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Int. J. Postharvest Technology and Innovation, Vol. X, No. Y, xxxx 1
Copyright © 200x Inderscience Enterprises Ltd.
Evaluation of indigenous Omani legumes for their nutritional quality, phytochemical composition and antioxidant properties
Amanat Ali* Department of Food Science and Nutrition, College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O. Box 34, Al-Khoud 123, Sultanate of Oman, Oman E-mail: [email protected] *Corresponding author
Nadiya A. Al-Saady Department of Crop Sciences, College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O. Box 34, Al-Khoud 123, Sultanate of Oman, Oman E-mail: [email protected] E-mail: [email protected]
Mostafa I. Waly and Neeru Bhatt Department of Food Science and Nutrition, College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O. Box 34, Al-Khoud 123, Sultanate of Oman, Oman E-mail: [email protected] E-mail: [email protected]
Ali M. Al-Subhi and Akhtar Jamal Khan Department of Crop Sciences, College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O. Box 34, Al-Khoud 123, Sultanate of Oman, Oman E-mail: [email protected] E-mail: [email protected]
Abstract: Four indigenous Omani legumes (faba bean, cowpeas, chickpeas and lentils), collected from three different regions of Oman, were evaluated for their proximate composition, phytochemical contents and antioxidant properties. The proximate composition varied significantly. Regional variability however, did not affect the proximate composition, except crude protein content of cowpea and chickpea. The average values for moisture,
2 A. Ali et al.
protein, fat, fibre and ash ranged from 8.5% to 9.6%, 22.5% to 23.9%, 1.1% to 1.8%, 4.5% to 7.6% and 3.1 to 3.5% respectively. Both variety and regional variability affected the phytochemical contents. The average total phenol contents, tannins, and flavonoids ranged from 15.1 to 131.8 mg GAE/100 g, 13.2 to 100.8 mg CAE/100 g and 1.7 to 19.9 mg CAE/100g respectively, whereas the oxalates and saponins contents ranged from 56.1 to 197.8 and 2,699.1 to 3,598.1 mg/100 g respectively. A significant correlation was observed between the total phenol contents and the reducing power of legumes.
Keywords: legumes; indigenous varieties; proximate composition; phytochemicals; Oman.
Reference to this paper should be made as follows: Ali, A., Al-Saady, N.A., Waly, M.I., Bhatt, N., Al-Subhi, A.M. and Khan, A.K. (xxxx) ‘Evaluation of indigenous Omani legumes for their nutritional quality, phytochemical composition and antioxidant properties’, Int. J. Postharvest Technology and Innovation, Vol. X, No. Y, pp.000–000.
Biographical notes: Amanat Ali is a Nutritionist who has over 35 years of experience working in academia and research in the area of nutritional sciences. He is currently working as an Associate Professor of Human Nutrition at Sultan Qaboos University. His current areas of research focus on exploring the diet and disease relationship, in particular to study role of dietary patterns and lifestyle factors in the prevention and control of non-communicable diseases. His research also includes studying the role of carbohydrates, lipids, bioactive components and biomarkers of oxidative stress in health and disease.
Nadiya Al-Saady is a Plant Geneticist previously working in academia in the field of plant genetics with an emphasis on molecular genetics. She is currently working as the Executive Director for the Oman Animal and Plant Genetic Resources Center at the Research Council. Her current focus is in the area of conservation, documentation, characterisation, sustainable utilisation and valuation of genetic resources in the Sultanate. Her research interests are in the areas of characterisation and adding value to plant genetic resources.
Mostafa I. Waly is a holder of Master of Public Health (MPH) Nutrition major, Master degree of Biochemistry (MSc) and Doctorate degree (PhD) in the field of Biomedical Sciences from Northeastern University, Boston, USA. He is currently holding the position of an Assistant Professor of Human Nutrition, College of Agricultural and Marine Sciences, Sultan Qaboos University, Oman. His main research area is nutritional biochemistry in relation to non-communicable diseases. He has a strong record of research activity as evident by authoring 1 h text book and published 54 articles in peer-review journals, ten book chapters, and 23 abstracts in international conferences. He is an active member in the American Society for Nutrition (ASN) and Society of Experimental Biology and Medicine (SEBM) and is the Editor-in-Chief of the Canadian Journal of Clinical Nutrition published by Global Science Heritage Publisher, Toronto, Canada.
Neeru Bhatt is an Animal Nutritionist who has nine years of research experience. She obtained her PhD in Animal Nutrition from G.B. Pant University of Agriculture and Technology, Pantnagar, India. She has worked as a Senior Researcher for two years with Indian Veterinary Research Institute, Izzatnagar, India. She is currently working as a Research Assistant in the Department of Food Sciences and Nutrition, Sultan Qaboos University, Oman.
Evaluation of indigenous Omani legumes for their nutritional quality 3
Ali Al-Subhi is a Plant Biotechnologist working in research. His research areas are plant biodiversity and plants production. He is currently working as a Lab Supervisor in the Biotechnology Laboratory, Department of Crop Sciences at the College of Agricultural and Marine Sciences (CAMS) at Sultan Qaboos University. His current areas of research focus on witches’ broom disease, identification, collection and morphological and molecular characterisation of germplasm of local Omani plants.
Akhtar Jamal Khan is a Plant Virologist and Pathologist. His research interests include molecular plant pathology, genomics and proteomics of plant viruses, genetic resistance in crops against plant viruses, phylogenetic studies of phytoplasmas, transgenic plants expressing salt and drought tolerance genes. He was working as an Associate Professor in the Department of Crop Sciences, Sultan Qaboos University Muscat, Oman.
This paper is a revised and expanded version of a paper entitled ‘Nutritional quality of indigenous Omani legumes and their significance in human nutrition’ presented at 7th International CIGR Technical Symposium ‘Innovating the Food Value Chain’, University of Stellenbosch, Stellenbosch, South Africa, 25–29 November 2012.
1 Introduction
Legumes are one of the economically important groups of annually flowering vegetation, which belong to the family Leguminosae/Fabaceae (Lewis et al., 2005). They are widely cultivated in the tropics and sub-tropics for multiple purposes such as food for humans, fodder for animal feeding and atmospheric biological nitrogen fixers in maintaining the soil productivity and are of immense value in the farming system (Wang et al., 2003; Bell et al., 2012). However, due to a variety of biotic and abiotic constraints, their productivity is still far from satisfactory. The dry grains of about 20 legumes (pulses/beans) are important for human consumption. Peas (Pisum sativum L.) are mostly consumed in Asia, whereas the common beans (Phaseolus vulgaris L.) are mainly consumed in Latin America and Africa. In India and Pakistan, chickpeas (Cicer arietinum L.) are commonly consumed whereas lentils (Lens culinaris Med.) are common in the Middle East and faba beans (Vicia faba) in Mediterranean region (Morrow, 1991). Legumes are consumed both as vegetables (green pods of peas and beans) and dry seeds (pulses) in combination with staple cereals and make an excellent human diet in many developing countries. Legumes also make an integral part of traditional Omani diet.
Legumes are one of the cheapest and richest sources of dietary protein that is mainly used as a substitute to relatively expensive animal protein sources in many parts of developing world. The protein content in legume grains ranges between 17% to 40%, which is higher as compared to cereal grains that contain 7% to 13% and being almost equal or even higher to the protein content of meats, which contain 18% to 25% (Lewis et al., 2005). The protein in legumes is mostly the storage protein and is a good source of certain essential amino acids such as lysine, leucine, and arginine but deficient in methionine and cysteine. The legume protein is also less digestible (Wang et al., 2003; Gilani et al., 2005; Iqabal et al., 2006). Legumes also provide carbohydrates, dietary fibre, some B-vitamins, in particular thiamin and niacin. They are also a good source of
4 A. Ali et al.
certain important minerals such as calcium, iron, potassium, magnesium and zinc (Grusak, 2002; Trinidad et al., 2009). Legumes have low glycemic index and therefore can help to improve the glycemic control, diabetes and coronary heart diseases (Flight and Clifton, 2006). The presence of resistant starch and fermentation of indigestible carbohydrate fraction in the colon is considered to lower the incidence of cardiovascular diseases and cancer (Roy et al., 2010; Higgins, 2012). Legumes also contain many different types of phytochemicals, which are shown to have antioxidant properties with a wide variety of health-promoting activities (Laurena et al., 1994; Wang et al., 2003; Campos-Vega et al., 2010; Bell et al., 2012). However, their therapeutic properties have not yet been fully and systematically explored.
The Sultanate of Oman occupies an area of 309,500 km2 and has a unique geography and climate as the intense heat and lack of rain are not suitable for intensive agriculture. However, the legumes are widely cultivated in many parts of the Sultanate. In 2007, a strategic research project on the collection and conservation of legume genetic resources was initiated at Sultan Qaboos University, Muscat, Oman, under which a total of 307 accessions of indigenous Omani landraces of legumes were collected from various regions of Oman. The widespread movement of these landraces of food legumes in different regions of Oman indicated their unique adaptation to local agro-climatic conditions as a result of century’s old traditions, socio-cultural factors, as well as adaptation and selection processes. The existing legume landraces have been inherited from generations in the families. The diversity of these legume landraces in Oman is however under threat by genetic erosion, in particular for chickpeas and lentils, the two ancient traditional crops of Oman. Chickpea and lentil are the earliest cultivated pulse crops believed to be originated in Middle East and Near East respectively several thousand years ago. Although the conservation of indigenous plant germplasm is of great significance in the development of new and improved plant species, the genetic diversity and nutritional quality of legume landraces in Oman has been poorly explored. No such data has previously been reported in literature about the nutritional quality and phytochemical composition of indigenous Omani legumes. The objective of the present study was to evaluate four different indigenous Omani legume varieties (Faba beans, Cowpeas, Chickpeas, and Lentils) collected from three different regions of Oman for their proximate composition, phytochemical contents and antioxidant properties.
2 Materials and methods
The representative samples of four different indigenous Omani legume varieties, Faba bean (Vicia faba), Cowpea (Vigna unguiculata), Chickpea (Cicer arietinum), and Lentil (Lens culinaris), were collected from 3 different regions of Oman; Al-Dakhaliyah (N 22 57.078, E 57 31.670), Al-Dhahirah (N 23 14 33.0, E 57 02 28.4), and Al-Batinah (N 23 12 47.205 E 57 27 33.622). The collection sites varied in their soil characteristics, environmental conditions, and altitude. The legume varieties were selected not only based on their socio-cultural and farming system significance but also because of their higher frequency of consumption in human nutrition.
The samples were evaluated for their proximate chemical composition and phytochemical contents as well as for their reducing potential (FRAP). The analysis for all the chemical parameters was carried out in triplicate. The samples were analysed for their proximate chemical composition as described by AOAC (1990). The crude protein
Evaluation of indigenous Omani legumes for their nutritional quality 5
content was determined by Macro-Kjeldhal’s method using Kjeltech-instrument. The crude fat was determined by Soxhlet’s ether-extraction method. The total carbohydrate content, i.e., the nitrogen free extract (NFE) was estimated by subtracting the sum of % moisture, % crude protein, % crude fat, % crude fibre and % ash from 100. The gross energy value (GE, KJ/100 g) was calculated by multiplying the % g of protein, lipids and carbohydrates with 16.7, 37.7 and 16.7, respectively.
2.1 Extraction of samples for phytochemicals determination
The samples of whole legumes were finely ground in a grinder (60 mesh sieve size). Half a gram of sample was placed in centrifuge tubes and 5 mL of acetone, water, methanol (50:30:20, v/v) extraction mixture was added. The tubes were shaken in an orbital shaker for 3 hours at 300 rpm at room temperature. The mixture was then kept overnight (12 hours) in the dark. The centrifugation of extracts was carried out at 3,000 rpm for 10 minutes and the residues were re-extracted with respective solvent. The extracts were combined and stored at 4°C for further analysis. The analysis of individual legume variety was done in triplicate.
2.2 Assay of total phenolic content
Folin-Ciocalteu assay was used to determine the total phenol content (Singleton and Rossi, 1965). Three mL of distilled water, 250 μL of Folin-Ciocalteu’s reagent solution and 750 μL of saturated NaCO3 were added to 50 μL of the sample extract and mixed thoroughly. The mixture was incubated for 8 minutes at room temperature and the 950 μL of distilled water was added and left for 2 hours at room temperature. The colour produced was measured at 765 nm against a blank. A standard calibration curve of gallic acid was prepared and the total phenolic content (TPC) of samples was expressed as mg of Gallic Acid Equivalents (mg GAE/100 g sample). All the values have been reported on dry matter basis.
2.3 Measurement of condensed tannins
The condensed tannin content (CTC) was determined as described by Broadhurst and Jones (1978). The extracted samples were mixed with 4% methanol-vanillin solution and concentrated hydrochloric acid and the mixture was left to stand for 15 minutes. The colour intensity was measured at 500 nm against a blank (methanol). The quantity of condensed tannins was calculated using the standard calibration curve for (+)-catechin. The results are expressed as mg of (+)-catechin equivalents (mg CAE/100 g sample).
2.4 Measurement of total flavonoids
Measurement of total flavonoids was carried out calorimetrically as described by Heimler et al. (2005). The legume extract was mixed with distilled water and 5% NaNO2 solution and then 10% AlCl3.6H2O solution was added and after 5 minutes 0.5 mL of 1M NaOH solution was added and mixed well. The colour intensity (absorbance) was measured against the blank at 510 nm using a UV-Visible Spectrophotometer (Thermospectronic 9423, England). A standard calibration curve of (+)-catechin was developed. The total
6 A. Ali et al.
flavonoids are expressed as micrograms of (+)-catechin equivalents (mg of CAE/100 g sample).
2.5 Determination of saponins
The saponins were determined according to AOAC (1990). Saponins were extracted in a Soxhlet’s extractor using acetone and methanol (2 hours for each solvent). The amount of saponins was calculated gravimetrically and expressed as g/100 g.
2.6 Determination of oxalates
The amount of oxalates in legumes was determined as suggested by Abaza et al. (1968). The finely ground samples were boiled with 6 N HCl in a volumetric flask in a water bath and the mixture was filtered through Whatman’s filter paper no. 41 and the volume was made to the mark. The supernatant was then mixed with 6 N HCl and the contents were evaporated to half and filtered again with repeated washing of the precipitate. The filtrate was then heated and filtered again to remove impurities and precipitated by adding 5% CaCl2 and filtered. The precipitate was dissolved in dilute sulphuric acid solution (1:4) and titrated against 0.5 N KMnO4 solution near the end point. The amount of oxalates is presented as mg/100 g of sample.
2.7 Measurement of reducing power (FRAP)
The reducing power of the sample extracts was measured as described by Pulido et al. (2002). It is described as the ability of the sample extracts to reduce the ferric chloride (FeCl3) solution. The sample extracts (0–1.0 mL) were mixed with 2.5 mL of sodium phosphate buffer (pH 6.6) and 2.5 mL of 1% potassium ferricyanide solution and incubated at 50ºC for 20 minutes. A 10% solution of trichloroacetic acid (2.5 mL) was added and the mixture was centrifuged for 10 minutes. The resulting supernatant (5 mL) was mixed with equal volume of water and 1 mL of 0.1% ferric chloride. The absorbance was measured at 700 nm against a reagent blank.
2.8 Statistical analysis of the data
The data was analysed using one way analysis of variance (ANOVA) and results are expressed as means ± standard deviation (SD). The means were compared with least significant difference (LSD) as described by Snedecor and Cochran (1989). The value of p < 0.05 was considered as statistically significant. The statistical software package SPSS v.16 was used.
3 Results and discussion
3.1 Proximate composition
The data on the proximate composition of indigenous Omani legume varieties is presented in Table 1. The proximate composition of different legumes varieties varied significantly (p < 0.05), with the exception of their ash content. Regional variability
Evaluation of indigenous Omani legumes for their nutritional quality 7
however did not show any significant (p > 0.05) differences in the proximate composition of these Omani legume varieties. However, the crude protein content of faba bean and chick pea differed significantly (p < 0.05) in the samples collected from various regions. The average moisture, protein, fat, fibre and ash contents in these varieties ranged from 8.5% to 9.6%, 22.5% to 23.9%, 1.1% to 1.8%, 4.5% to 7.6% and 3.1 to 3.5%, respectively. The highest crude protein content was observed in lentil (23.9) followed by cowpea, faba bean and chickpea (22.5%). The crude fat content in faba bean, cowpea, chickpea and lentil was relatively low and ranged from 1.1% to 1.8%. The average total carbohydrate values ranged from 48.5% to 58.5%, with the highest values in chickpea. The average gross energy values ranged from 1,365 kJ/100 g to 1,438 kJ/100 g. The highest energy value was found in cowpea followed by chickpea, lentil and faba bean. The crude protein content of legumes can range from 17% to 40%. Our results are in line with the data reported in various studies for cowpeas, kidney beans and peas (Olakenon and Bosede, 2010). Iqabal et al. (2006) reported slightly higher amounts of protein (24.0% to 26.1%) in four important legume varieties from Pakistan than the values observed in this study. Cowpeas, chickpeas, lentils and faba beans are regarded as good sources of protein. No significant differences were observed in the average ash content of these indigenous Omani legume varieties. The mineral content in legumes depends on the mineral status of soil and the efficacy of mineral uptake by plants, which may be attributed to these differences. Our results are in line with the data reported in the literature from various parts of the world for different varieties of legumes (Iqabal et al., 2006; Olakenon and Bosede, 2010). The variability in the reported results on the proximate composition may be attributed to variety, agro-climatic conditions and other agricultural practices (Hoeck et al., 2000; Bell et al., 2012).
3.2 Phytochemical composition
Table 2 shows data on the phytochemical composition of indigenous Omani legumes. The phytochemical components (total phenol content, tannins, flavonoids, oxalates, and saponins), in different varieties of indigenous Omani legumes, varied significantly (p < 0.05) (Figure 1). The regional variability also significantly (p < 0.05) affected the phytochemical contents of these legumes. The average total phenol content (TPC) in different indigenous Omani legumes ranged from 15.1 to 132.3 mg GAE/100 g. The highest value was observed in cowpea followed by lentil, faba bean and chick pea. The chickpea showed the lowest value (15.1 mg GAE/100 g). Variable results have been reported in the literature about the total phenol content of different varieties of legumes (Berger and Hosfield, 2003; Ganiyu, 2006; Xu et al., 2007). The results of this study on TPC are in agreement with some of the reported values in the literature while in partial agreement with the others. Both the genetic factors and environmental conditions can influence the level of polyphenols in plant foods (Hoeck et al., 2000). The variability observed in our results may be attributed to these factors. The variety, germination, degree of ripeness, processing conditions and stage of growth may also influence the amount of phenolics (Bravo, 1998). The TPC has also been suggested as a cultivar-distinguishing factor in plant products (Klepacka et al., 2011).
8 A. Ali et al.
Table 1 Proximate chemical composition of indigenous Omani legume varieties
Legu
me
Engl
ish
nam
e Re
gion
of
Om
an
Moi
sture
(%)
Cru
de p
rote
in
(%)
Cru
de fa
t (%
) C
rude
fibe
r (%
) As
h (%
) N
FE (
%)
Gro
ss e
nerg
y kJ
/100
g
Faba
bea
n D
akha
liyah
8.
5±1.
3 20
.9±1
.1a
1.4±
0.4
7.5±
0.9
3.7±
0.4
58.0
±1.9
1,
374±
17
Faba
bea
n D
hahi
rah
9.5±
1.5
23.7
±1.7
b 1.
5±0.
6 7.
2±0.
6 3.
3±0.
6 54
.8±1
.4
1,37
1±12
Fa
ba b
ean
Batin
ah
9.1±
1.2
23.4
±1.3
b 1.
2±0.
3 8.
1±0.
4 3.
5±0.
4 54
.5±2
.5
1,35
0±21
**
Mea
n ±
SD
9.
3±1.
3a 22
.7±1
.5b
1.4±
0.5ab
7.
6±0.
5a 3.
5±0.
5 55
.7±2
.3
1,36
5±15
c C
owpe
a D
akha
liyah
8.
6±1.
5 23
.4±1
.1
1.8±
0.3
4.8±
1.1
3.3±
0.3
58.1
±1.1
1,
432±
9 C
owpe
a D
hahi
rah
8.7±
1.4
23.6
±1.7
1.
7±0.
7 4.
3±0.
7 3.
1±0.
7 58
.6±1
.8
1,44
1±7
Cow
pea
Batin
ah
8.6±
1.2
23.8
±1.4
1.
8±0.
4 4.
5±0.
8 3.
2±0.
5 58
.1±1
.5
1,44
0±8
**M
ean
± SD
8.5±
1.0b
23.6
±1.2
a 1.
8±0.
7a 4.
5±0.
5b 3.
2±0.
4 58
.3±1
.6
1,43
8±9a
Chi
ck p
ea
Dak
haliy
ah
9.3±
1.3
20.2
±1.1
c 1.
4±0.
5 5.
3±1.
0 3.
4±0.
4 60
.4±1
.7
1,40
3±16
C
hick
pea
D
hahi
rah
9.4±
1.9
24.6
±1.3
a 1.
9±0.
4 4.
1±1.
2 3.
2±0.
3 56
.8±2
.1
1,43
5±9
Chi
ck p
ea
Batin
ah
9.5±
1.1
22.8
±1.7
b 1.
6±0.
5 4.
5±1.
2 3.
3±0.
7 58
.8±1
.4
1,42
0±8
**M
ean
± SD
9.4±
1.3a
22.5
±1.9
b 1.
7±0.
3a 4.
6±0.
9b 3.
3±0.
5 58
.5±1
.7
1,41
9±9b
Lent
il D
akha
liyah
9.
8±1.
0 23
.8±1
.1
1.1±
0.3
4.5±
1.0
2.9±
0.1
57.9
±1.8
1,
410±
13
Lent
il D
hahi
rah
9.5±
1.6
23.5
±1.2
1.
0±0.
4 4.
4±1.
1 3.
1±0.
3 58
.5±2
.2
1,41
0±17
Le
ntil
Batin
ah
9.6±
1.2
24.6
±1.2
1.
1±0.
3 5.
1±1.
0 3.
4±0.
4 56
.2±1
.5
1,40
0±11
**
Mea
n ±
SD
9.
6±1.
2a 23
.9±1
.1b
1.1±
0.3b
4.7±
1.0b
3.1±
0.3
57.6
±1.1
1,
408±
12b
Not
es: *
Diff
eren
t sup
ersc
ripts
in sa
me
colu
mn
with
in e
ach
varie
ty in
dica
te s
igni
fican
t reg
iona
l diff
eren
ces w
ithin
the
sam
e va
riety
(p <
0.0
5).
**D
iffer
ent s
uper
scrip
ts in
sam
e co
lum
n on
the m
ean
valu
es in
dica
te s
igni
fican
t diff
eren
ces a
mon
g th
e va
rious
legu
me
varie
ties (
p <
0.05
).
Evaluation of indigenous Omani legumes for their nutritional quality 9
Table 2 Phytochemical composition of indigenous Omani legumes (on dry matter basis)
Legu
me
Regi
on o
f Om
an
Tota
l phe
nolic
s mg
GAE
/100
g
Tann
ins m
g
CAE
/100
g
Flav
onoi
ds m
g C
AE/1
00 g
O
xala
tes m
g/10
0g
Sapo
nins
mg/
100
g
Faba
bea
n D
akha
liyah
30
.0±1
.8b
17.3
±3.8
b 3.
4±0.
9 20
0.0±
15.0
a 2,
679.
5±15
4.4b
Faba
bea
n D
hahi
rah
34.8
±3.1
a 17
.7±2
.3b
3.2±
0.8
130.
0±12
.0c
2,68
5.5±
137.
8b Fa
ba b
ean
Batin
ah
31.1
±3.6
ab
20.5
±2.1
a 2.
8±1.
0 17
7.0±
17.0
b 2,
732.
4±26
8.2a
**M
ean
± SD
32.1
±2.1
c 18
.5±1
.7c
3.1±
1.1b
169.
3±5.
8b 2,
699.
1±28
.97c
Cow
pea
Dak
haliy
ah
123.
3±7.
0b 80
.5±5
.9b
23.7
±4.6
a 18
2.3±
14.6
b 3,
686.
1±10
9.7b
Cow
pea
Dha
hira
h 13
3.7±
12.7
a 11
4.5±
18.5
a 14
.9 ±
2.0
b 19
9.4±
19.6
ab
3,37
6.6±
47.6
c C
owpe
a Ba
tinah
13
8.5±
14.1
a 10
7.5±
11.1
a 21
.3±3
.5a
211.
8±13
.5a
3,73
1.5±
99.2
a **
Mea
n ±
SD
13
1.8±
7.5a
100.
8±13
.4a
19.9
±4.2
a 19
7.8±
12.9
a 3,
598.
1±88
.8a
Chi
ckpe
a D
akha
liyah
11
.3±1
.3b
8.6±
2.7c
1.6±
0.7
56.0
±6.8
ab
3,40
6.0±
246.
9b C
hick
pea
Dha
hira
h 17
.5±2
.2a
13.8
±2.9
b 1.
8±0.
5 62
.0±7
.0a
3,72
4.9±
234.
4a C
hick
pea
Batin
ah
19.5
±1.3
a 17
.3±2
.8a
1.7±
0.4
50.3
±5.8
b 3,
815.
4±23
8.2a
**M
ean
± SD
15.1
±1.8
d 13
.2±2
.1d
1.7±
0.6c
56.1
±4.2
d 3,
548.
8±22
1.5a
Lent
il D
akha
liyah
10
8.8±
7.9b
67.4
±3.9
b 14
.6±2
.1b
114.
0±3.
8a 3,
145.
6±11
6.6a
Lent
il D
hahi
rah
119.
3±9.
3a 71
.2±5
.7a
18.3
±1.1
a 10
4.0±
5.0b
3,09
5.8±
106.
8b Le
ntil
Batin
ah
123.
5±8.
9a 75
.3±4
.6a
19.8
±1.5
a 11
9.0±
4.0a
3,11
0.8±
146.
2a **
Mea
n ±
SD
11
7.3±
7.42
b 71
.3±3
.9b
17.6
±2.6
a 11
2±5.
7c 3,
117.
4±13
2.2b
Not
es: *
Diff
eren
t sup
ersc
ripts
in sa
me
colu
mn
with
in e
ach
varie
ty in
dica
te s
igni
fican
t reg
iona
l diff
eren
ces a
mon
g th
e va
riety
(p <
0.0
5).
**D
iffer
ent s
uper
scrip
ts in
sam
e co
lum
n on
the m
ean
valu
es in
dica
te s
igni
fican
t diff
eren
ces a
mon
g th
e va
rious
legu
me
varie
ties (
p <
0.05
). G
AE
= G
allic
aci
d eq
uiva
lent
; CA
E =
Cat
echi
n eq
uiva
lent
.
10 A. Ali et al.
Figure 1 Phytochemical content of different indigenous Omani legumes
The average tannin contents in indigenous Omani legumes ranged from 13.2 to 100.8 mg CAE/100 g. The highest value (100.8 mg CAE/100 g) was found in cowpea whereas the lowest (13.2 mg CAE/100 g) in chickpea. Condensation of simple phenolics leads to the formation of condensed tannins, which consist of a variety of molecular structures and are widely present in lentils, peas, coloured soybeans, and common beans in variable concentrations (Beninger and Hosfield, 2003; Almeida et al., 2008; Xu et al., 2007). Our results are in line with these findings as the tannins content of legumes can vary because of genetic and environmental conditions similar to that of total phenols.
The average flavonoids contents ranged from 1.7 to 19.9 mg CAE/100 g. The highest value was observed in cowpea and the lowest value in chickpea. Based on the variation in their heterocyclic C-ring structure, flavonoids are mainly divided into six major sub-classes, including flavones, flavonols, flavanones, catechins, anthocyanidins and Isoflavones (Ross and Kasum, 2002). The flavonoids contribute to maintain the peculiar taste in prepared foods and can act as potent antioxidants. They can scavenge the free radicals preventing the oxidative cell damage and are therefore capable of treating certain physiological disorders including protection against all stages of carcinogenesis (Ross and Kasum, 2002; Velaquez et al., 2010). The flavonoids are the basic components of fruits and vegetables and have been well studied (Ignat et al., 2011). However, studies about the identification and quantification of flavonoids in legumes are scanty. Our results are in good agreement with the data reported in the literature on the flavonoids content of legumes (Xu et al., 2007; Velaquez et al., 2010).
The average oxalate values in different indigenous Omani legumes ranged from 56.1 to 197.8 mg/100 g. The highest value (197.8 mg/100 g) was observed in cowpea, whereas the lowest value (56.1 mg/100 g) was found in chickpea. Oxalates are widely found in many plant species and occur as end products of metabolism both in soluble and insoluble forms. They are generally considered as undesirable components in foods as they can form non-absorbable insoluble compounds with Ca+2, Fe+2 and Mg+2 rendering these minerals unavailable and can lead to kidney stone formation (Almeida et al., 2008; Akhtar et al., 2011). The oxalate content in foods has been reported to vary greatly. The results of this study are in line with those reported in the literature for various types of
Evaluation of indigenous Omani legumes for their nutritional quality 11
legumes (Massey et al., 2001; Akhtar et al., 2011). However, the amount of oxalates present in the indigenous Omani legume varieties appears to be a little higher than those reported in the literature for similar type of legumes.
The mean values for saponins in different indigenous Omani legume varieties ranged from 2,699.1 to 3,598.1 mg/100 g. The highest amount of saponins (3,598.1 mg/100 g) was found in cowpea, followed by chickpea and lentil, with the lowest values in faba bean (2,699.1 mg/100 g). Variable results have been reported in the literature on the saponin content of various legumes from different parts of the world (Lyan et al., 2006; Mbagwu et al., 2011). Our results are in line with these findings and the existing variability in reported results may be attributed many factors as discussed earlier including genetic variability, agronomic practices and environmental condition as well as the methodological approaches used to determine the phytochemical constituents. Saponins are bitter in taste and contribute to the foaming characteristic of seeds. Under experimental conditions, the saponins have been shown to produce some toxic effects. However, the acute poisoning in humans and animals is relatively rare under normal dietary consumption patterns (Cortes-Giraldo et al., 2012). Diets containing foods rich in saponins (300–500 mg/day), such as soybean, chickpea and beans have been reported to reduce the plasma cholesterol by 16% to 24% (Thompson, 1993).
3.3 The antioxidant properties (reducing power, FRAP) of legumes
The data on the reducing ability of methanolic extracts of different legume varieties is presented in Figure 2. The reducing power (FRAP) was measured over a concentration of 0.2 to 5 mg/ml. The highest value for reducing power was observed in cowpea, followed by lentil, chickpea and faba bean. A linear increase in the reducing ability with increasing concentration of methanolic extracts was observed that indicated a dose-dependent relationship. The reducing potential of the legumes was significantly (p < 0.05) correlated with the TPCs. The balance between the reducing equivalents and level of oxidants is termed as redox. The redox balance is tightly regulated and controls many biochemical pathways and cellular events occurring in living cell. The reducing power represents the overall ability of the cells, tissues, biological fluids or chemicals to donate electrons to other chemicals (free radicals) or to supply the attachable hydrogen atoms that can be used for reduction of other compounds. Estimation of the reducing power is an indicator of antioxidant activity and directly relates to the amount of phenolic compounds present in different foods including legumes (Campos-Vega et al., 2010; Doss et al., 2011; Siger et al., 2012). The excessive production of free radicals or their imbalance is implicated in the pathogenesis of many chronic diseases including atherosclerosis, ischemic heart disease, cancer, Alzheimer’s disease, Parkinson’s disease and in the aging process. The antioxidant substances (reductants) block the action of free radicals and maintain the redox balance (Campos-Vega et al., 2010; Siger et al., 2012). Our findings are in good agreement with the findings reported in the literature for the reducing power of different legume varieties (Sreemulu et al., 2009; Campos-Vega et al., 2010; Doss et al., 2011; Siger et al., 2012). The antioxidants present in foods are used to preserve its quality mainly because of their ability to arrest the oxidative deterioration of lipids. The variability in the reported results may be due to different methodologies used for the assessment of various parameters and need to be clarified in further studies. Although there is no bearing on the toxicity of natural or synthetic chemicals, the
12 A. Ali et al.
plant-based antioxidants are generally preferred as compared to the synthetic ones because of safety concerns. In addition to their nutritional value, the legumes can therefore be used as a good source of natural antioxidants (Doss et al., 2011).
Figure 2 The reducing power (FRAP) of extracts of indigenous Omani legumes
0
0.1
0.2
0.3
0.4
0.5
0.6
0.2 0.4 0.6 0.8 1 5
Redu
cing
Pow
er (O
D at 70
0 nm
)
Concentration (mg/ml)
Faba Bean
Chickpea
Lentil
Cowpea
4 Conclusions
Significant varietal and regional differences were observed in the proximate composition, phytochemical contents and the antioxidant potential of indigenous Omani legumes. The results indicated that these indigenous Omani legumes are good source of protein, carbohydrates, fibre, minerals and many antioxidant phytochemicals that may have great potential health benefits. This is the first study to report such data about the indigenous Omani legumes. As the legumes make an integral part of traditional Omani diet, it is suggested that the genetic diversity of these indigenous Omani legume landraces should be further explored to improve their nutritional quality and contents of bioactive components for improved health benefits in human nutrition.
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