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Paper No. 03-347
Conditioning and Dehulling of Pigeon Peas and Mung Beans
A. Opoku1, L. Tabil1, J. Sundaram1, W.J. Crerar1 and S.J. Park2
1Department of Agricultural and Bioresource Engineering
University of Saskatchewan
57 Campus Drive
Saskatoon, Sk S7N 5A9
2Agriculture and Agri-Food Canada
Research Station
Harrow, ON N0R 1G0
Written for presentation at the
CSAE/SCGR 2003 Meeting
Montréal, Québec
July 6 - 9, 2003
Abstract: About 90% of the world production of mung bean (Vigna radiata) is produced in Indo-Burma
region. Pigeon pea (Cajanus cajan) accounts for about 5% of the world’s legume production. Mung bean
and pigeon pea provide rich sources of protein for animals and humans in many parts of the world. They
also supply a significant amount of minerals and vitamins. Pigeon pea and mung bean can be consumed
as dehulled splits, whole, canned, boiled, roasted or ground into flour to make a variety of desserts,
noodles, snacks and main dishes. Pigeon pea and mung bean are normally dehulled to improve cooking
and nutritional qualities and to reduce cooking time. Dehulling mung beans and pigeon peas helps to
remove antinutritional compounds such as polyphenols located in the seed coat. Cooking and soaking can
eliminate or reduce the phytic acid content present in these legumes. These legumes are classified as
hard-to-dehull because of the presence of mucilage and gum forming a strong bond between the hulls and
the cotyledons. To dehull these legumes, the hulls must be loosened from the cotyledons before they can
be abrasively separated from the cotyledons. Different preconditioning treatments consisting of drying,
soaking and drying, steaming and drying in addition to tempering and no tempering were investigated. A
tangential abrasive dehulling device (TADD) was used to study the dehulling characteristics of these
legumes. Results indicate that tempering appears to increase the yield of dehulled cotyledons (splits and
whole). Overall, steam treatment at 97±1oC for 10 min, followed by drying at 120oC for 10 min and
tempering for 12 h yielded the highest dehulled kernels for both pigeon pea and mung bean compared to
the other treatments when the kernels were considered dehulled with 90% hull removal. Also, steam
treatment at 97±1oC for 10 min, followed by drying at 120oC for 10 min and tempering for 24 h yielded the
highest dehulled kernels for both pigeon pea and mung bean compared to the other treatments when the
kernels were considered dehulled with complete hull removal.
Keywords: legumes, preconditioning, soaking, steam treatment, tempering
2
Conditioning and Dehulling of Pigeon Peas and Mung Beans
A. Opoku, L. Tabil, J. Sundaram, W.J. Crerar and S.J. Park
INTRODUCTION
The world production of pulses is estimated to be 57.5 million metric tonnes annually. Pigeon
pea (Cajanus cajan L.) accounts for about 5% of the world’s pulse production. India produces
about 2 million tonnes of pigeon peas annually, which is about 70% of the world production.
About 90% of the world production of mung beans (Vigna radiata L.) is produced in Indo-
Burma region.
Pulses including pigeon pea and mung bean are rich sources of protein for animal and human
consumption. They also supply a significant amount of minerals and vitamins. Typically, the
average nutritional composition of pigeon pea is 19.2% protein, 57.3% carbohydrates, 1.5% fat,
8.1% fiber and 3.8% ash (Smartt 1976), and that of mung bean is 22.9% protein, 61.8%
carbohydrate, 1.2% fat, 4.4% fiber and 3.5% ash (Duke 1981). Pigeon pea and mung bean can be
consumed as dehulled splits, whole, canned, boiled, roasted or ground into flour to make a
variety of desserts, snacks and main dishes.
After harvest, pigeon pea and mung bean are dehulled to improve cooking and nutritional
qualities and to reduce cooking time. Structurally, whole legume grain may consist of the seed
coat (hull), embryo and the cotyledons. Mung bean may consist of 12.1% seed coat, 2.3%
embryo and 85.6% cotyledons (Singh et al. 1968). The legume grains may differ in color, shape,
size and thickness. The process of removing the seed coat (hull) is referred to as dehulling.
Dehulling plays a significant part in processing and utilization of legume grains. Dehulling
legume grains may lower the tannin content and improve their digestibility (Deshpande et al.
1982). Dehulling may also lead to the loss of fiber and sometimes ash, protein, starch and fat.
Legume grains may be classified as easy-to-dehull and hard-to-dehull. Legume grains such as
pigeon pea and mung bean belong to the hard-to-dehull group because of the presence of
mucilage and gum forming a strong bond between the hulls and the cotyledons. Ramakrishnaiah
and Kurien (1985) reported that pigeon pea grains of poor dehulling characteristic contained
higher amounts of uronic acid. The variability in dehulling characteristics of legume grains may
be affected by the grain genotypes and their physical characteristics (Ramakrishnaian and Kurien
1983; Ehiwe and Reichert 1987; Singh et al. 1992)
To diversify the Canadian agricultural production, increased efforts have been placed on
breeding pulses, including mung beans and pigeon peas, which are adapted to the climatic and
soil conditions in Canada. Dehulling characteristic of mung bean and pigeon pea is certainly one
of the primary traits which may be considered by breeders. Legumes with good dehulling
characteristics are required by processors to satisfy both domestic and the export markets.
Cultivars that are easy to dehull coupled with high dhal yield recovery may be required by
processors.
3
The grain kernels are usually preconditioned to loosen the hulls from the cotyledons before they
can be separated using mechanical means. Preconditioning methods to loosen the hulls may
involve heat treatment alone or soaking in water or chemical solution for a period of time,
together with heat treatment followed by hot dehulling or tempering before dehulling
(Ramakrishnaiah and Kurien 1983; Srivastava et al. 1988; Phirke et al. 1992; Phirke and Bhole
2000). The effect of steam preconditioning on the physical and dehulling characteristics of locust
bean was investigated by Adewumi and Igbeka (1993). Kernel preconditioning is generally
designed to toughen the hull and loosen the gummy bond between the hull and the cotyledon and
to harden the cotyledon to reduce damage.
The main objective of this investigation was to identify and test different preconditioning
treatments on dehulling pigeon pea and mung bean. Specifically, the following treatments were
studied:
1. drying without tempering and with tempering before dehulling,
2. soaking in distilled water, 8% urea solution and 8% sodium biocarbonate solution,
followed by drying without tempering and with tempering, and
3. steaming followed by drying without tempering and with tempering.
MATERIALS AND METHODS
Materials
Mung bean and pigeon pea samples were supplied by Agriculture and Agri-Food Canada
Research Station, Harrow, ON. The samples were placed in polyethylene bags and stored in an
airtight Coleman® rubber container at room temperature. The samples were manually cleaned
before the experiments. Mature and intact grains selected from the mass of pigeon pea and mung
bean were used for the experiments.
Preconditioning
The main purpose of preconditioning is to loosen the hull and facilitate its separation from the
kernel, thereby reducing dehulling losses. Five types of preconditioning methods were used to
dehull the pigeon pea and mung bean. Table 1 shows the detailed preconditioning treatments for
pigeon pea and mung bean.
The methods followed were:
1) Drying with and without tempering (Treatment A),
2) Soaking in distilled water, followed by drying and tempering (Treatment B),
3) Soaking in 8% urea solution, drying with and without tempering (Treatment C),
4) Soaking in 8% sodium bicarbonate solution, drying with and without tempering (Treatment
D), and
5) Steam treatment followed by drying with and without tempering (Treatment E).
Drying and tempering (Treatment A): About 150 g of each grain was taken and dried for 6
min at 120oC using a laboratory fluidized bed dryer (Model 23850, Lab line Instruments Inc.,
Melrose Park, IL) as shown in Figure 1. The dried samples were divided into 3 parts. Two parts
were kept in two separate glass bottles and properly covered. One was tempered for 4 hours and
4
the other one for 24 hours at room temperature of 22±2oC before dehulling. The third part was
dehulled without tempering.
Water soaking, drying and tempering (Treatment B): A sample of 150 g each was taken from
mung bean and pigeon pea and soaked separately in distilled water for 4 h at room temperature
of 22±2oC. At the end of soaking, the water was drained completely. From each sample, about 50
g was taken and dried for 6 min at 120oC using the laboratory fluidized bed dryer. The dried
samples were tempered for 4 hours. The rest of the soaked samples about 100 g each were dried
for 10 min at 120oC. Each sample was divided into two parts. One part was tempered for 4 h and
the other part for 24 h before dehulling.
Soaking in urea solution, drying and tempering (Treatment C): About 8% urea solution was
prepared using distilled water at room temperature (22±2oC). Approximately 150 g of each grain
was placed separately in glass bottles. Grains were soaked in 8% urea solution for 4 h at room
temperature. After soaking, the solution was drained properly and the samples were dried for 10
min at 120oC using the laboratory fluidized bed dryer. Before dehulling, 50 g of each sample was
tempered for 4 h and the other 50 g was tempered for 24 h. Dehulling was carried out for the
remaining sample without any tempering.
Soaking in sodium bicarbonate solution, drying and tempering (Treatment D): About 100 g
of each grain (mung bean and pigeon pea) was placed separately in glass bottles. The grains were
soaked in 8% sodium bicarbonate solution for 4 h at room temperature. After soaking, the
solution was drained and the samples were dried for 10 min at 120oC. Dehulling was carried out
without tempering for one part of the dried sample and the other part was tempered for 24 h
before dehulling.
Steaming, drying and tempering (Treatment E): About 250 g of each grain type was taken
and subjected to steam treatment at 97±1oC for 10 min using the laboratory steam conditioning
system (Figure 2). After steaming, the samples were dried at 120oC for 10 min. The dried
samples were divided into five parts. Four parts were tempered at room temperature (22±2oC) for
4 h, 8 h, 12 h and 24 h before dehulling. The fifth part was dehulled without any tempering
process.
Control: Dehulling of control sample was also done at room temperature of 22±2oC for both
pigeon pea and mung bean. All the treatments were done in triplicate.
Tangential Abrasive Dehulling Device (TADD)
Dehulling of the grain was carried out using a laboratory model tangential abrasive dehulling
device (TADD). Figure 3 shows the schematic diagram of the tangential abrasive dehulling
device used to dehull the mung bean and pigeon pea samples (Reichert et al. 1986). The TADD
was manufactured by Venables Machine Works Ltd., Saskatoon, Saskatchewan as model 4E-
230. The TADD consists of a horizontally rotating abrasive disk; a stationary head plate holds
eight stainless steel open-bottomed sample cups, which are mounted vertically over the rotating
disk. A cover plate with a rubberized material attached to it is used to cover the cups when the
machine is in operation. Shims are used to adjust the clearance between the rotating disk and
sample cups to allow a fan to blow the hulls, broken particles and fines into a cyclone and a
5
receptacle attached to the dehuller. A digital electronic timer (Model 8683-10, ColeParmer
Instrument Company, Chicago, IL) automatically controls the residence time during a test.
Spring-operated solenoid rubs on two “O” rings on the shaft mount, acting as a brake when the
current supplied to the motor is terminated. A test was done after placing the samples into the
sample cups and running the machine for a specified duration. After the test, the abraded
materials in the sample cups are removed by a vacuum aspirating collector described by Oomah
et al (1981).
Grit Size Selection
To determine the appropriate grit size for dehulling mung bean and pigeon pea, grit sizes 24, 36
and 50 were tested. Untreated samples, with moisture content of about 10% (wb), were used in
the tests. The samples were dehulled for 60 s and the abraded materials were separated into hulls,
whole dehulled, split dehulled, undehulled (whole and split) and fines. Since a good percentage
of brokens were obtained using grit size 24 and time required for dehulling was long using grit
size 50, 36 grit size was selected and used for the rest of the experiments to obtain optimum
result.
Dehulling
Two batches of about 20 g (total 40 g) of good quality preconditioned grains were selected from
each sample and placed in two sample cups of the TADD, which were located opposite to each
other. Retention time in the TADD was set at one minute. After dehulling, the abraded samples
were collected using a vacuum aspirating collector device from the cups, and the hulls, split
dehulled, split undehulled and fines blown by the fan were collected through a cyclone separator
device, connected to the TADD.
Dehulled Sample Separation
The collected, dehulled samples were separated manually into different fractions such as whole
dehulled kernels, split dehulled kernels, partially dehulled kernels, broken and hull. A kernel was
considered completely dehulled when there was no hull adhering to it. For treatments D1, D2, E3
and E4 for pigeon pea and mung bean, the kernels were considered dehulled when about 90% of
the hulls had been removed.
Hulls, fines and split dehulled and undehulled (split) that were blown into the receptacle attached
to the TADD were also collected and separated. The material collected in the receptacle was first
separated using a stack of sieves, consisting of Canadian Standard sieve numbers 14 (1.41 mm),
16 (1.19 mm), 18 (1.00 mm), 20 (850 µm) and pan. Each fraction on top of each sieve was then
separated using a fractionating aspirator (Style No. CFZ1, Carter-Day Company, Minneapolis,
MN). The separated fractions in the fractionating aspirator were then manually separated. The
hulls, split dehulled and undehulled seeds were added to earlier manually separated fractions and
weighed. The fraction in the pan was considered as fines and it was also weighed. Figure 4
shows the process flow diagram for dehulling and separation of the mung bean and pigeon pea
grains.
6
Manual Dehulling
About 30 g sample each of pigeon pea and mung bean was soaked in distilled water and the seed
coat was removed manually. The seed coat and the cotyledons were dried at 71.1oC for 2 nights
and they were weighed. The test was duplicated.
Moisture Content of Samples
Initial moisture content, moisture content after soaking with distilled water, 8 % urea solution
and 8% sodium bicarbonate solution, drying, steaming and tempering at each stage of the
samples were measured using the method given by AACC (1995). The one-stage procedure was
used for samples with moisture contents less than 13% and the two-stage procedure was used for
samples containing moisture contents of 13% or higher. A 2– to 3-g portion of a ground sample
was weighed and transferred into 2 or 3 dishes, and the dishes were covered with lids
immediately. The dishes were uncovered and placed in an oven at a temperature of 130±1oC for
one hour.
Data Analysis
Dehulling Index,
η
The dehulling index was calculated using the following equation:
i
fudhk
m
)mm()mm( +−+
=η (1)
where,
mk is the mass of dehulled kernel including whole and split, (g)
m
h is the mass of hull (g),
m
ud is the mass of undehulled kernel (g),
m
f is the mass of fine fraction (g) and
m
i is initial mass of sample taken for dehulling (g).
The dehulling index may vary from a maximum value of +1 to a minimum of -1. A value of +1
indicates that the entire original grain sample is completely dehulled into two fractions of
cotyledons (mc) and hulls (mh) with no fines and undehulled grains. A value of -1 indicates that
the dehulling is not complete, thus the grains have split into fines (mf) and /or not dehulled (muh)
at all (Ikebudu et al. 2000).
Degree of dehulling (Mh)
The degree of hull removal is the ratio of mass of hull removed during dehulling to the initial
mass of sample used for the dehulling process.
Effectiveness of dehulling (Ed)
Effectiveness of dehulling is the ratio between the mass of the material remaining undehulled
and the initial mass of material taken for dehulling.
Yield of fines (Yf)
It is the ratio between the mass of fine generated during dehulling and the initial mass of sample
used for dehulling.
7
Coefficient of dehulling (Cdh)
This can be calculated using the following equation:
()
[]
dfdh EY1100C +−= (2)
Overall dehulling efficiency (
η
o)
This is calculated using the following relationship:
dhdho C)QM( ×+=η (3)
where, Qd is quality of dehulling which can be calculated as ratio between the weight of dehulled
kernel (both split and whole) and initial weight of material taken for dehulling.
RESULTS AND DISCUSSIONS
Pigeon Pea
Table 2 shows the yield fractions of whole dehulled kernels and split dehulled kernels for the
various preconditioning treatments used for the pigeon pea grains. Table 2 also shows the
dehulling index, coefficient of dehulling, overall dehulling efficiency along with effectiveness of
dehulling, degree of dehulling, yield of fines and moisture content at the time of dehulling.
For the drying and tempering method (Treatment A), the highest dehulled fraction (47.3% whole
plus split kernels) was obtained for the sample tempered for 4 h (Treatment A2) and it was
followed by the Treatment A3 (46.6%) in which 24 h tempering was carried out. Treatment A1
(without tempering) had the lowest dehulled fraction of 17.8%. These results showed that after
heating, tempering was necessary to produce more dehulled fraction. There was no significant
variation (0.7%) between tempering for 4 h and 24 h. Therefore, reduction in tempering time
from 24 h will not affect the fraction of dehulled kernels. Treatment A1 yielded the highest
amount of fines compared to Treatments A2 and A3. The degree of dehulling was the same
(10.7%) for Treatments A2 and A3. The amount of undehulled kernels (effectiveness of
dehulling) was high when there was no tempering Treatment (A1). The highest dehulling index
of 0.19 was obtained for Treatment A2, followed by A3 with a dehulling index of 0.17.
For Treatment B (distilled water soaking, drying and tempering) higher percentage of dehulled
kernels (56.3%, whole including splits) was obtained by Treatment B3, soaking and drying for
120oC and tempering for 24 hours. Drying up to 6 min and tempering for 4 h produced the
lowest dehulled kernels (26.9%) and the lowest yield of fines (3.4%) compared to all the other
treatments. Moisture content for this treatment was very high (21.39%).
Soaking of pigeon pea in 8% urea solution did not give any favorable result. Treatment C1 had
the lowest dehulling index (-0.53) and the lowest percentage of dehulled kernel (whole including
split, 15.6%). Consequently, the effectiveness of dehulling was the highest at 69.0%. Treatments
C2 (4 h tempering) and C3 (24 h tempering) had dehulling indices of 0.05 and 0.16, respectively.
The overall dehulling efficiency obtained for C2 was 27.4% and C3 was 33.8%. For these
Treatments, C3 produced better result than C2.
8
Treatment D consisted of soaking with 8% sodium bicarbonate solution for 4 h, followed by
drying and tempering for 24 h. Compared to urea solution and distilled water soakings, sodium
bicarbonate solution soaking gave better results. This is probably due to the fact that the kernels
were considered dehulled when 90% of the hulls were removed. D1 (soaking and drying)
produced 59.4% of dehulled kernels (whole including split) and D2 (soaking, drying, 24 h
tempering) gave 70.8%. The dehulling indices were 0.39 and 0.65 for D1 and D2, respectively.
Higher amounts of dehulled kernels were produced when pigeon pea was subjected to steaming,
drying and tempering. After steaming and drying, the samples were tempered for 4, 8, 12 and 24
h. There were also samples that were not tempered. Tempering for 8 h and 12 h did not show any
significant differences in the degree of dehulling, effectiveness of dehulling, dehulling index and
overall dehulling efficiency. Both resulted in higher percentage of dehulled kernels (75.9% for
E3 and 76.1% for E4) and the dehulling indices were 0.77 for E3 (8 h tempering) and 0.79 for E4
(12 h tempering). But in the case of yield of fines, E4 gave a lower percentage (3.8%) than E3
(5.3 %). Similarly, the overall dehulling efficiency was very high for E4. By comparing the
overall efficiency of all the treatments the highest value of 80.3% was obtained for E4, which
was followed by E3 with 78.4%. This may be attributed to the fact that the kernels were
considered dehulled when 90% of the hulls were removed. Treatment E1 (steaming and drying)
gave low percentage of dehulled kernels (29.5%) with a dehulling index of -0.17 and an overall
dehulling efficiency of 17.3% compared to other treatments in the steaming method. Treatment
E5 produced a higher amount of dehulled kernels (66.8%) than E1 (31.5%) and E2 (57.4%)
when the kernels were considered dehulled with complete removal of hulls.
The above results show clearly that tempering is necessary for achieving better dehulling results
after soaking and drying or steaming and drying. All the treatments yielded more whole
dehulled kernels compared to split dehulled kernels.
The control treatment yielded the lowest dehulled pigeon pea kernels (6.0%) compared to the
other preconditioning treatments. It produced the highest amount of undehulled kernels and also
the highest amount of fines. The amount of hulls produced was lower than the other treatments
since the amount of undehulled kernels was higher. The lowest dehulling index was obtained for
this control treatment. A manual dehulling of the pigeon pea grains yielded 15.0% hulls and
85.0% percent dehulled kernels at 13.98% moisture content.
Mung Bean
The average results for mung bean with various preconditioning treatments are given in Table 3.
Table 3 shows that the percentage of split dehulled kernels was higher than the whole dehulled
kernels unlike pigeon pea, where there were more whole kernels compared to splits. Treatment
A1 (drying) gave higher percentage of dehulled kernels (49.9%, whole including splits) with a
dehulling index of 0.14 and an overall dehulling efficiency of 32.3% compared to Treatments A2
and A3. Treatment A2 produced higher undehulled kernels (46.8%) compared to Treatments A1
and A3. Treatment A3 produced 45.1% whole dehulled kernels with an overall dehulling
efficiency of 27.8%, and the yield of fines (5.7%) was higher compared to A1 and A2. These
results show that tempering did not influence the mung bean samples compared to the pigeon pea
samples during the drying and tempering treatments. During dehulling, the cotyledons of the
9
mung beans tended to split once the seed coat was abraded. This probably indicates that pigeon
pea cotyledons have a stronger bond between them than the mung bean cotyledons.
Water soaking, drying and tempering (Treatments B2 and B3) produced higher dehulled kernels
and overall dehulling efficiency compared to soaking in urea solution, drying and tempering
(Treatments C2 and C3). Treatment C1 produced a higher amount of undehulled kernels with
effectiveness of dehulling of 59.4%. The dehulling index was high when the grains were soaked
in distilled water, dried and tempered for 24 h. All the three treatments in urea soaking method
resulted in negative dehulling index. Similar results were obtained for water soaking except B3
(drying for 10 min and tempering for 24 h). Compared to all the pre-dehulling treatments C1
gave the lowest dehulling index (-0.50), which was followed by B1 at -0.35.
Sodium bicarbonate solution soaking was done with two treatments. One was soaking and drying
(Treatment D1) and the other was soaking, drying and tempering for 24 h (Treatment D2).
Treatment D1 produced more dehulled whole kernels than any other treatment methods for mung
bean except the control treatment. For both D1 (7.2%) and D2 (7.0%), the percentage yield of
fines were very low. The overall dehulling efficiency and dehulling indices of Treatment D2
(50.0% and 0.42) were higher than Treatment D1 (31.0% and 0.13). But both were higher than
water (Treatment B) and urea (Treatment C) soaking treatments as well as drying and tempering
(treatment A). This is probably due to the fact that the kernels were considered dehulled when
90% of the hulls were removed.
For mung bean, the steam treatment produced better result compared to any other
preconditioning treatment. Treatment E4 yielded the highest amount of dehulled mung bean
kernels of 72.42% compared to treatments E1, E2, E3 and E5 since the kernels were considered
dehulled when 90% of the hulls were removed. E5 produced a higher amount of dehulled kernels
compared to E1 and E2 when the kernels were considered dehulled with a complete removal of
hulls. In the case of mung bean, tempering for 12 h and 24 h gave better results compared to
tempering for 8 h and 4 h. The overall dehulling efficiency and dehulling indices for 12 h
tempering (69.1% and 0.67) were higher compared to 8 h (58.8% and 0.54). Treatment E3 and
E5 gave close result with the difference of 2.5% for percentage of dehulled kernel, 1.2% for
overall dehulling efficiency and 0.01 for dehulling index. But the yield of fines for E5 (12.6%)
was higher compared to E3 (8.8%). Treatment E1 (without tempering) did not give good result.
The result shows that the tempering process is necessary for obtaining higher percentage of
dehulled kernels, dehulling index, as well as overall dehulling efficiency.
The control treatment yielded the lowest dehulled mung bean kernels (9.2%) compared to the
other pre-dehulling treatments. Treatment C1 (59.4%) produced a higher amount of undehulled
kernels compared to the control treatment (57.4%). The control treatment generated the highest
amount of fines (21.9%). Since the amount of undehulled kernels was higher, the amount of hulls
produced was lower than the other treatments. The control had the lowest dehulling index. A
manual dehulling of the mung bean grains yielded 9.1% hulls and 90.9% percent dehulled
kernels at 12.28% moisture content.
Tables 2 and 3 show that steam treatment at 97±1oC for 10 min and drying at 120oC for 10 min
followed by tempering for 12 h yielded the highest dehulled kernels for both pigeon pea and
10
mung bean compared to the other treatments. In all sets of experiments, the maximum overall
dehulling efficiency and dehulling index were obtained after the tempering process.
CONCLUSIONS
From the results of preconditioning treatments and dehulling tests conducted on pigeon pea and
mung bean, the following conclusions were drawn:
1) Drying the pigeon peas at 120oC and tempering for 4 h yielded total dehulled kernels of
47.3% with lesser fines (5.7%).
2) Soaking with distilled water at room temperature and drying at 120oC for 10 min
followed by tempering for 24 h yielded more dehulled pigeon pea kernels (56.3%) than
soaking in 8% urea solution (46.9%).
3) Soaking in 8% sodium bicarbonate solution at room temperature and drying at 120oC for
10 min followed by tempering for 24 h yielded more dehulled pigeon pea kernels
(70.8%) than urea and water soaking when the kernels were considered dehulled with
90% hull removal.
4) Steaming and drying followed by tempering for 12 h yielded slightly more dehulled
pigeon pea kernels (76.1%) than tempering for 8 h (75.9%) when the kernels were
considered dehulled with 90% hull removal. Steaming and drying followed by 24 h
tempering had a higher dehulled kernels (66.8%) compared to treatments E1 (31.5%) and
E2 (57.4%) when the kernels were considered dehulled with a complete removal of hulls.
5) The control treatment produced low dehulled pigeon pea kernels and generated more
fines compared to the other treatments.
6) Drying the mung beans at 120oC without tempering yielded a higher amount of dehulled
kernels (49.9%) with lesser fines than with tempering.
7) Water soaking, drying and tempering for 24 h yielded more dehulled mung bean kernels
(42.2%) than urea soaking (38.8%).
8) Soaking in 8% sodium bicarbonate solution, drying and tempering for 24 h yielded more
dehulled mung bean kernels (59.8%) than no tempering (43.9%) when the kernels were
considered dehulled with 90% hull removal.
9) Steaming and drying followed by tempering for 12 h yielded a higher amount of dehulled
mung bean kernels (72.4%) than tempering for 8 h when the kernels were considered
dehulled with 90% hull removal. Steaming and drying followed by tempering for 24 h
had higher dehulled kernels compared to E1 and E2 when the kernels were considered
dehulled with a complete removal of hulls
10) The control treatment produced the lowest amount of dehulled mung bean kernels and
generated more fines than the other treatments.
11) Overall, steam treatment at 97±1oC for 10 min, followed by drying at 120oC for 10 min
and tempering for 12 h yielded the highest dehulled kernels for both pigeon pea and
mung bean compared to the other treatments when the kernels were considered dehulled
with 90% hull removal. Also, steam treatment at 97±1oC for 10 min, followed by drying
at 120oC for 10 min and tempering for 24 h yielded the highest dehulled kernels for both
pigeon pea and mung bean compared to the other treatments when the kernels were
considered dehulled with a complete hull removal.
11
ACKNOWLEDGEMENT
We acknowledge the funding support of the Strategic Research Program of Agricultural
Development Fund, Saskatchewan Agriculture, Food and Rural Revitalization. Agriculture and
Agri-Food Canada, Research Station, Harrow, Ontario also partially supported this research. The
Agri-Food Innovation Fund (AFIF) is hereby acknowledged for the renovations of the
Bioprocess Engineering Laboratory.
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12
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13
Table 1. Preconditioning methods investigated
Treatments Description
A. Drying and tempering Drying at 120oC for 6 min, and
A1. No tempering
A2. Tempered for 4 h
A3. Tempered for 24 h
B. Water soaking, drying
and tempering
Soaked for 4 h at room temperature, and
B1. Dried at 120oC for 6 min and tempered for 4 h
B2. Dried at 120oC for 10 min and tempered for 4 h
B3. Dried at 120oC for 10 min and tempered for 24 h
C. 8% urea solution
soaking, drying and
tempering
Soaked for 4 h and dried at 120oC for 10 min, and
C1. No tempering
C2. Tempered for 4 h
C3. Tempered for 24 h
D. 8% Sodium bicarbonate
solution soaking, drying
and tempering
Soaked for 4 h and dried at 120oC for 10 min, and
D1. No tempering
D2. Tempered for 24 h
E. Steaming, drying and
tempering
Steamed at 98.0oC for 10 min and dried at 120oC for 10
min, and
E1. No tempering
E2. Tempered for 4 h
E3. Tempered for 8 h
E4. Tempered for 12 h
E5. Tempered for 24 h
Control No treatment, material at room temperature (22 ± 2oC
14
Table 2. Average result of dehulling pigeon pea with different pre-dehulling treatments (number of replicates = 3)
Treatment Whole
Dehulled
kernels
(%)
Split
dehulled
kernels
(%)
Effectiveness of
dehulling
(Ed)
(%)
Degree of
dehulling
(Mh)
(%)
Yield of
fines
(Yf)
(%)
Dehulling
index
Coefficient of
dehulling
(Cdh)
(%)
Overall
dehulling
efficiency
(ηo)
(%)
Moisture
content at the
time of
dehulling
(%, w.b.)
A1 15.7 2.1 63.5 7.4 8.8 -0.47 27.7 7.0 7.40
A2 43.5 3.8 33.2 10.7 5.7 0.19 61.1 35.4 7.10
A3 41.6 5.0 33.9 10.7 6.1 0.17 60.0 34.4 7.57
B1 24.6 2.3 57.1 7.9 3.4 -0.26 39.5 13.8 21.39
B2 43.0 4.4 33.3 10.3 5.1 0.19 61.6 35.5 11.19
B3 53.9 2.4 25.0 10.7 4.7 0.37 70.3 47.1 11.34
C1 14.8 0.8 69.0 6.6 6.2 -0.53 24.8 5.5 12.77
C2 40.5 1.2 41.4 9.3 4.9 0.05 53.7 27.4 13.58
C3 45.4 1.5 36.0 9.7 4.3 0.16 59.7 33.8 11.38
D1
56.5
2.9
22.0
7.8
6.3
0.39
71.7
48.2
9.12
D2 67.4 3.4 11.0 10.0 5.3 0.65 83.7 67.7 9.75
E1 29.5 2.0 49.6 9.1 7.5 -0.17 42.9 17.3 9.30
E2 54.2 3.2 22.8 11.0 5.7 0.40 71.5 48.9 8.39
E3 72.3 3.6 4.3 11.0 5.3 0.77 90.4 78.4 9.19
E4 72.1 4.0 4.4 11.0 3.8 0.79 91.8 80.3 9.24
E5 62.5 4.3 13.0 11.3 5.5 0.60 81.5 63.7 9.07
Control 5.0 1.0 73.7 4.6 11.1 -0.74 15.2 1.6 10.53
15
Table 3. Average result of dehulling mung bean with different pre-dehulling treatments (number of replication = 3)
Treatment Whole
Dehulled
kernels
(%)
Split
dehulled
kernels
(%)
Effectiveness of
dehulling
(Ed)
(%)
Degree of
dehulling
(Mh)
(%)
Yield of
fines
(Yf)
(%)
Dehulling index
Coefficient of
dehulling
(Cdh)
(%)
Overall
dehulling
efficiency
(ηo)
Moisture
content at
dehulling (%,
w.b.)
A1 0.1 49.8 26.7 4.5 14.0 0.14 59.3 32.3 7.31
A2 0.3 28.8 46.8 4.8 15.0 -0.28 38.2 13.0 8.47
A3 0.3 44.8 29.7 5.7 15.5 0.06 54.8 27.8 8.67
B1 0.2 25.6 51.7 4.8 13.6 -0.35 34.7 10.6 10.59
B2 0.2 35.0 41.1 4.9 13.1 -0.14 45.8 18.4 8.26
B3 0.5 41.7 33.1 5.5 13.3 0.01 53.6 25.6 9.60
C1 0.1 18.9 59.4 4.2 13.9 -0.50 26.7 6.2 9.37
C2 0.3 34.9 42.0 5.3 13.7 -0.15 44.3 17.9 9.23
C3 0.2 38.6 38.0 5.6 13.9 -0.08 48.1 21.4 9.38
D1
0.9
43.8
30.0
4.9
7.2
0.13
63.3
31.0
10.15
D2 0.0 59.8 16.0 5.4 7.0 0.42 77.1 50.0 10.46
E1 0.4 44.0 32.5 5.6 13.5 0.04 54.0 27.0 8.26
E2 0.3 62.1 14.7 6.7 12.9 0.41 72.4 50.0 6.77
E3 0.0 66.1 9.3 5.8 8.8 0.54 81.9 58.8 7.58
E4 0.0 72.4 4.0 6.2 8.0 0.67 87.9 69.1 7.62
E5 0.5 68.1 8.0 7.0 12.6 0.55 79.4 60.0 7.18
Control 2.0 7.2 57.4 3.5 21.9 -0.67 20.7 2.6 10.38
15
Figure 1. Laboratory model fluidized bed dryer.
Figure 2. Laboratory steam conditioning system.
16
Figure 3. Schematic diagram of tangential abrasive dehulling device (Reichert et al. 1986)
17
Figure 4. Typical process flow diagram for dehulling and separation of the grains
Clean intact
g
rains
Soakin
g
in 8% urea solution
Drying
Tempering No tempering
TADD dehulling
Abraded fraction Blown fraction (Broken mixture)
Sieving
Aspiration (fractionator)
Fines
Manual separation
Whole
dehulled
Split
dehulled
Undehulled
(split and
whole)
Hulls
