Physicochemical and Sensory Characteristics of Bread from Flour,
Starch, Fiber, and Anthocyanin of Purple Sweet Potato
Elisa Julianti
1,2
, Mimi Nurminah
1
and Jasmine Aldrina Iswara
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: Anthocyanin, Fiber, Flour, Purple Sweet Potato Bread, Starch.
Abstract: Purple fleshed sweet potato (PFSP) is a plant with many health benefits such as anthocyanin content with
high antioxidant activity, fiber, starch, and mineral. The focus of this study was to evaluate the effect of ratio
of PFSP flour and starch, fiber (solid waste of PFSP starch processing), and anthocyanin pigment (liquid
waste of PFSP starch processing) on the physicochemical and sensory characteristics of bread. Ratio of flour
: starch : fiber : anthocyanin pigment used in making breads were 73:25:0:2; 73:20:5:2; 73:15:10:2;
73:10:15:2; 73:5:20:2; and 73:0:25:2. The results showed that flour, starch, fiber, and anthocyanin pigments
enhanced the color and nutritional value when incorporated into the bread formulation. Bread with the best
quality and more accepted by consumers was the bread made from a ratio of 73 g of purple sweet potato flour,
25 g fiber and 2 g anthocyanin pigment. Based on these results, flour, fiber, and anthocyanin pigments can
be used as natural colorant and functional food ingredients.
1 INTRODUCTION
Sweet potato (Ipomoea batatas L) is one of the most
important tubers in the world with a production of 133
million tons and is included in seven important plants
as a source of carbohydrates (CIP). In North Sumatra,
sweet potato production in 2016 was 91.531,4 tons,
and in 2017 there was an increase to 92.380,3 tons
(Statistics of Sumatera Utara, 2017). In addition to
carbohydrates as its main ingredient, sweet potatoes
contain vitamins, minerals, antioxidants (β-carotene
and anthocyanin) and fiber (pectin, cellulose,
hemicellulose) (ILSI, 2008) (Zhang, et al., 2009). The
purple fleshed sweet potato (PFSP) has a high
anthocyanin content which shows an intense purple
color (Van Hall, 2000) and provide some biological
functions such as antioxidant activity,
anticarcinogenic activity and antihypertensive effects
(Oki, et al., 2002) (Yang, and Gadi, 2008).
Sweet potato is very potential to be used as a
material for making flour, starch and functional food
(Phomkaivon, et. al., 2018) (Jangchud, et al., 2003).
Application of flour and starch of sweet potato have
been widely studied in making various food products
such as puffed-starch based snacks (Phomkaivon, et
al., 2018), cakes (Hutasoit, et al., 2018) (Chuango, et
al., 2019) (Azzahra, et al., 2019), noodle (Julianti, et
al., 2019), biscuits (Aziz, et al., 2018), cookies (Ulfa,
et al., 2019), and breads (Santiago, et al., 2015)
(Hathorn, et al., 2008).
In the PFSP starch processing, the fiber and
anthocyanin pigments were discharged as waste.
Therefore, the integrated processing of PFSP starch
was being necessary to produce starch, utilization its
solid waste as a source of fiber and its liquid waste as
a source of anthocyanin pigment. Starch, fiber, fiber
and anthocyanic pigments produced can be used in
making bread.
Usually, breads are made from wheat flour. The
use of whole sweet potato flour or starch in making
bread is limited because the lack of gliadin and
glutenin proteins that resulted in inferior bread
making quality (Hathorn, et al., 2008). In this study,
bread was made by using the composite flour from
PFSP flour, starch, solid waste of PFSP starch
processing that then was processed into fiber rich
flour, and liquid waste of PFSP starch processing as a
coloring agent. The purpose of this study was to
determine the effect of comparison of flour, starch,
solid and liquid waste from processing purple sweet
potato on the physicochemical and sensory
characteristics of sweet bread.
Julianti, E., Nurminah, M. and Iswara, J.
Physicochemical and Sensory Characteristics of Bread from Flour, Starch, Fiber, and Anthocyanin of Purple Sweet Potato.
DOI: 10.5220/0009981600002964
In Proceedings of the 16th ASEAN Food Conference (16th AFC 2019) - Outlook and Opportunities of Food Technology and Culinary for Tourism Industry, pages 61-65
ISBN: 978-989-758-467-1
Copyright
c
2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
61
2 MATERIALS AND METHODS
Material used in this study is purple sweet potato with
optimal level of maturity that have deep purple color
from sweet potato farmer in Phak-Phak Barat
Regency, North Sumatera. Sodium metabisulphite
was used as pretreatment agent for making purple
sweet potato flour, starch, solid and liquid waste.
Other materials that used for bread making are sugar,
shortening, margarine, bread improver, yeast, egg,
liquid full cream milk, and xanthan gum. Chemicals
that used to analyzed sweet bread product are ethanol,
methanol, sulphite acid, distilled water, sodium
hydroxide, hydrochloride acid, potassium chloride
acid, acetic acid buffer pH 4.5, trichloro acetic acid.
2.1 Preparation of Purple Sweet Potato
Flour
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 Preparation of Purple Sweet Potato
Starch and Fiber
The extraction process was carried out by cleaning
purple sweet potatoes and then peeling and shredding
with a mechanic grater then sodium metabisulfite
2000 ppm using 1: 3 (w / v) was added. Then
squeezed and filtered, pulp consisting of sweet potato
solid waste which is rich in fiber were dried in an
oven at 60
o
C, and then dry solid waste were
smoothed with a hammer mill, filtered with a size of
60 mesh mechanical sieve so will obtained fiber rich
solid waste of sweet potato. The filtrate was collected
and allowed to stand undisturbed for 3 hours, so the
liquid (supernatant) and starch were obtained. The
starch was washed until the water is clear. The starch
was dried in an oven at 50
o
C for 12 hours. This dried
starch was milled again with a blender and filtered
with a size of 80 mesh sieve. Then, the supernatant is
filtered and concentrated using a waterbath at 50ºC
until the volume becomes half of the initial volume,
and the resulted product was anthocyanin rich liquid
waste of sweet potato.
2.3 Preparation of Sweet Bread
The sweet potato bread was made by mixing flour,
starch, solid waste and liquid waste from the
processing of purple sweet potato mixed according to
treatment. Other ingredients were prepared and
weighed according to the formula in Table 1. Dry
ingredients as flour, instant yeast, sugar, salt, xanthan
gum, and bread improver were stirred using a low
speed mixer until homogeneous, then added eggs and
liquid full cream milk little by little and stirred with a
mixer to form a mixture. Shortening is added while
still stirring until a smooth dough is formed. Next the
dough is weighed. After that, divided by a weight of
50 g each and formed a circle. Then the mixture is put
into a baking sheet that has been smeared with
margarine. Then let it rest for 30 minutes. The bread
dough with its baking sheet is put in an oven at 165
°C for 25 minutes, and cooled to room temperature
for 30 minutes, after which it is packaged with
polyethylene plastic before analysis.
2.4 Analysis of Sweet Bread Quality
Resulting biscuits were analyzed for their physical
characteristics such as color profile (L*, a*, b*, and
ohue (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)
where x was calculated by using following equation:
x = (a + 1.75L*) / (5.645L*+ a* – 3.01b*) (2)
Specific volume by using displacement test
(AACC, 2000) and chemical characteristics such as
anthocyanin content (Giusti and Wrostad, 2001) and
crude fiber content (AOAC, 2012).
Sensory evaluation of resulting biscuits were
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
16th AFC 2019 - ASEAN Food Conference
62
provided. Panelists was asked to evaluate the color,
aroma, taste, texture, and overall acceptance of the
sweet breads.
Table 1: Sweet bread making formula.
Ingredients
Treatment
P
1
P
2
P
3
P
4
P
5
P
6
P
7
P
8
PSP flour
(g)
100
73
73
73
73
73
73
0
PSP starch
(g)
0
25
20
15
10
5
0
0
PSP solid
waste (g)
0
0
5
10
15
20
25
0
PSP liquid
waste (g)
0
2
2
2
2
2
2
0
Wheat
flour (g)
0
0
0
0
0
0
0
100
Sugar (g)
30
30
30
30
30
30
30
30
Instant
yeast (g)
2
2
2
2
2
2
2
2
Shortening
(g)
10
10
10
10
10
10
10
10
Liquid full
cream
milk (g)
60
60
60
60
60
60
60
60
Salt (g)
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Bread
improver
(g)
5
5
5
5
5
5
5
5
Egg (g)
30
30
30
30
30
30
30
30
Xanthan
Gum (g)
1.5
1.5
1.5
1.5
1.5
1.5
1.5
0
3 RESULTS AND DISCUSSION
3.1 Effect of Purple Sweet Potato
Flour, Starch, Solid and Liquid
Waste Ratio on Physical Properties
of PFSP Bread
The results showed that ratio between PFSP flour,
starch, solid and liquid waste affected the physical
properties of bread as shown in Table 2 and Table 3.
Table 2 shows that there were significant
differences in the L*, a*, b* values but there was no
significant difference in the ºhue value among the
sample. Tabel 2 shows that P
1
bread had a lowest L*
and b* value (22.67 and -0.63) and highest a* value
(8.98). This is caused of P
1
bread was made from
100% PFSP flour. The higher L* value caused a
brighter color of bread, while the lower L* value will
produce a darker color of bread (Hutchings, 1999).
Table 3 shows that bread made from 100% wheat
flour had the higher browning index than those in
PFSP bread. P
1
bread has the highest value of
browning index (29.32 g/mL) and P
2
has the lowest
value of browning index (21.79) among the PFSP
bread. Browning index of breads were determined by
protein content and reducing sugars, the higher
protein and reducing sugars content will promote the
Maillard reaction and resulting in the increasing of
browning index of bread (Goesaert, et al., 2009).
Table 2: Effect of blending ratio of flour, starch, solid and
liquid waste on the color value of the PFSP breads.
Treatment
L*
b*
ºhue
P
1
22.67±0.33
cd
-0.63±0.02
a
355.92±0.13
P
2
25.67±0.58
a
-0.53±0.03
c
355.82±0.45
P
3
24.78±0.51
a
-0.54±0.01
c
355.88±0.14
P
4
24.78±0.51
ab
-0.55±0.01
c
355.85±0.03
P
5
24.22±0.38
b
-0.58±0.02
b
355.82±0.30
P
6
23.67±1.00
bc
-0.61±0.02
a
355.54±0.34
P
7
22.44±0.69
d
-0.62±0.01
a
355.65±0.29
P
8
66.2±0.84
19.02±0.19
69.79±1.67
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 3: Effect of blending ratio of flour, starch, solid and
liquid waste on the browning index and specific volume of
the PFSP breads.
Treatment
Specific
Volume (g/mL)
Browning Index
P
1
2.00±0.12
cd
24.94±2.03
a
P
2
2.60 ±0.10
b
2209±0.21
d
P
3
2.56±0.17
b
23.14±1.27
d
P
4
2.24±0.14
c
26.58±1.16
cd
P
5
2.17±0.14
c
25.50±1.16
bc
P
6
2.13±0.15
c
25.37±1.36
b
P
7
1.86 ±0.15
d
25.78±1.06
a
P
8
3.78±0.25
a
41.07±1.75
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 3 shows that P
8
bread has highest value of
specific volume that was 3.78(g/mL). The presence of
gluten affects the power of development, and the
specific volume of bread. Gluten functions to form a
skeleton of bread because of its ability to expand and
hold the gas produced during fermentation (Shewry,
et al., 2002).
3.2 Effect of Purple Sweet Potato
Flour, Starch, Solid, and Liquid
Waste Ratio on Chemical
Properties of Sweet Bread
Table 4 shows that there were as significant
differences in anthocyanin content and crude fiber
content among the PFSP bread samples. Table 4
shows that P
7
sweet bread had the highest crude fiber
content of 4.20%, while the lowest crude fiber content
was found in whole wheat (P
8
)
bread which is 2.59%.
The more addition of solid waste from PFSP starch
Physicochemical and Sensory Characteristics of Bread from Flour, Starch, Fiber, and Anthocyanin of Purple Sweet Potato
63
processing, it will increase the crude fiber content of
breads. Wheat flour had a lower crude fiber content
than sweet potatoes, so that the fiber content of bread
made from wheat flour is also lower than those in
PFSP breads. This result is in agreement with the
report of (Oluwalana, et al., 2012) who found that
bread made from composite with more sweet potato
flour had a higher fiber content than bread with more
wheat flour.
Table 4: Effect of blending ratio of flour, starch, solid and
liquid waste on the anthocyanin and crude fiber of the PFSP
breads.
Perlakuan
Anthocyanin
(ppm)
Crude Fiber (%)
P
1
55.54±4.44
a
4.15±0.10
a
P
2
39.30±3.87
b
2.71±0.16
e
P
3
39.44±3.20
b
3.01±002
d
P
4
39.50±2.97
b
3.28±0.12
c
P
5
39.93±0.88
b
3.42±0.20
bc
P
6
41.99±1.40
b
3.57±0.13
b
P
7
42.26±3.00
b
4.20±0.20
a
P
8
-
2.59±0.08
e
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. P
8
sweet bread anthocyanin content was not
analyzed because P
8
was considered to have no anthocyanin content.
Table 4 shows that the anthocyanin content of
bread made from 100% PFSP flour (P
1
) is higher than
other breads. Higher starch composition in bread
formulation will reduce anthocyanin contents. Bread
with higher levels of solid waste of PFSP starch
processing (P
7
) had a higher anthocyanin content.
PFSP had a natural pigmen called anthocyanin that
give a purple color in products (Zhang, et al., 2009).
3.3 Effect of Purple Sweet Potato
Flour, Starch, Solid and Liquid
Waste Ratio on Sensory Properties
of Sweet Bread
Table 5 shows that in general panelist acceptance of
the color, aroma, taste, texture and overall acceptance
of bread made from purple sweet potato is lower than
bread made from wheat flour (P
8
). Among breads
made from composite flour of PFSP flour and starch,
and waste products from the processing of PFSP
starch, bread made from 100% PFSP flour (P
1
) is
preferred by consumers in terms of color, texture and
general acceptance. But statistically, there is no
significant difference between P
1
and P
7
bread in
terms of consumer acceptance for aroma, texture,
taste and overall acceptance. The lower organoleptic
value of PFSP bread than that of wheat flour bread
can be caused of unpleasant odor a bitter after taste in
PFSP breads that affects the panelist assessment of
the organoleptic value. Sweet potatoes contain
polyphenol compounds that can cause an unpleasant
odor and a bitter taste (Yang and Gadi, 2008).
Table 5: Effect of blending ratio of flour, starch, solid and
liquid waste on the anthocyanin and crude fiber of the PFSP
breads.
Treatment
Color
Aroma
Taste
Texture
Overall
Acceptance
P
1
5.32±
0.06
b
4.76±0.1
9
b
4.67±
0.08
c
4.82±0.6
1
b
4.83±
0.07
b
P
2
5.07±
0.07
de
4.80±0.0
6
b
4.85±
0.02
b
4.60±0.0
5
bc
4.70±
0.08
bc
P
3
5.04±
0.04
e
4.84±0.1
1
b
4.84±
0.16
b
4.49±0.0
2
bc
4.88±
0.03
b
P
4
5.17±
0.04
cd
4.83±0.2
2
b
4.82±
0.12
bc
4.46±0.0
3
bc
4.74±
0.15
bc
P
5
5.22±
0.07
bc
4.80±0.0
9
b
4.78±
0.05
bc
4.55±0.0
2
bc
4.77±
0.17
bc
P
6
5.29±
0.08
b
4.63±0.1
4
b
4.73±
0.05
bc
4.37±0.1
3
c
4.58±
0.24
c
P
7
5.31±
0.08
b
4.85±0.0
7
b
4.70±
0.02
bc
4.63±0.0
4
bc
4.78±
0.06
bc
P
8
5.51±
0.05
a
5.50±0.1
5
a
5.20±
0.02
a
5.42±0.0
8
a
5.40±
0.08
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.
4 CONCLUSIONS
This study results have demonstrated the potential
utilization of purple sweet potato flour and starch,
solid and liquid waste of purple sweet potato starch
processing as composite flour in bread making.
Physical properties of bread made from 100% wheat
flour was better than those in bread from sweet potato
composite flour, but certain chemical properties of
bread from composite flour such as anthocyanin and
fiber content were found higher than that of bread
from wheat flour. Although bread from whole wheat
flour is more liked by consumers, but in general bread
made from 100% of PFSP flour and bread made from
73% PFSP flour, 25% solid waste and 2% liquid
waste of PFSP starch processing is still accepted by
consumers. The PFSP bread had a lower specific
volume, so treatment is needed to increase its the
specific volume。
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.
16th AFC 2019 - ASEAN Food Conference
64
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