Physicochemical and Sensory Characteristics of Biscuits from Purple
Sweet Potato Flour and Wheat Flour
Elisa Julianti
1,2
, Ridwansyah
1,2
and Yerika Putri
1
1
Department of Food Science and Technology, Faculty of Agriculture, Universitas Sumatera Utara,
Medan, North Sumatera, Indonesia
2
Centre for Tubers and Roots Crop Study, Universitas Sumatera Utara, Medan, North Sumatera, Indonesia
Keywords: Anthocyanins, Biscuits, Purple Sweet Potato Flour, Sensory Characteristics.
Abstract: Purple-fleshed sweet potato (PFSP) was the source of anthocyanin which provide the powerful antioxidant
activity. The combination of PFSP flour and wheat flour for biscuits manufacturing will give benefits in terms
of color and nutritional value. In this work, PFSP flour was combined with wheat flour in ratio of 100:0;
90:10; 80:20; 70:30; 60:40; 50:50; 40:60; 30:70; 20:80; 10:90; and 0:100. The physicochemical and sensory
characteristics of biscuits were analyzed to evaluate the acceptability of biscuits. Biscuits containing 70% of
PFSP flour had a higher anthocyanin content and accepted by consumers in all attributes of sensory
characteristics. The biscuits from PFSP flour were not only had a higher nutritional value than those of made
from 100% wheat flour (control), but also had an attractive color and high potential for accepting by
consumers.
1 INTRODUCTION
Ipomoea batatas L., also known as sweet potato, is
one of agricultural commodities with abundant
production in Indonesia especially in North Sumatera.
In Indonesia, the amount of sweet potato production
in 2015 is around 2.297.634 tons (Statistics
Indonesia, 2015). In 2017, sweet potato production in
North Sumatra in 2017 was 92.380,3 tons, which is
848,9 tons higher than production in 2016 (Statistics
of Sumatera Utara, 2017). Sweet potato contains a lot
of carbohydrates, dietary fibers, folic acids, and
minerals (International Life Science Institute, 2017;
Zhang et al., 2009; Van Hall, 2000). Purple fleshed
sweet potato (PFSP) is one of sweet potato genotypes
which is contains anthocyanin pigment in their tubers
(Bovell-Benjamin, 2007; Oki et al., 2002). Sweet
potato now is widely used as human diet around the
world (Kamal et al., 2013).
PFSP is a seasonal, perishable and bulky tuber
(Kamal et al., 2013). In order to extend the shelf life,
purple sweet potato needs to be processed into flour.
PFSP flour can be utilized as wheat flour as a
substitute for wheat flour in making various food
products such as cakes (Hutasoit et al., 2018;
Chuango et al., 2019; Azzahra et al., 2019), cookies
(Ulfa et al., 2019), noodles (Julianti, et al., 2019),
biscuits (Aziz et al., 2018) and bread (Santiago et al.,
2015). Biscuit is a dry bakery product made of flour,
oils/fats, with or without addition of other food
ingredients and food additives with baking process.
In Indonesia, 13.4 % of the population consume
biscuits at least 1 time per day (Health Research and
Development Agency, Ministry of Health Republic of
Indonesia, 2013). The increasing number of biscuits
consumption also increase wheat imports in
Indonesia. Although many studies on the evaluation
and utilization of sweet potato flour in many food
products but a little information about improving
PFSP flour quality by giving pretreatment on PFSP
chips before drying and then the flour were used to
make biscuits. The aim of this research was to
determine the physicochemical and sensory
characteristics of biscuit from various ratio of
pretreated PFSP flour and wheat flour.
2 MATERIALS AND METHODS
Sweet potato with deep purple color flesh from
Phakphak Bharat Residence North Sumatera, was
used in the making of PFSP flour. Sodium
Julianti, E., Ridwansyah, . and Putri, Y.
Physicochemical and Sensory Characteristics of Biscuits from Purple Sweet Potato Flour and Wheat Flour.
DOI: 10.5220/0009981100002964
In Proceedings of the 16th ASEAN Food Conference (16th AFC 2019) - Outlook and Opportunities of Food Technology and Culinary for Tourism Industry, pages 55-60
ISBN: 978-989-758-467-1
Copyright
c
 2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
55

metabisulphite was also used as antibrowning agent
in the purple sweet potato flour making. Other
materials such as margarine, sugar, salt and baking
powder for biscuit making was purchased in some
markets in Medan. Chemical reagents used in this
research was chemical reagents for biscuit chemical
analysis.
2.1 Purple Sweet Potato Flour
Production
Purple sweet potato flour was produced by sorting
and cleaning purple sweet potato tubers. Sweet potato
tubers were peeled and sliced into chips with 2 mm
thickness using a slicer machine. The sweet potato
chips were pretreated by soaking in a 2000 ppm
sodium metabisulfite solution for 15 minutes and
washed with running water until the sodium
metabisulfite washed off. The pretreated sweet potato
chips were dried using a drying oven at a temperature
of 55 °C for 18 hours until the chips dry completely.
The PFSP flour was obtained by milling the dried
chips using a milling machine and then sifted using
80 mesh sieving to gain the fine purple sweet potato
flour. Fine PFSP flour was sealed in polyethylene
bags and stored in room temperature.
2.2 Biscuits Production
Biscuits dough was prepared by using the following
formula: 100 g flour (contain different combination
of sweet potato flour and wheat flour (Table 1), 30 g
sugar, 50 g margarine, 1.5 g baking powder, and 0.5
g salt. Biscuits were produced by creaming and
doughing method. Margarine and sugar were mixed
into cream. Flour, baking powder and salt were mixed
separately and added to the cream. The ingredients
were mixed using a low speed mixer. Various
proportion of water (Table 1) were added for making
required dough consistency, and mixing was
continued until the dough was smooth. The smooth
dough was then flattened into sheet using a rolling pin
with 2 mm thickness. The sheet was formed into a
round shape with a diameter of 4 cm and then baked
in 165 °C preheated oven for 15 minutes. After
baking, the biscuits were cooled and stored in room
temperature in an air tight container.
2.3 Analysis of Biscuits Quality
Resulting biscuits were analyzed for their physical
characteristics such as color profile (L*, a*, b*, and
hue (tan
-1
b/a)) (Hutchings, 1999) by using a Minolta
Chromameter CR-400 (Minolta Camera
Co.,Ltd.,Tokyo, Japan), and browning index
(Jimenez et al., 2001) by using the following
equation:
Browning Index = [100 (x-0.31)] / 0,172 (1)
x was calculated by using following equation:
x = (a + 1.75L*) / (5.645L*+ a* – 3.01b*) (2)
Table 1: Combination of sweet potato flour and wheat flour
and proportion of water added for biscuit preparation.
Treatment PSP flour Wheat flour Water
P
1
100 0 45
P
2
90 10
35
P
3
80 20
30
P
4
70 30
30
P
5
60 40
25
P
6
50 50
20
P
7
40 60
15
P
8
30 70
15
P
9
20 80
10
P
10
10 90
10
P
11
0 100
5
Specific volume of biscuits was carried out by
using displacement test (AACC, 2000) and spread
factor was observed according to Toan and Anh
(2018). Texture profile (hardness, adhesiveness, and
% deformation) were carried out by using Brookfield
CT-3 Texture Analyzer. Chemical characteristics
such as anthocyanin content was analysed according
to Giusti and Wrostad (2001), and crude fiber content
was determined according to AOAC (2012).
Sensory evaluation of resulting biscuits was
analyzed using 7 points hedonic test (1= extremely
dislike, 2= dislike, 3= quite dislike, 4= neutral, 5=
quite like, 6= like, 7= extremely like) by 70 panelists
both genders without training. Biscuits were cracked
into quarter and identified by a three digits random
number. The sample was offered to the panelists on a
white plate at room temperature and drinking water
provided. Panelists were asked to evaluate the color,
aroma, taste, texture, and overall acceptance of the
biscuits.
16th AFC 2019 - ASEAN Food Conference
56

3 RESULTS AND DISCUSSION
3.1 Effect of Purple Sweet Potato Flour
and Wheat Flour Ratio on Physical
Characteristics of Biscuits
The results showed that the ratio of purple sweet
potato flour and wheat flour had highly significant
effect on all biscuits physical characteristics. The
results can be seen in Table 2, Table 3, and Table 4.
Table 2: Effect of purple sweet potato flour and wheat flour
ratio on biscuits hue, L*, a* and b* value.
Treatment hue (
o
) L* a* b*
P
1
329.80
±1.18
f
24.67
±0.31
f
15.00
±0.20
bc
-8.73
±0.31
a
P
2
329.97
±1.32
f
26.40
±1.25
f
15.80
±0.40
ab
-9.13
±0.31
a
P
3
330.54
±2.19
f
30.20
±0.40
e
14.40
±0.53
cd
-8.13
±0.50
b
P
4
332.94
±0.74
e
31.20±0.
92d
e
15.53
±0.95
ab
-7.93
±0.31
b
P
5
336.95
±0.32
d
31.60
±0.87
de
16.67
±0.61
a
-7.07
±0.31
c
P
6
342.81
±0.95
c
32.13
±0.31
d
15.80
±0.60
ab
-4.87
±0.23
d
P
7
342.90
±0.72
c
34.73
±2.32
c
15.87
±0.76
ab
-4.87
±0.12
d
P
8
348.99
±0.61
b
38.87
±0.76
b
16.13
±0.46
ab
-3.07
±0.23
e
P
9
353.06
±0.01
a
40.53
±0.58
b
16.00
±1.04
ab
-1.93
±0.12
f
P
10
354.54
±0.64
a
50.67
±0.83
a
13.40
±0.69
d
-1.27
±0.12
g
P
11
85.72
±0.42
72.00
±0.87
3.33
±0.31
44.27
±0.95
Values in the table are averages of 3 replications, ± standard
deviation. Different letter notations in the same column
show significantly different effect at 5% level.
The results showed that the ratio of purple sweet
potato flour and wheat flour had highly significant
effect on biscuits hardness, adhesiveness, and %
deformation. As shown in Table 3, biscuit hardness,
adhesiveness, and % deformation were increasing as
the decreasing of purple sweet potato flour used and
increasing of wheat flour used in biscuits making.
Wheat flour contains a water-insoluble protein called
gluten which consists of gliadin and glutenin
components which produce viscoelastic properties
and can affect the compactness of biscuits. Gliadin
will cause gluten to be elastic while glutenin will
cause the dough to be strong to hold the gas and
determine the structure of the product (Shewry et al.,
2002).
Table 3: Effect of purple sweet potato flour and wheat flour
ratio on biscuits hardness, adhesiveness, and %
deformation.
Treatment
Hardness
(g)
Adhesiveness
(gs)
Deformation
(%)
P
1
582.25
±68.23
c
-0.52±0.01
c
25.88±0.23
e
P
2
724.25
±35.00
c
-0.42±0.04
c
25.91±1.28
e
P
3
1086.25
±44.90
b
-0.39±0.01
b
27.69±1.14
de
P
4
1099.25
±20.15
b
0.22±0.01
b
29.31±2.91
ce
P
5
1023.25
±44.19
b
-0.18±0.01
ab
31.46±0.84
bcd
P
6
1144.50
±101.82
b
-0.15±0.01
ab
32.42±1.92
bc
P
7
1155.50
±133.64
b
-0.08±0.01
ab
32.82±3.03
bc
P
8
1170.50
±118.09
b
-0.05±0.01
ab
33.52±2.93
bc
P
9
1189.50
±42.43
b
-0.04±0.01
ab
33.85±0.73
bc
P
10
1451.00
±10.61
a
-0.02±0.00
a
35.58±0.52
b
P
11
1520.50
±55.86
a
0.01±0.01
a
45.03±2.45
a
Values in the table are averages of 3 replications, ± standard
deviation. Different letter notations in the same column
show significantly different effect at 5% level.
Table 4 shows that the highest specific volume
was obtained by P
11
biscuits with 0.376 and the lowest
was obtained by P
1
biscuits with 0.284. The specific
volume of biscuits were increasing with the
increasing use of wheat flour in biscuits making. This
is because wheat flour contains gluten which can
cause the biscuits bind each other tighter and capture
the gases so that the biscuits expanded and the volume
increased (Shewry et al., 2002).
As shown in Table 4, the highest biscuit browning
index was P
11
biscuits with a value of 91,98 and the
lowest biscuit browning index was P10 with a value
of 20,54. Biscuits browning index were gradually
decreased from P
1
to P
10
and then went up to the
highest in P
11
biscuits.This shows that ohue and
browning index of biscuits had and inverse
correlation. Table 4 also shows that the spread factor
of biscuits were decreasing with the increasing use of
wheat flour in biscuits making. Biscuit dough with
higher gluten protein will be more solid than biscuits
with less gluten protein and will affect biscuits
compactness so that the spread factor of biscuits were
decreasing gradually from P
1
to P
11
treatments. The
decrease in spread factor with increasing protein
content was also reported by Toan and Anh (2018).
Physicochemical and Sensory Characteristics of Biscuits from Purple Sweet Potato Flour and Wheat Flour
57

Table 4: Effect of purple sweet potato flour and wheat flour
ratio on biscuits specific volume, browning index, and
spread factor.
Treatment
Specific volume
(mL/g)
Browning
index
Spread
factor
P
1
0.284±0.011
e
84.29±2.61
b
12.69±0.09
a
P
2
0.286±0.022
e
82.44±3.34
b
12.69±0.07
a
P
3
0.3.18±0.006
d
63.66±1.93
c
12.39±0.40
a
P
4
0.339±0.022
c
d
63.11±4.94
c
11.81±0.16
b
P
5
0.341±0.024
b
c
d
60.51±2.93
c
11.66±0.09
b
P
6
0.342±0.025
b
c
d
49.21±1.04
d
11.58±0.20
b
P
7
0.367±0.014
abc
46.02±4.32
d
10.77±0.39
c
P
8
0.371±0.015
ab
35.33±1.67
e
10.21±0.18
d
P
9
0.371±0.010
ab
31.25±1.75
e
9.82±0.25
de
P
10
0.375±0.009
a
20.54±1.01
f
9.68±0.22
e
f
P
11
0.376±0.011
a
91.98±3.18
a
9.40±0.17
f
Values in the table are averages of 3 replications, ± standard
deviation. Different letter notations in the same column
show significantly different effect at 5% level.
3.2 Effect of Purple Sweet Potato Flour
and Wheat Flour Ratio on
Chemical Characteristics of
Biscuits
The results showed that the ratio of purple sweet
potato flour and wheat flour had highly significant
effect on all biscuits chemical characteristics. The
results can be seen in Table 5. Table 5 shows that the
anthocyanin content of biscuits were decreasing
gradually as the decreasing of purple sweet potato
flour used in biscuits making. Purple sweet potato
flour gives the biscuit a purple color due to the
presence of a natural purple sweet potato pigment
called anthocyanin (Zhang et al., 2009).
Table 5 also shows the biscuit's crude fiber
content were decreasing as the decreasing of purple
sweet potato flour used in biscuits making. The
highest crude fiber content of biscuits was obtained
by P
1
biscuits (made from 100% sweet potato flour)
with a value of 4,64 % and the lowest crude fiber
content was obtained by P
11
biscuits (made from
100% wheat flour) with a value of 1,63 %. This was
because the crude fiber content in wheat flour is lower
than purple sweet potato flour crude fiber content so
that the more purple sweet potato flour was used in
biscuits making, the higher the crude fiber content
was (Toan and Anh, 2018; Srivastava et al., 2012).
3.3 Effect of Purple Sweet Potato Flour
and Wheat Flour Ratio on Sensory
Characteristics of Biscuits
The effect of purple sweet potato flour and wheat
flour ratio on biscuits color, aroma, taste, texture and
Table 5: Effect of purple sweet potato flour and wheat flour
ratio on biscuits anthocyanin content and crude fiber
content.
Treatment
Anthocyanin
content (ppm)
Crude fiber
content (%)
P
1
62.79±1.51
a
4.64±0.15
a
P
2
51.46±1.51
b
3.92±0.12
b
P
3
45.06±2.68
c
3.54±0.08
c
P
4
42.73±0.87
c
3.22±0.05
d
P
5
36.05±1.32
d
2.93±0.17
e
P
6
33.14±0.88
e
2.87±0.15
e
P
7
27.33±1.33
f
2.51±0.14
f
P
8
17.73±1.33
g
2.40±0.17
f
P
9
11.05±0.50
h
2.04±0.06
g
P
10
5.81±050
i
1.84±0.09
gh
P
11
- 1.63±0.14
h
Values in the table are averages of 3 replications, ± standard
deviation. Different letter notations in the same column
show significantly different effect at 5% level.
overall acceptance hedonic value results can be seen
in Table 6.
Table 6: Effect of purple sweet potato flour and wheat flour
ratio on biscuits color, aroma, taste, texture and overall
acceptance hedonic value.
Treatment Color Aroma Taste Texture
Overall
acceptance
P
1
5.50±
0.16
a
5.00±
0.15
b
4.95±
0.06
bc
4.75±
0.12
cd
5.21±
0.17
abc
P
2
5.26±
0.39
abc
4.75±
0.45
b
4.55±
0.73
c
4.65±
0.56
dC
5.10±
0.56
abc
P
3
5.40±
0.04
ab
5.06±
0.18
b
4.82±
0.21
bc
4.75±
0.18
cd
5.18±
0.19
abc
P
4
5.27±
0.17a
bc
5.19±
0.10
ab
5.22±
0.19
ab
5.15±
0.13
abc
5.31±
0.18
ab
P
5
5.35±
0.15
ab
5.12±
0.17
ab
5.05±
0.15
bc
4.92±
0.27
bcd
5.37±
0.02
ab
P
6
4.83±
0.09
cd
4.77±
0.36
b
4.83±
0.47
bc
5.14±
0.28
abc
5.00±
0.25
bc
P
7
4.95±
0.20
bcd
5.11±
0.16
ab
5.09±
0.16
bc
4.94±
0.10
bcd
5.08±
0.07
abc
P
8
4.65±
0.16
d
4.90±
0.04
b
5.15±
0.09
ab
5.20±
0.25
abc
5.03±
0.18
bc
P
9
4.58±
0.07
d
5.14±
0.14
ab
5.35±
0.32
ab
5.30±
0.18
ab
5.10±
0.10
abc
P
10
4.07±
0.59
e
4.90±
0.22
b
5.28±
0.18
ab
5.32±
0.10
ab
4.80±
0.31
c
P
11
5.45±
0.13
a
5.48±
0.20
a
5.72±
0.09
a
5.59±
0.09
a
5.55±
0.14
a
Values in the table are averages of 3 replications, ± standard
deviation. Different letter notations in the same column
show significantly different effect at 5% level.
Table 6 shows that the panelists quite like the
color, aroma, taste, texture and overall acceptance of
the biscuits. The results showed that the ratio of
purple sweet potato flour and wheat flour had highly
significant effect on biscuits color and texture
hedonic value. The results also showed that the ratio
of purple sweet potato flour and wheat flour had
16th AFC 2019 - ASEAN Food Conference
58

significant effect on biscuits aroma and taste hedonic
value, but had no significant effect on biscuits overall
acceptance.
4 CONCLUSIONS
This research concluded that the substitution of wheat
flour with purple sweet potato flour produce a more
attractive color of biscuits, and also have better health
benefits due to the presence of anthocyanin
components and higher fiber content. The best
physicochemical and sensory characteristics of
biscuits from purple sweet potato flour and wheat
flour was produced with the ratio of purple sweet
potato flour and wheat flour of 70:30.
ACKNOWLEDGEMENTS
We wish to thank to Directorate General of Research
Strengthening and Development, Ministry of
Research, Technology and Higher Education
Republic of Indonesia for funding this research
through “Penelitian Terapan “2019” project.
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