African Journal of Biochemistry Research Effect of fermentation methods on the mineral, amino and fatty acids composition of Cyperus esculentus

Abstract

Tiger nut (Cyperus esculentus) was subjected to different fermentation methods such as traditional, back slope and control. The raw and fermented samples were analyzed for mineral, amino and fatty acids. The results of mineral analysis revealed potassium and sodium as the most abundant mineral element with their value ranging from 546 to 91.6 mg/100 g and 64.00 to 3383.33 mg/100 g, respectively while copper was found in trace amount with value ranging from 0.03 mg/100 g to 0.05 mg/100 g. All the fermented samples shows significant increase in calcium ranging from 8.50 to 9.83 mg/100 g compared to raw samples (7.66 mg/100 g). Amino acid result showed arginine (23.02 g/100 g) as the most abundant amino acid present in back slope fermented tiger nut while tyrosine was the least amino acid (0.05 g/100 g). The oil in tiger nut showed a greater percentage of oleic acid (73.08%) which was recorded in back slope fermented milled sample. The overall result of the investigation revealed that back slope fermentation was the best method that may enhance mineral, amino and fatty acids content of tiger nut.

Full text

Vol. 9(7), pp. 89-94, August, 2015
DOI: 10.5897/AJBR2015.0847
Article Number: 9B18A7654708
ISSN 1996-0778
Copyright © 2015
Author(s) retain the copyright of this article
http://www.academicjournals.org/AJBR
African Journal of Biochemistry Research
Full Length Research Paper
Effect of fermentation methods on the mineral, amino
and fatty acids composition of Cyperus esculentus
Agbaje, R. B.
1
*, Oyetayo, V. O.
2
and Ojokoh, A. O.
2
Department of Food Science and Technology Rufus Giwa Polytechnic, Owo, P. M. B 1019 Owo, Ondo State, Nigeria.
Department of Microbiology, Federal University of Technology, P. M. B 704, Akure, Ondo State, Nigeria.
Received 9 June, 2015; Accepted August 10, 2015
Tiger nut (Cyperus esculentus) was subjected to different fermentation methods such as traditional,
back slope and control. The raw and fermented samples were analyzed for mineral, amino and fatty
acids. The results of mineral analysis revealed potassium and sodium as the most abundant mineral
element with their value ranging from 546 to 91.6 mg/100 g and 64.00 to 3383.33 mg/100 g, respectively
while copper was found in trace amount with value ranging from 0.03 mg/100 g to 0.05 mg/100 g. All the
fermented samples shows significant increase in calcium ranging from 8.50 to 9.83 mg/100 g compared
to raw samples (7.66 mg/100 g). Amino acid result showed arginine (23.02 g/100 g) as the most abundant
amino acid present in back slope fermented tiger nut while tyrosine was the least amino acid (0.05 g/100
g). The oil in tiger nut showed a greater percentage of oleic acid (73.08%) which was recorded in back
slope fermented milled sample. The overall result of the investigation revealed that back slope
fermentation was the best method that may enhance mineral, amino and fatty acids content of tiger nut.
Key words: Tiger nut, mineral, amino acid, fatty acid, fermentation.
INTRODUCTION
Tiger nut (Cyperus esculentus var. sativa) is an under-
utilized crop which belongs to the division magnoliophyta
and was found to be a cosmopolitan perennial crop of the
same genus as the papyrus plant (Odoemelan, 2003;
Belewu and Belewu, 2007). Despite its name, tiger nut is
a tuber. However, its chemical composition shares
characteristics with tubers and nuts (Umerie et al., 1997).
The tubers are spherical in shape and edible.
There are varieties of tiger nuts readily available in the
market, which are brown and yellow varieties. The yellow
variety is preferred to all other variety because of its
inherent properties such as larger size, attractive colour
and fleshy body. The yellow variety is also reported to
yield more soluble extracts, contains lower fat more
protein and possesses less anti-nutritional factors (Okafor
et al., 2003). Its tubers can be eaten raw, roasted with
sugar, soaked in water or processed into starch and flour
(Oladele and Aina, 2007; Cortes et al., 2005). It can be
processed into a milky beverage called “Horchata de
Chufa” in Spain or “Atadwe” milk in Ghana (Rita, 2009).
*Corresponding author. E-mail: bukola.agbaje@yahoo.com. Tel: +2348034956833.
Author(s) agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0
International License

90 Afr. J. Biochem. Res.
In Nigeria, tiger nut is well grown and available in semi-
dried form in Nigerian markets where it is sold locally and
consumed uncooked (Omode et al., 1995).
Tiger nut have long been recognized to contain almost
twice the quantity of starch as potato or sweet potato
tubers. This tuber is a good source of energy (carbohydrate,
fibre and protein), minerals (mainly phosphorus and
potassium), and vitamins E and C (Arafat et al., 2009).
Processing techniques such as boiling, roasting, fer-
mentation and germination are means of improving the
nutritional value of foods (Nergiz and Gokgoz, 2007).
Although little study have been carried out on the effect of
fermentation on the nutritional composition of tiger nut. It
is therefore important to investigate the effect of different
fermentation methods on the mineral, amino and fatty
acids content of tiger nut. Therefore, this research was
conducted to determine the effect of fermentation
methods on mineral, amino and fatty acid contents of
Cyperus esculentus.
MATERIALS AND METHODS
Source of tiger nut
Raw tiger nut were purchased from Adedeji market in Akure, Ondo
State, Nigeria. The nuts were stored in the laboratory till the second
day when they were sorted, weighed and washed.
Processing of tiger nut
The sorted and washed nut were divided into six portions
designated A to F. Each of the portion contained 500 g of cleaned
tiger nut. Part A was analyzed raw and this serves as control. Part
B was fermented whole that is, submerged in 1500 ml of portable
water in a cleaned container that was covered for four days at 25°C
and allowed to ferment with indigenous micro flora (spontaneous).
C was milled and subjected to spontaneous fermentation. Part D
and E were fermented by addition of the steep water from the
previously fermented culture used as starter culture (back slope)
but part E was milled before fermentation while F was allowed to
undergo control fermentation, in which pure culture of Lactobaccilus
plantarum isolated in part B was used to inoculate the sixth part F.
The fermented nuts were dried in oven at 50°C for 24 h and dry
milled to powder using attrition mill. The milled samples were
packaged in polythene prior to analysis.
Chemical analysis
Mineral analysis
The mineral composition (potassium, sodium, calcium, magnesium,
zinc, iron and copper) of each sample was determined by wet
ashing method followed by reading of the level of mineral. Triplicate
samples of 1 g each were weighed into porcelain crucibles and
placed in a muffle furnace. The temperature was raised gradually to
450°C. The sample was ashed at 450°C for 5-6 h. After cooling to
room temperature, the ash was dissolved in 1 ml of 0.5% HNO
3
.
The sample volume was brought to 100 ml, and the levels of
mineral present were analyzed by Atomic absorption spectro-
photometer Buck 201 VGP. The mineral content was calculated
using the formula below.
Where, R = Solution concentration obtained from graph, V =
Volume of sample digest, D = Dilution factor and Wt = Weight of
sample. Sodium (Na) and K were analyzed using flame photometer
(Perkin-Elmer, 1982).
Amino acid determination
Amino acid composition was determined by the method of
Spackman et al. (2006) 2.0 g of each sample was weighed into the
extraction thimble and the fat extracted with chloroform methanol
mixture using a Soxhlet extraction apparatus. The extraction lasted
for 5-6 h. The defatted samples (30 to 35 mg) were weighed into
glass ampoules. Seven milliliters of 6 MHCl were added and
oxygen was expelled by passing nitrogen gas into the ampoule (to
avoid possible oxidation of some amino acid during hydrolysis).
Each glass ampoule was then sealed with a Bunsen flame and put
into an oven at 105 ± 5°C for 22 h. The ampoule was allowed to
cool before breaking open at the tip and the content was filtered to
remove the humins. The filtrate was then evaporated to dryness at
40°C under vacuum in a rotary evaporator. Each residue was
dissolved with 5 ml of acetate buffer and stored in a plastic
specimen bottle and kept in the deep freezer. The amount loaded
was between 5 to 10 µl. This was dispensed into the cartridge of
the analyzer. The TSM (technicon sequential multisample amino
acid analyzer) analyze free acidic, neutral and basic amino acids of
the hydrolysate. The period of an analysis lasted for 76 min. The
net height of each peak produced by the chart recorder of TSM
(each representing an amino acid) was measured. The half-height
of the peak on the chart was found and width of the peak on the
half-height was accurately measured and recorded. Approximate
area of each peak was then obtained by multiplying the height with
the width at half-height. The norcleucine equivalent (NE) for each
amino acid in the standard mixture was calculated using the
formula:
Fatty acid determination
Fifty milligram (50 mg) of fat extracted from raw and fermented tiger
nut was esterified for 5 min at 95°C with 3.4 ml of the 0.5 M KOH in
dry methanol. The mixture was neutralized using 0.7 M HCL. About
3 ml of boron triflouride (14%) in methanol was added. The mixture
was heated for 5 min at the temperature of 90°C to achieve
complete methylation process. The Fatty Acid Methyl Esters were
thrice extracted from the mixture with redistilled n-hexane. The
content was concentrated to 1 ml for gas chromatography analysis
and 1 µL was injected into injection port of gas chromatography
(Alejandro, 2013).
Statistical analysis
The experiment was carried out in triplicates. Data obtained were
analyzed by one-way analysis of variance and mean were
compared by Duncan’s multiple range tests (SPSS 17.0 version).
Differences were considered significant at p<0.05.
RESULTS AND DISCUSSION
Mineral composition (mg/100 g) of raw and fermented
Mineral (mg/100 g)
=
R × V × D
Wt
NE =
Area of norcleucine peak
Area of each amino acid

Agbaje et al. 91
Table 1. Mineral composition of raw and fermented Tiger nut (mg/100 g).
Mineral
Raw
TFM
TFW
BFM
BFW
CF
Ca
7.66
c
±0.28
9.33
ab
±0.28
9.50
ab
±0.50
8.50
bc
±1.00
9.00
ab
±0.50
9.83
a
±0.28
Cu
0.04
a
±0.00
0.00
b
±0.00
0.00
b
±0.00
0.05
a
±0.06
0.03
a
±0.00
0.04
a
±0.00
Fe
0.09
b
±0.00
0.23
ab
±0.30
0.14
b
±0.00
0.13
b
±0.00
0.14
b
±0.00
0.41
a
±0.00
K
606.33
b
±0.57
533.66
f
±1.15
562.00
d
±1.00
577.00
c
±1.00
546.00
e
±1.00
91.6
a
±1.00
Na
3383.33
a
±28.8
3250.00
b
±0.00
3366.67
a
±76.37
3166.66
b
±76.37
2950.00
b
±50.00
64.00
c
±1.00
Pb
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
Zn
0.07
c
±0.00
0.64
a
±0.10
0.00
e
±0.00
0.51
b
±0.00
0.02
d
±0.00
0.51
b
±0.38
Values are (mean±SD) of replicates. Values with the same alphabet are not significantly different at (p =0.05). RAW: Raw, TFM:
traditional fermented milled, TFW: traditional fermented whole, BFM: back slope fermented milled, BFW: back slope fermented
whole, CF: controlled fermented sample.
tiger nut is shown in Table 1. Sodium was the most
abundant mineral with value 3383.3 mg/100 g which was
recorded in raw sample while copper (0.03 mg/100 g) is
the least mineral obtained which was found in back slope
fermented whole sample. Micronutrients such as
potassium, sodium and calcium were found to be
appreciable in tiger nut samples analysed earlier reported
by Bosch et al. (2005) and, Oladele and Aina (2007).
Potassium and sodium are important in maintaining the
normal water balance, conservation of osmosis and acid
balance in the body. Potassium is necessary for the
metabolism of carbohydrates and proteins. It also
protects the internal arterial walls against any damages,
prevents haemorrhages and brain/heart attack (Oladele
et al., 2009). Hence, tiger nut is a good source of these
elements.
The result of amino acid composition revealed that tiger
nut is rich in essential amino acid such as lysine,
threonine, leucine, phenylalanine and cystine. The most
concentrated essential amino acid lysine (5.14 g/100 g)
was recorded in back slope fermented whole sample.
Tyrosine (0.50 g/100 g) was the least amino acid which
was recorded in raw sample (Table 2). Some essential
amino acid (threonine, leucine, phenylalanine and
cystine) present in back slope fermented whole tiger nut
were found to compare favourably with food and
Agriculture Organization Standard (FAO, 1998). Back
slope fermented whole sample showed significant
increase (p≤0.05) in lysine (5.14 g/100 g), Threonine
(3.15 g/100 g), leucine (4.39 g/100 g), phenylalanine
(3.25 g/100 g) and cystine (2.56 g/100 g) content when
compared to FAO standard (Table 3).
Oyetayo and Agbaje (2012) has earlier reported that
amino acids of fermented Acha was higher than the raw
sample. Also Oyetayo et al. (2007) reported that food rich
in total essential amino acid will contribute to the supply
of essential amino acid in diet. Amino acids distribution in
controlled fermented sample is smaller to what was
obtained in traditional and backslope fermented samples,
this may be due to the effect of sterilization on the control
sample, high temperature denature protein.
LAB fermentation has been shown to improve the
nutritional value and digestibility of foods (Nout, 2009).
The acidic nature of the fermentation products enhances
the activity of microbial enzymes at a temperature range
of 22-25°C (Mokoena et al., 2005). The enzymes, which
include amylases, proteases, phytases and lipases,
modify the primary food products through hydrolysis of
polysaccharides, proteins, phytates and lipids respectively.
This is in line with this paper finding.
Results shown in Tables 2 and 3 show an increment in
some nonessential and essential amino acid of fermented
samples when compared with unfermented (raw) sample,
these was in agreement with Steinkraus report (1997)
that bacterial enzymatic hydrolysis may enhance the
bioavailability of protein and fat and increase the
production of free amino acids, short chain fatty acids
and also reported that fermentation increase biological
environment of food substrates with protein essential
amino acids and vitamins.
The result of the fatty acid composition of oil extracted
from raw and fermented tiger nut are as shown in Table
4. This study shows that all the sample contain appre-
ciable amount of oleic acid with value recorded ranging
from 64.91 to 73.08%, but low in erucic acid with values
ranging from 0.02±0.00 to 0.05±0.01%. Key et al. (1986)
reported that epidemiological studies also suggested that
the presence of a high proportion of monounsaturated
acid especially oleic acid in the diet is linked with a high
reduction in the risk of coronary heart diseases. Oleic
acid is also reported to be useful for building cellular
membranes, attracting oxygen to tissues, to transform
energy into nerve impulses, and as precursors to mole-
cules of cellular communication such as prostaglandins
(Odutuga et al., 1992).
Result also reveals that traditional fermentation had
reduces the value of linolenic acid from 0.65 to 0.57%.
High percentage of linolenic acid is not desirable in edible
oils because of the off-flavours and potentially harmful
oxidation products formed. As reported by Warner and
Gupta (2003), a decrease from 2 to 0.8% linolenic acid
content in oils improved flavor quality and oxidative

92 Afr. J. Biochem. Res.
Table 2. Amino acids composition of raw and fermented tiger nut (g/100 g).
Amino acid
Raw
TFW
TFM
BFW
BFM
CF
Alanine
2.77
e
±0.12
3.42
bc
±0.02
3.27
cd
±0.00
3.56
ab
±0.04
3.10
d
±0.08
3.76
a
±0.24
Arginine
17.78
c
±0.51
21.53
b
±0.51
20.93
b
±0.00
23.02
a
±0.13
19.91
c
±0.25
21.27
b
±0.34
Aspartic
5.01
d
±0.09
5.95
b
±0.05
5.43
c
±0.06
7.07
a
±0.19
5.11
d
±0.09
6.08
b
±0.11
Cystine
1.97
e
±0.10
2.38
b
±0.03
2.28
c
±0.00
2.56
a
±0.00
2.14
d
±0.00
2.42
b
±0.07
Glutamic
5.79
e
±0.18
7.64
b
±0.04
6.39
c
±0.07
8.63
a
±0.15
6.11
d
±0.07
7.64
b
±0.11
Glycine
2.40
e
±0.10
3.03
c
±0.03
2.89
c
±0.02
3.80
a
±0.19
2.70
d
±0.04
3.31
b
±0.03
Histidine
2.02
c
±0.11
2.41
a
±0.02
2.23
b
±0.01
2.50
a
±0.03
2.08
c
±0.02
2.42
a
±0.01
Isoleucine
0.78
d
±0.03
1.71
c
±0.01
1.24
d
±0.03
2.80
a
±0.35
0.89
d
±0.01
1.81
b
±0.05
Leucine
2.74
d
±0.07
3.91
b
±0.10
3.36
c
±0.10
4.39
a
±0.13
2.51
e
±0.04
4.12
b
±0.19
Lysine
3.31
e
±0.09
4.89
b
±0.08
4.06
c
±0.05
5.14
a
±0.11
3.87
d
±0.05
4.91
b
±0.10
Methione
0.57
d
±0.01
0.91
b
±0.02
0.76
c
±0.04
1.11
a
±0.15
0.71
c
±0.01
1.11
a
±0.06
Phenylalanine
1.80
cd
±0.04
2.42
bc
±0.04
2.24
bc
±0.04
3.25
a
±0.85
1.38
d
±0.80
2.59
b
±0.04
Proline
1.50
d
±0.00
2.03
b
±0.06
1.80
c
±0.06
2.44
a
±0.00
1.68
c
±0.06
2.14
b
±0.17
Serine
2.14
e
±0.08
2.62
b
±0.01
2.48
c
±0.01
2.91
a
±0.09
2.32
d
±0.03
2.57b
c
±0.01
Threonine
2.24
f
±0.02
2.78
c
±0.03
2.55
d
±0.02
3.15
a
±0.05
2.42
e
±0.02
2.89
b
±0.05
Tyrosine
0.50
d
±0.00
0.83
b
±0.00
0.66
c
±0.00
1.15
a
±0.16
0.58c
d
±0.08
1.07
a
±0.08
Valine
1.65
d
±0.07
2.31
b
±0.06
2.10
c
±0.03
3.21
a
±0.11
1.71
d
±0.07
2.41
b
±0.04
Values are (mean±SD) of replicates. Values with the same alphabet are not significantly different at (p =0.05). RAW: Raw,
TFM: traditional fermented milled, TFW: traditional fermented whole, BFM: back slope fermented milled, BFW: back slope
fermented whole, CF: controlled fermented sample.
Table 3. Essential amino acid of raw and fermented tiger nut
(g/100 g of protein) compared with FAO std`
Amino acid
Raw
BFW
FAO value
Lysine
3.31±0.09
5.14±0.11
4.20
Threonine
2.24±0.02
3.15± 0.05
2.80
Valine
1.65±0.07
3.21± 0.11
4.20
Methionine
0.57±0.01
1.11± 0.15
2.20
Isoleucine
0.78±0.03
2.07± 0.35
4.20
Leucine
2.74±0.07
4.39 ± 0.13
4.20
Tyrosine
0.05±0.00
1.15± 0.16
2.80
Phenylalanine
1.80 ±0.04
3.25± 0.85
2.80
Tryptophan
-
-
1.40
Cystine
1.97± 0.10
2.56 0.00
2.20
Values are (mean±SD) of replicates. RAW: raw, BFW:
backslope fermented whole.
Table 4. Fatty acids composition of raw and fermented tiger nut (%).
Fatty acid
Raw
TFM
TFW
BFM
BFW
CF
Arachidic
4.93
a
±0.02
4.23
c
±0.15
4.71
b
±0.01
2.77
d
±0.02
4.32
c
±0.02
5.40
a
±0.40
Arachidonic
0.06
a
±0.00
0.13
c
±0.01
0.10
d
±0.00
0.04
b
±0.00
0.05
ab
±0.01
0.00
a
±0.00
Behenic
0.05
b
±0.01
0.09
a
±0.01
0.08
a
±0.01
0.03
e
±0.0
0.04
c
±0,00
0.00
a
±0.00
Capric
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
Caprylic
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00±
a
0.00
0.00
a
±0.00
Erucic
0.03
bc
±0.00
0.05
a
±0.01
0.04
a
±0.00
0.02
c
±0.00
0.02
c
±0.00
0.00
a
±0.00
Lauric
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00

Agbaje et al. 93
Table 4. Contd.
Fatty acid
Raw
TFM
TFW
BFM
BFW
CF
Lignoceri
0.11
b
±0.01
0.23
a
±0.05
0.22
a
±0.01
0.07±0.00
0.06
c
±0.02
0.00
a
±0.00
Linoleic
9.00
b
±0.01
10.12
a
±0.01
7.74
c
±0.00
10.17
a
±0.01
10.45
a
±0.01
8.86
c
±0.01
Linolenic
0.65
c
±0.01
0.71
c
±0.01
0.57
d
±0.00
3.50
a
±4.61
0.90
b
±0.00
0.66
c
±0.01
Margaric
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
0.00
a
±0.00
Myristic
1.73
a
±0.02
1.13
c
±0.01
1.15
c
±0.04
0.73
e
±0.02
1.02
d
±0.02
1.28
b
±0.01
Oleic
69.77
b
±0.02
70.61
b
±0.01
69.33
b
±0.03
73.08
a
±0.01
69.10
b
±0.01
64.91
c
±0.01
Palmitolic
0.04
d
±0.00
0.08
c
±0.00
0.28
b
±0.01
0.03
d
±0.00
0.03
d
±0.01
0.32
a
±0.01
Plamitic
10.23
b
±0.01
9.51
c
±0.01
10.75
b
±0.18
9.16
c
±0.01
10.55
b
±0.02
12.43
a
±0.03
Stearic
3.38
c
±0.02
3.16
d
±0.01
5.34
b
±0.02
3.01
d
±0.01
3.40
c
±0.11
6.10
a
±0.00
Values are (mean±SD) of replicates. Values with the same alphabet are not significantly different at (p =0.05).
Raw: Raw, TFM: traditional fermented milled, TFW: traditional fermented whole, BFM: back slope fermented
milled, BFW: back slope fermented whole, CF: controlled fermented sample.
stability of fried foods. This therefore shows that the lower
the linolenic acid content in oil, the more suitable is the oil
for frying. This indicates that tiger nut oil is a good source
of edible oil for cooking and frying that may be useful for
the fight against cardiovascular diseases (Muhammad et
al., 2011).
Conclusion
This study established the effect of different fermentation
methods on the mineral, amino and fatty acids content of
tiger nut (Cyperus esculentus). The result of mineral
composition revealed that tiger nut was rich in potassium,
sodium and calcium. Also tiger nut is a poor source of
copper and zinc. Back slope fermented sample was
found to be high in the following amino acid: Arginine,
glutamic, lysine and aspartic acid. Oleic is the most
abundant fatty acid present in tiger nut. In conclusion,
back slope fermentation is the best processing method
that enhances the mineral, amino and fatty acids content
of tiger nut. This method is the best because there is an
increase in essential amino acid such as lysine,
threonine, valine, methionine, isoleucine, leucine,
tyrosine, phenylalanine and cystine recorded in back
slope fermentation method
Conflict of interests
The authors did not declare any conflict of interest.
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