Rheological Properties of Purple Sweet Potato Flour and
Its Application to Noodle Product
Atchara Boonpichai and Piyarat Sirivongpaisal
Department of Food Technology, Faculty of Agro-industry, Prince of Songkla University, Songkhla, Thailand
piyarat.n@psu.ac.th
Keywords: Anthocyanin, Function Properties, Noodle Product, Purple Sweet Potato.
Abstract: Purple sweet potato is a nutritious and abundantly available food crop in Asia, that it has received much
attention because of its nutritional and the accumulation of anthocyanins. The functional properties and
anthocyanin content of purple sweet potato flour (PSPF) were investigated. The pasting profiles of PSPF
measured by Rapid Visco Analyzer (RVA) with respect to temperature, viscosity and time attributes were
investigated. The pasting curve and viscosity parameters were demonstrated that final viscosity and setback
were 1677.33, 817.33 mPa.s, respectively. However, it did not show peak viscosity. The flour paste of
PSPF showed a shear thinning behavior of pseudo-plastic materials, the apparent viscosity decreased with
increasing shear rate. The parameter values, consistency coefficient (k) and flow behavior index (n) were
0.45 Pa.s
n
and 0.55, respectively. In addition, the PSPF contained anthocyanin content of 2.36 mg/g dry
sample. The quality characteristics and anthocyanin content of noodle substituted with different levels at
10%, 20%, 30%, and 40% were investigated. While the substitution of PSPF increased, the anthocyanin
content of noodles increased from 0.48 to 1.02 mg/g dry sample. However, the PSPF had affected the
lightness and texture properties of noodle products. The tensile strength and the elasticity decreased as the
levels of PSPF increased from 20.54 to 16.61 g and 16.07 to 7.79 mm, respectively.
1 INTRODUCTION
Sweet potato is an abundant and inexpensive crop in
Asia. Purple sweet potato has received the most
attention compared to white, yellow and orange
sweet potato because of nutritional value. It contains
a high content of anthocyanin which possess
biological functions such as free radicals
scavenging, antimutagenicity, hepato-protective,
antihypertensive and antihyperglycemic activities
(Suda et al., 2003; Shan et al., 2013). Purple sweet
potato is normally processed to the flour and used as
an ingredient for food products. Flour processing
was able to preserve of anthocyanin ( Shan et al. ,
2013; Kim et al., 2012; Xu et al., 2015).
Noodle products are a traditional food in Asia.
Therefore, traditional noodles are prepared mainly
from basic ingredients (wheat flour, water, and salt)
thus lack of essential nutritional components, such
as dietary fiber, vitamins, and minerals ( Choo and
Aziz, 2010) .
Noodle in which substitution with
purple sweet potato flour ( PSPF) is the one
promising option for healthy products. However,
there is a lack of data about the functional properties
of PSPF and nutritional information of noodle
products substituted with PSPF. This study aims to
investigate the rheological properties of PSPF and
the influence of PSPF on the texture, color, and
anthocyanin content of noodle products.
2 MATERIALS AND METHODS
2.1 Materials
Purple sweet potatoes (Okinawa varieties) are
harvested about 90 days were purchased from
Rajamangala University of Technology Srivijaya,
Nakhon Si Thammarat province, Thailand. Wheat
flour and salt (NaCl) were purchased from the local
supermarket. All chemicals and reagents used in this
study were of analytical grade.
330
Boonpichai, A. and Sirivongpaisal, P.
Rheological Properties of Purple Sweet Potato Flour and Its Application to Noodle Product.
DOI: 10.5220/0009992200002964
In Proceedings of the 16th ASEAN Food Conference (16th AFC 2019) - Outlook and Opportunities of Food Technology and Culinary for Tourism Industry, pages 330-334
ISBN: 978-989-758-467-1
Copyright
c
2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
2.2 Methods
2.2.1 The Preparation of Purple Sweet
Potato Flour
Purple sweet potato flour (PSPF) was prepared using
a modified method of Chainarong et al. ( 2014).
PSPF was packed in silver aluminum foil bags and
stored at 4 ˚C for further analysis.
2.2.2 Pasting Characteristics
Pasting characteristics of PSPF was determined
using a Rapid Visco Analyzer (RVA). The
suspension of PSPF (12% w/w, db) was started at 25
°C and then heated to 95 °C at a rate 1.5 °C/min,
held at this temperature for 3 min and then the
sample was cooled to 25 °C at a rate 1.5 °C/min and
held for 5 min. The parameters pasting temperature
(Tp), peak viscosity (PV), breakdown (BD), setback
(SB) and final viscosity (FV) were recorded.
2.2.3 Flow Behaviour
Flow behavior of PSPF was determined using a
modified method Noosuk et al. (2003). PSPF 8%
(db, w/w) was heated at 95 °C for 15 min and was
transferred to a rheometer equipped with coaxial
cylinder geometry (Z41). The sample was measured
the viscosity and shear stress with shear rates range
10-1000 s
-1
at 60 ˚C. The consistency coefficient and
the flow behavior index were calculated.
2.2.4 Determination of Anthocyanin Content
Purple sweet potato flour was extracted and
determined for anthocyanin content using a modified
method of Yang and Gadi (2008).
2.2.5 Noodle Preparation
Noodles were prepared using a modified method
Zhou et al. ( 2015) . In this study, wheat flour was
substituted by PSPF at levels of 10% , 20% , 30% ,
and 40%.The noodle dough was through a noodle
machine to form a noodle dough sheet and was slit
into 2.5 mm thickness. The noodle strands were pre-
cooked in boiling water 30 sec and cooled for further
analysis.
2.2.6 Color Measurement
The color of noodles was measured using a
colorimeter by Hunter Lab Colorflex.
2.2.7 Textural Properties of Noodle
The textural properties of noodles were determined
as described by Shan et al. (2013) using a texture
analyzer (TA-XT2i). The maximum tension force
and the maximum distance was measured.
2.2.8 Statistical Analysis
The data were expressed as mean ± standard
deviation (SD) of triplicate, in a completely
randomised design. The data were analyzed using
analysis of variance (ANOVA), followed by Ducan's
multiple range test to determine the significant
differences among the means at the 95% confidence
level.
3 RESULTS AND DISCUSSION
3.1 Rheological Properties of Purple
Sweet Potato Flour
The pasting profiles of PSPF measured by RVA are
shown in Figure 1, with respect, viscosity and time
during the heating and cooling cycle. According to
the classification of Schoch and Maywald (1968) are
shown PSPF exhibited restricted-swelling (c-type)
and curve did not show pasting peak, but rather a
very high viscosity during decreasing of
temperature. In addition, viscosity parameters are
shown in Table 1. BD, SB and FV of PSPF were
12.33, 817.33, 1677.33 mPa.s, respectively. Pasting
properties are influenced by the size and shape of
starch granules, amylose content, branched chain-
length distribution of amylopectin.
Figure 1: Pasting profiles of purple sweet potato flour.
The flow behavior at 60˚C over the shear rate
range of 10-1000 s
-1
of PSPF followed the power
Rheological Properties of Purple Sweet Potato Flour and Its Application to Noodle Product
331
law equation (R
2
= 0.99, p<0.05). The relationship of
apparent viscosity and shear rate of PSPF are shown
in Figure 2, the apparent viscosity decreased with
increasing shear rate. In addition, flow behavior (n)
of PSPF was less than 1 ( Table 1) , indicating that
PSPF exhibited shear-thinning behavior of pseudo-
plastic materials ( Evans and Haisman, 1980;
Doublier, 1981; Ellis et al., 1989). Figure 2 showed
PSPF occurred hysteresis loops, indicating that it
was time-dependent non-newtonian flow behavior
of thixotropy.
Table 1: Viscosity parameters from Rapid Visco Analyzer
(RVA) and consistency coefficient and flow behavior
index of purple sweet potato flour.
Pasting parameters
Value
Tp (°C)
-
PV (mPa.s)
-
BD (mPa.s)
12.33±1.53
SB (mPa.s)
817.33±7.02
FV (mPa.s)
1677.33±6.66
Flow behavior
k (Pa.s
n
)
0.45±0.06
n
0.55±0.01
area
940.78±62.33
Note: Each value is mean of triplicate ± SD. PSPF, purple sweet
potato flour; Tp, pasting temperature; PV, peak viscosity; BD,
breakdown; SB, setback; FV, final viscosity; k, consistency
coefficient; n, flow behavior index.
3.2 Application of Purple Sweet Potato
Flour to Noodle Product
3.2.1 Anthocyanin Content of Noodle
Substituted with Purple Sweet Potato
Flour
The anthocyanin content of PSPF and noodles
substituted with PSPF are shown in Table 2. The
anthocyanin content of PSPF and noodles
substituted with PSPF were significantly different
( p0. 05) . PSPF had high anthocyanin content of
2. 36 mg/ g dry sample. The anthocyanin content
increased as the levels of PSPF substitution
increased significantly ( p0. 05) from 0. 48 to 1.02
mg/g dry sample.
3.2.2 Color of Noodle Substituted with
Purple Sweet Potato Flour
The color of PSPF and noodles substituted with
PSPF are shown in Table 3. Noodles substituted
with PSPF at different levels were significantly
Figure 2: Relationship of apparent viscosity and shear rate
of purple sweet potato flour at 60 ˚C over the shear rate
range of 10-1000 s
-1
(a) and relationship of shear stress
and shear rate of purple sweet potato flour (b).
Table 2: Anthocyanin content of purple sweet potato flour
and noodles substituted with purple sweet potato flour.
Samples
Anthocyanin content
(mg/g dry sample)
PSPF
2.36±0.02
a
PSPF substitution (%)
0
0.27±0.03
f
10
0.48±0.01
e
20
0.72±0.01
d
30
0.83±0.01
c
40
1.02±0.01
b
Note: Each value is mean of triplicate ± SD.
a-f
Means with
different small letter superscripts in the same column are
significantly different at 95% confidence level. PSPF, purple
sweet potato flour.
different from the color in terms of L*, a*, and b*
(p<0.05). Increasing levels of PSPF decreased the
lightness (L* value) significantly (p<0.05) from
44.96 to 30.59 with increasing levels of PSPF from
10% to 40%. In similarly, b* value decreased from
4.42 to -0.13. However, the substitution of PSPF
increased, a* value significantly increased (p<0.05).
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332
Table 3: Color of purple sweet potato flour and noodles
substituted with purple sweet potato flour.
Samples
L*
a*
b*
PSPF
57.77 ± 0.70
b
17.97 ± 0.33
a
-3.09±0.09
f
PSPF substitution (%)
0
70.46±0.28
a
2.19±0.07
f
19.72±0.23
a
10
44.96±0.62
c
12.25±0.09
e
4.42±0.09
b
20
38.01±0.18
d
14.76±0.09
d
1.46±0.07
c
30
33.59±0.02
e
15.19±0.11
c
0.57±0.07
d
40
30.59±0.58
f
15.64±0.21
b
-0.13±0.05
e
Note: Each value is mean of triplicate ± SD.
a-f
Means with
different small letter superscripts in the same column are
significantly different at 95% confidence level. PSPF, purple
sweet potato flour.
3.2.3 Texture Properties of Noodle
Substituted with Purple Sweet Potato
Flour
The textural properties of noodles substituted with
PSPF are shown in Table 4. Increasing levels of
PSPF decreased the tensile strength and the elasticity
significantly ( p<0. 05) from 20. 54 to 16. 78 g
f
and
16.07 to 7.79 mm, respectively. It might be due to
flour has a low protein content and the relative
amounts of gluten protein fractions are also
important on the texture properties of noodles will
be soft (Kovacs et al., 2004; Fu, 2008). The tensile
strength of noodle substituted with 10% PSPF was
not significantly different ( p<0.05) comparing with
wheat noodle (0%PSPF).
Table 4: Textural analysis of noodles substituted with
purple sweet potato flour.
Tensile Strength
(g
f
)
Elasticity
(mm)
20.83±1.48
a
63.95±3.78
a
20.54±1.51
a
16.07±1.92
b
18.85±0.58
b
14.17±1.92
b
16.18±0.78
c
9.76±1.10
c
16.61±0.94
c
7.79±1.74
c
Note: Each value is mean of triplicate ± SD.
a-c
Means with
different small letter superscripts in the same column are
significantly different at 95% confidence level. PSPF, purple
sweet potato flour.
4 CONCLUSIONS
The pasting profiles of PSPF measured by RVA did
not show peak viscosity. The flour paste of PSPF
exhibited a shear thinning behavior of pseudo-plastic
materials. The substitution of PSPF increased the
anthocyanin of noodles increased. Moreover, the
PSPF had affected the lightness and texture
properties of noodle products. The tensile strength
and the elasticity decreased as the levels of PSPF
increased. The utilization of PSPF as an ingredient
in noodles might be beneficial that provides
nutritional value and is a healthy food choice for
consumers.
ACKNOWLEDGEMENTS
The authors would like to express their sincere
thanks to Agro-Industry research grant, Prince of
Songkla University, Thailand for supporting
research fund.
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