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International Journal of Food Process Engineering
Vol. 1, No. 1, June 2013, PP: 01 – 15
Available online at http://acascipub.com/Journals.php
1
Research article
Influence of soaking on biochemical components of
tiger nut (Cyperus esculentus) tubers cultivated in
Cameroon
Djomdi, MSc1,2,6, Kramer JKG, PhD3, VanderJagt, DJ, PhD4, Ejoh R, PhD1,
Ndjouenkeu R, PhD1 and Glew RH, PhD4,5
1 Department of Food Science and Nutrition
University of Ngaoundere
Ngaoundere, Cameroon
and
2Higher Institute of the Sahel
University of Maroua
Maroua, Cameroon
and
3Food Research Program
Agriculture and Agri-Food Canada
Guelph, Ontario, Canada
and
4Department of Biochemistry and Molecular Biology
University of New Mexico School of Medicine
Albuquerque, New Mexico
and
5National Institute of Occupational Safety and Health (NIOSH)
Cincinnati, Ohio
6To whom all correspondence should be addressed: Djomdi, Higher Institute of the Sahel, University of Maroua,
P.O.Box 46 Maroua, Cameroon
E-mail: ngdjomdi@yahoo.fr
International Journal of Food Process Engineering
Vol. 1, No. 1, June 2013, PP: 01 – 15
Available online at http://acascipub.com/Journals.php
2
____________________________________________
Abstract
Wild edible plants contribute significantly to the diets of populations in the hot, arid regions of the western
Sahel, especially during periods of food scarcity. Tiger nut tubers (Cyperus esculentus) which are used by local
populations as nibble food were collected in the Northern of Cameroon are treated by soaking in different
solutions and analyzed for their biochemical components. The tubers were soaked four different ways for
consumption: non-treated (i.e., raw tubers), soaking in vitamin C, soaking in Ca(OH)2 and soaking in kanwa
solutions (1 g/L) at 40°C. In general, the nutrient content of tiger nut tubers was dependent on soaking solution.
After the analysis, we noted that tiger nut tubers contained significant amounts of fatty acid (26% of dry weight)
which were contained mostly in triacylglycerols (triacylglycerides) and consisted of palmitic acid (16:0; 40.4
mg/g dry weight), oleic acid (18:1n-9; 167 mg/g), linoleic acid (18:2n-6; 30.7 mg/g), and α-linolenic acid (18:3n-
3; 0.7 mg/g). This plant contained 7.54% protein and it scored well the WHO protein standard. C. esculentus
contained nutritionally useful amounts of many minerals and trace elements, including, copper, iron, manganese,
zinc, chromium, selenium and molybdenum, and, it is a very good source of potassium, phosphorus and
magnesium. Soaking in alkaline solutions (Ca(OH)2 and kanwa) leads to significant loss of soluble proteins (7.54
to 4.85%), ascorbic acid (250 to 61.58% mg/100g DM ) and vitamin E (120 to 94.05 mg/100g DM ), in return,
vitamin C solution preserves biochemical components of tiger nut tubers.
These data should provide public health officials in sub-Saharan Africa with information that would be useful in
advising local populations about influence of treatment on the nutrient value of various spontaneous edible plants
that grow in the region. Copyright © www.acascipub.com, all rights reserved.
Keywords: nutrients, Cameroon, Cyperus esculentus, fatty acids, amino acids, minerals, soaking.
_____________________________________________
Running title: Influence of soaking on biochemical Composition of tiger nut tubers cultivated in Cameroon
List of abbreviations: EFAs, Essential Fatty Acids; FA, Fatty Acid; FAME, Fatty Acid Methyl Ester; FFAs,
Free Fatty Acids; FID, Flame Ionization Detector; MUFAs, Monounsaturated Fatty Acids; PUFAs,
Polyunsaturated Fatty Acids; RT, Raw Tuber; SFAs, Short-chain Fatty Acids; TAGs, Triacylglycerols; WHO,
World Health Organization.
Introduction
Though it is widely acknowledged that hundreds and perhaps even thousands of wild edible plants play a
significant role in the economic and cultural life and diets of communities in sub-Saharan Africa, the literature
contains little in the way of quantitative information about the nutrient composition of these plants that are
especially important as ‘famine foods’ in times of severe food shortage. Tiger nut tubers belong to the foodstuffs
having a high nutritional potential but which remain under-exploited (Ukwuru et al., 2011 and Bamishaiye et al.,
International Journal of Food Process Engineering
Vol. 1, No. 1, June 2013, PP: 01 – 15
Available online at http://acascipub.com/Journals.php
3
2010). This nutritional value of the tubers is appreciable and it varies from an area to another. Many authors
evaluated the chemical composition of this foodstuff in various regions; it comes out from this work that the
chemical characteristics of the tubers are influenced by the zones of culture (Eteshola, and Orasedu, 1996 and
Pascual, Maroto, San Bautista, Alagarda and Lopez-Galarza, 2003).
In Cameroon, tiger nut tubers are cultivated in the Soudano-sahelian zone, more precisely in the soudanian sector
of altitude although it is found on sale on all the local markets. With more than 17000 T of production, the Far
North region of Cameroon seems to be the principal area of culture in the country. The tubers are usually
consumed like food of nibbling, in spite of its abundance in the area, its valorization is very weak, which justifies
its low price on the market (less than 0,5 $.kg-1). Moreover, the plant has attracted very little scientific and
technological attention apart work from Kapseu, Mbofung & Kayem (1997). The development produced again
starting from the tubers can raise the interest granted to this plant. For this purpose, several opportunities are
offered by the plant like: source of food fibers, production of milky drink (horchata de chufa), and use of its oil
in the culinary field or the preparation of salads, production of caramel to be used like food additive. The major
use of the tiger nut tubers comes from Spain where the tubers are used for the production of commercial milk
called “horchata” (Pascual, Maroto, Lopez-Galarza, Sanbautista & Alagarda, 2000). These forms of use can
imply, according to the case, a treatment of saoking (in acid or alkaline solutions). These treatments are suitable
for induce modifications of the nutritional value of the tuber.
Although the literature does contain reports of the nutrient content of tubers of C. esculentus (Bosch, Alegria and
Fare, 2005; Djomdi and Ndjouenkeu, 2007; Ejoh, Djomdi and Ndjouenkeu, 2006; Glew et al., 2005; Glew et al.,
2006, in press), we were interested in determining how different methods used to treat the tubers for
consumption in northern Cameroon might influence their biochemical composition. We therefore compared the
content of these nutrients in raw tubers and tubers that had been either soaked in vitamin C solution or under
alkaline conditions (pH 9.8-10.1) using a locally-prepared natural rock salt called ‘kanwa’ comprised of sodium
carbonate and sodium bicarbonate (Makanynola and Beetlestone, 1975) and Ca(0H)2 solutions.
Materials and Methods
Collection of samples
Tiger nut tubers were purchased in the local market in the town of Guily in Far-North Region of Cameroon,
washed with distilled water and sun-dried for four days. One portion was set aside and designated ‘untreated raw
tubers’. A second portion was soaked in vitamin C solution (1 g/L) at 40°C for maximums turgescent while a
third and fourth portion was soaked for maximums turgescent in kanwa and Ca(OH)2 1 g/L at 40°C respectively
and designated ‘alkali-soaked- tubers’. Soaking experiments, carried out according to Turhan et al. (2002). All
plant samples were shipped via air-mail to Albuquerque, New Mexico for analysis. Prior to analysis, samples
were ground once again with the aid of a mortar and pestle and dried to constant weight after maintaining them
under a vacuum over anhydrous calcium chloride for four days at room temperature.
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Analysis
Dry matter and ash were determined by UICPA (1979) methods; starch by Mestres et Mestres (2011) procedure;
fiber, ascorbic acid, reducing sugar, caloric value were determined by AOAC (1984) procedures; vitamin E was
determined by Chase et Long (1998) method.
Lipid analysis
Total lipids from 1 g of sample were extracted using 20 mL of chloroform/methanol (1:1). The mixture was
thoroughly mixed using a Virtis homogenizer (Gardiner, NY) and then left standing at room temperature for 1 h
before filtering. The residue was re-dissolved in a further 15 mL of chloroform/methanol (1:1), mixed and
filtered. The filtrates were combined and the solvent was removed using a rotary evaporator. The lipid residue
was dried under vacuum, weighed, and then dissolved in chloroform for storage at -70oC. Analyze was
conducted as describe by Kramer, Cruz-Hernandez and Zhou (2001) and Cruz-Hernandez et al. (2004). The
FAME were identified by comparison with known FAME standards that included gas chromatography standard
mixture plus three separately purchased FAMEs (21:0, 23:0 and 26:0) from Nu Check Prep. The FID response
was used to quantify all the FAMEs.
Amino acid analysis
Each plant sample was analyzed in triplicate. Five to nine mg of each samples were weighed and placed in 2-ml
ampoules, to which the internal standard (norleucine) and 0.45 ml of 6 N HCl were added. Norleucine was used
as internal standard because this amino acid is not commonly found in proteins. The ampoules were evacuated,
sealed and placed in an oven for 24 h at 110oC. After hydrolysis, 20 µl aliquots of the hydrolysates were dried,
mixed with 10 μl of redry solution (ethanol:water:triethylamine, 2:2:1), dried again, and finally derivatized with
20 μl phenylisothiocyanate reagent (ethanol :water: triethylamine: phenylisothiocyanate, 7:1:1:1) for 20 min at
room temperature (Cohen and Strydom, 1988) with gradient conditions as described elsewhere (Glew et al.,
2005). The tryptophan content was determined in a separate analysis (Hugli and Moore, 1972) and the solvents
and gradient conditions were as described by Hariharan and coworkers (Hariharan, Sundar and Van Noord,
1993).
Mineral analysis
A single sample (50-500 mg) from each of the dried, powdered sample was weighed, then wet-ashed by
refluxing overnight with 15 ml of concentrated HNO3 and 2.0 ml of 70% HClO4 at 150oC. The samples were
dried at 120°C and the residues were dissolved in 10 ml of 4.0 N HNO3 in 1% HClO4 solution. The mineral
content of each sample solution was determined by inductively coupled argon plasma atomic emission
spectroscopy (ICP-AES, Jarrel-Ash, Perkin-Elmer, Palo Alto, CA) as described elsewhere (Glew et al., 2005).
The mineral contents of the samples were quantified against standard solutions of known concentrations which
were analysed concurrently.
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5
Results
Biochemical composition of tiger nut tubers
Results of the different levels of biochemical components are found in table 1. No significant changes in starch
and total sugars content were observed for the different treatments (P< 0.05). The analysis of variance indicates
the existence of a significant difference (p < 0.05) between soaking solutions on proteins, ascorbic acid and
vitamin E content. Alkaline solutions lead to loss of these components by their solubilisation in soaking
solutions. Medoua (2005) observed the same effect on yams soaked in kanwa solution; and Yudkin (1988)
specified that soaking in alkaline solutions of foodstuff cause loss of ¾ of vitamins. In fact, ascorbic acid and
vitamin E are unsteady in these solutions as a consequence of oxidation and the dissolution of those vitamins in
soaking solutions (Boudier et Luquet, 1981). On the other hand, vitamin C solution has stabilizing effect on
vitamin E but increases ascorbic acid in tiger nut tubers soaked in this solution (Table 1).
Table 1: Biochemical composition of tiger nut tubers soaked in alkaline solutions (1 g/L) (Ca(OH)2 et Kanwa)
and acid solution (Vitamin C, 1 g/L) at 40°C.
Soaking solution (1 g/L)
Characteristics
(mg/100 DM)
Vitamin C Ca(0H)2 Kanwa RT1 (Control)
Water content 57.342 ± 0.23
b
57.385 ± 0.54
b
57.297 ± 0.35
b
7.385 ± 0.141a
Proteins 7.428 ± 0.42
b
5.62 ± 0.49a 4.85 ± 2.12a 7.54 ± 0.33
b
Lipids 26.25 ± 0.53
b
26.47± 0.18
b
27.74 ± 1.02c 25.08 ± 0.32a
Starch 25.13 ± 2.10a 24.90 ± 0.15a 24.59 ± 3.93a 25.28 ± 4.03a
Fibers 11.03 ± 0.94a 12.53 ± 0.53a 12.79 ± 0.54a 14.14 ± 0.38a
Ash 1.84 ± 0.07a 3.73 ± 0.14
b
4.60 ± 1.35b 2.60 ± 0.05a
Total sugar 47.52 ± 0.84a 48.54 ± 0.94ab 48.84 ± 0.83ab 49.78 ± 0.74
b
c
Reducing sugar 23.74 ± 0.74a 25.56 ± 1.52
b
26.05 ± 0.85
b
26.12 ± 0.24
b
Ascorbic acid
(mg/100g) 328 ± 4.37d 80.47 ± 1.39b 61.58 ± 3.52a 250 ± 0.62c
Vitamin E (mg/100g) 118.79 ± 3.26c 101 ± 1.23
b
94.05 ± 2.15a 120 ± 0.56c
Caloric value (kcal) 450 (1881 kJ)c 446 (1864 kJ)b 451 (1885 kJ)c 442 (1847 kJ)a
Values on the same row with the same superscript are not significantly different at P<0.05
1RT, Raw Tuber
Fatty acid content and composition
Separation of the total lipid extracts by thin layer chromatography was used to assess the lipid class profile of
each of the tiger nut tubers preparation. The total lipid content in the four different preparations of C. esculentus
tubers varies from 25.08 (RT) to 27.74% of total dry matter (Tubers soaked in kanwa solution) (Table 2) was
considerably higher than in the other varieties and location (24.2% of total dry matter, Temple, Ojebe and Kapu
(1989). There were no significant differences in the FA composition of the different preparations of C.
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6
esculentus. The lipids of the tuber consisted mainly of oleic acid (18:1n-9) (64%) and much lower levels of total
SFAs (22%) compared to legumes. They had 18:2n-6 levels (11%) that were similar to what was seen with the
other plant specimens, but only trace amounts of 18:3n-3 (0.2%) were present (Table 2). The trans fatty acid
(TFA) content was investigated in the plant lipids to assess product quality. Soaking in the alkaline conditions of
the samples may have contributed to the increased levels of TFAs. Possibly the higher oil content and the TAG
structure may have provided greater protection of the PUFAs in the tuber lipids of C. esculentus against
isomerization. Table 2 shows the amount of selected FA or FA groups present in 100 g of plant foods. The value
of 100 g was arbitrarily chosen to represent a reasonable portion that one might consume. Based on the
recommendations for adequate intake of the essential fatty acids (EFAs) in the US for men and women ages 19
to 50 (National Academy of Sciences, 2002), the percent of adequate intake of the two EFAs provided in 100 g
was calculated (Table 2).
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Table 2: Fatty acid composition of Cyperus esculentus from Cameroon soaked in alkaline and acid solutions (1
g/L) at 40°C
Fatty acids1 (%) Vitamin C Ca(OH)2Kanwa RT2
Myristic 14:0 0.12±0.00a0.12±0.00a0.12±0.00a0.11±0.01
a
Palmitic 16:0 15.40±0.23a15.44±0.05a15.80±0.22a14.50±0.31
b
Palmitoleic 16:1n-9 0.03±0.00a0.03±0.02a0.03±0.04a0.03±0.00
a
Stearic 18:0 4.59±0.41
b
5.03±0.08a5.19±0.11a4.51±0.21
b
Oleic 18:1n-9 65.47±0.19a62.69±0.41c62.33±0.45c64.84±0.42
b
Linoleic 18:2n-6 12.69±0.83a10.87±0.11c10.64±0.31c11.38±0.11
b
Arachidic 20:0 0.84±0.04a0.76±0.07
b
0.73±0.03
b
0.75±0.02
b
Gadoleic 20:1n-9 0.25±0.07a0.24±0.01a0.23±0.01a0.23±0.03
a
Linolenic 18:3n-3 0.25±0.03a0.17±0.00c0.18±0.02c0.20±0.02
b
Béhenic 22:0 0.24±0.09a0.20±0.01
b
0.19±0.00
b
0.19±0.01
b
Lignocetric 24:0 0.28±0.01a0.25±0.03a0.23±0.01a0.24±0.02
a
Cerotic 26:0 0.08±0.00a0.09±0.00a0.08±0.00a0.08±0.00
a
Sum SFAs 20.75±0.87
b
22.07±0.12a22.54±0.21a20.58±0.23
b
20:0 -26:0 1.53±0.05a1.37±0.03
b
1.31±0.03
b
1.35±0.03
b
cis MUFAs 65.18±0.19
b
6 3.48±0.44c63.15±0.09c66.61±0.83
a
Sum TFAs 1.02±0.04
d
1.25±0.08
b
1.35±0.02a1.07±0.05c
n-6 PUFAs 11.69±0.64a10.88±0.55c10.64±0.07
d
11.39±0.34
b
n-3 PUFAs 0.25±0.04a0.17±0.02c0.16±0.01c0.20±0.00
b
n-6/n-3 46.68±0.84
d
54.78±0.17c60.74±0.44a57.44±0.64
b
Total lipids 26.25±0.93b26.47±0.19b27.74±0.32a25.08±0.27c
Values on the same row with the same superscript are not significantly different at P<0.05
All values are mean of two separate methylation procedures; see Material and Methods section.
Values on the same row with the same superscript are not significantly different at P<0.05
1 MUFAs, monounsaturated fatty acids; PUFAs, polyunsaturated fatty acids; SFAs, saturated fatty acids; TFAs,
trans fatty acid.
2RT, Raw Tuber
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Table 3: Amounts of selected fatty acid (mg/g dry wt) in Cyperus esculentus from Cameroona treated in
different ways by soaking in alkaline and acid solutions (1 g/L, at 40°C)
Fatty acid (mg/g)b RT1 Vitamin C Ca(0H)2 Kanwa
16:0 36.37 40.44 40.88 43.84
18:0 11.31 12.04 13.31 14.40
18:1n-9 175.70 166.63 168.59 163.63
18:1n-7 2.74 2.73 2.92 3.08
18:2n-6 29.52 30.69 28.78 28.55
20:0 1.88 2.19 2.00 2.03
20:1n-9 0.57 0.65 0.63 0.64
18:3n-3 0.53 0.66 0.50 0.49
22:0 0.49 0.62 0.52 0.51
23:0 0.05 0.06 0.06 0.05
24:0 0.61 0.73 0.65 0.64
25:0 0.07 0.09 0.09 0.09
26:0 0.21 0.22 0.23 0.22
28:0 0.05 0.05 0.05 0.04
Sum SFAs 51.61 57.10 58.43 62.53
20:0 -28:0 3.39 4.01 3.63 3.62
cis MUFAs 167.09 171.12 173.33 180.74
Sum TFAs 2.69 2.68 3.31 3.75
n-6 PUFAs 29.53 30.69 28.79 28.56
n-3 PUFAs 0.50 0.66 0.53 0.49
n-6/n-3 57.44 46.68 54.78 60.74
g/100gc
n-6 PUFAs 2.95 3.07 2.88 2.86
n-3 PUFAs 0.05 0.07 0.05 0.05
Men (% of requirement)
d
n-6 PUFAs 17.37 18.05 16.94 16.80
n-3 PUFAs 3.11 4.11 3.29 3.04
Women (% of requirement)e
n-6 PUFAs 24.61 25.58 23.99 23.80
n-3 PUFAs 4.52 5.98 4.78 4.42
a All values were calculated based on the lipid content of each sample.
b MUFAs, monounsaturated fatty acids; PUFAs, polyunsaturated fatty acids; SFAs, saturated fatty acids; TFAs,
trans fatty acids.
c The n-6 and n-3 PUFA content expressed as g per 100 g of dried plant food.
d The adequate intake of 18:2n-6 and 18:3n-3 for men 19 to 50 years of age was estimated at 17 g/d and 1.6 g/d,
respectively (National Academy of Sciences, 2002).
e The adequate intake of 18:2n-6 and 18:3n-3 for women 19 to 50 years of age was estimated at 12 g/d and 1.1
g/d, respectively (National Academy of Sciences, 2002)
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1RT, Raw Tuber
The total lipid fraction of tiger nut tubers contained a relatively low percentage of all SFAs, it provided nearly
double the amount of total SFAs (about 6 g/100 g). The availability of EFAs in these plant foods and the levels
needed to meet the daily human requirements was of primary interest in this study. The tubers of tiger nut
analyzed in the present study are the good source mainly in their content of 18:2n-6 which represented about
17% and 25% of the daily requirements for men and women, respectively, but very low levels of 18:3n-3 (about
4% of daily requirement for an adult).
Processing of the tiger nut tubers had no effect of the total content of EFAs or the ratio of the two EFAs.
Protein content and amino acid composition
The four samples of C. esculentus tubers from Cameroon (including the raw tuber) contained 4.29%-4.82%
protein (average, 4.6%) from tubers soaking in alkaline solutions, which was lower than the protein content of
untreated tubers of tiger nut (7.58%). In addition to wanting to know their protein content, we were interested in
comparing the nutritional quality of the various sample proteins. We therefore compared the percentages of
essential amino acids in the different treatments to the percentages of these same amino acids in a World Health
Organization protein standard (WHO, 1985) and determine the chemical index (Table 4 and 5); a score of 100 or
more for a particular amino acid means the sample protein meets or exceeds the WHO standard protein. In the
present study the leucine and lysine score were below the WHO standard for all treatment of the sample proteins,
ranging from 73-86 and 79-91% respectively. The tryptophan percentage for all of the different treatment of
plants analyzed in the present study exceeded that of the WHO standard. The amino acid scores for the different
preparations of C. esculentus were not similar, indicating that the different treatment methods (e.g., alkali-
soaking) had significant effect on the amino acid composition of the proteins they contained. Alkali treatment
reduces significantly chemical index from 107 to 92.
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Table 4: Aminoacids composition (mg/g dry weight) of Cyperus esculentus from Cameroon treated in different
ways by soaking in alkaline and acid solution (1 g/L, at 40°C)
Aminoacids Vitamin C Ca(OH)2 Kanwa RT*
Essential aminiacids (mg/g)
His 0.94±0.16a 0.82±0.14b 0.78±0.09b 0.98±0.07a
Ile 1.44±0.22a 1.15±0.09b 1.21±0.05b 1.32±0.07a
Leu 2.73±0.48a 2.14±0.14b 2.22±0.04b 2.41±0.13b
Lys 2.48±0.43a 2.26±0.13a 2.09±0.06b 2.37±0.14a
Met 0.57±0.18b 0.55±0.09b 0.58±0.04b 0.71±0.01a
Phe 1.63±0.28a 1.23±0.11b 1.30±0.05b 1.45±0.06a
Thr 1.99±0.21a 1.40±0.23b 1.49±0.18b 1.44±0.17b
Tyr 1.12±0.20a 0.79±0.21b 0.89±0.05b 1.04±0.07a
Trp 0.85±0.02b 0.86±0.03b 0.71±0.06b 0.92±0.04a
Val 2.10±0.25a 1.72±0.19b 1.80±0.08b 1.90±0.12a
Banal aminoacids (mg/g)
Ala 2.34±0.31a 1.93±0.15c 2.22±0.09
b
c 2.30±0.14a
Arg 4.74±0.41
d
6.51±0.51
b
5.05±0.30c 6.89±0.61a
Asp 4.11±0.85a 4.47±0.22a 3.76±0.17
b
4.27±0.56a
Cys 0.63±0.04a 0.65±0.02a 0.56±0.02
b
0.75±0.12a
Glu 6.09±1.02
b
c 6.69±0.45
b
5.86±0.36
d
7.37±0.73a
Gly 1.67±0.31a 1.44±0.10
b
1.32±0.08
b
1.54±0.06a
Pro 1.73±0.34a 1.38±0.16
b
1.44±0.10
b
1.78±0.06a
Ser 2.04±0.43a 1.51±0.11
b
1.63±0.11
b
1.88±0.11a
Tyr 1.12±0.20a 0.79±0.21
b
0.89±0.05
b
1.04±0.07a
Total (mg/g) 78.20±0.73a 44.53±0.52b 42.92±0.49b 75.4±0.68a
Values on the same row with the same superscript are not significantly different at P<0.05
*RT, Raw Tuber
Minerals and trace elements
The sodium content of the plant foods was relatively low, and not surprisingly high, for the alkali-treated tubers
of C. esculentus (1.41 g per g dry weight). All of the four sample contained nutritionally significant amounts of
copper, iron, phosphorus, manganese, magnesium, zinc, chromium, selenium and molybdenum. Of those
elements and trace minerals not required by humans, it is noteworthy that several of the sample contained large
quantities of aluminium and strontium. Alkali treatment seemed to be associated with an increase in the content
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11
of several minerals (e.g., calcium, molybdenum, phosphorus, zinc, sodium but a decrease in the content of others
(e.g., copper, iron, manganese) in tiger nut tubers.
Table 5: Comparison of the essential aminoacids content of plant foods from Cameroon with that of the World
Health Organization ideal pattern (% of total amino acids)
Essential
aminoacids
WHO1
Standard
Vitamin C Ca(OH)2 Kanwa RT2
% % % %
Ile 2.8 2.82 101 2.58 92 2.69 96 2.85 102
Leu 6.6 4.97 75 4.81 73 5.17 78 5.21 79
Lys 5.8 5.01 86 5.08 88 4.87 84 5.12 88
Met-Cys 2.5 2.82 113 2.70 108 2.66 106 3.15 126
Phe-Tyr 6.3 4.93 78 4.54 72 5.10 81 5.38 85
Thr 3.4 3.47 102 3.15 93 3.11 91 3.38 99
Trp 1.1 1.93 176 1.77 166 1.66 160 1.76 150
Val 3.5 3.92 117 3.80 109 4.20 120 4.10 112
Chemical Index 100 111 100 92 107
1WHO, World Health Organization
2RT, Raw Tuber
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Table 6: Trace mineral content of Cyperus esculentus from Cameroon soaked in alkaline and acid solutions (1
g/L) at 40°C
Mineral
(mg/100 g DM) RT1 Vitamin C Ca(0H)2 Kanwa
Al 9.410 10.300 2.400 2.200
Ba 0.352 0.344 0.290 0.360
Ca 33 31.500 53.400 36.700
Cd 0.010 0.010 0.008 0.008
Co 0.014 0.013 nd Nd2
Cr 0.261 0.224 0.181 0.202
Cu 0.442 0.434 0.312 0.252
Fe 15.90 18 9.860 8.210
K 504 476 454 403
Li 0.007 0.008 0.012 0.009
Mg 115 101 104 107
Mn 0.741 0.682 0.622 0.620
Mo 0.032 0.032 0.018 0.025
Na 30.80 33.100 12.100 141
Ni 0,113 0.091 0.048 0.048
P 240 238 232 239
Pb Ns3nd ns ns
Se 0.062 0.067 0.086 0.064
Sr 0.485 0.465 0.503 0.481
Zn 2.890 2.600 1.640 2.920
1RT, Raw Tuber
2nd, not detected;
3ns, below detection limit
DISCUSSION
The C. esculentus tubers, regardless of how they were prepared for consumption, had a relatively high oil
content (about 26%) that was even greater than that of tiger nuts (about 15%) collected in the border region
between the Republic of Niger and Nigeria (Ejoh et al., 2006; Glew et al., 2006). However, the fatty acid
composition of the C. esculentus tubers in the present study was about identical to that from Niger (Glew et al.,
2006): the main fatty acids were oleic acid (18:1n-9)(63-65%) and linoleic acid (18:2n-9)(10-12%), with much
lower levels of α-linolenic acid (18:3n-3)(0.2-0.3%).
Although the level of total SFAs in C. esculentus tubers was relatively high (20-23%) compared to most oil
seeds (7-15%), the relatively high palmitic acid (16:0) to stearic acid (18:0) ratio is typical of plant oils.
Therefore, the oil from C. esculentus does not appear to provide a balanced fatty acid profile even though it does
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contain relatively high amounts of one of the essential fatty acids, namely linoleic acid. All four preparations of
C. esculentus contained such low amounts of α-linolenic acid that they should be considered deficient in this
essential fatty acid, particularly in light of the high linoleic acid content. The high linoleic acid/α-linolenic acid
ratio (approximately 55) we found for C. esculentus is similar to that reported for a number of vegetable oils
such as sunflower, corn and safflower oils. A more nutritionally desirable ratio would be in the range of 5/1 to
15/1 (Smit, et al., 2003; Food and Nutrition Board, 2002). However, this ratio is only one component that should
be considered when evaluating the EFA status of a diet; other factors include the amount and type of all the
PUFAs in the diet and an individual’s total energy intake (Gebauer et al., 2005).
The lipid quality of the oil-rich C. esculentus tubers was excellent as judged by the low trans fatty acid content
(<1%). The trans fatty acid isomer pattern was random, ranging from 6trans to 8trans-18:1 to 12trans-18:1,
indicating that the deterioration was probably oxidative and thermal in nature. The trans fatty acid (TFA) content
was investigated in the plant lipids to assess product quality. Soaking in the alkali conditions of the samples may
have contributed to the increased levels of TFAs. Possibly the higher oil content and the TAG structure may
have provided greater protection of the PUFAs in the tuber lipids of C. esculentus against isomerization.
The tubers of C. esculentus from Cameroon in the present study contained about one-third less protein than tiger
nut tubers from Niger (Glew et al., 2006). This difference could be due to differences in the strains of C.
esculentus that grow in Cameroon and Niger, or to differences in soil and climate. The amino acid composition
of C. esculentus tubers reported herein also differs significantly from that of the raw tiger nuts from Niger (Glew
et al., 2006). Whereas the percentages of essential amino acids in tiger nuts from Niger met or exceeded the
WHO standard in every amino acid category, the amino acid patterns of soaking in alkaline solutions of tiger nut
tubers from Cameroon was inferior to the WHO standards for two of the eight essential amino acid or amino acid
pairs (leucine, lysine, phenylalanine plus tyrosine, and threonine). An implication of these apparent differences
in the protein content and amino acid composition of tiger nut tubers from Cameroon versus tiger nut tuberss
gathered in Niger is that, at least from the perspective of protein quantity and quality, the later appear to be a
superior protein source. Noteworthy is the fact that the essential amino acid scores for the raw tiger nut tubers
and acid solution soaked tubers (Table 4) were somewhat better than the corresponding scores for the other
preparations of tiger nut. These observations are in accord with those of Khalil and Monsour (1995) but
contradict those of Ziena (1989) who conducted similar studies with faba beans. C. esculentus contained
nutritionally useful amounts of many minerals and trace elements, including, copper, iron, manganese, zinc,
chromium, selenium and molybdenum, and, it is a very good source of potassium, phosphorus and magnesium.
The quantitative and qualitative nutritional information provided in this report should be regarded as provisional
since the full value of the minerals, fatty acids and proteins contained in the plant foods we have analyzed will
necessarily be determined by the bioavailability of these nutrients, which in turn will depend upon the efficiency
of their digestion and absorption. For example, although a plant food may contain significant amounts of
calcium, the presence of chelating agents (e.g., phytates, oxalates) can markedly decrease the bioavailability of
that calcium. The rapidly increasing number of published reports of the content of nutrients in wild edible plants
of sub-Saharan Africa underscores the need for studies aimed at determining the bioavailability of the specific
nutrients they contain, calcium being an excellent case in point. Nevertheless, the data in the present report will
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provide public health officials in sub-Saharan Africa with nutritional information that should be helpful in
advising local populations about the particular nutrient value of various plants foods that grow in the region.
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