Polish Journal of Food and Nutrition Sciences
2024, Vol. 74, No. 1, 82–91
DOI: 10.31883/pjfns/183995
ISSN 1230-0322, e-ISSN 2083-6007
ORIGINAL ARTICLE
http://journal.pan.olsztyn.pl
High-Fiber Extruded Purple Sweet Potato (Ipomoea batatas)
and Kidney Bean (Phaseolus vulgaris) Extends the Feeling
of Fullness
Eny Palupi1* , Naufal M. Nurdin1 , Ghina Mufida1 , Fadhilah N. Valentine1 , Ricter Pangestika1 ,
Rimbawan Rimbawan1 , Ahmad Sulaeman1 , Dodik Briawan1 , Fitry Filianty2
1
Department of Community Nutrition, Faculty of Human Ecology, IPB University, Indonesia
Department of Food Industrial Technology, Faculty of Agroindustrial Technology, Padjadjaran University, Indonesia
2
Low intake of dietary fiber is closely related to an increased risk of various non-communicable diseases globally. This study
aimed to develop a formulation for high-fiber extrudate based on purple sweet potato and kidney bean and evaluate the nutritional value of the products and their satiety index after consumption. Optimization of the formula was carried out using four
levels of purple sweet potato flour substitution with kidney bean flour: 0, 20, 30, and 40% (w/w). The extrudates were obtained
using a double-screw extruder at 60°C, with the auger, screw, and cutter speeds of 40, 40 and 50 Hz, respectively. The satiety
index determination involved 16 subjects with body mass index in optimal range, and data from the visual analogue scale
(VAS) questionnaire were used at 0, 30, 60, 90, 120, 150, and 180 min after consumption of the test food. The product with
the highest substitution (40%) of kidney bean was selected as the best based on the sensory acceptability and nutritive value
– contents of protein and total fiber were 13.20 and 17.00 g in 100 g dry matter, respectively. The estimated shelf-life of this
extrudate was 19 months. Satiety index values for commercial cereals, extruded purple sweet potato, and extruded purple
sweet potato with kidney bean were 99, 104, and 140, respectively. This research showed that the consumption of high-fiber
extruded sweet potato with kidney bean could significantly extend the feeling of fullness with low energy contribution so that
it might prevent excess calorie intake contributing to overweight and obesity.
Key words: calorie, extruded food, high-fiber food, satiety, obesity
INTRODUCTION
A high-fiber diet plays a critical role in controlling various health-related biomarkers, including blood glucose, blood pressure,
cholesterol levels, and others [Khalid et al., 2022]. However, majority of adults globally consume less than 20 g of fiber per day
[Stephen et al., 2017], whereas the recommended fiber intake
for adult ranges from 25 to 29 g per day [Reynolds et al., 2019].
Fiber aids in smooth bowel movements and prevents constipation. It also forms a matrix with carbohydrates in food, slowing
down digestion and glucose absorption to maintain stable blood
glucose levels. Additionally, the fermentation of fiber in the large
Obesity is a chronic inflammatory condition that is characterized by an increase in total body fat. As many as 39% of world
adults aged over 18 years are overweight, with 13% classified as
obese [WOF, 2023]. The consumption of foods high in energy,
fat, and simple carbohydrates, combined with a low fiber intake
and a lack of balanced energy expenditure, can act as triggers
for obesity [Lasimpala et al., 2021]. Alongside the prevalence
of obesity, the risk of metabolic syndrome issues also increases,
being an initial bridge to various non-communicable diseases.
*Corresponding Author:
Submitted: 31 August 2023
Accepted: 12 February 2024
Published on-line: 7 March 2024
e-mail: enypalupi@apps.ipb.ac.id (E. Palupi)
© Copyright by Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences
© 2024 Author(s). This is an open access article licensed under the Creative Commons Attribution-NonCommercial-NoDerivs License
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
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r Production of purple sweet potato and kidney bean
flakes
The production of flakes from purple sweet potato and kidney bean was consisting of three main stages, i.e., tuber flour
production, legumes flour production, and ingredient mixing
followed by extrusion. The production of purple sweet potato
flour began with cleaning the sweet potatoes to remove any
soil adhering to their skin. Once cleaned, the sweet potatoes
were manually cut into medium-sized pieces (3×3 cm), which
were then steamed at a temperature of 100°C for 20 min using
a PM-3A steamer (Armfield, Bogor, Indonesia) with a capacity
of approximately 15 kg of cut sweet potatoes. Subsequently,
the steamed sweet potatoes were mashed using a planetary
mixer (Gansons, Bombay, India) until smooth. The mass was
then dried using a model T of double drum dryer (Simon Dryers,
Nottingham, UK) at a temperature of 110°C. The drying process
resulted in purple sweet potato sheets and various-sized pieces
that were still slightly moist. Therefore, they were further dried
in a cabinet dryer (Gelenkwellendienst H. Orth GmbH, Ludwigshafen, Germany) for a minimum of 90 min at 60°C. Once
the sheets and pieces were completely dry, they were ground
using a ZS A300 pin disc mill (Phoenix, Jakarta, Indonesia) to
obtain purple sweet potato flour with a particle size <0.25 mm
(screen with 60 mesh). A single batch of purple sweet potato
flour yielded as much as 46% of the fresh tuber weight.
As for the production of kidney bean flour, the kidney beans
were washed and sorted to remove poor quality beans, such
as rotten, sprouted, broken, and dried before soaking at room
temperature (approximately 25°C) for 30 min. The soaked kidney
bean was boiled using a PM-3A steam jacket kettle (Armfield)
for 60 min until softened. This boiling was performed to fully
cook the beans and enhance the texture (softened), palatability,
and ease the subsequent grinding. Subsequently, the cooked
kidney bean was finely mashed using a planetary mixer (Gansons). The drying of mashed kidney bean was performed using
a double drum dryer (Simon Dryers) and a cabinet dryer (Gelenkwellendienst H.), followed by further grinding using a ZS A300
pin disc mill (Phoenix), similar to the processing of purple sweet
potato flour. The yield of obtaining flour from kidney beans was
as much as 80%.
The development and testing of the purple sweet potato
and kidney bean extrudate formulations were conducted as
a trial-and-error process before producing the final extruded
product. This stage aimed to assess the feasibility of the product
concept and estimate formulas for the best quality products.
The feasibility and the quality of the concept and formula were
tested based on the qualitative sensory evaluation by the selected panelists who met International Organization for Standardization (ISO) standard of sensory panelist [ISO 8586:2014]. The results
of this evaluation are shown in Table S1 in Supplementary Materials. The development and optimization also included determining the temperature and time of extrusion. The final formulas,
F0, F1, F2, and F3 (with different ratios of sweet potato flour to
kidney bean flour – 100:0, 80:20, 70:30, 60:40 (w/w), respectively),
used to obtain extruded purple sweet potato and kidney bean
intestine helps maintain pH balance and gut microbiota, reducing the risk of colorectal cancer [Dhingra et al., 2012].
Purple sweet potato (Ipomoea batatas L.) is a common tuber
found in Indonesia. It might be served as a staple food containing up to 2.01–3.87 g/100 g of fiber in their fresh matter. Even
in the form of flour, purple sweet potatoes have a high fiber
content of up to 11.9 g/100 g [Huang et al., 1999; Palupi et al.,
2023]. Kidney bean (Phaseolus vulgaris L.) is a type of legume
known for its nutritional value as 100 g of kidney bean flour
contains 13.12 g of fiber [Palupi et al., 2023]. These two foods not
only have a high fiber content, but they also contain proteins
with noticeable essential amino acids [Audu & Aremu, 2011;
Kurnianingsih et al., 2021]. According to Herreman et al. [2020],
the combination of proteins of tubers and legumes represents
one of the suitable plant-based amino acid profiles. Purple sweet
potato was detected as poor in methionine [Kurnianingsih et al.,
2020], whereas, among common legumes, kidney beans are
considered high in methionine, i.e., 0.105 g/100 g [Margier et al.,
2018].
A diet rich in fiber and high-quality protein can help people with obesity and pre-diabetes feel fuller for longer periods
of time, improve their lipid profiles, and lose weight by lowering
insulin resistance [Clark & Slavin 2013; Dhillon et al., 2016; Lesgards, 2023; Rebello et al., 2014; Starr et al., 2019]. As a result, this
kind of diet is also linked to a lower risk of developing a number
of diseases linked to the metabolic syndrome [Amankwaah et al.,
2017; Glynn et al., 2022; Reynolds et al., 2020]. A previous study
reported that a high-quality protein diet helped prevent cardiovascular disease and type II diabetes by ameliorating the blood
lipid profile and insulin resistance index in obese middle-aged
and older adults [Starr et al., 2019].
Considering the above, it seems reasonable to make an effort
to formulate a product from purple sweet potatoes and kidney
beans, which can serve as a source of fiber and valuable protein, increasing the feeling of satiety and reducing the need
for additional meals that could lead to excessive caloric intake.
A product that can be formulated using purple sweet potatoes and kidney beans is flakes. These products are typically
consumed for breakfast due to their convenience [Priebe &
McMonagle, 2016]. The aim of our research was to optimize
the formulation of a high-fiber extrudate using purple sweet
potatoes and kidney beans and characterize the nutritional,
physical and sensory characteristics of the final product, as well
as the satiety index after consumption, as part of an initiative to
enhance fiber intake in the population.
MATERIALS AND METHODS
r Materials
There were two main materials that have been used in this
research, i.e., purple sweet potato and kidney bean. The variety
of purple sweet potato was Ayamurasaki, which was procured
from the local farmer in Dramaga, Bogor, Indonesia. In a single
run of purple sweet flour, as many as 100 kg of tubers have
been used. A common kidney bean (50 kg) was purchased from
the local market (Bogor, Indonesia).
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Pol. J. Food Nutr. Sci., 2024, 74(1), 82–91
TABLE 1. Formulas (F0–F3) of extrudates.
Ingredient (g)
F0
F1
F2
F3
2,100
1,680
1,470
1,260
0
420
630
840
Rice flour
330
330
330
330
Corn flour
45
45
45
45
Milk powder
25
25
25
25
Salt
10
10
10
10
1
1
1
1
Water
200
200
200
200
Oil
50
50
50
50
Main ingredients
Purple sweet potato flour
Kidney bean flour
Complements
Liquid ingredients (10% of dry ingredients)
Emulsifier
products are presented in Table 1. The dry ingredients, such as
purple sweet potato flour, kidney bean flour, rice flour, cornstarch,
milk powder, and salt, were mixed until well blended. Separately,
the liquid ingredients, such as water, oil, and emulsifier, were
homogenously combined. Subsequently, all the ingredients were
mixed together using a Ueno noodle machine (Siraitodai Fhutuu
Tokyo Manufacture, Japan) before being fed into the Twinscrew
Bex 2256 extruder (Berto Food & Beverage Processing Machines,
Jakarta, Indonesia). This extruder features three different speed
settings, i.e., auger, screw, and cutter. The auger, also known
as the feeder screw, is located at the beginning of extrusion
process and is responsible for feeding the raw material into
the extruder. The screw is located inside the extruder barrel
and plays an important role in melting, mixing, and shaping
the material as it moves along the barrel. The cutter is located
at the end of the extrusion process. The faster the cutter operates the smaller the size of the resulting product. The extrusion
temperature, auger, screw, and cutter speed were monitored, as
well as the selection of the appropriate mold during the development and optimization of the formulation. The optimal extrusion
temperature has been achieved at 60°C for the third temperature
setting, with the first and second temperature settings were
turned off. This setting is suitable for raw materials with a water
content of up to 15%. During the trial process, the optimal speed
settings were also obtained for the auger, screw, and cutter, with
speeds set at 40, 40, and 50 Hz, respectively, where 10 Hz equals
to 600 rpm. Based on the formulas F0, F1, F2 and F3 (Table 1), four
extrudates of purple sweet potato with kidney bean substitution (E0, E1, E2 and E3, respectively) were produced. The flakes
were then cooled at room temperature (25°C) for 30 min before
being packaged in aluminum foil using a sealer. These products
were subsequently subjected to determination of color and texture characteristics, sensory evaluation, analysis of nutrients,
shelf-life and satiety index. As many as three experiments were
performed for physical, sensory, and nutritional analysis. While
the assessment of shelf-life has been conducted through eight
batches of experiments as eight time series experiment. Furthermore, as many as three batches of production have been
carried out for satiety index assessment, with all batches being
homogenized prior to the packing and testing.
r Physical characteristics analysis
The analysis of the physical characteristics included the assessment of the color and texture of the extrudates. The color analysis was conducted using an AMT511 Chroma Meter (Amtast,
Lakeland, FL, USA), which measures the color of the samples
based on the CIELab system. This system provides color measurement results expressed in L*, a*, and b* coordinates, which
represent lightness (dark-bright), redness (green-red), and yellowness (blue-yellow), respectively. The texture of the flakes was
tested for hardness using a CT3-100 Brookfield texture analyzer
(Brookfield, Toronto, Canada).
r Nutrient content determination
The nutrient content analysis of purple sweet potato and kidney
bean extrudates includes determining the moisture content using the gravimetric AOAC International method [AOAC 952.10,
2005], ash content using the gravimetric method [AOAC 923.03,
2005], lipid content using the direct extraction method with
a Soxhlet apparatus [AOAC 922.06, 1922], protein content using
the Kjeldahl method [AOAC 920.87, 1920], and total fiber content
using the enzymatic-gravimetric method [AOAC 985.29, 2003].
Carbohydrate content was estimated on the basis of balance.
Results of nutrient content were expressed based on dry matter
(DM) of extrudates.
r Sensory evaluation
The sensory evaluation consisted of two tests, i.e., quantitative
descriptive analysis (QDA) and overall acceptance rating test,
also known as the hedonic test. QDA has been done by involving
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physiological conditions to return to their baseline [Becker et al.,
2022; Nolan et al., 2016].
A total of 16 subjects was included in the study, following
Forde’s [2018] recommendation of requiring 15–18 subjects to
compare satiety between products. The subjects participating in this research met the inclusion and exclusion criteria.
The inclusion criteria were as follows: individuals with body
mass index (BMI) in optimal range (BMI 18.5–22.9 kg/m2), man
or woman aged between 20–22 years, willing to be interviewed
and complete the questionnaire, not currently on any specific
diet, willing to undergo measurements of body weight, height,
body composition, and participate in all activities, and not allergic
to nuts. On the other hand, the exclusion criteria were suffering
from chronic illnesses or complications.
The data was obtained through the completion of questionnaires and direct measurements on the subjects. The primary
data included subject characteristics (name, age, and gender),
anthropometry (height and weight), satiety levels, as well as
the macro-nutrient content of the test foods, (white bread, commercial cereals, extruded purple sweet potato, and extruded purple sweet potato with kidney bean). Data related to the subjects’
nutritional status was collected through direct measurements
using a digital floor scale for body weight (HN-289, Omron,
Kyoto, Japan) and a microtoise for height (GEA SH2A stature
meter, Bogor, Indonesia). Data was collected through a visual
analogue scale (VAS) satiety score questionnaire at 0, 30, 60, 90,
120, 150, and 180 min after consumption of the food products,
which was then used to calculate the area under the curve for
each flake type and compare it with the area under the curve
for white bread to determine the satiety index (%) for each
subject [Forde, 2018]. Moreover, the curve was calculated using
a trapezoid system for satiety parameters including hunger,
fullness, desire, and food intake. The curve was scaled in units
of time of sampling (counted in hour) and fullness index, which
was expressed as a ruler scale at mm. Therefore, the area under
the curve was expressed as mm×h.
8 trained panelists which met the requirements specified by ISO
standard [ISO 8586:2014]. In QDA, the assessors participated
in a focus group discussion (FGD) to determine the representative attributes, attribute definitions, and the standard scales to
be used. The panelists then quantified each attribute by using
10-point intensity scales (weak-strong intensity) in a separate
testing booth and recorded their ratings on evaluation sheets.
The gathered data was processed and presented in a radar
chart format.
The overall acceptance rating test was conducted to determine how well the products were accepted by the panelists. In this test, the level of acceptance of each attribute was
measured using a 9-point hedonic scale, with 1 being “dislike
extremely” and 9 being “like extremely”. In this research, the observed attributes were appearance, aroma, finger-feel texture,
taste, mouthfeel, aftertaste, and overall perception. The panelists
involved at this test were 40 initiated assessors, who have previously conducted sensory evaluations and understand the rules
of sensory testing but have not yet been selected as assessors.
r Shelf-life estimation
The flakes were stored at three different temperatures, i.e., 25,
35, and 45oC, at 1 till 8 weeks to estimate their self-life. Only E3
has been used for shelf-life estimation. Sensory acceptability (S)
of extrudate was used as a parameter defining changes during
storage. Sensory evaluation of acceptability was performed by
8 selected assessors at 1–7 scale with following interpretation,
7 – equal or better to control, 6 – slight difference to control,
5 – more distinct difference but still acceptable, 4 – beginning to
lose acceptability, 3 – more distinct loss of acceptability, 2 – very
distinct loss of acceptability, and 1 – unacceptable. The control
here was the fresh E3, which was produced on the day of testing. It has been assumed that the test food would start to lose
acceptability at S4 or ln S=ln 4=1.386. The shelf-life was predicted
based on the regression equation of each storage temperature.
Temperature of 30oC was used to calculate the final estimated
shelf-life [Hough, 2010].
r Statistical analysis
Data processing in this research was conducted using Excel 2010
for Windows software (Microsoft, Redmond, WA, USA) and Statistical Product and Service Solution (SPSS) 16.0 software (IBM,
Armonk, NY, USA). The processed and analyzed data included
the results of color and texture analysis, sensory evaluations,
shelf-life estimation and nutrient content, as well as satiety index. The data was then subjected to one-way analysis of variance (ANOVA) using SPSS software (IMB) and further tested with
Duncan post hoc test if significant effects were found among
the treatments. Results of the analysis were considered significantly different if p<0.05.
r Satiety index determination
The satiety index assessment has been approved by the Ethics
Committee of IPB University in Bogor, Indonesia, with the approval number 857/IT3.KEPMSM-IPB/SK/2023. It was measured
after consumption of the flakes with 0% kidney beans flour (E0)
and with 40% kidney beans flour (E3) compared with commercial cereals and using white bread as the reference. White
bread was made from flour (all-purpose flour/medium protein) (70.4 g/100 g), water (10.0 mL/100 g), sugar (6.3 g/100 g),
shortening (4.5 g/100 g), sweet whey powder (4.2 g/100 g),
salt (2.1 g/100 g), yeast (0.8 g/100 g), and whole milk powder (0.8 g/100 g). The design used in this study was a partial
crossover study, where each subject was given isocaloric food
with 240 kcal after 10 h fasting. The test foods were given four
times on four different days, but on the same day, all subjects
were given the same type of food. There was a 3-day interval or
washout period between the test foods to allow the subjects’
RESULTS AND DISCUSSION
r Formulation and processing
The key steps in optimizing the formula for extruded products with purple sweet potato and kidney bean were adjusting
the composition of additional flours, reducing or eliminating
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Pol. J. Food Nutr. Sci., 2024, 74(1), 82–91
certain ingredients, and controlling the moisture content
of the raw dough. It was also important to optimize the extruder settings, including the extrusion temperature based on
thermo-control and the rotations of the screw, auger, and cutter.
For this purpose, a series of trial-and-error experiments were
carried out. The selection of the extrusion temperature and machine speed settings was performed based on the optimization trials conducted as part of preliminary research. Thirteen
trials (Table S1) were conducted to develop the formulation
and determine the extruder’s auger, screw, and cutter rotations,
as well as the dough’s moisture content to achieve an optimal
product quality. The screw type and also its speed have a significant impact on the rheological properties of the final product
[Tomaszewska-Ciosk et al., 2012].
During the development of the extrudate formula, liquid
ingredients (water, oil and emulsifier) were added (Table 1). They
played a vital role in the drying process during the extrusion
and in forming a matrix between starch and protein present
in the dough. When heated, the starch experiences high pressure during extrusion, causing the dough to expand as it exits
the extruder, resulting in expanded products. Without the addition of water to the product, the extruded dough cannot fully
be formed, leading to non-expansion or burnt dough, causing it
to adhere inside the extruder and obstructing extrusion [Yacu,
2020]. On the other hand, excessive liquid level leads to a resulting product with a soggy or mushy texture. The addition
of oil to the dough could increase the crispiness of the product
and prevent hollowness in the final products. This is because oil
can reduce the friction between the dough and the extruder
screw, thus preventing a rapid increase in temperature due
to mechanical friction in the extruder. In this study, based on
the preliminary research, the optimal liquid percentage was
determined to be 10% (w/w) with oil-to-water ratio of 1:4 (w/v).
The extruder employed in this study was a double-screw
extruder equipped with three thermo-controls. Temperature for
extrusion was reached at 60oC regulated only on the third thermo-control of the machine. Meanwhile, thermo-controls 1 and 2
remined switched off. This configuration is suitable for dough
with a water content of less than 15 g/100 g [Budi et al., 2016].
If the dough’s water content exceeds 15 g/100 g, all thermo-controls must be activated [Budi et al., 2016]. Trials conducted at
higher temperatures (>60°C) resulted in a burnt product. The low
heating setting was chosen as the flours used in this study were
fully cooked during the flouring stages. Through experimentation, it was determined that the optimal settings for the auger
and screw speeds during the extrusion process of this study
were 40 Hz, while the cutter speed was set at 50 Hz. A detailed
evaluation of the trials is provided in Table S1.
r Physical, nutritional and sensory characteristics
The selected formulas (Table 1) were used to obtain extrudates
based on purple sweet potato without or with kidney bean
substitution. The physical, chemical and sensory characteristics
of these products are shown in Table 2. As the percentage
of kidney bean flour substitution increased in the extruded
formulation, there was a corresponding increase in lightness
(L*) and yellowness (b*), but a decrease in redness (a*) of products. The significant variances in extrudate color, particularly
TABLE 2. Physical and nutritional characteristics of extrudates.
Characteristic
E0
E1
E2
E3
L*
47.57±1.23d
51.22±1.29c
53.11±0.88b
56.14±0.99a
a*
27.88±0.83a
24.64±2.58ab
23.54±1.56b
21.57±1.41c
b*
−9.17±0.69c
−2.02±2.10b
−2.65±0.37b
3.12±0.50a
124.44±22.36b
194.25±44.35ab
207.8±10.55a
232.2±81.27a
Moisture (g/100 g)
5.58±0.08a
5.48±0.18a
5.41±0.11a
5.25±0.12a
Ash (g/100 g DM)
2.80±0.06c
2.99±0.01b
3.12±0.04ab
3.26±0.05a
Protein (g/100 g DM)
5.51±0.19d
9.33±0.19c
11.50±0.09b
13.20±0.11a
Lipid (g/100 g DM)
0.56±0.08b
0.67±0.07ab
0.76±0.05ab
0.87±0.04a
85.57±0.25a
81.54±0.29b
79.23±0.28c
77.43±0.14d
369.28±0.47a
369.47±1.03a
369.70±0.32a
370.35±0.49a
16.47±0.09b
16.58±0.01b
17.04±0.11a
17.00±0.04a
5.67±0.04a
4.46±0.15b
4.11±0.02b
3.25±0.11c
10.80±0.13d
12.12±0.09c
12.93±0.13b
13.75±0.07a
Physical characteristics
Hardness (N)
Nutrient content and energy value
Carbohydrate (g/100 g DM)
Energy (kcal/100 g)
Total fiber (g/100 g DM)
Soluble fiber (g/100 g DM)
Insoluble fiber (g/100 g DM)
E0, E1, E2, and E3, extrudates obtained on the basis of formulas with different ratios of sweet potato flour to kidney bean flour – 100:0, 80:20, 70:30, 60:40 (w/w), respectively; L*, lightness;
a*, redness; b*, yellowness; DM, dry matter. Values with different superscript letters (a–d) in a row are significantly different at p<0.05.
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indicating that children generally show a strong preference for
extruded food products made from ingredients like potatoes,
sweet potatoes, fruit extracts, and various cereals [Gumul et al.,
2023; Natabirwa et al., 2020; Potter et al., 2013; Shah et al., 2019].
Children’s inclination toward crispy textures, visually appealing
appearances, and easy-to-consume food products contributes
to their acceptance [Natabirwa et al., 2020]. Past studies have
utilized ready-to-eat extrudates as supplemental foods to enhance nutrient intake in children [Gumul et al., 2023; Natabirwa
et al., 2020; Potter et al., 2013; Shah et al., 2019]. Furthermore,
the extrudate obtained in our study from a formula with 40%
replacement of purple sweet potato flour with kidney bean flour
has a potential to be labeled as a high-fiber, source of protein,
and low-fat food item. The cut off of each claim is 6, 12, 3 g per
100 g flakes, respectively [Indonesian Food and Drug Authority 2022].
The result of QDA showed that the higher portion of the purple sweet potato flour in the extrudate formula provided a greater smoothness and homogeneity, a reduced porosity, a stronger tuber flavor with a milder earthy and beany undertone,
and a sweeter taste of the final products (Figure 1). Additionally,
it was noted that the purple sweet potato resulted in a harder
mouthfeel and a less earthy aftertaste. Purple sweet potato contributed to sweet taste and tuber flavor. Moreover, the significant
content of carbohydrate in purple sweet potato [Kurnianingsih
et al., 2020] seemed to support the consistency of the mixture,
making its texture smoother. While, the kidney bean contributed
to the beany and earthy flavor. The substitution of kidney beans
at 20%, 30%, and 40% did not significantly influence (p≥0.05)
the overall acceptance level (Figure 1), with acceptance ratings
consistently above six on a nine-point hedonic scale, corresponding to a “like moderately” according to the categorization
proposed by Wichchukit & O’Mahony [2014]. Consequently,
the extrudate with 40% kidney bean (E3) substitution was further
evaluated for shelf-life and satiety index. The extrudate without
a bean substitute and commercially available breakfast cereals
were used for comparison.
the reduced redness observed in the flakes with the higher
bean portion. The presence of anthocyanin in purple sweet
potatoes seemed the plausible reason for this phenomenon.
These pigments, found in significant quantities in purple sweet
potatoes (ranging from 3.31 to 13.9 mg/g), are known to influence coloration [Rodríguez-Mena et al., 2023]. Our prior investigation revealed that although some of these anthocyanins
undergo degradation during flour extrusion, their presence
remains notable in the end product [Palupi et al., 2023]. The hardness of the extrudates also varied depending on the proportion
of kidney bean flour in the formula – higher kidney bean flour
content led to a higher hardness (Table 2). Visually, the produced
flakes in our study exhibited a dense consistency with a slightly
flat, concave round shape and a slight porosity. The number
of pores increased with the quantity of kidney beans used. It is
worth noting that the extrusion process has a significant impact
on the composition and physical appearance of the products
[Lisiecka et al., 2021; Ménabréaz et al., 2021].
A similar pattern was also observed in the content of key
nutrients in the extrudates. With increased kidney bean substitution, the levels of ash (crude minerals), protein, lipid, and total
fiber increase (Table 2). The extrudate with 40% bean substitution had the highest contents of crude minerals, protein, lipid,
and fiber at 3.26, 13.20, and 0.87, 17.00 g in 100 g of dry matter
(DM), respectively. It is worth paying attention to the content
of soluble and insoluble fiber in the formulated flakes. Higher
kidney bean flour substitution led to an increase in insoluble
fiber content and a significant decrease in soluble fiber content
(p<0.05). This phenomenon may be attributed to kidney beans’
higher total fiber content compared to purple sweet potatoes,
which predominantly consists of insoluble fiber [Kan et al., 2017].
According to Leite et al. [2022], purple sweet potatoes contain
fiber ranging from 6.5 to 12.6% of their dry matter, depending on the variety. The fiber content of purple sweet potatoes
is primarily composed of cellulose, hemicellulose, and pectin,
at 2.7, 3.6, and 0.47%, respectively [Yuansah & Laga, 2023]. In
contrast, kidney beans are known to contain 26.3% fiber in their
dry matter, primarily composed of cellulose and hemicellulose
[Kan et al., 2017].
Flakes are a ready-to-eat food product that meets the nutritional needs of individuals seeking a convenient source of essential nutrients [Priebe & McMonagle, 2016]. This product is
well-suited to be part of a breakfast menu. The breakfast menu
is capable of satisfying 22.4% of the daily energy requirement
and provides 32.7% of the daily protein requirement, 21.8%
of the daily fat requirement, 21.5% of the daily carbohydrate
requirement, and 33.6% of the daily dietary fiber requirement for
adults aged 19–64 years, both males and females [Gibney et al.,
2018]. A single breakfast serving of the extrudate with purple
sweet potato and kidney bean optimized in our study (50 g),
when accompanied by a glass of fresh cow’s milk, a boiled egg,
and a medium-sized banana, can adequately fulfill the breakfast
requirements of adults. This developed product is also suitable
for consumption by children, as supported by previous studies
r Shelf-life estimation
Determining the shelf-life of a food product is a critical step
before it is introduced to consumers. This process is essential to
ensure food safety, protect consumers, and maintain product
quality. In this study, the shelf-life estimation was conducted
using a sensory approach, which is known for its sensitivity compared to other methods [Hough, 2010]. A first-order kinetic reaction was chosen as the model for shelf-life estimation. Like many
common foods, the developed product experiences a faster
rate of deterioration as storage time and temperature increase
(Figure 2). The correlation between these factors was particularly pronounced at higher storage temperatures. The equation
with a lower slope was derived for 45°C (y = −0.0716x + 1.8891),
in contrast to the equations for 35°C and 25°C, which were
y = −0.0184x + 1.9667 and y = −0.0075x + 1.9684, respectively.
By applying these formulations, a shelf-life estimation graph
87
Pol. J. Food Nutr. Sci., 2024, 74(1), 82–91
Smoothness*
10
Overall acceptance*
6
E0: 7.04a
E1: 6.74ab
E2: 6.62ab
E3: 6.19b
Earthy aftertaste*
Homogenity*
8
4
Porosity*
2
E2
E0
E1
0
E2
Tuber flavor*
Crispness mouthfeel
Hardness mouthfeel*
Earthy flavor*
Beany aroma*
Sweet taste*
Figure 1. Quantitative descriptive analysis (QDA) results and overall acceptance rating of extrudates (E0, E1, E2, and E3) obtained on the basis of formulas with
different ratios of sweet potato flour to kidney bean flour – 100:0, 80:20, 70:30, 60:40 (w/w), respectively. *, Significantly different at p<0.05. Values of overall
acceptance with different superscript letters are significantly different at p<0.05.
A
B
2.0
120
y25 = -0.01x + 1.97
R2 = 0.333
25, 100.10
100
1.8
y35 = -0.02x + 1.97
R2 = 0.910
1.7
1.6
1.5
T = 45°C
1.4
T = 35°C
1.3
T = 25°C
Shelf-life (weeks)
Sensory acceptability (ln S)
1.9
y = -4.65x + 209.05
R2 = 0.930
80
60
40
20
y45 = -0.07x + 1.89
R2 = 0.981
35, 31.50
45, 7.06
0
1.2
0
1
2
3
4
5
6
7
8
9
Storage time (weeks)
20
25
30
35
40
45
50
Temperature of storage (°C)
Figure 2. Sensory acceptability on eight storage times (A) and estimated shelf-life (B) of the extrudates made of purple sweet potato flour with kidney bean
flour substitution. T, temperature of storage; S, sensory acceptability at 1–7 scale with the following interpretation: 7 – equal or better to control, 6 – slight
difference to control, 5 – more distinct difference but still acceptable, 4 – beginning to lose acceptability, 3 – more distinct loss of acceptability, 2 – very distinct
loss of acceptability, and 1 – unacceptable; the test food start to lose acceptability at S=4 or ln S=ln 4=1.386. Control sample, the fresh E3 which was produced
on the day of testing.
commercial cereals had the highest energy value (370 kcal/100 g)
and total carbohydrate content (83.14 g/100 g) (Table 3). In contrast, the extruded purple sweet potato with kidney bean had
the highest protein content (12.5/100 g) and higher fiber content
(16.1 g/100 g) compared to commercial cereals.
The study revealed significant differences in satiety indexes after consumption of extrudates based on purple sweet potato with
and without kidney bean and commercial cereal. The satiety index
for the tested foods, in the order of commercial cereal, extruded
purple sweet potato, and extruded purple sweet potato with
kidney bean, were 99.29, 103.87 and 140.03, respectively (Table 3).
The satiety index computed for the extruded purple sweet potato
with kidney bean (E3) was significantly higher compared to that
calculated for commercial cereals, indicating that the addition
of kidney bean to purple sweet potato flakes resulted in a greater
was constructed for different temperatures, resulting in the final
equation: y = −4.6472x + 208.84. Assuming that the anticipated
storage temperature will be around 30°C, the estimated safe storage time was 19 months. This is a favorable estimation, indicating
that the developed product can be stored at room temperature
for over a year without a significant reduction in acceptability.
r Satiety index
The satiety index serves as a measure of how filling and satisfying
a food is, and it provides valuable information into its potential to
control hunger and regulate food intake. This experiment enabled
the researchers to compare the satiety effects of the test foods,
providing insights into their potential as satisfying food options.
Many factors contributed to the satiety index, one of them being nutrient content. Between products examined in our study,
88
E. Palupi et al.
TABLE 3. Nutritional characteristics of food products used to assess the satiety index and results of this assessment.
Characteristic
White bread
Commercial cereals
Extruded purple sweet
potato
Extruded purple sweet
potato with kidney bean
Energy value (kcal/100 g)
238.70±1.62c
370.24±4.27a
286.56±0.47b
286.48±0.49b
Protein content (g/100 g)
9.90±0.04b
9.90±0.05b
5.20±0.19c
12.50±0.11a
Lipid content (g/100 g)
4.70±0.02a
1.30±0.37b
0.54±0.04b
0.80±0.04b
Total carbohydrate content (g/100 g)
48.38±3.62c
83.14±1.70a
80.8±0.34ab
73.4±0.25b
Available carbohydrate content
(g/100 g)
39.28±0.32d
79.80±0.11a
65.24±0.25b
57.26±0.14c
Total dietary fiber content (g/100 g)
9.10±3.30ab
3.33±1.59b
15.55±0.09a
16.11±0.11a
Soluble fiber content (g/100 g)
2.66±0.96b
0.64±0.31c
5.64±0.03a
3.08±0.02b
Insoluble fiber content (g/100 g)
6.44±2.34bc
2.66±1.28c
9.86±0.06ab
13.02±0.09a
2.57±0.28c
7.03±0.08b
6.85±0.12b
Water content (mL/100 g)
Weight (g) of serving (240 kcal)
35.37±0.37a
100
51.3
ab
66.3
a
66.3
ab
Hunger (mm×h)
17.89±1.32
20.54±2.06
15.15±1.85
13.39±1.94b
Fullness (mm×h)
30.54±1.78ab
28.73±1.64b
33.32±1.84ab
35.98±1.82a
Desire to eat (mm×h)
19.87±2.22ab
22.51±2.15a
16.49±2.17ab
12.96±2.04b
Food intake (mm×h)
20.72±1.77ab
22.80±2.05a
16.78±2.05ab
14.10±2.10b
Satiety index (%)
Reference
99.29±7.43b
103.87±22.47ab
140.03±29.46a
Values with different superscript letters (a–d) in a row are significantly different at p<0.05.
sense of fullness. At the determination at 180-min, the visual
analogue scale (VAS) score for the sensation of fullness resulting
from the consumption of extruded tuber with kidney bean was
49.84 mm (Figure 3). This score was subsequently utilized in conjunction with the regression equation derived from white bread
as a reference (y = −0.30x + 87.96). Then, the calculation yielded
a projected duration of 126 min for white bread to induce the same
level of fullness. Consequently, it can be inferred that the consumption of extruded tuber with kidney bean led to an extended feeling
of fullness by 54 min compared to the white bread.
The study suggests that fiber was the primary factor responsible for prolonging the feeling of satiety compared to protein,
carbohydrates, lipids, and water. The fiber content showed a significant correlation with feelings of hunger (p=0.02, r=–0.30),
fullness (p= 0.00, r=0.35), desire to eat (p=0.00, r=–0.40), and food
intake (p=0.00, r=–0.38). Thus, consuming foods high in fiber can
increase the feeling of fullness (satiety), making the extruded
purple sweet potato with kidney bean a potential source of fiber
to improve daily fiber intake and prevent overeating. The testing
method used in this study can be applied to try other satiating
foods based on total energy. However, during fasting periods
after satiety testing, subjects should not be allowed to leave
the area to minimize variations in physical activity and any disruptions that could affect satiety perception.
90
Prolongs feeling
of fullness
54 min longer
Fullness index (mm)
70
180, 49.84
50
y = -0.30x + 87.96
R2 = 0.994
30
White bread
Comercial cereals
Extruded purple sweet potato
Extruded purple sweet potato
with kidney bean
10
0
30
126 min
60
90
120
Time of sampling (min)
150
180
Figure 3. The visual analogue scale (VAS) for fullness index at fasting intervals
of 30, 60, 90, 120, 150, and 180 min after the consumption of extrudate made
of purple sweet potato flour with and without kidney bean flour compared
with commercial cereals and white bread (as reference) which showed
that the consumption of extruded purple sweet potato with kidney bean
substitution led to an extended feeling of fullness by 54 min compared to
white bread.
CONCLUSIONS
In conclusion, this research optimized the formula of flakes
from the extrusion of purple sweet potatoes with kidney beans.
The extrudate obtained on the basis of the selected formula,
89
Pol. J. Food Nutr. Sci., 2024, 74(1), 82–91
2.
which replaced 40% of purple sweet potato flour with kidney
bean flour, showed good sensory acceptability, nutritional value
(high contents of protein and fiber), and caused a high satiety
index after consumption. The estimated shelf-life of flakes was
as much as 19 months. This product might provide an alternative fiber-rich food that has been proved to prolong the feeling
of fullness compared to the reference and commercial food, so it
is expected to prevent eating more food, which is an initial trigger for excess calorie intake. However, before mass production
of this extrudate, future research is needed on its physical properties such as its wetting capacity, rehydration, milk absorption,
and sedimentation. To ensure the safety of extrudates for mass
production, it is also necessary to assess the content of heavy
metals and microbiological tests. Furthermore, future research
could investigate the long-term effects of consuming extruded
purple sweet potatoes, especially as a main breakfast food, on
other biological markers like blood glucose level and lipid profile.
3.
4.
5.
6.
7.
8.
9.
SUPPLEMENTARY MATERIALS
10.
The following are available online at http://journal.pan.olsztyn.
pl/High-Fiber-Extruded-Purple-Sweet-Potato-Ipomoea-batatas-and-Kidney-Bean-Phaseolus,183995,0,2.html. Table S1. Optimization of the development of extruded purple sweet potato
and kidney beans.
11.
12.
INFORMED CONSENT STATEMENT
This research has obtained permission from the Commission
on Research Ethics Involving Human Subjects, IPB University
Number: 857/IT3.KEPMSM-IPB/SK/2023.
13.
14.
RESEARCH FUNDING
The authors acknowledge to IPB University for financial support
of the research as a “Young Lecturer Grant” for this research entitled “High Fiber and Antioxidants Extruded Purple Sweet Potato
to Prevent Obesity and Non-Communicable Diseases” No. RKA
B1.006.02 and the Article Processing Charge. The authors also
would like to thank for the support of research grant from Southeast Asian Regional Center for Graduate Study and Research
in Agriculture (SEARCA).
15.
16.
CONFLICT OF INTERESTS
17.
The authors declare no conflict of interest.
18.
ORCID IDs
D. Briawan
F. Filianty
G. Mufida
N.M. Nurdin
E. Palupi
R. Pangestika
R. Rimbawan
A. Sulaeman
F.N. Valentine
https://orcid.org/0000-0002-3241-4983
https://orcid.org/0000-0002-2956-3566
https://orcid.org/0009-0009-0236-4717
https://orcid.org/0000-0002-0532-9492
https://orcid.org/0000-0003-2029-3106
https://orcid.org/0009-0007-7503-5741
https://orcid.org/0000-0002-2421-5933
https://orcid.org/0000-0002-9618-7214
https://orcid.org/0009-0007-2141-7947
19.
20.
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