fat absorption, and it is found the linier
White
Cultivars
Yellow
Orange
Moisture (%)
Firmness (N)
Shearing force (N)
52.45
1.02 a
4.72 a
53.92
0.52 b
2.38 b
39.61 b
0.71 c
3.97 a
TPA:
Hardness (N)
Springiness (%)
Cohesiveness (Ns)
Chewiness (N)
13.65 a
78.33 a
0.38 a
3.45 a
8.19 b
70.67 b
0.36 b
1.90 b
15.37 a
71.33 ab
0.23 c
1.86 b
a
a
a – c
Means within rows followed by different superscripts letters are
significant different at P < 0.05
N = Newton ; Ns = Newton second
Textural characteristics of RSS made of 3 cultivars
evaluated using three methods is shown in Table 5. In
puncture test, result showed that the firmness value of White
RSS was the highest and different from two other samples,
whereas Orange was higher than Yellow RSS. Cutting-shear
test generated the force needed to cut the RSS. The value of
shearing force was higher than puncture test. RSS made
from White had the highest value of firmness and shearing
force, and Orange produced RSS with medium firmness and
shearing force, though for shearing force it was not
significant different (P>0.05). Yellow cultivar generated the
RSS with the lowest firmness and shearing force. According
to the statistical calculation, it appeared that the puncture test
was more sensitive than shear test proved by lower
coefficient of variation compared with shear test. Even
though, shear test still need to be done due to know the force
needed to cut the sample as a simulation of biting the RSS as
conducted by many researchers.
19
was brighter than Yellow which was resulted of significantly
higher L value of White RSS than Yellow RSS. The different
of Orange with White and Yellow RSS was the a or redness
value. Orange cultivars generated RSS having very high
redness colour. However, the colour of the final product
turned darker after final frying. The colour change occurred
during frying which might be caused by browning.
Browning might be caused by the activity of polyphenol
oxidase enzymes in the presence of tannin or tannin-like
compounds that exists in SP flour and also non enzymatic
browning, especially caramelization, occurred during frying
due to the high content of sugar in sweet potato. It is
possible that SP flour contains high sugar leading to
browning during frying.
The chemical characteristic of RSS made from 3 cultivars
is shown in Table 7. Fat is considered to be an important
factor in fried product. Fat content of frozen and fried RSS
made of Orange was higher than White and Yellow. It’s
because the decreasing of moisture content from mashed to
frozen, and frozen to fried RSS was higher than others
(Figure 2). High fat content in restructured product occurred
by the fat replacing water during frying. Oil absorption
occurs as moisture is removed from the food during frying
[22] and there is a linear relationship between oil uptake and
water content of final product (Gamble et al., 1987). Figure
2 shows that decreasing of moisture content during frying in
Orange was sharper compared to the other 2 cultivars.
Protein is not an important compound in sweetpotato and its
product and it is well known that SP is not a source of
protein. As not a source of protein, protein content of RSS
was found between 2.55 and 3.59% (db), whereas
carbohydrate ranged from 59.19 to 71.83% (db) within the 3
cultivars. The result found that RSS was a good source of
mineral based on the ash content.
Based on TPA, White and Orange cultivars generated
RSS which was not significant value (P>0.05) of hardness
compared with Yellow RSS. This result was similar tendency
as hardness of the tubers (Table 2). The similar pattern was
also occurred in springiness, that RSS made of White and
Orange cultivars had the higher springiness value than
Yellow. Adhesiveness of the RSS could not be determined
because the oil covering the surfaces that avoid attaching
samples into platform of texture test instrument. White
cultivar produced the RSS with the highest cohesiveness and
followed by Yellow and Orange, moreover White and
Orange generated RSS that were higher in chewiness value
than Yellow. The TPA method resulted in similar trend
between hardness and shearing force. White and Orange
generated insignificant difference (P>0.05) hardness of RSS,
whereas Yellow RSS was significant different (P<0.05) with
two others. Hardness of the RSS was significantly negative
correlation with moisture content of the fresh tuber through
the final product. Besides that, hardness of RSS was also
having similar tendency with the hardness of cooked tubers.
White and Orange cultivars had higher springiness value
than Yellow. Cohesiveness of RSS was not affected by the
cohesiveness value of tubers. It’s because of the mashing,
addition of SP flour and CMC. Chewiness indicates the force
needed to masticate the product. White cultivar generated
RSS with the highest chewiness compared with Yellow and
Orange.
TABLE VI
COLOUR OF RSS MADE OF 3 CULTIVARS
Cultivars
a – b
L
a
a
6.17
b
b
16.33 a
White
55.63
Yellow
44.09 b
5.84 b
12.63 b
Orange
45.28 b
21.84 a
16.94 a
TABLE VII
CHEMICAL CHARACTERISTICS OF RSS MADE OF 3 CULTIVARS
Means within columns followed by different superscripts letters are
significantly different at P < 0.05
Cultivars
According to the result of the colour measurement in
Table 6, White RSS had the highest L value meaning it was
brighter compared with Yellow and Orange RSS. It might be
because of the colour of raw materials and the changes
during RSS preparation. The a and b value expresses the
intensity of redness and yellowness respectively. Statistically,
White and Yellow RSS had similar a value; and exhibits
significant difference (P<0.05) with Orange that had very
high a value. Even though insignificant difference (P>0.05)
was found between White and Yellow RSS, the dissimilarity
of L and b generated the difference colour visually. The
Colour of RSS was depended on the colour of tubers. White
tubers produced white frozen stick and light yellow RSS;
and Yellow cultivar generated darker frozen stick and RSS
compared with White. Moreover, bright orange frozen stick
and RSS was produced from Orange cultivar. Colour of
fresh tubers was the decisive factor to the colour of RSS.
White cultivar produced the frozen RSS as white as the
colour of the tubers. Yellow RSS was looked darker than
White result of lower L value. The colour of Orange RSS
was the combination of high redness and high yellowness.
Based on the colour attributes values in Table 6, White RSS
Chemical characteristics
White
Yellow
Orange
Frozen stick:
Moisture (%)
Fat (%, db)
61.10 b
15.68 b
63.91a
16.98 b
53.08 c
32.94 a
Fried Stick:
Moisture (%)
Fat (%, db)
Protein (%, db)
C.hydrate (%,db)
Ash (%, db)
52.45 a
21.44 b
3.59 a
71.83 a
3.13 ab
53.92 a
24.80 b
2.55 b
69.40 a
3.25 a
39.61 b
35.91 a
2.74 ab
59.19 b
2.17 b
a – c
Means within rows followed by different superscripts letters are
significant by different at P ≤ 0.05
D. Sensory properties
Table 8 presents the mean panel scores for quality
attributes of RSS affected by different raw materials. With
regards to colour, panels significantly (P<0.05) preferred
RSS made from Orange cultivar having the bright orange
colour compared to White and Yellow. The mean score of
colour for Orange RSS was 5.8 (slightly below like
20
moderately), whereas White RSS had a mean score 5.4
(midway between like slightly and like moderately). There
was no significant different (P>0.05) of the texture
preferences decided by the panels with the mean score
around 5.0 (“like slightly”). Although the firmness or
shearing force or hardness measured by instrument exhibit
the different value, the panel did not detect any differences
or in other words the texture was in the range of their
preferences.
REFERENCES
[1]
[2]
[3]
[4]
TABLE VIII
SENSORY SCORES1 FOR COLOUR, TEXTURE, FLAVOUR AND OVERALL
ACCEPTABILITY OF RSS MADE FROM 3 CULTIVARS
[5]
[6]
Cultivars
White
Yellow
Orange
a–c
1
Colour
Texture
Flavour
Overall Acceptability
5.4 b
4.9 c
5.8 a
5.0 a ns
4.9 a
5.0 a
5.1 ab
4.9 b
5.2 a
5.1 b
5.0 b
5.2 a
[7]
Means within columns followed by different superscripts letters are
significantly different at P < 0.05
[8]
Hedonic scale: 1 = dislike extremely; 2 = dislike moderately; 3 = dislike
slightly; 4 = neither like nor dislike; 5 = like slightly; 6 = like
moderately; 7 = like extremely
[9]
The panel significantly (P<0.05) preferred the RSS made
of White and Orange for flavour, which had a mean score
slightly above 5.0 (“like slightly”). Flavour of RSS might be
from the specific sweet potato flavour and also the flavour
produced during processing such as caramelization.
Caramelization flavour is produced when sugars contained
in sweet potato were burned by the frying temperature.
Although the significant difference (P<0.05) was found for
overall acceptability, the mean sensory score was slightly
different and above “like slightly”. The significant difference
(P<0.05) was found for overall acceptability between RSS
made from White and Yellow, and Orange. From these
finding, one may conclude that the suitable cultivars for RSS
were Orange and White.
[10]
[11]
[12]
[13]
[14]
[15]
[16]
IV. CONCLUSIONS
RSS is a “fabricated” product from SP patties which is
moulded into finger like and fried to be a french-fry type.
Textural characteristics of 3 commercial cultivars varied
significantly. Fresh tuber of White and Orange cultivars had
a hard texture, elastic and not sticky, whereas Yellow was
soft, less elastic and sticky. These characteristics were
affected by starch and amylose content of the tubers. White
cultivar contained high starch with medium amylose content;
Yellow had low starch with low amylose content; and
Orange contained medium starch with high amylose content.
White cultivar produced the RSS having yellow bright colour,
high firmness and low fat content, whereas Orange cultivar
generated RSS with bright orange colour, medium firmness
but high fat content. RSS made of both varieties were
evaluated as acceptable by a sensory panel. RSS made from
White and Orange cultivars were preferred with sensory
score above the average. Result from this study illustrates
that White and Orange sweetpotato cultivars can be used to
make a convenient restructured product (RSS).
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