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Soaking and cooking modify the alpha-galacto-oligosaccharide and dietary fibre content in five Mediterranean legumes

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The effects of soaking and cooking on soluble sugars, alpha-galacto-oligosaccharides (α-GOS) and soluble dietary fibres (SDF) and insoluble dietary fibres (IDF) were assessed in five legumes (lentil, chickpea, fenugreek, faba bean and Egyptian faba bean). In raw seeds, total α-GOS content ranged from 2500 mg/100 g (chickpea) to over 4000 mg/100 g (fenugreek). Stachyose was predominant in fenugreek, lentil and chickpea, whereas verbascose was the main α-GOS in faba bean and Egyptian faba bean. IDF represented 69–87% of the total dietary fibres in all studied legumes, while SDF content varied noticeably. During soaking, total α-GOS content decreased between 10% (lentil and faba bean) and 40% (chickpea). In fenugreek, soaking reduced IDF and increased SDF concentration, possibly due to partial IDF solubilisation from the cell wall. Cooking further decreased α-GOS and increased total dietary fibre content. The different behaviours of these five legumes during processing illustrate the high biodiversity within legume species. © 2019, © 2019 Sondos Njoumi, Marie Josephe Amiot, Isabelle Rochette, Sihem Bellagha, Claire Mouquet-Rivier. Published with license by Taylor & Francis.
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Soaking and cooking modify the alpha-galacto-
oligosaccharide and dietary fibre content in five
Mediterranean legumes
Sondos Njoumi, Marie Josephe Amiot, Isabelle Rochette, Sihem Bellagha &
Claire Mouquet-Rivier
To cite this article: Sondos Njoumi, Marie Josephe Amiot, Isabelle Rochette, Sihem Bellagha &
Claire Mouquet-Rivier (2019): Soaking and cooking modify the alpha-galacto-oligosaccharide and
dietary fibre content in five Mediterranean legumes, International Journal of Food Sciences and
Nutrition, DOI: 10.1080/09637486.2018.1544229
To link to this article: https://doi.org/10.1080/09637486.2018.1544229
© 2019 Sondos Njoumi, Marie Josephe
Amiot, Isabelle Rochette, Sihem Bellagha,
Claire Mouquet-Rivier. Published with
license by Taylor & Francis.
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RESEARCH ARTICLE
Soaking and cooking modify the alpha-galacto-oligosaccharide and
dietary fibre content in five Mediterranean legumes
Sondos Njoumi
a,b
, Marie Josephe Amiot
c
, Isabelle Rochette
b
, Sihem Bellagha
a
and Claire
Mouquet-Rivier
b
a
INAT, University of Carthage, Tunis, Tunisia;
b
NUTRIPASS, IRD, SupAgro, University of Montpellier, Montpellier, France;
c
MOISA, CIRAD,
CIHEAM-IAAM, INRA, SupAgro, University of Montpellier, Montpellier, France
ABSTRACT
The effects of soaking and cooking on soluble sugars, alpha-galacto-oligosaccharides (a-GOS)
and soluble dietary fibres (SDF) and insoluble dietary fibres (IDF) were assessed in five legumes
(lentil, chickpea, fenugreek, faba bean and Egyptian faba bean). In raw seeds, total a-GOS con-
tent ranged from 2500 mg/100 g (chickpea) to over 4000 mg/100 g (fenugreek). Stachyose was
predominant in fenugreek, lentil and chickpea, whereas verbascose was the main a-GOS in faba
bean and Egyptian faba bean. IDF represented 6987% of the total dietary fibres in all studied
legumes, while SDF content varied noticeably. During soaking, total a-GOS content decreased
between 10% (lentil and faba bean) and 40% (chickpea). In fenugreek, soaking reduced IDF and
increased SDF concentration, possibly due to partial IDF solubilisation from the cell wall. Cooking
further decreased a-GOS and increased total dietary fibre content. The different behaviours of
these five legumes during processing illustrate the high biodiversity within legume species.
ARTICLE HISTORY
Received 12 September 2018
Revised 26 October 2018
Accepted 31 October 2018
KEYWORDS
Nutritional quality; galacto-
oligosaccharides; monosac-
charides; disaccharides;
diffusion; high-performance
anion-exchange chromatog-
raphy; total dietary fibre
Introduction
Legumes are key foods in the Mediterranean diet and
excellent candidates to help ensuring the sustainability
of food systems. Legume cultures improve the soil
nitrogen level and the net primary productivity, and
may deliver additional ecosystem benefits. Legumes
play a central role in food systems as a source of plant
proteins and thanks to their various beneficial health
effects (Viguiliouk et al. 2017). Indeed, besides their
protein content, legumes are an excellent source of
nutrients, including carbohydrates (soluble sugars and
dietary fibres) (Berrios et al. 2010), B-group vitamins
and minerals. However, they also contain several com-
pounds that display anti-nutritional activity (for
instance, polyphenols and phytic acid) and inhibit
mineral absorption, or that are non-digestible, such as
alpha-galacto-oligosaccharides (a-GOS) (Aguilera
et al. 2009; Wang et al. 2009; Vasishtha and Srivastava
2013). a-GOS contain 13 units of galactose linked to
sucrose by a-1,6 linkages that are not hydrolysed in
the upper part of the human gastrointestinal tract,
due to the absence of the enzyme a-galactosidase. In
the colon, they are fermented together with soluble
dietary fibres by the colon microbiota, generating sig-
nificant amounts of short-chain fatty acids (SCFA).
These fermentation substrates stimulate the growth of
lactobacilli and bifidobacteria and the decrease of
enterobacteria in the intestinal microflora. This pre-
biotic action (Mart
ınez-Villaluenga et al. 2008; Slavin
2013) is beneficial for the hosts well-being and health.
However, fermentation also produces gases (carbon
dioxide, hydrogen and methane) that generate bloat-
ing and flatulence. Flatus production is considered to
be the most important deterrent to the consumption
of grain legumes (Aguilera et al. 2009; Berrios
et al. 2010).
Legumes are recognised as good sources of dietary
fibres and their consumption is promoted for their
positive effects on the treatment and prevention of
constipation, the control of serum cholesterol levels,
the reduction of the risk of diabetes and intestinal
cancer, and the stimulation of the growth of beneficial
CONTACT Claire Mouquet-Rivier claire.mouquet@ird.fr IRD (Institut de Recherche pour le D
eveloppement), University of Montpellier, UMR 204
Nutripass, 911 avenue Agropolis, Montpellier 34094, France; Marie-Jos
ephe Amiot marie-josephe.amiot-carlin@inra.fr INRA (Institut National de la
Recherche Agronomique), UMR MOISA, CIRAD, CIHEAM-IAAM, INRA, SUPAGRO, University of Montpellier, 2 Place Pierre Viala, Montpellier 34000, France.
Supplemental data for this article can be accessed here.
ß2019 Sondos Njoumi, Marie Josephe Amiot, Isabelle Rochette, Sihem Bellagha, Claire Mouquet-Rivier. Published with license by Taylor & Francis.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-
nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed,
or built upon in any way.
INTERNATIONAL JOURNAL OF FOOD SCIENCES AND NUTRITION
https://doi.org/10.1080/09637486.2018.1544229
microorganisms. Soluble dietary fibres (SDF) have
been linked to cholesterol lowering in blood, while
insoluble dietary fibres (IDF) have been associated
with water absorption and regulatory intestinal effects
(Perry and Ying 2016). IDF has a mechanical and irri-
tating effect on the mucosa of the large bowel, thus
stimulating the secretion of water and mucous as a
defence mechanism against abrasion. IDF are poorly
fermented, and remain relatively intact throughout the
large intestine (McRorie and McKeown 2017).
As all dietary poorly absorbed short-chain carbohy-
drates have similar and additive effects in the intestine,
they have been collectively designated as fermentable
oligosaccharides, disaccharides, monosaccharides and
polyols (FODMAPs) (Shepherd et al. 2013).
FODMAPs, among which a-GOS, trigger gastrointes-
tinal symptoms in patients with irritable bowel syn-
drome, while SDF could have a protecting effect.
Therefore, FODMAP reduction in the diet, possibly
associated with other dietary strategies, could be an effi-
cient approach for managing irritable bowel syndrome.
Legumes are widely used in many traditional
Mediterranean dishes. Several traditional household
food-processing methods, including soaking and cook-
ing (Hotz and Gibson 2007), can reduce their anti-
nutritional factors, particularly dietary fibres and
a-GOS (Lestienne et al. 2005). Bahthoula is a Tunisian
dish prepared with various soaked legume species
(lentil, faba bean, Egyptian faba bean, fenugreek and
chickpea). Using this dish as a model, we studied the
changes in dietary fibres and a-GOS content during
soaking and cooking. This study was undertaken (i) to
determine the content in soluble sugars, especially
a-GOS (raffinose, stachyose and verbascose), and in
SDF and IDF in the five Mediterranean legumes used
for Bahthoula preparation; (ii) to investigate and elab-
orate hypotheses on the mechanisms of their changes
during soaking in traditional conditions; and finally
(iii) to study the effect of cooking on the whole
Bahthoula dish, as eaten. This study was performed in
the framework of the Medinaproject (http://www6.
inra.fr/medina) with the aim of preserving the cultural
heritage of the Mediterranean diet, as an outstanding
resource for sustainable development because it con-
tributes to promote the consumption of locally pro-
duced traditional foods.
Materials and methods
Legumes
Whole lentil (Lens culinaris), faba bean (Vicia faba L.
var. major), fenugreek (Trigonella foenum-graecum),
chickpea (Cicer arietinum) and Egyptian faba bean
(Vicia faba L. var. minor; hereinafter, Egyptian FB)
seeds were purchased from a local market in Tunis
(Tunisia). As usual, Egyptian FB seeds were decorti-
cated and split. Samples of the five raw seed species
were ground using a laboratory mill (IKA M20,
Labortechnik, Staufen, Germany) before soaking
and cooking.
Soaking
Seeds (24 g) and mineral water (Volvic
TM
) were mixed
at a ratio of 1:4 (w/v), except for fenugreek seeds
where the ratio was 1:5 (w/v) due to their high swel-
ling capacity, and left to soak at 25 C in an oven
incubator for different times (1, 3, 6, 16 and 24 h).
Before soaking, the containers and water were kept at
25 C for few hours to reach the soaking temperature.
At each time point during soaking, the water was
drained from the container and stored at 18 C for
analysis. The soaked seeds were washed and blotted
dry (by patting with paper towel) and then water
absorption by the seeds was monitored by weighing.
The dry matter (DM) content of the soaked seeds and
pH of the soaking waters were also measured. Soaked
seeds were then frozen, lyophilised, ground using a
laboratory mill (IKA M20) and stored at 18 C for
chemical analysis. Soaking waters were also kept at
18 C before analysis.
Experimental preparation of Bahthoula based on
the traditional Tunisian recipe
An average recipe and a standard preparation proced-
ure were derived from preparations of Bahthoula
observed in four Tunisian households. The cooks
were also asked to indicate a mean portion size at the
end of the preparation. Each legume species (100 g)
used for the preparation of the dish was separately
soaked for 16 h in mineral water to mimic the over-
night soaking performed in the households. Shortly
before cooking, dried salted anchovies were bleached
for 5 min to reduce saltiness. Bahthoula was prepared
by mixing the five soaked legumes (lentil, faba bean,
Egyptian FB, fenugreek and chickpea) with 70 g of
anchovies, 150 g of Mhamsa (couscous of coarse grain
size obtained by rolling wheat semolina), 50 g of olive
oil, 100 g of tomato paste, 90 g of onions, 15 g of garlic
and spices (14 g of a caraway-coriander mixture, 10 g
of red pepper powder, 2 g of black pepper, 3 g of
cloves, 12 g of curcuma and 10 g of salt). Then, 3 L of
2 S. NJOUMI ET AL.
boiling demineralised water was added, leading to a
hot and heterogeneous mixture.
The preparation was simmered on a hot plate for
1 h at boiling temperature. Analyses were carried out
on raw and cooked samples to determine the effect of
the traditional cooking practice on mono, di and
oligosaccharide content. Samples were freeze-dried,
grinded to obtain a homogeneous sample and kept at
18 C until analysis.
Physico-chemical analyses
The thousand seed weight (TSW) was measured for
the five legume species (three replicates) as described
in Ribeiro et al. (2012). The soaking water pH was
monitored at different time points (1, 3, 6, 16 and
24 h). The DM content was measured gravimetrically
in triplicate, by drying in an oven at 105 C until con-
stant weight (AOAC 1995).
Insoluble and soluble dietary fibres
A standardised enzymatic-gravimetric method
(Megazyme K-TDFR Kit) was used for determination
of SDF and IDF, the sum of the two fractions corre-
sponding to the TDF, also designed as the high
molecular weight dietary fibres. The method is based
on the procedure of the methods AOAC 985.29 and
the Prosky method (Prosky et al. 1992). Each deter-
mination was made on duplicate samples. Shortly,
MES-TRIS blend buffer solution (pH 8.2) was added
to 1 g of dried sample and stirred until complete dis-
persion. Samples were incubated with pancreatic
a-amylase at 96 C in a shaking water bath for 30 min.
Proteins in the sample were denatured and digested
with protease at 60 C for 30 min. Then, after adjust-
ing the pH to 4.14.8, samples were incubated with
amyloglucosidase at 60 C for 30 min. IDF was recov-
ered in a crucible after vacuum filtration of the aque-
ous reaction mixture; the residue R1 was washed
twice with distilled water preheated to 70 C. The fil-
trate and water washings were saved for determination
of SDF. The residue was then washed twice again
with 10 ml of 95% ethanol and acetone, and dried at
105 C overnight before weighing to determine R1
weight. For the determination of SDF, the mixture of
filtrate and water washings was precipitated by adding
four volumes of 95% ethanol. The precipitated mix-
ture was vacuum-filtered and washed successively
with ethanol 78%, ethanol 95% and acetone. The resi-
due R2 was dried at 105 C overnight and weighed.
For both R1 and R2 residues, one duplicate was
analysed for protein using the method of Kjeldahl
(ISO 1871:2009) and the other was mineralised at
525 C to determine ash. R1 and R2 weights were cor-
rected for protein and ash contents for the final calcu-
lation of the IDF and SDF contents. The whole
procedure was done in duplicate for all samples, and
results were averaged.
Analysis of mono, disaccharides and a-GOS
Mono and disaccharides (glucose, fructose, arabinose,
galactose, melibiose and sucrose) and a-GOS (raffinose,
stachyose and verbascose) were extracted by mixing
80 mg of each sample with ethanol (3ml, 78%). Tubes
were placed in a water bath at 80 C for 20 min. After
centrifugation at 4500 rpm at 4 C for 15 min, superna-
tants were transferred to special Speedvac tubes and
centrifuged again. Pellets were then rinsed with 2ml of
ethanol (without heating), centrifuged and transferred
to new tubes. The supernatants of each sample from
the three centrifugation steps were pooled (8 ml) and
evaporated under vacuum (Speedvac RC 10). The dry
extract was resuspended in 12ml of H
2
Obeforehigh-
performance anion-exchange chromatography
(HPAEC) analysis (Dionex), as previously described
(Baye et al. 2013). HPAEC analyses were performed
with a CarboPac PA1 Guard pre-column (450 mm)
and a CarboPac PA1 Analytical Column (4 250 mm).
The mobile phase was 60 mM sodium hydroxide
(NaOH), the flow rate was set at 1ml/min, and the
injection volume was 30 lL.
Statistical analysis
Data were analysed using one-way ANOVA and the
SPSS software version 24.0 (SPSS Inc., Chicago, IL).
The Tukeys multiple comparison test was used for
pair-wise comparisons. A p-value <.05 was the chosen
level of significance.
Results and discussion
Characterisation of raw legume seeds
The TSW ranged from 24.6 ± 1.3 to 2098.8 ± 31.6 g
depending on the species and variety (Table 1), high-
lighting the great differences in seed size (fenugreek
seeds were the smallest and faba bean seeds the largest
in this study). Moreover, seeds had very different
morphologies: lens-shaped, spherical, or kidney-
shaped (or elongated cardioid). The main sugars
detected in the five legume species were monosacchar-
ides (fructose, glucose, arabinose and galactose),
INTERNATIONAL JOURNAL OF FOOD SCIENCES AND NUTRITION 3
disaccharides (sucrose and melibiose) and a-GOS (raf-
finose, stachyose and verbascose) (Table 1). The quali-
tative sugar and fibre profiles of the studied legumes
were comparable, but with quantitative differences
illustrating the diversity within this food group.
Monosaccharide content was low in all seeds, mostly
below 30 mg/100 g DM, except for glucose and fruc-
tose in faba bean (80 mg/100 g DM). Arabinose was
present in minor concentration in fenugreek and len-
til, and only in traces in faba bean, Egyptian FB and
chickpea. Egyptian FB had the lowest contents in
monosaccharides. Sucrose was the main disaccharide
in raw seeds. The highest quantities were found in
faba bean and chickpea, where it represented more
than 2.5% of the seed weight. Melibiose was present
in minor concentration in lentil and faba bean and in
trace amounts in fenugreek, chickpea and Egyptian
FB. Raw legume seeds contained large amounts of
total a-GOS (Table 1), from about 2500 mg/100 g DM
in chickpea to more than 4000 mg/100 g DM in fenu-
greek. The main a-GOS were raffinose, stachyose and
verbascose. Huge differences in a-GOS content were
observed among the five legume seeds. Raffinose was
present in moderate to low amounts in most legumes,
as reported by Reddy et al. (1984), and the highest
quantities were detected in fenugreek and chickpea.
Stachyose was clearly the predominant a-GOS in
fenugreek, lentil and chickpea, while verbascose was
the main a-GOS in faba bean and Egyptian FB.
Although Egyptian FB seeds were decorticated, their
sugar profile was similar to that of the faba bean
(both are of the same species) because these sugars
are mainly located inside the seeds, and not in the
external coat. Overall, the sugar profiles of the five
types of legume were consistent with the literature
data (Rup
erez 1998; Sanchez-Mata et al. 1998; Martin-
Cabrejas et al. 2006).
IDF represented between 69 and 87% of all dietary
fibres in all five legumes (Table 1). SDF contents var-
ied noticeably among legume species. They repre-
sented about 30% of all dietary fibres in fenugreek
and 1327% in the other legume seeds. Fenugreek
seeds were the richest in both IDF and SDF (almost
two thirds of the total DM). This could be partly
explained by the small seed size, as indicated by their
low TSW, making the proportion of seed coat larger.
In agreement, Zdunczyk et al. (1997) reported that
smaller-sized pea seeds have significantly higher fibre
content than larger-sized seeds. However, in fenugreek
seeds, the seed coat is separated from the embryo by a
whitish translucent endosperm that is mainly com-
posed of soluble galactomannan gum (Sakhare et al.
2015). These authors found that fenugreek seeds con-
tain about 30% of gel-forming soluble fibres, like guar
and psyllium seeds. In the other four legume seeds,
fibre content was still high, although not as high as in
fenugreek. Their SDF fractions were comparable,
whereas the IDF fraction was higher in faba bean due
to its tough seed coat (Rowland 1977), and much
lower in decorticated Egyptian FB because IDF is
mainly located in the seed coat (Rowland 1977).
Effect of soaking
Water absorption
The legume seed samples displayed typical water
absorption behaviours, characterised by an initial
Table 1. Mono, di, oligosaccharide and dietary fibre contents in five raw legumes.
Fenugreek Lentil Chickpea Faba bean Egyptian FB
Thousand seed weight (g) 24.6 ± 1.3 44.2 ± 1.1 633.6 ± 14.0 2098.8 ± 31.6 267.1 ± 2.6
Dry matter (DM) (%) 89.4 ± 0.2 89.2 ± 0.0 90.5 ± 0.2 89.4 ± 0.1 88.5 ± 0.1
Monosaccharides (mg/100 g DM)
Galactose 11.1
a
± 1.2 24.9
b
± 5.7 8.2
a
± 1.7 11.1
a
± 2.0 10.0
a
± 1.8
Glucose 10.5
a
± 1.5 23.9
b
± 1.1 7.8
a
± 1.1 81.1
c
± 7.2 3.9
d
± 1.1
Fructose 16.0
a
± 1.1 20.4
a
± 3.3 14.6
a
± 4.4 90.4
b
± 15.7 2.5
c
± 0.4
Arabinose 5.0
a
± 0.6 7.9
b
± 2.7 1.2
c
± 0.4 0.7
c
± 0.3 0.3
c
± 0.2
Disaccharides (mg/100 g DM)
Sucrose 762
a
± 68 1885
b
± 233 2561
c
± 339 2533
c
± 105 2038
b
±40
Melibiose 0.1
a
± 0.0 3.1
b
± 1.6 1.3
c
± 0.2 0.1
a
± 0.0 0.1
a
± 0.0
a-GOS (mg/100 g DM)
Raffinose 504
a
± 47 283
b
± 13 516
a
± 15 290
b
± 80 167
c
±20
Stachyose 3656
a
± 307 1829
b
± 75 1824
b
± 140 960
c
± 51 720
d
±98
Verbascose 313
a
± 25 850
b
±62 82
a
± 8 2354
c
± 165 2573
c
± 507
Total 4463
a
± 379 2962
b
± 150 2487
b
± 37 3504
b
± 296 3460
b
± 625
Dietary fibre (g/100 g DM)
Insoluble dietary fibres 44.2
a
± 0.8 20.2
c
± 0.0 21.4
c
± 3.4 30.3
b
± 0.0 11.5
d
± 0.4
Soluble dietary fibres 20.2
a
± 0.7 3.9
b
± 0.0 4.6
b
± 0.1 4.6
b
± 0.2 4.2
b
± 0.2
Total 64.4
a
± 1.5 24.0
c
± 0.0 25.9
c
± 3.5 34.9
b
± 0.2 15.7
d
± 0.6
Results are the mean ± standard deviation of three independent measurements. Values in the same row with different superscript letters are
significantly different (p<.05, Tukeys test was used for post-hoc comparison).
4 S. NJOUMI ET AL.
phase of rapid water imbibition (water gain increased
sharply), followed by an equilibrium phase, during
which the legumes approached their full soaking cap-
acity (the water absorption rate steadily decreased)
(Figure 1(a)). Similar curves were previously reported
for other grains and seeds (Sayar et al. 2001). The
rapid initial water uptake is attributed to the filling of
capillaries on the surface of the seed coat. Then, the
water absorption rate decreases sharply when water
fills open capillary and inter-micellar spaces. The
decrease in water absorption rate could also be
explained by the fact that water filling reduces the
driving force (i.e. the concentration difference between
the soaking medium and the legumes) (Sayar
et al. 2001).
Again, fenugreek exhibited a different behaviour
compared with the other seeds. The other four seeds
reached the saturation moisture content (around
100110% DM) after 6 h of soaking. Conversely, fenu-
greek absorbed higher quantity of water and faster,
and continued to absorb water, reaching around 250%
DM after 24 h and without attaining a clear equilib-
rium. This huge water absorption capacity is due to
the soft and mucilaginous layer of the seed coat, rich
in galactomannans, as reported by Meghwal and
Goswami (2012).
Dry matter and pH of soaking water
For all seeds, the pH of the soaking water decreased
from approximatively 7.0 to 6.04.7 (lowest value for
Egyptian FB) after 24 h of soaking (Figure 1(b)). This
acidification suggests leaching of acidic compounds,
such as malic or citric acids, during soaking
(Sarmento et al. 2015) and/or spontaneous lactic acid
fermentation. Indeed, it was reported that pH
decreases during lentil fermentation (Vidal-Valverde
et al. 1994; Frias et al. 1996).
After 24 h of soaking, the DM leached in soaking
water was 1.35, 1.55, 3.15, 2.86 and 2.67% in faba
bean, lentil, chickpea, Egyptian FB and fenugreek
seeds, respectively (Figure 1(c)). The amount of DM
leached in the soaking water was lower than the DM
amount lost by the seeds during soaking (results not
shown), and this could be explained by losses in gas-
eous form, by respiration or fermentation (Dung
et al. 2010).
Changes in soluble sugar and a-GOS content
during soaking
For all legumes, soaking led to a variable reduction in
the total a-GOS content (Figure 2), depending on the
seed type and soaking time point. This decrease could
result from leaching i.e. diffusion in the soaking water,
or from enzymatic degradation that can take place in
the seeds or in the soaking water (Coffigniez et al.
2018). After 16 h of soaking (the traditional soaking
time in Tunisian households), the total a-GOS loss
ranged from 10% (lentil and faba bean) to 40%
(chickpea seeds). Longer soaking time further reduced
the a-GOS content only in fenugreek that exhibited
an almost linear decrease of a-GOS content. In the
other seed types, a slight increase in total a-GOS was
observed between 16 and 24 h. This could be a passive
40
50
60
70
80
90
100
0 3 6 9 12 15 18 21 24
Total D-GOS %
Soaking me (h)
Fenugreek
Lenl
Faba bean
Chickpea
Egypan FB
Figure 2. Changes in total a-GOS content in legumes dur-
ing soaking.
0
40
80
120
160
200
240
280
0 3 6 9 12 15 18 21 24
Water absorpon % DM
Soaking me (h)
Lenl
Chickpea
Faba bean
Egypan FB
Fenugreek
4,0
4,5
5,0
5,5
6,0
6,5
7,0
7,5
03691215182124
pH
Soaking me (h)
Lenl
Chickpea
Faba bean
Egypan FB
Fenugreek
0
1
1
2
2
3
3
4
0 3 6 9 12 15 18 21 24
Leached DM %
Soaking me (h)
Lenl
Chickpea
Faba bean
Egypan FB
Fenugreek
(a)
(b)
(c)
Figure 1. Effects of soaking on (a) water absorption of legume
seeds, (b) pH of the soaking water and (c) leached DM.
INTERNATIONAL JOURNAL OF FOOD SCIENCES AND NUTRITION 5
increase caused by the leaching of other soluble com-
pounds from the seeds in the soaking water.
Analysis of the changes in the content of each
a-GOS (expressed as percentage of the initial content;
Figure 3) showed that verbascose displayed the fastest
and largest decrease during the first 3 h of soaking,
except in fenugreek. Previous works reported that
a-GOS spatial distribution in legume seeds can be
heterogeneous (Sreerama et al. 2010). In chickpea and
horse grain, higher concentrations of a-GOS are pre-
sent in cotyledons than in seed coat, and verbascose is
the major a-GOS in the seed coat (Sreerama et al.
2010). Stachyose is present in higher amounts in both
cotyledon and embryonic axe fractions, although sub-
stantial amounts of raffinose and verbascose can also
be found in these fractions. This could explain why
verbascose content decreased early during soaking.
However, verbascose content strongly decreased also
in decorticated Egyptian FB seeds. The decreases in
stachyose and raffinose, the two lower forms of
a-GOS, was slower and moderate, particularly in faba
bean and Egyptian FB. Their leaching could be offset
40
60
80
100
120
140
0 3 6 9 12 15 18 21 24
D-GOS content (% of inial content)
Soaking me (h)
Lenl
Raffinose
Stachyose
Verbascose
40
60
80
100
120
140
0 3 6 9 12 15 18 21 24
D-GOS content (% of inial content)
Soaking me (h)
Chickpea
Raffinose
Stachyose
Verbascose
40
60
80
100
120
140
0 3 6 9 1215182124
D-GOS content (% of inial content)
Soaking me (h)
Egypan FB
Raffinose
Stachyose
Verbascose
40
60
80
100
120
140
03691215182124
D-GOS content (% of inial content)
Soaking me (h)
Faba bean
Raffinose
Stachyose
Verbascose
40
60
80
100
120
140
03691215182124
D-Gos content (% of inial content)
Soaking me (h)
Fenugreek
Raffinose
Stachyose
Verbascose
Figure 3. Effect of soaking at 25 Conthea-GOS content of legume seeds. Error bars are for average deviation.
6 S. NJOUMI ET AL.
by partial verbascose hydrolysis by a-galactosidase, as
indicated by the increase (147% after 1 h of soaking)
of galactose content in both seed varieties (Figure 4).
Significant decreases in stachyose and raffinose con-
tents were observed in chickpea (40% for both
a-GOS) and fenugreek (26 and 49%, respectively)
(Figure 3). As a consequence of this more pronounced
a-GOS hydrolysis, galactose production was more
important (above 200% after 1 h and around 1000%
after 24 h of soaking).
A significant sucrose hydrolysis occurred in all five
legumes during soaking. This resulted in an increase
in the glucose and fructose content particularly in
fenugreek (Figure 4). Conversely, in the other
legumes, glucose and fructose increased, but then
mostly diffused in the soaking water. At the end of
soaking period, their concentration decreased probably
because they were used for respiration (in the seed)
and/or fermentation (in the soaking water).
Significant a-GOS reduction by soaking has been
previously reported in soybean (Mulimani et al. 1997)
and various legumes, including lentil and faba bean
(Abdel-Gawad 1993). During soaking, seeds absorb
water, while raffinose, stachyose and verbascose,
which are all water-soluble, may leach out of the seeds
into the soaking water (Han and Baik 2006; Coffigniez
et al. 2018), or are enzymatically degraded to lower
molecular weight sugars (Vidal-Valverde et al. 2002;
Mart
ınez-Villaluenga et al. 2008; Berrios et al. 2010).
Indeed, very low amounts of a-GOS were found in
soaking water (Supplementary Figure 1). And large
amounts of hydrolysis products, such as galactose,
glucose and fructose, were found in the soaked
seeds and also in the soaking water (Supplementary
Figure 1). This indicated that enzymatic degradation
occurred in the seeds and in the soaking water, after
leaching. Endogenous alpha-galactosidase is present in
seeds (Coffigniez et al. 2018) and produces raffinose
from stachyose, and stachyose from verbascose, at low
soaking temperatures. Alpha-galactosidase hydrolyses
a-GOS by cutting the terminal galactose, and this
could explain the increase in galactose content
0
100
200
300
400
500
600
0 3 6 9 12 15 18 21 24
Glucose (% of inial content)
Soaking me (h)
Fenugreek
Lenl
Faba bean
Chickpea
Egypan faba bean
0
100
200
300
400
500
600
0 3 6 9 12 15 18 21 24
Fructose( %of inial content)
Soaking me (h)
Fenugreek
Lenl
Faba bean
Chickpea
Egypan faba bean
0
200
400
600
800
1000
1200
0 3 6 9 1215182124
Galactose (% of inial content)
Soaking me (h)
Fenugreek
Lenl
Faba bean
Chickpea
Egypan faba bean
0
20
40
60
80
100
120
0 3 6 9 1215182124
Saccharose (% of inial content)
Soaking me (h)
Fenugreek
Lenl
Faba bean
Chickpea
Egypan faba bean
Figure 4. Effect of soaking at 25 C on the content of some mono and disaccharides in the five legume seeds. Error bars are for
average deviation.
INTERNATIONAL JOURNAL OF FOOD SCIENCES AND NUTRITION 7
observed in fenugreek, faba bean, Egyptian FB and
chickpea during soaking.
Overall, similar changes were observed for the five
legumes. Nevertheless, the more detailed analysis
revealed specific behaviours that could be due to
several factors, such as the presence and thickness of
the seed coat, the shape and size of the seeds and also
the metabolic specificity of each legume species,
related for example to the presence of mucilage or
a-galactosidase activity.
Changes in insoluble and soluble dietary fibre
content during soaking
The impact of soaking on the dietary fibres was vari-
able. In some legumes, IDF content decreased signifi-
cantly during the first hours of soaking (fenugreek
showed the highest reduction (28% at 6 h) while in
other legumes, the reduction was low (lentil, 17% at
6 h) or even not significant (Table 2). This reduction
could be due to partial IDF solubilisation from cell
wall material (Rehman et al. 2004; Aguilera et al.
2009), which is not closely linked to the fibre matrix.
In chickpea, faba bean and Egyptian FB, a small IDF
reduction could have been masked by its passive
increase due to leaching of other soluble compounds
after several hours of soaking. On the other hand, the
SDF fraction showed a quantitative increase of þ41%
in fenugreek and of þ3% in lentil seeds at 1 h. In the
other legumes, SDF content tended to increase during
the first-hour soaking, but this was significant only
for Egyptian FB (þ27% at 1 h).
SDF increase can be of health interest because
fibres have recognised positive effects on health and
are better tolerated when soluble (Fernandes et al.
2010). Similar results (significant increase in SDF with
a concomitant decrease in IDF contents) were
previously reported for chickpea, pink mottled cream
bean, and white bean (Aguilera et al. 2009).
Legumes display different behaviours due to the
specific structure and composition of their cell wall
network (Martin-Cabrejas et al. 2006). The compos-
ition of the dietary fibre fraction depends on its local-
isation in the seed coat (outer fibres) or in the
cotyledons (inner fibres). The relative content of cellu-
losic and non-cellulosic polysaccharides is significantly
different between inner and outer dietary fibres. The
cotyledon cell walls contain mainly a range of polysac-
charides with various degrees of solubility (e.g. hemi-
cellulose and pectin and cellulose). The seed coat
contains mainly water-insoluble, non-digestible carbo-
hydrates (primarily cellulose) and lower amounts of
hemicellulose and pectin (Guillon and Champ 2002).
Effect of cooking
Changes in mono, di, oligosaccharide and soluble
and insoluble fibre content in the Bahthoula dish at
the end of cooking
Cooking after soaking led to a further decrease in
raffinose (32%), stachyose (25%) and verbascose
(35%) and to a significant increase in galactose
content (þ54%) in the whole dish (Supplementary
Table 1). This should be attributed to further enzym-
atic degradation, due to better conditions for the
expression of a-galactosidase activity. Alpha-galactosi-
dase from lentils are active in the temperature range
2050 C and up to 65 C, and have optimal pH of
4.7, 5.5 or 6.1, depending on their isoforms (Dey et al.
1983; Celem et al. 2009). Indeed the pH of all soaked
legumes after 16 h-soaking was around 6.0 as shown
in Figure 1. During heating, the temperature increased
Table 2. Changes in soluble and insoluble fibre contents during seed soaking.
Soaking time (h) Fenugreek Faba bean Chickpea Lentil Egyptian FB
IDF (g/100 g DM)
0 44.2
a
±0.8 30.3 ± 0.0 21.4 ± 3.4 20.2
ab
±0.0 11.5 ± 0.4
1 34.3
b
±1.3 29.0 ± 0.2 20.6 ± 1.3 21.0
a
±0.0 11.8 ± 1.9
3 33.9
b
±0.2 27.7 ± 0.5 19.2 ± 2.7 18.6
cd
±0.2 11.6 ± 0.2
6 31.9
b
±0.5 29.8 ± 1.8 17.7 ± 0.2 17.2
d
±0.3 12.1 ± 0.1
16 34.7
b
±1.5 28.9 ± 0.2 19.0 ± 0.3 19.0
bc
±0.3 12.1 ± 0.6
24 34.8
b
±0.5 30.8 ± 1.4 21.8 ± 0.0 17.3
d
±0.8 12.2 ± 0.2
SDF (g/100 g DM)
0 20.2
a
±0.7 4.6 ± 0.2 4.6 ± 0.1 3.9± 0.0 4.2
a
±0.2
1 28.7
b
±1.2 5.6 ± 0.6 5.1 ± 0.3 4.2 ± 0.2 6.0
b
±0.6
3 30.5
b
±1.4 5.7 ± 0.7 5.6 ± 0.4 4.1 ± 0.2 5.7
ab
±0.1
6 32.6 5.4 ± 0.1 5.6 ± 0.7 4.2 ± 0.6 5.8
ab
±1.0
16 30.8
b
±1.2 5.8 ± 0.0 5.6 ± 0.0 4.3 ± 0.6 5.3
ab
±0.8
24 31.2
b
±1.2 5.7 ± 0.1 5.1 ± 0.0 4.0 ± 0.0 5.3
ab
±0.6
Results are the mean ± average deviation of two independent repetitions. Values in the same column with different superscript letters are significantly
different (p<.05, Tukeys test was used for post-hoc comparison).
DM: dry matter; IDF: insoluble dietary fibres; SDF: soluble dietary fibres.
8 S. NJOUMI ET AL.
progressively and conditions were met for higher
a-galactosidase action.
Cooking also increased the IDF content of the
Bahthoula dish (þ23%), while the SDF fraction
remained almost constant (Supplementary Table 1).
Similarly, a previous study showed that cooking mark-
edly increases IDF content in chickpea (Perez-Hidalgo
et al. 1997; Vasishtha and Srivastava 2013). This IDF
increase can be due to the formation of resistant
starch that is partially measured by the method used
in our study for fibre determination. Authors sug-
gested that such IDF increase during cooking could
be due to Maillards reaction (Vasishtha and
Srivastava 2013). However, Maillards reaction is usu-
ally limited during hydrothermal processing.
Contribution of the Bahthoula dish to the fibre
and a-GOS intake
The minimum total dietary fibre intake recommended
by WHO and FAO (2003) is at least 25 g/d, with an opti-
mal intake of 30 g/d for adults. The consumption of a
portion of 296g of Bahthoula (the mean usual portion
indicated by Tunisian cooks) would provide 18.7g of
total dietary fibres, thus covering 62% of the average rec-
ommended intake for adults. The Bahthoula dish could
be considered as an outstanding source of total dietary
fibres. a-GOS act as beneficial compounds due to their
prebiotic action, but could also cause digestive troubles
and act as anti-nutritional factors. The balance between
the beneficial and adverse effects mainly depends on the
dose at which the a-GOS are consumed. It has been sug-
gested that a daily amount of 3 g of a-GOS is enough to
obtain the beneficial prebiotic action, while higher doses
could cause too much flatulence and digestive troubles
(Mart
ınez-Villaluenga et al. 2008). A portion of 296 g of
Bahthoula provides 0.7 g of total a-GOS, thus contribu-
ting to 22% of the effective daily dose. However, for peo-
ple suffering from irritable bowel disease, further
decrease in a-GOS content would be desirable. This
could be obtained by determining the optimal tempera-
ture and pH conditions to allow the maximum alpha-
galactosidase activity. Characterizing and modelling
alpha-galactosidase activity as a function of the process-
ing conditions has been proposed in order to identify
optimised pathways to enhance enzymatic degradation
and hence reduce a-GOS content more efficiently
(Coffigniez et al. 2018). This would require the develop-
ment of models specific for each seed species.
The results of this study highlight that traditional
dishes, which prominently include legumes, represent
an important component of healthy diets and contrib-
ute to human nutrition and food security. This may,
in turn, foster strategies of sustainable gastronomy,
promoting awareness for the need of healthy and bal-
anced diets (Marinangeli et al. 2017).
Conclusion
The consumption of legumes is generally recom-
mended to improve dietary profiles, but is hindered
by gastrointestinal discomfort associated with their
richness in a-GOS and fibre. This study shows that
traditional soaking in water (i) reduces total a-GOS
content due to partial leaching and enzymatic degrad-
ation occurring both inside and outside the seeds and
(ii) induces partial solubilisation of IDF with a con-
comitant increase of SDF. Cooking further decreased
the levels of total a-GOS but increased IDF. Further
studies will be carried out to explore the effects of
germination/fermentation that are usual in
Mediterranean countries, and could enhance a-GOS
and fibre degradation. Traditional culinary practices
offer healthy legume-based dishes that contribute to
the adequate amounts of dietary fibres and a-GOS
required for a well-balanced diet.
Disclosure statement
All authors have no conflicts of interest.
Funding
The authors thank the Agence Nationale de la Recherche
for its financial support [grant number ANR-12-
TMED-0004].
ORCID
Sondos Njoumi http://orcid.org/0000-0003-0326-2367
Marie Josephe Amiot http://orcid.org/0000-0003-
4563-4587
Sihem Bellagha http://orcid.org/0000-0003-0164-0395
Claire Mouquet-Rivier http://orcid.org/0000-0002-
3775-4610
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... Ash contents were determined by calcination in a furnace at 530 • C. Dry matter contents were determined by oven drying at 105 • C for 24 h. The total dietary fibre (TDF) was determined using an enzymatic-gravimetric method (Megazyme K-TDFR Kit), as described by Njoumi et al. [21]. Available carbohydrates were determined by difference using the following formula: (100 − (Water content + Lipid + Protein + Ashes + TDF)), and the energy value using the Atwater coefficients [22]. ...
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A hydropomc nutrient solution was used to raise barley sprouts to compare with sprouts raised using tap water irrigation (two treatments). In both treatments, the sprouts were raised in continuous light in a temperature-controlled room for a period of 7 days. There was no difference (p>0.05) in DM loss after 7 days of sprouting. The DM losses after 7 days of sprouting were 16.4 vs. 13.3% for tap water irrigation and hydroponic nutrient solution, respectively. Sprouts grown with nutrient solution had a higher protein concentration than those grown with tap water irrigation (17.3 vs. 15.9%), respectively. There was however, no difference (p>0.05) in in sacco degradation of sprouts in the rumen of Merino sheep. There was no advantage in the use of nutrient solution for producing hydroponic sprouts compared to sprouting with tap water only. If these sprouts were fed to ruminants, the DM losses would have represented a loss in digestible energy which would otherwise have been available for productive purposes. On a large scale these losses could add to the cost of animal production.
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A modelling approach was developed to better understand the behavior of the flatulence-causing oligosaccharides in cowpea seeds during isothermal water soaking-cooking process. Concentrations of verbascose, stachyose and raffinose were measured both in the seed and in the soaking water during the process (T = 30, 60 and 95 °C). A reaction-diffusion model was built for the three considered alpha-galactosides both in the seed and in the soaking water, together with a model of water transport in the seed. The model reproduced coupled reaction-diffusion of alpha-galactosides during the soaking-cooking process with a good fit. Produced, diffused and degraded alpha-galactoside fractions were identified by performing a mass balance. During soaking at 30 °C, degradation predominated (maximum found for raffinose degradation rate constant of 3.22 × 10⁻⁴ s⁻¹) whereas diffusion predominated at higher temperatures (95 °C).
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The distribution of calcium, potassium, iron, zinc and copper in the embryo and seed coat fractions of 16 common bean cultivars of the Middle American and Andean gene pools, obtained in two crop cycles, was investigated. Genetic factors affected the accumulation of minerals in the embryo and seed coat. Common bean seeds contained over 94.5% calcium in their seed coat and from 76.0 to 89.7% potassium in their embryo. Iron, zinc and copper concentrations varied widely between the embryo and seed coat fractions in different cultivars. The BRS Supremo cultivar has a high concentration of calcium (1044 mg 100 g(-1) dry matter [DM]) and iron (24.88 mg 100 g(-1) DM) in its seeds, whereas the Irai cultivar stands out for its potassium (1720 mg 100 g(-1) DM), zinc (6.51 mg 100 g(-1) DM) and copper (0.47 mg 100 g(-1) DM) concentrations. The BRS Supremo and the Irai cultivars have high nutritional value, and their dietary use is therefore recommended. Crown Copyright
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The fenugreek seed is the richest source of soluble and insoluble fiber and also known for its medicinal and functional properties. The major objective of this present study is fractionation of the fenugreek by roller milling method and characterization of roller milled fractions. The effects of moisture conditioning on fenugreek roller milling were studied using standard methods. The results observed were increase in coarse husk from 33.75–42.46 % and decrease in flour yield from 49.52–41.62 % with increase in addition of moisture from 12–20 %. At 16 % conditioning moisture, the yield of coarse husk was 40.87 % with dietary fiber and protein content of 73.4 % and 6.96 % respectively. The yellowness value (b) for the coarse husk (29.68) found to be lowest at 16 % conditioning moisture compared to the other coarse husk samples, showing maximum clean separation. The fiber fractions showed the viscosity of 6,392 cps at 2 % w/v concentration. The flour fraction was higher in protein (41.83 %) and fat (13.22 %) content. Roller milling process of fenugreek was able to produce > 40 % of coarse husk with 73.4 % dietary fiber (25.56 % soluble & 47.84 % insoluble) and > 48 % flour with 41.83 % protein content, where as the whole fenugreek contained 22.5 % protein & 51.25 % dietary fiber. Thus roller milling has proved to be a valuable method for the fractionation of fenugreek to obtain fiber and protein rich fractions.
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Background The use of traditional foods can enrich our diet, perpetuating important elements of local knowledge and cultural inheritance. Raw, soaked and cooked samples of two Fabaceae species (Cicer arietinum L. and Lathyrus sativus L.) were characterized regarding nutritional and bioactive properties.ResultsL. sativus gave the highest carbohydrate, protein, ash, SFA and PUFA content, and lowest fat and energy value. Furthermore, it also showed the highest concentration in flavonoids and antioxidant activity. C. arietinum gave the highest concentration of sugars, organic acids and tocopherols. Soaking process did not affect significantly macronutrients, but cooking (boiling) decreased protein, ash, sugars and organic acids, and increased carbohydrates, fat, tocopherols, bioactive compounds and antioxidant activity. No differences were obtained for fatty acids composition.Conclusion The present study highlights the nutritional profile and bioactive properties of these farmer varieties of C. arietinum and L. sativus pulses, and valorises their traditional consumption and the use in modern diets.
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(Trigonella foenum-gracum) is one of the most promising medicinal herbs, known from ancient times, having nutritional value too. Its green leaves and seeds are used for multipurpose. 100 g of seeds provide more than 65% of dietary fibre due to its high fibre content and it has an ability to change food texture. It is well known for its gum, fibre, alkaloid, flavonoids, saponin and volatile contents. In various medicinal applications, it works as antidiabetic, anticarcinogenic, remedy for hypocholesterolemia and hypoglycemia, antioxidant, antibacterial agent, gastric stimulant, and anti-anorexia agent. In modern food technology, it is used as food stabilizer, adhesive and emulsifying agent due its fibre, protein and gum content. Its protein is found to be more soluble (91.3%) at alkaline pH of 11. This review article presents the major medicinal and other beneficial uses of fenugreek discovered through last 30 years of research in animal and human subjects as well as in other experimental studies.