ORIGINAL RESEARCH
Effect of processing methods on nutritional, sensory, and
physicochemical characteristics of biofortified bean flour
Marie Grace Nkundabombi, Dorothy Nakimbugwe & John H. Muyonga
Department of Food Technology and Nutrition, Makerere University, Kampala, Uganda
Keywords
Extrusion cooking, iron biofortified beans,
malting, mineral bioavailability, roasting
Correspondence
Dorothy Nakimbugwe, Department of Food
Technology and Nutrition, Makerere
University, Kampala, Uganda.
Tel: +256782246089; Fax: +256414533676
E-mail: dnakimbugwe@gmail.com
Funding Information
This work was supported by: International
Centre for Tropical Agriculture (CIAT)/Pan
African Bean Research Alliance (PABRA)
(Grant Number: BSB850/BSC47) and the
USAID - Pulse Collaborative Research Support
Program (Pulse-CRSP), Grant/Award Number:
EDH-A-00-07-0005-00).
Received: 9 June 2015; Revised: 8 September
2015; Accepted: 12 September 2015
[Corrections added on 26 April 2016, after
first online publication: the first name of the
second author was incorrect and has been
changed from “Dororthy” to “Dorothy”; the
name, contact numbers, and email address of
the corresponding author have been changed
from “Marie Nkundabombi”,
“+250788826506”, and nkundabombi@
gmail.com to “Dorothy Nakimbugwe”, “Tel:
+256782246089, Fax: +256414533676”,
and dnakimbugwe@gmail.com respectively;
the Funding Information has been revised.”]
Abstract
Common beans (Phaseolus vulgaris L.) are rich, nutritious and affordable by
vulnerable groups, thus a good choice for biofortification to address malnutrition. However, increasing micronutrients content of beans, without
improving micronutrients bioavailability will not improve the micronutrients
status of consumers. Effect of different processing methods on the physicochemical characteristics of biofortified bean flour was determined. Processing
methods used in this study were malting (48 h), roasting (170°C/45 min),
and extrusion cooking using a twin screw extruder with three heating sections, the first set at 60°C, the second at 130°C, and the last one at 150°C.
The screw was set at a speed of 35 Hz (123 g) and bean flour moisture
content was 15%. Mineral extractability, in vitro protein digestibility, pasting
properties, and sensory acceptability of porridge and sauce from processed
flour were determined. All processing methods significantly increased
(P < 0.05) mineral extractability, iron from 38.9% to 79.5% for K131 and
from 40.7% to 83.4% for ROBA1, in vitro protein digestibility from 58.2%
to 82% for ROBA1 and from 56.2% to 79% for K131. Pasting viscosities of
both bean varieties reduced with processing. There was no significant difference (P < 0.05) between sensory acceptability of porridge or sauce from
extruded biofortified bean flour and malted/roasted biofortified bean flour.
Acceptability was also not affected by the bean variety used. Mineral bioavailability and in vitro protein digestibility increased more for extruded flour
than for malted/roasted flours. Sauce and porridge prepared from processed
biofortified bean flour had lower viscosity (extruded flour had the lowest
viscosity), thus higher nutrient and energy density than those prepared from
unprocessed biofortified bean flour. Estimated nutritional contribution of
sauce and porridge made from processed ROBA1 flour to daily requirement
of children below 5 years and women of reproductive age found to be high.
These results show that processing methods enhanced nutritional value of
biofortified bean flour and that processed biofortified bean flour can be used
to prepare nutrient and energy-dense gruel to improve on nutritional status
of children under 5 years and women of reproductive age.
Food Science & Nutrition 2016; 4(3):
384–397
doi: 10.1002/fsn3.301
Introduction
Micronutrient malnutrition especially iron deficiency anemia and zinc deficiency affect at least half of the world’s
population (Nestel et al. 2006). In Uganda, by considering
384
iron deficiency anemia, the most affected age groups are
children below 5 years (22%) and women of reproductive
age (24%) (UBOS 2012). This is caused by low intake
of daily required amount of micronutrients. Food fortification has been used as one of the approaches to
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. This is an open access article under the terms of
the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
M. G. Nkundabombi et al.
Development of Biofortified Bean Flour
overcome micronutrient deficiencies, but it is hard for
vulnerable and poor people to access fortified processed
food. Biofortification of popular food crops like beans
was therefore proposed as a better intervention to address
micronutrients malnutrition (Kimani et al. 2006; Pfeiffer
and McClafferty 2007).
Common beans (Phaseolus vulgaris L.) are rich in protein (20–28%) and micronutrients (Fe = 34–89 mg/kg
and Zn = 21–54 mg/kg) (Beebe et al. 2000). Beans are
commonly consumed in East and central Africa (50–60 kg
per capita) and are affordable by vulnerable groups making them a good choice for biofortification. Increasing
micronutrients content of beans, without improving micronutrients bioavailability, will not have impact on micronutrients status of consumers (Petry et al. 2012).
Bioavailability of micronutrients is limited by inhibitors,
especially polyphenols and phytates (Gibson 1994; Luo
and Xie 2012). Different processing techniques, such as
germination, roasting, and extrusion cooking have been
reported to reduce the level of antinutrients, thus to improve nutritive value of beans (Marzo et al. 2002; Audu
and Aremu 2011). Processing can also improve cooking
characteristics and physicochemical properties of beans.
Extrusion processing reduces paste viscosity contributing
to enhancement of nutrient content of dishes from beans,
and making products suitable for vulnerable groups like
children and women of child bearing age with high nutrient requirements (Edwards et al. 1994; Thaoge et al.
2003).
The aim of this study was to develop bean flour from
biofortified beans, using malting, roasting, and extrusion
processing, and evaluate the effect of these processing
methods on the nutritional and physicochemical characteristics of the developed bean flour.
for 48 h in a dark place on a wet cloth. Germinated
beans were then roasted at 170°C for 45 min in an
oven (Infrared food oven GL-2A, China) (Nakitto et al.
2015). After roasting, the beans were milled using a
wonder mill (Grain of Truth Bread Company, Smithfield,
North Carolina, USA). Flour was stored in plastic
bags until further analysis. The second part (5 kg) of
each bean variety were extruded using a twin screw
extruder model DP-70-III (Jinan Eagle Food Machinery
Co., Ltd. Jinan City-Shandong Province, China) with
three heating sections, the first was set at 60°C, the
second at 130°C, and the last one at 150°C. The extruder filler was set at a speed of 30 Hz (900 rpm),
the screw was set at a speed of 35 Hz (1050 rpm),
and the cutters were set at a speed of 30 Hz (900 rpm).
The diameter was 4 mm and the flour was extruded
at 15% moisture content. The extruded beans were
milled into flour and packed in plastic bags until further
analysis.
Materials and Methods
Iron and zinc contents of raw, extruded, and malted/
roasted bean flours of both K131 and ROBA1 bean varieties were analyzed by the method described by Duhan
et al. (2002). One gram of sample was placed in 150 mL
conical flash, and wet acid digested with 30 mL of nitric
acid–perchloric acid mixture (HNO3:HClO4; 5:1 v/v) by
heating until clear white precipitates settled at the bottom.
The digested samples were dissolved in double distilled
water and filtered through Whatman # 42 filter paper.
The filtrate was made to 50 mL with double distilled
water and used for determination of iron and zinc contents using Atomic Absorption Spectroscopy (AAS) (model;
PerkinElmer 235, Norwalk, CT).
Preprocessing of bean flour
Iron biofortified bean variety (ROBA1) was purchased
from Community Enterprise Development Organization
(CEDO), a local nongovernmental organization (NGO)
based in Rakai District. K131 beans were purchased from
the Bean program of the National Crops Resource Research
Institute (NaCRRI) in Namulonge, Uganda. K131 bean
variety was selected because it is high yielding but takes
long to cook due to a hard seed coat (Kalyebara 2005;
Nyakuni 2008).
Two varieties of beans, ROBA1 and K131, were subjected to two different processing methods to produce
flour. For each variety, 10 kg of beans were sorted.
One part (5 kg) was soaked in distilled water at 1:2
(w/v) for 24 h. The soaked beans were germinated
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Formulation of composite flour
The composite flour was formulated using processed
bean, amaranth, and rice flours. Amaranth and rice were
previously ground into flour using a wonder mill (Bread
of Truth Company). Amaranth, rice, and bean flours
were mixed at a ratio of 30:30:40, respectively, a proportion reported to be highly acceptable (Ndagire et al.
2012).
Determination of nutritional and
physicochemical characteristics of the
flours
Iron and zinc contents determination
Iron and zinc extractability
Iron and zinc extractability were determined using a
method by Duhan et al. (2002). The minerals in the
385
Development of Biofortified Bean Flour
samples were extracted with 0.03 N HCl by shaking in
water bath (Grant OLS200, Cambridge, UK) at 37°C for
3 h. The clear extract obtained after filtration with
Whatman # 42 filter paper was oven dried (M/S Scientific
Instruments, New Delhi, India) at 100°C and wet acid
digested. The amounts of the HCl-extractable zinc and
iron in the digested samples were determined by the
methods described earlier for determination of mineral
contents:
Mineral extractability %
=
Mineral extractable in 0.03 N HCl
× 100
Total mineral
In vitro protein digestibility
Initial protein content
Protein content was determined by Kjeldahl method #46-12
(AACC 2004). Approximately 0.5 g sample was weighed
into digestion flasks into which 1 g of potassium sulfate,
1 mL of 10% copper sulfate, and 10 mL of concentrated
sulfuric acid were added. A blank with no sample was
similarly prepared. The flasks were heated on a digestion
rack until white fumes were emitted, and the heating
continued for another 2 h.
Flasks were cooled, after which the digests were transferred quantitatively to 50 mL volumetric flasks, made
to volume with distilled water, and mixed immediately.
Distillation of samples was done by pipetting 50 mL
of sample into the distillation chamber and slowly adding approximately 50% NaOH solution to raise the pH.
A conical flask containing 10 mL of 2% boric acid
solution plus two drops of bromocresol green methyl
red indicator was placed under the condenser stem to
collect the distillate. The distillation was allowed to
proceed for 7.5 min after which the receiving flasks
were lowered so that the distillate could wash any remaining ammonia from the tip of the condensing unit.
Titration was done using a burette filled with 0.05 N
H2SO4. The end point was determined by the sample
solution turning from blue-green to pink. The volume
of the acid used (titer) was noted. The percentage crude
protein (% cP) in the sample was calculated using the
following formula:
T × 14 × b × 50 × 100 × 6.25
% cP =
1000 × 5 × Wt
T: titer; 14: atomic weight of N; b: normality of acid
which was approximate 0.05 N; Wt: sample weight; 6.25:
conversion factor for protein from % nitrogen.
386
M. G. Nkundabombi et al.
Pepsin digestion
This was determined using the method of Mertz et al.
(1984). Approximately 0.2 g of the samples was weighed
into 50 mL centrifuge tubes. To each sample, 2 mL of
distilled water was added, shaken, and the tubes were then
placed in a boiling water bath for 20 min. Phosphate buffer
with pepsin solution was added to the mixtures (20 mL
of 0.1 mol/L phosphate buffer and 1:3000 IU Hog pepsin/L,
pH 2.0). A blank was prepared in a similar way without
the sample. The tubes were incubated in a shaking water
bath (Grant OLS200, Cambridge, UK) at 37°C for 2 h
and then centrifuged at 4032 g (225, Fisher Scientific,
Missouri City, Texas, USA) for 15 min and the supernatant
was removed with a dropper and discarded. To each tube,
10 mL of phosphate buffer was added and centrifuged at
4032 g and the supernatant was discarded. The residue
was removed and placed in the center of a filter paper
on a Buchner funnel. Suction was applied to the filter
flask and the remaining residue was rinsed from the tube
into the funnel using 5 mL buffer. The filter paper were
rolled and inserted into Kjeldahl flasks containing filter
paper and sample, and concentrated H2SO4 (10 mL), 1 g
of potassium sulfate, and 1 mL of 10% copper sulfate
solution were added. Digestion, distillation, and titration
were done to determine the protein content.
In vitro protein digestibility =
A−B
A
where A is % protein in sample before digestion and B
is % protein in sample after pepsin digestion
Determination of pasting properties
Pasting properties were determined using the Rapid Visco
Analyzer (RVA-4, Newport Scientific Pty Ltd., Warriewood,
NSW, Australia) with Thermocline for windows software
(AACC # 76-21, 1999). Four grams of flour was suspended
in 25 mL of distilled water in an RVA canister. The
canister was loaded into the RVA and analyzed with a
constant speed (3 g). The holding viscosity, peak viscosity,
final viscosity, and pasting temperature of bean flour and
bean-based composite flour were determined in
duplicates.
Consumer acceptability of porridges and
sauces prepared using the processed flour
of biofortified and conventional beans
Porridge preparation
Porridge was prepared from both extruded and malted/
roasted bean flours of both the ROBA1 and K131 bean
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Development of Biofortified Bean Flour
M. G. Nkundabombi et al.
varieties. The flour (250 g) was mixed with 750 mL of
cold water. The mixture was brought to the boil while
stirring to avoid lumping then cooked for 10 min after
which 50 g of sugar was added.
Sauce preparation
Sauce was prepared from both extruded and malted bean
flours of both the ROBA1 and K131 bean varieties.
Ingredients (26 g of onions or ½ of an onion; 23 g or
½ a green pepper; 69 g or 1 medium sized tomato) were
all chopped. The onions and green pepper were shallow
fried in 50 mL of vegetable cooking oil. About 2 g of
curry powder and 10 g of salt were added. The bean
flour (250 g) was stirred into the mixture, 1200 mL of
water was added gradually with constant stirring to avoid
lumping, and the sauce was cooked for 10 min.
Porridge and sauce acceptability were determined by
50 panelists using a 9-point hedonic scale (Kemp et al.
2009). The flavor, color, appearance, thickness, texture,
taste, smell, and overall acceptability were determined.
below 5 years and women of reproductive age (15–
49 years). The comparison was based on flour rate and
nutrient and energy density of each sauce and porridge
prepared from unprocessed flour, malted/roasted bean
flour, and extruded bean flour. For children aged between
1 and 5 years, contribution of sauce/porridge to their
energy and nutrients intake was computed by considering
300 mL of sauce/porridge as the serving (Pipes and Trahms
1994; Thaoge et al. 2003), whereas for women of reproductive age (15–49 years), 500 mL of sauce/porridge was
considered as the serving. The contribution of iron and
zinc to dietary requirements was calculated based on bioavailable content, while for protein it was calculated based
on digestible protein content.
Data analysis
Data were entered into excel spread sheet and subjected
to analysis of variance (ANOVA) using Statistix software
(version 9.0) at P ≤ 0.05.
Results and Discussion
Nutrients and energy density of flour from
biofortified beans
The processed flour rate, which resulted in porridge or
sauce with a spoonable consistency (2500–3000 cP) (Thaoge
et al. 2003), was determined by measuring viscosities of
the sauce and porridge using Brookfield Viscometer (Model
DVII Rheometer V2.0 RV; Middleboro, MA). The nutrient
content of the gruels with spoonable viscosities were computed and compared to the recommended daily intake
of iron, zinc, protein, and energy (Table 1) for children
Effect of different processing methods on
the nutritional and physicochemical
characteristics of iron biofortified bean
flour
Iron and zinc contents of flours of ROBA1 and
K131 bean varieties
The iron and zinc contents of ROBA1 beans were higher
than that of K131 (Table 2). ROBA1 is a micronutrientenriched variety and is one of the 960 bean population
Table 1. Recommended daily intake of iron, zinc, protein, and energy for target groups.
Age/sex
Male
1–3 years
4–5 years
Female
1–3 years
4–5 years
15–18 years
19–49 years
Pregnancy
≤18 years
19–49 years
Lactation
≤18 years
19–49 years
Iron (mg/day)
Zinc (mg/day)
Protein (g/day)
Energy (kcal/day)
7
10
3
5
13
19
1046
1742
7
10
15
18
3
5
9
8
13
19
46
46
992
1642
2368
2403
27
12
11
First trimester
Second trimester
Third trimester
46
71
71
(+340)
(+452)
10
9
13
12
First 6 months
Second 6 months
71
71
(+330)
(+400)
Source: Adapted from the Dietary Reference Intake series, National Academies Press. Copyright 1997, 1998, 2000, 2001, 2002, 2004, 2005 by the
National Academy of Sciences, (Rolfes et al. 2011).
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
387
Development of Biofortified Bean Flour
M. G. Nkundabombi et al.
Table 2. Results for iron and zinc contents of flours from ROBA1 and
K131 bean varieties.
Table 3. Results for iron and zinc extractability of flours from ROBA1
and K131 bean varieties (%).
Sample
Sample
Iron
ROBA1
K131
Mean
Zinc
ROBA1
K131
Mean
Raw (mg/kg) Malted/roasted (mg/kg) Extruded (mg/kg)
70.25 ± 1.5a 58.40 ± 0.6a
66.45 ± 1.5b 47.75 ± 2.6b
68.35a
53.07b
83.50 ± 0.56a
75.85 ± 1.03b
79.67c
26.75 ± 0.2a 23.00 ± 1.00a
23.00 ± 0.7b 22.95 ± 0.04a
24.87a
22.97b
22.65 ± 0.73a
21.25 ± 0.75a
21.95b
Iron
ROBA1
K131
Mean
Zinc
ROBA1
K131
Mean
Raw
Malted/roasted
Extrusion
40.75 ± 1.06d
38.92 ± 1.02d
39.83c
74 ± 1.41c
70.5 ± 2.12c
72.25b
83.41 ± 1.34a
79.45 ± 0.91b
81.43a
51.5 ± 2.12c
55 ± 1.41c
53.25c
68.62 ± 0.8b
66.89 ± 1.2b
67.75b
73.68 ± 1.8a
72.28 ± 2.4a
72.98a
Means in each column with different superscripts are significantly different (P < 0.05).
The last row of each mineral compares processing methods across the
row (P < 0.05).
Means in each column with different superscripts are significantly
different (P < 0.05).
The last row of each mineral compares processing methods across the
row (P < 0.05).
that have been developed and identified by the national
research programs of east and central African countries,
as being high in iron (above 70 mg/kg compared to 50
mg/kg for conventional beans) and zinc (above 30 mg/
kg compared to 20 mg/kg for conventional beans) (Ugen
et al. 2012).
The results of iron and zinc contents obtained were
in the same range as that reported by Blair et al. (2009)
between 40.0 and 84.6 mg/kg for iron and 17.7 and
42.4 mg/kg for zinc. The recorded iron and zinc contents
for unprocessed sample were higher than the respective
values of 51.1 and 24.9 mg/kg reported by Tryphone and
Nchimbi-Msolla (2010), except the zinc content of K131.
The data for iron and zinc contents of ROBA1 are higher
than those reported for ROBA1 beans grown in Ethiopia
(63.13 and 15.9 mg/kg, respectively) (Shimelis and Rakshit
2005). This difference may be due to the different growing field conditions.
Processing by germination/malting followed by roasting resulted in a slight and statistically significant decrease in mineral content of both the ROBA1 and K131
bean varieties compared to the mineral content of raw
flour. This can be attributed to leaching of iron and
zinc ions into the soaking water (Afify et al. 2011;
Carvalho et al. 2012). After extrusion, the iron content
of both varieties apparently increased (about 58% for
ROBA1 and 50% for K131). A similar observation was
made in other studies (Alonso et al. 2001; Camire 2002;
Murekatete et al. 2010; Mutambuka 2013); according
to Camire (2002), this increase may be attributed to
the migration of iron from extruder parts, manly screws.
After extrusion, zinc content of both samples decreased.
Murekatete et al. (2010) also reported significant changes
in mineral content after extrusion cooking where iron
content increased and zinc content decreased. The reported increase in iron content was 50% for one sample
and 30% for the second sample; for Camire (2002),
the increase was 38% in iron after extrusion cooking,
while for Alonso et al. (2001), the increase in iron
after extrusion was 20% for pea and 76% for kidney
beans.
There were significant differences in both zinc and iron
contents (P < 0.05) of the ROBA1 and K131 bean varieties studied in this work. Processing malting/roasting and
extrusion also significantly (P < 0.05) affected the iron
and zinc contents of flour compared to raw beans flour.
388
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Iron and zinc extractability
The iron extractability was in a range of 38.92–83.41%,
while for zinc the range was between 51.5% and 73.68%
(Table 3).
A significant difference (P < 0.05) was observed between
the mineral extractability of processed bean flour samples
and unprocessed bean flour samples for both the ROBA1
and K131 bean varieties. Flour of extruded beans had
the highest iron and zinc extractabilities. Similar results
were reported for the effect of processing on mineral
bioavailability (Khatoon and Prakash 2006; Viadel et al.
2006; Al-numair et al. 2009). On comparing varieties, a
significant difference in iron extractability is observed with
ROBA1 having higher extractability than K131. Results
for zinc extractability, however, did not reveal any significant differences between the two bean varieties.
Increase in mineral extractability following the malting/
roasting process can be attributed to reduction in phytate
and polyphenol contents which are inhibitors of mineral
absorption. Increase in enzymatic activity during malting
(phyatase and polyphenoloxidase) results in enzymatic
degradation of phytates and polyphenols (Savelkoul et al.
1992; Reddy and Pierson 1994; Alonso et al. 1998; Sandberg,
2002). Soaking, which is part of the malting process, was
also reported to reduce phytates by water solubilization
and subsequent leaching of some phytic acid salts (Afify
Development of Biofortified Bean Flour
M. G. Nkundabombi et al.
Table 4. Protein content (g/100 g) of the raw, extruded, and malted/
roasted ROBA1 and K131 bean flours.
Bean variety
ROBA1
K131
Raw
Extruded
Malted
Raw
Extruded
Malted/roasted
Protein content
(g/100 g)
Digestibility (%)
20.65 ± 0.8c
20.97 ± 0.1c
21.37 ± 0.2c
23.14 ± 0.04b
21.69 ± 0.3c
24.66 ± 0.9a
58.27 ± 1.5c
82.00 ± 1.4a
72.50 ± 1.7b
56.28 ± 0.04c
79.00 ± 1.6a
70.50 ± 0.7b
Means in each column with different superscripts are significantly different (P < 0.05).
et al. 2011). Roasting has also been reported to reduce
antinutrients, especially phytates, by increasing phytase
(El-adaway 2002; Ramakrishna et al. 2006; Afify et al.
2011; Subuola et al. 2012). In addition, extrusion cooking
was also reported to improve mineral bioavailability by
reducing other factors that inhibit absorption such as
phytates. The high extrusion temperatures were proposed
to result in phytate hydrolysis, resulting in higher availability of minerals after processing than other processing
methods (Alonso et al. 2001; Singh et al. 2007).
In vitro protein digestibility
Of the two bean varieties used in this study, K131 had
higher protein content (Table 4). However, there was no
significant difference between the protein content of raw
and extruded bean flours of both varieties. Malted/roasted
samples, however, had higher protein content compared
to raw and extruded samples. Osman (2007) reported the
similar increase in protein content after malting/germination, he related this result to increasing water activity
during germination due to hydrolytic enzymes.
Increase in protein content in malted beans has been
reported in other studies and attributed to mobilization
of protein reserves in cotyledons which take place during
malting, together with the synthesis of new proteins necessary for growth of the sprout (El-adaway 2002; Rodriguez
et al. 2008; Taraseviciene et al. 2009). Wang et al. (2008)
attributed this increase in protein content to the loss of
soluble solids in soaking water done before malting. Protein
content of ROBA1 variety in this study was quite similar
to the protein content reported by Shimelis and Rakshit
(2005) for ROBA1 variety grown in Ethiopia
(20.5 g/100 g).
In vitro protein digestibility increased significantly
(P < 0.05) after both malting/roasting and extrusion
cooking, and for both varieties compared to raw samples.
Extruded samples had a significantly higher in vitro protein digestibility than samples processed by malting and
roasting. There was also a significant difference (P < 0.05)
between the in vitro protein digestibility of the two bean
varieties with ROBA1 bean flour having a higher in vitro
protein digestibility. Similar results were reported by
Shimelis and Rakshit (2007) who observed a higher in
vitro protein digestibility of ROBA1 variety compared
to two other varieties studied. However, the in vitro
protein digestibility values reported by their study were
generally higher than those in the current study.
Improvement of in vitro protein digestibility after processing may be not only due to removal or reduction
of antinutrients, but may also be attributed to breakdown
of the native protein structure, including enzyme inhibitors and lectins; differential solubility of oligosaccharides
and their diffusion rates; phytase activity to break down
phytic acid in the seeds; and the development of endogenous α-galactosidase activity to reduce oligosaccharides. Combination of processing methods has been
reported to be more effective than use of single treatments, especially when one of the methods is heat processing (Shimelis and Rakshit 2007). Extrusion has been
reported to improve protein digestibility by reducing
antinutrient factors (Prakrati et al. 1999).
Pasting properties
Significant differences (P < 0.05) were observed in the
different pasting characteristics of flours from both processing methods and varieties (Table 5; Fig. 1). There
were no significant differences between the two varieties
Table 5. Pasting properties of raw, extruded, and malted/roasted ROBA1 and K131 bean flours.
Sample
ROBA1
K131
Raw
Extruded
Malted/roasted
Raw
Extruded
Malted/roasted
PT (°C)
PV (cP)
TV (cP)
BV (cP)
FV (cP)
SV (cP)
94.9 ± 1.6a
54.7 ± 3.1c
93.9 ± 0.2ab
94.9 ± 0.02a
53.2 ± 0.49c
90.3 ± 3.2b
906 ± 2.7ab
488.3 ± 2.1c
877.6 ± 0.7ab
979 ± 2.9a
399.6 ± 2.1c
798.3 ± 3.0b
871.6 ± 3.9ab
156.33 ± 0.7d
490.00 ± 2.2c
980 ± 4.5a
129 ± 1.6d
798.6 ± 2.3b
6 ± 1.1c
749.6 ± 2.7a
−1.6 ± 1.15c
−1 ± 1.7c
270.6 ± 2.3b
−0.3 ± 1.7c
1539 ± 2.2b
631 ± 0.96d
1264.7 ± 1.3c
1810.7 ± 1.8a
387.3 ± 1.9e
1799 ± 1.4a
667.3 ± 2.5c
474.7 ± 0.8d
774.7 ± 2.3bc
830.7 ± 1.9b
258.3 ± 2.4e
1000.3 ± 1.5a
PT, pasting temperature; PV, peak viscosity; TV, trough viscosity; BV, breakdown viscosity; FV, final viscosity; SV, setback viscosity.
Means in each column with different superscripts are significantly different (P < 0.05).
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
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Development of Biofortified Bean Flour
M. G. Nkundabombi et al.
Figure 1. Pasting properties of unprocessed and processed ROBA1 and K131 bean flours.
studied for pasting temperature, setback viscosity, trough
viscosity, and peak viscosity. Pasting temperature of flours
ranged from 94.9°C to 53.2°C, being significantly lower
(P < 0.05) for extruded flour compared to raw (unprocessed) and malted/roasted flours. Pasting temperature of
raw flour was higher than reported by Akinjayeju and
Ajayi (2011) for black bean flour (80–82°C). Extruded
flour had the lowest pasting temperature (53.2°C for K131
flour and 54.7°C for ROBA1 flour). Jozinovic et al. (2012)
reported a decrease in pasting temperature after extrusion
of corn meal. Pasting temperature is an indication of the
minimum temperature required to cook the flour (Kaur
et al., 2007). Previous studies reported that germination/
malting did not have any effect on pasting temperature
of flours (Moongngarm 2011; Ritruengdech et al. 2011;
Borijindakul and Phimolsiripol 2013), and Sade (2009)
in his study on pearl millet (Pennisetum glaucum) did
not observe any effect on pasting temperature due to
roasting or germination of pearl millet. Similarly, malting/
roasting of beans in this study had no effect on pasting
temperature. High pasting temperature may be an indication of the presence of resistant starch, to swelling and
rupturing (Kaur and Singh, 2007).
The highest peak viscosity was observed for raw flour
(906 cP for ROBA1 flour and 979 cP for K131 flour),
while the lowest was observed for extruded flour (399.6
cP for K131 flour and 488.3 cP for ROBA1 flour). Peak
viscosity is the maximum viscosity attained by gelatinized
starch during heating in water. It indicates the water
binding capacity of the starch granules (Shimelis et al.,
2006). In the present study, processing methods were
observed to reduce peak viscosity. The low peak viscosity
values of extruded compared to unprocessed flours may
be attributed to the denaturation of protein as well as
the starch–protein interactions which result in structures
with low capacity for interaction with water (HernandezNava et al. 2011). The highest trough viscosity value was
recorded for raw K131 flour (980 cP) and the lowest was
recorded for extruded K131 flour (129 cP). Breakdown
viscosity (measure of the ease with which the swollen
granules can be disintegrated) (Kaur and Singh, 2007)
ranged from −1.67 cP for malted/roasted ROBA1 flour
to 749 cP for extruded ROBA1 sample. Extruded flour
exhibited significantly (P < 0.05) higher breakdown viscosity (270.6 cP for extruded K131 flour and 749.6 cP
for extruded ROBA1 flour) than the malted and unprocessed flours. Pastes from flours with low final viscosity
were reported to be less stable when cooked and thus to
commonly have high values of breakdown viscosity (Ikegwu
et al. 2010). Similarly, in the current work, extruded flour
had low final and high breakdown viscosities. ROBA1
beans exhibited higher breakdown viscosity values compared to K131, regardless of processing method. High
breakdown viscosity is indicative of lower ability of starch
390
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
M. G. Nkundabombi et al.
to resist shear stress during cooking (Adebowale et al.
2005). The results of this study therefore indicate that
extended cooking under shear would lead to significant
alterations in extruded samples compared to malted or
raw (unprocessed) samples.
Final viscosity (which indicates the ability of the starch
to form a viscous paste (Ashogbon and Akintayo 2012)
ranged from 387 cP to 1, 810.7 cP, with no significant
difference between raw (unprocessed) flour and malted/
roasted flour. However, the final viscosity for extruded
samples was significantly lower (387.3 cP for extruded
K131 flour and 631 cP for extruded ROAB1 flour) than
the raw (unprocessed) and malted flour. Of the two varieties studied, ROBA1 exhibited lower final viscosity compared
to K131. Generally, the final viscosities of all samples were
higher than other viscosity values in the pasting cycle.
This is attributable to the reassociation of amylose molecules (Miles et al. 1985; Ashogbon and Akintayo 2012).
Setback viscosity (measure of retrogradation tendency of
flours upon cooling of cooked flour pastes; Kaur and Singh,
2007) ranged from 258 cP for extruded K131 to 1000.3
cP for malted/roasted K131. Extruded samples exhibited
the lowest setback viscosity (258.3 cP for extruded K131
flour and 474 cP for extruded ROBA1 flour). This implies
that extrusion cooking reduced the retrogradation tendency
of flour. Gonzalez and Perez (2002) also reported a reduction in setback viscosity after extrusion cooking of lentil
starches. This may be due to starch degradation during
extrusion cooking (Ozcan and Jackson 2005).
Borijindakul and Phimolsiripol (2013) reported that
germination reduced all pasting viscosities, as observed
in the present study. During germination/malting, there
is an activation of α amylase which hydrolyzes starch
thus reducing viscosity (Moongngarm 2011; Ritruengdech
et al. 2011).
During extrusion cooking, starch is pregelatinized and
when the pregelatinized starch granules are heated with
water, swelling, rupture, crystallinity loss, and amylose
leaching occur. Extruded flour could thus absorb water
and become viscous instantly, but it recorded low paste
viscosity (Ritruengdech et al. 2011). Hagenimana et al.
(2006) also reported a decrease in all viscosity values of
extruded rice flour compared to unprocessed rice flour,
like this study. Extrusion cooking has been used to reduce
viscosity in other to increase energy density of gruels
(Onyango et al. 2004; Magala-nyago et al. 2005).
Processing methods used in the present study generally
reduced pasting viscosity. This leads to increase in the
flour rate or solid matter when preparing porridge to
reach the acceptable viscosity (2500–3000 cP) (Thaoge
et al. 2003), resulting in porridges with higher nutrient
and energy density.
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Development of Biofortified Bean Flour
Consumer acceptability of porridges and
sauces prepared using flours of extruded or
malted biofortified or conventional beans
Acceptability of porridges from both bean varieties
The overall acceptability was highest for porridges prepared
from the composite flour of both extruded and malted/
roasted ROBA1 beans which scored 7 on the 9-point
hedonic scale (Table 6). The composite porridges were
significantly more acceptable (P < 0.05) than those prepared from pure malted/roasted ROBA1 and K131 flours.
There was no significant difference in the acceptability
of composite porridges prepared from K131 and extruded
pure ROBA1 (P < 0.05). The color of composite malted/
roasted K131 porridge and extruded pure K131 porridge
were significantly different and less acceptable than the
colors of the other porridges. Moreover, for thickness
and texture of extruded pure K131 and malted/roasted
pure K131 porridges were also significantly different from
other porridges (P < 0.05). Similarly, the appearances of
the extruded composite K131and extruded pure K131
porridges were less acceptable than the other porridges
(P < 0.05). For other attributes no significant differences
were observed.
Acceptability of sauces of bean varieties
Sauces prepared from extruded and malted/roasted pure
ROBA1 and K131 flours had higher overall acceptability
than the composite sauces (Table 7). The taste of the
sauce made from malted/roasted composite flour was
significantly different from other sauces (P < 0.05). The
flavor of sauces made from extruded pure K131 and extruded composite ROBA1 was significantly less liked than
the flavor of the other sauces (P < 0.05). The color,
thickness, and appearance of sauces made from extruded
pure K131 flour, malted/roasted composite ROBA1, and
malted/roasted composite K131 flour were less accepted
than for other sauces (P < 0.05). No difference was found
for smell among all sauces.
The composite flour of ROBA1 made the most acceptable porridge after both processing methods (extrusion
and malting/roasting). Similarly, the sauce made from the
pure ROBA1 flour was the most acceptable after extrusion
processing, while for malting/roasting method, both K131
and ROBA1 pure sauce were equally acceptable. Sensory
scores of all products were higher than 5, with overall
acceptability scoring higher than 6 (which correspond to
6 = like slightly, 5 = neither like nor dislike). The high
acceptability may be attributed to the elimination of the
beany flavor, which characterizes all legumes. Products
prepared from beans are likely to have this flavor which
391
Malted/roasted
Extruded
Samples
Taste
Flavor
Color
Smell
Thickness
Texture
Appearance
Overall
acceptability
Pure ROBA1
Pure K131
Composite ROBA1
Composite K131
Pure ROBA1
Pure K131
Composite ROBA1
CompositeK131
5.43 ± 2.1a
6.23 ± 2.2a
6.55 ± 1.5a
6.07 ± 1.8a
6.85 ± 1.6a
5.70 ± 1.9a
6.87 ± 1.9a
6.00 ± 1.8a
5.25 ± 2.0a
6.20 ± 2.0a
6.07 ± 1.7a
6.18 ± 1.6a
5.9 ± 1.6a
5.65 ± 1.7a
6.07 ± 1.7a
5.85 ± 1.6a
6.55 ± 1.8a
6.75 ± 1.7a
6.15 ± 1.6ab
5.33 ± 2.0b
5.68 ± 1.8ab
4.75 ± 1.7b
6.10 ± 1.8a
5.12 ± 1.7ab
5.48 ± 2.1a
6.18 ± 1.8a
6.15 ± 1.6a
5.92 ± 1.4a
5.92 ± 2.0a
4.98 ± 2.1a
6.05 ± 1.9a
5.70 ± 1.6a
5.90 ± 1.8a
6.65 ± 1.6a
6.40 ± 1.5a
6.00 ± 1.7a
5.55 ± 2.3a
4.72 ± 2.6b
6.85 ± 2.0a
6.28 ± 2.3a
5.82 ± 1.79a
6.30 ± 1.41a
6.45 ± 1.26a
6.00 ± 1.72a
6.35 ± 1.9a
4.72 ± 2.6b
6.98 ± 1.5a
6.55 ± 2.0a
6.33 ± 2.1ab
6.83 ± 1.4a
6.18 ± 1.6ab
5.30 ± 1.8b
7.30 ± 1.7a
6.15 ± 2.4b
7.73 ± 1.9a
5.80 ± 1.8b
6.22 ± 1.5b
6.07 ± 1.2b
7 ± 0.9a
6.52 ± 1.4ab
6.4 ± 1.6ab
5.78 ± 1.6b
7 ± 1.7a
6.18 ± 1.4ab
Development of Biofortified Bean Flour
392
Table 6. Acceptability of porridge prepared from processed ROBA1 and K131 bean flours.
Means in each column with different superscripts are significantly different (P < 0.05).
Extruded
Malted/roasted
Samples
Taste
Flavor
Color
Smell
Thickness
Texture
Appearance
Overall acceptability
Pure ROBA1
Pure K131
Composite ROBA1
Composite K131
Pure ROBA1
Pure K131
Composite ROBA1
Composite K131
7.0 ± 1.6a
6.0 ± 2.1a
6.0 ± 2.3a
6.4 ± 1.9a
5.92 ± 2.05ab
6.70 ± 2.03a
5.48 ± 2.19b
5.92 ± 1.93ab
6.65 ± 1.3a
5.55 ± 1.9b
6.0 ± 1.5b
6.18 ± 1.3ab
5.72 ± 1.83a
6.30 ± 1.87a
5.52 ± 2.20a
5.55 ± 1.82a
6.55 ± 1.8a
5 ± 1.7b
6.45 ± 1.7a
5.85 ± 1.6a
7.55 ± 2.01a
6.63 ± 1.1a
5.20 ± 1.9b
5.18 ± 1.8b
6.17 ± 2.1a
5.35 ± 2.2a
5.40 ± 2.2a
5.87 ± 1.6a
6.0 ± 1.88a
6.3 ± 2.18a
6.05 ± 1.78a
6.10 ± 1.82a
6.20 ± 1.9a
4.80 ± 2.5b
6.52 ± 1.9a
6.92 ± 1.7a
7.07 ± 1.91a
7.1 ± 1.78a
5.32 ± 2.1b
5.8 ± 1.28b
6.60 ± 1.4a
5.23 ± 1.8b
6.70 ± 1.6a
7.00 ± 1.9a
5.97 ± 2.1a
6.3 ± 1.9a
5.58 ± 2.1a
5.20 ± 1.2a
6.50 ± 1.7a
5.08 ± 1.7b
6.70 ± 1.6a
6.17 ± 1.4a
7.4 ± 2.11a
7.20 ± 1.3a
5.2 ± 2.21b
4.7 ± 1.45b
7.0 ± 1.a
6.12 ± 1.5b
6.63 ± 1.7ab
6.22 ± 1.9ab
7.0 ± 1.63a
7.0 ± 1.50a
6.0 ± 1.65b
5.45 ± 1.23b
Means in each column with different superscripts are significantly different (P < 0.05).
M. G. Nkundabombi et al.
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
Table 7. Acceptability of sauce made from processed ROBA1 and K131 bean flours.
Development of Biofortified Bean Flour
M. G. Nkundabombi et al.
Nutrients and energy density of flour from
biofortified beans
Raw (unprocessed), malted/roasted, and extruded beans
flour from ROBA1 were used to determine the flour rate
which resulted in spoonable consistency (2500–3000 cP)
(Thaoge et al. 2003) (Table 8). Unprocessed flour required
a lower flour rate compared with processed flour, and
extruded flour required the highest flour rate. Current
results are in the same range with what was reported by
Rombo et al. (2001) in a study irradiation processing for
maize and kidney bean flour. Most of traditional porridges
or gruels are made from cereal-based food, and their flour
concentration is between 5% and 10% to reach the maximum consistency (3000 cP) (Lorri 1993; Wambugu et al.
2003), the current flour had higher flour concentration.
Unprocessed flour (raw) attained the maximum viscosity
(3000 cP) at a lower flour concentration compared to
extruded and malted/roasted flours (Fig. 2 and Table 8).
Malted/roasted flour attained the viscosity range at a slight
lower flour concentration compared to extruded flour,
but the difference was not significant.
Energy and nutrient density of both sauce and porridge
were computed based on their flour rates. The highest flour
rates within the range were selected for comparison (Table 9).
Sauce prepared from unprocessed flour had significantly
lower nutrients and energy density compared to malted/
Table 8. Flour concentrations of unprocessed and processed ROBA1
bean flours.
Samples
Flour rate (%)
Viscosity (cP)
Unprocessed bean flour
10
13
15
17
15
20
22
23
15
20
21
22
1530
2400
28591
3229
1700
2571
28151
3009
1684
2603
27701
3100
Extruded flour
Malted/roasted flour
1Selected
to compare nutrient density.
3500
3000
Viscosity (cP)
is considered unpleasant to most consumers (Enwere 1998).
Processes such as roasting and extrusion cooking are reported to decrease this beany flavor thus improve sensory
attributes of bean based products (Nyombaire et al. 2011).
Overall, when the acceptability of the sauces and porridges is compared, porridge from the composite flour was
more acceptable than that from the pure bean flour while
sauce from the pure bean flour was more acceptable than
that from the composites. Jackson et al. (2013) also reported
that composite sorghum–bean porridge was more accepted
than sorghum porridge. It is therefore recommended that
the pure flour be promoted for use as sauces and the
composite flour be promoted for use as porridges.
2500
2000
1500
Extruded
1000
Malted/roasted
500
Raw
0
10
13
15
17
20
21
22
23
Flour concentration %
Figure 2. Variation in the viscosity of unprocessed and processed bean
pastes with flour concentration.
roasted flour and extruded flour. Extruded sauce had a
slightly higher nutrients and energy density than malted/
roasted sauce, but the difference was not significant. This
difference may be due to the high nutrient bioavailability
of extruded ROBA1 flour and also the high flour concentration. Similar results were reported by Saalia et al. (2012)
who reported that porridge or gruel prepared with low
Table 9. Energy and nutrients densities of sauces (100 mL) prepared from malted and extruded bean flours.
Parameters
Energy (Kcal)
Iron
Zinc
Protein
Total content (mg)
Extractable (mg)
Total content (mg)
Extractable (mg)
Total content (g)
Digestible (g)
Unprocessed flour (15%)
Malted/roasted flour (21%)
Extruded flour (22%)
49.95
1.05
0.43
0.40
0.21
3.09
1.80
90.72
1.23
0.91
0.48
0.33
4.50
3.26
99.12
1.8
1.50
0.51
0.37
4.77
3.91
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
393
Development of Biofortified Bean Flour
M. G. Nkundabombi et al.
Table 10. Contribution (%) of three servings per day of sauces to the recommended daily intake of children and women of reproductive age.
Iron (%)
Age/sex
Zinc (%)
Protein (%)
Energy (%)
US
MS
ES
US
MS
ES
US
MS
ES
US
MS
ES
55
39
117
82
193
135
51
37
100
60
112
67
125
85
226
154
270
185
43
26
78
47
85
51
125
85
59
59
226
154
106
106
270
185
127
127
45
27
32
31
82
50
57
57
90
54
63
62
Male
1–3 years
4–5 years
Female
1–3 years
4–5 years
15–18 years
19–49 years
Pregnancy
≤18 years
19–49 years
55
39
43
34
117
82
91
76
193
135
150
126
51
37
34
39
100
60
55
62
112
67
62
70
24
50
83
26
28
41
45
46
51
First trimester
Second trimester
Third trimester
59
38
38
106
69
69
127
82
82
31
27
26
57
50
48
62
54
52
Lactation
≤18 years
19–49 years
64
71
136
151
225
250
24
26
38
41
43
46
First 6 months
Second 6 months
38
38
69
69
82
82
27
27
50
48
54
53
US, sauce from unprocessed flour; MS, sauce from malted/roasted flour; ES, sauce from extruded flour.
solid content had low nutrients and energy density.
Consequently, consumers especially children need to take
a large volume of such porridge to meet their daily requirement. There is a risk that children do not meet their nutrient
requirements given their limited stomach capacities.
Contribution of sauces to the recommended
dietary intake of key nutrients and energy
intake for vulnerable groups
Women of reproductive age and young children are the
most affected by malnutrition, especially micronutrient
deficiency (iron and zinc). The contribution of sauces to
the recommended dietary intake (Table 10) was calculated
and compared. It was observed that extruded sauce supplied the highest amount of nutrients (iron, zinc, and
protein) and energy followed by malted/roasted sauce.
Sauce from unprocessed flour supplied the lowest amounts
of nutrients. The estimates were based on three servings
per day (300 mL of sauce/porridge per serving for children
and 500 mL of sauce/porridge per serving for women of
reproductive age).
For children (1–5 years), the lowest nutritional contribution for iron, zinc, protein, and energy were 38.6%,
37.0%, 85.4%, and 25%, respectively (all from unprocessed
flour), while the highest nutritional contribution were
192.9%, 111.6%, 270.4%, and 89.9%, respectively (all from
extruded flour). For women of reproductive age (15–
50 years), the lowest nutritional contribution for iron,
zinc, protein, and energy were 23.8%, 23.7%, 38.1%, and
26.2%, respectively, while highest nutritional contribution
were 250.1%, 69.7%, 127.4%, and 62.7%, respectively, all
from extruded flour. Based on these results, it showed
394
that processed biofortified bean flour can highly improve
nutritional status of consumers.
Conclusion
Malting/roasting and extrusion processes improve nutritional and physicochemical characteristics of biofortified beans. In the present study it is was found that
both processing methods increase the mineral bioavailability and improve in vitro protein digestibility of bean
flour. Extruded products had higher mineral bioavailability and in vitro protein digestibility than malted/roasted
samples. The pasting properties of bean flour were modified by processing, with extruded flour exhibiting lowest
pasting viscosities and pasting temperature compared to
malted/roasted samples, and malted/roasted samples exhibiting lower pasting viscosities than raw samples.
Products from conventional bean flour (K131) and products from biofortified bean flour (ROBA1) are equally
acceptable by consumers. Gruel or sauce prepared from
processed biofortified beans exhibited higher nutrients
and energy density than gruel/sauce prepared from unprocessed biofortified bean flour. It can be thus concluded
that processed biofortified bean flour can be utilized to
prepare highly acceptable nutrient and energy dense sauce
or gruel suitable for feeding nutritional vulnerable
populations.
Acknowledgments
This work was supported by: International Centre for
Tropical Agriculture (CIAT)/Pan African Bean Research
Alliance (PABRA) (Grant Number: BSB850/BSC47) and
© 2015 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc.
M. G. Nkundabombi et al.
the USAID - Pulse Collaborative Research Support
Program (Pulse-CRSP), Grant/Award Number: EDH-A-00-070005-00).
[Corrections added on 26 April 2016, after first online publication: The “Acknowledgments” section was changed from
“This work was sponsored by CIAT-PABRA” into “This
work was supported by: International Centre for Tropical
Agriculture (CIAT)/Pan African Bean Research Alliance
(PABRA) (Grant Number: BSB850/BSC47) and the USAID Pulse Collaborative Research Support Program (Pulse-CRSP),
Grant/Award Number: EDH-A-00-07-0005-00).”]
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Conflict of Interest
None declared.
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