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Estimation of Nutritional and Starch Characteristics of Dioscorea alata (Water Yam) Varieties Commonly Cultivated in the South-Eastern Nigeria

Authors:
  • Alex Ekwueme Federal University Ndufu Alike Ikwo Ebonyi State Nigeria

Abstract and Figures

Background: Studies on the nutritional and mineral compositions of staple foods will provide evidence to regulate intake of certain common foods for optimal health condition. Aim: To estimate the proximate, mineral and starch characteristics of five local varieties, D. purpurea, D. atropurpurea, D. liliopsida (purple yam), D. vilgaris, and D. villosa of Dioscorea alata grown in Izzi Area of Ebonyi State, Nigeria. Methodology: Five (5) commonly cultivated varieties of D. alata were sampled, each variety in triplicates, and prepared for analysis by peeling, dicing, drying and milling into flour. The proximate, nutritional and starch characteristics were determined by standard methods. Minerals were quantified by Atomic Absorption Spectrophotometric Method. Results: The results showed that the varieties has moisture content 9.20-10.30%, ash content 2.48-3.53%, fiber content 3.31-3.53%, fat content 1.62-2.41%, protein content 8.40-10.46%, and carbohydrate content 70.88-73.90%. There were significant differences (P<.05) in the proximate compositions within the varieties. The ranges of minerals in mg per kg (dry weight) were Na 16.38-24.84, K 97.78-141.14, Ca 79.99-269.75, Mg 18.55-31.53, P 114.65-211.63, Fe 15.18-30.86. Glycaemic index ranged from 35.56-41.31, amylose content 12.42-16.11% and gelatinization temperature 85.00-87.00°C. Conclusion: The results indicate that the protein and fiber contents of D. alata varieties estimated in this study were high. The low glycemic index confirmed the yam varieties as low glycemic index food. It was concluded that the yam varieties are good sources of protein nutrient and suitable staple food for the diabetics. However, low mineral compositions were reported. Therefore, there is a need for intense cultivation of improved varieties for improved mineral intake from the yam by the consumers.
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*Corresponding author: E-mail: clementademola@yahoo.com;
British Journal of Applied Science & Technology
6(2): 145-152, 2015, Article no.BJAST.2015.075
ISSN: 2231-0843
SCIENCEDOMAIN international
www.sciencedomain.org
Estimation of Nutritional and Starch Characteristics
of Dioscorea alata (Water Yam) Varieties Commonly
Cultivated in the South-Eastern Nigeria
A. O. Oko
1
and A. C. Famurewa
2*
1
Department of Biotechnology, Ebonyi State University, P.M.B. 053 Abakaliki, Ebonyi State,
Nigeria.
2
Department of Medical Biochemistry, Faculty of Basic Medical Sciences, Federal University,
Ndufu-Alike Ikwo, P.M.B. 1010, Abakaliki, Nigeria.
Authors’ contributions
This work was carried out in collaboration between all authors. Author AOO designed the study,
performed the statistical analysis. Author AOO carried out the sample analyses. Author ACF wrote the
first draft of the manuscript and managed literature searches. All authors read and approved the final
manuscript.
Article Information
DOI: 10.9734/BJAST/2015/14095
Editor(s):
(1) Teresa De Pilli, University of Foggia, Department of Science of Agriculture of Food of Environnement (SAFE), Via Napoli,
25; 71100 Foggia, Italy.
Reviewers:
(1)
Anonymous, National Yang-Ming University, Taiwan.
(2)
Otegbayo Bolanle, Department of Food Science and Technology, Bowen University, Iwo, Osun State, Nigeria.
(3)
Sophia Wan-Pyo Hong, Natural Products Research Institute, Department of Pharmacy, Seoul, National University, Seoul
151-742, South Korea.
(4)
Viktorija Maksimova, Faculty of Medical Sciences, University “Goce Delcev” Stip, Republic of Macedonia.
Complete Peer review History:
http://www.sciencedomain.org/review-history.php?iid=765&id=5&aid=7223
Received 18
th
September 2014
Accepted 4
th
November 2014
Published 15
th
December 2014
ABSTRACT
Background:
Studies on the nutritional and mineral compositions of staple foods will provide
evidence to regulate intake of certain common foods for optimal health condition.
Aim: To estimate the proximate, mineral and starch characteristics of five local varieties, D.
purpurea, D. atropurpurea, D. liliopsida (purple yam), D. vilgaris, and D. villosa of Dioscorea alata
grown in Izzi Area of Ebonyi State, Nigeria.
Methodology: Five (5) commonly cultivated varieties of D. alata were sampled, each variety in
triplicates, and prepared for analysis by peeling, dicing, drying and milling into flour. The proximate,
nutritional and starch characteristics were determined by standard methods. Minerals were
quantified by Atomic Absorption Spectrophotometric Method.
Original Research Article
Oko and Famurewa; BJAST, 6(2): 145-152, 2015; Article no.BJAST.2015.075
146
Results:
The results showed that the varieties has moisture content 9.20-10.30%, ash content
2.48-3.53%, fiber content 3.31-3.53%, fat content 1.62-2.41%, protein content 8.40-10.46%, and
carbohydrate content 70.88-73.90%. There were significant differences (P<.05) in the proximate
compositions within the varieties. The ranges of minerals in mg per kg (dry weight) were Na 16.38-
24.84, K 97.78-141.14, Ca 79.99-269.75, Mg 18.55-31.53, P 114.65-211.63, Fe 15.18-30.86.
Glycaemic index ranged from 35.56-41.31, amylose content 12.42-16.11% and gelatinization
temperature 85.00-87.00°C.
Conclusion: The results indicate that the protein and fiber contents of D. alata varieties estimated
in this study were high. The low glycemic index confirmed the yam varieties as low glycemic index
food. It was concluded that the yam varieties are good sources of protein nutrient and suitable
staple food for the diabetics. However, low mineral compositions were reported. Therefore, there is
a need for intense cultivation of improved varieties for improved mineral intake from the yam by the
consumers.
Keywords: Dioscorea alata; proximate composition; mineral composition; nutritional quality; starch.
1. INTRODUCTION
Nutritional quality and mineral composition of
primary agricultural and cultural foods in
developing countries is a major health problem
which has manifested as diet-associated
disorders among the African population. Food
and nutrition are known important modifiers of
disease initiation and development. The major
causes of illness and death appear to be the
chronic degenerative diseases, such as cancer,
heart disease, arthritis, respiratory diseases,
diabetes, hypertension, cognitive impairment and
various toxic states, which could be averted with
proper nutrition and diet. Beside good quality of
water, a well-balanced diet of essential
macronutrients and micronutrients is required to
achieve optimal health condition [1]. In recent
years, there has been a tremendous interest in
the field of nutrition on the assessment of
nutrients, vitamins and mineral composition of
staple foods considered to be economically,
socially and culturally important in many tropic
and subtropic regions of the world. In these
regions, yam is being investigated for its whole
nutritional quality. It is traditionally known that
yam tubers have potential ability to provide one
of the cheapest sources of dietary energy in the
form of carbohydrate [2,3].
Yam (Dioscorea species) is a climbing,
vigorously twining herbaceous plant that coils
swiftly around the stake. They are perennial
through root system but are grown as annual
crops [4]. Yams are of great economic
importance and nourishment to the people of
Africa, the Caribbean, Asia and America [5].
They are well integrated into the social, cultural
and religious lifestyle of the people who cultivate
and consume them [6]. Large quantity
consumption has been reported to provide the
body not only with carbohydrate but also with
vitamins and minerals [7]. It is second to cassava
in tropical root crops but first in higher vitamin C
content (40-120 mg/g edible portion) and crude
protein content (40-140 g/kg dry matter) [8].
Yam belongs to a family of Dioscorea with over
600 species in which only few are cultivated for
food and medicines [9]. The most cultivated
species in Nigeria are the white yam (D.
rotundata), yellow yam (D. cayenensis), water
yam (D. alata) and trifoliate yam (D.
dumentorum) [10].
Dioscorea alata, commonly called water yam or
ten month yam is the most widespread yam
species and more important as food in West
Africa and the Caribbean than in Asia and in
America where it originated and has been
competing with the most important native
species, D. rotundata. D. alata is an excellent
source of starch, which provides calorific energy
and protein three times more superior than the
one of cassava and sweet potato [11,12]. It has
low sugar content necessary for diabetic patients
[13]. Cultivars of D. alata possess higher
contents of protein, vitamin C and low lipids than
D. cayanensis, D. rotundata and D. trifida [14]. It
has comparative advantage for sustainable
production due jto its better agronomic
characteristics such as ease of propagation and
yield, high nutritive value and longer storage of
the fresh tubers [5]. It is considered to be among
the most primitive of the angiosperms and
contains many species of which only about few
are considered edible. D. alata is popular and
prevalent within Abakaliki agro-ecological zone of
Ebonyi State where it is called “Mbala or Nvula”
(Igbo names) [4]. Cultivated varieties of
Dioscorea alata in this area includes, D.
Oko and Famurewa; BJAST, 6(2): 145-152, 2015; Article no.BJAST.2015.075
147
purpurea (Okwale nkata), D. atropurpurea (Nvula
ite), D. liliopsida (Nvula eke) or purple yam, D.
vilgaris (Nvula ji), D. villosa (Akpuru akputo), D.
harmiltonii, D. persimilis etc [9].
The objective of this study was to determine the
nutritional and starch characteristics of five major
varieties of D. alata commonly cultivated by the
Igbo people of Ebonyi State. Results from the
study will provide scientific evidence for the
nutritional quality of the varieties, and possibly
the need for improved varieties for cultivation in
the area.
2. MATERIALS AND METHODS
2.1 Sample Collection
Five (5) variety samples of D. alata, sample A (D.
purpurea), sample B (D. atropurpurea), sample C
(D. liliopsida), sample D (D. vilgaris) and sample
E (D. villosa) were obtained from different parts
of Izzi Local Government Area of Ebonyi State,
Nigeria. The yam tubers were carefully selected
to avoid rot, bruises or sign of spoilage.
2.2 Sample Preparation for Analysis
The yam tubers were cut into two, thoroughly
washed, peeled and cut into small pieces
(cubes). It was sun-dried for 3 to 4 days,
packaged and labeled sample A-E. Each sample
variety was prepared in triplicates. The dried
pieces were milled into powdered samples and
sieved through 250 µm mesh and stored in
plastic container for nutritional and mineral
analysis.
2.3 Determination of Proximate Composi-
tions and Starch Characteristics
The moisture and crude fibre content of each
variety were determined by drying the sample in
an oven at 105°C for 6 hrs and values expressed
in percentage. The ash content was determined
by incinerating in a muffle furnace 2 g of each
sample at 550°C for 2 hrs [15]. Protein content,
expressed in percentage, was obtained using
Kjeldhal method (N × 6.25) by AOAC [15]. Crude
fat content was estimated by Soxhlet extraction
technique using petroleum ether (40-50°C) [16].
The carbohydrate content was determined by
difference (% carbohydrate = 100% - sum of
percentages of moisture, fat, ash, fibre and crude
protein contents). Iodo-colorimetric method [17]
based on the chemical reaction of starch and
iodine was used to determine amylose content.
Glycemic Index was calculated from the
hydrolysis index expressed in percentage (area
under curve procedure) as described by
Hettiaratchi et al. [18]. To determine the
gelatinization temperature, 10% suspension of
the flour sample was prepared in a test tube.
The aqueous suspension was heated in a
boiling water bath, with continuous stirring.
Gelatinization was observed after 30s and
measured accurately as the gelatinization
temperature.
2.4 Determination of Mineral Content
Sodium, potassium, calcium, magnesium,
phosphorus and iron were analysed after
digestion with HNO
3
and H
2
SO
4
, using Atomic
Absorption Spectrophotometer (Model Buck
2006, Buck Scientific, USA). Phosphorus content
was determined with the use of
phosphomolybdate complex method.
2.5 Statistical Analyses
All measurements were carried out in triplicates
and the mean triplicate values of the five
varieties were subjected to One-Way ANOVA
Duncan’s t-test. Differences considered
significant at 5% (P<.05).
3. RESULTS AND DISCUSSION
3.1 Proximate Compositions of D. alata
Varieties
The proximate composition of D. alata varieties is
presented in Table 1. The moisture content of the
local varieties ranged from 9.2% for D.
atropurpurea to 10.30% for D. vilgaris, with a
mean of 9.76%. The mean values for moisture
content showed significant differences (P<.05).
Moisture content is an important factor in food
quality, preservation, and resistant to
deterioration. It is related to many properties that
affect the quality and shelf life of food and food
products, including bacterial growth and texture
[19]. Low moisture content of a food indicates its
stability for prolonged storage or permissive rate
of spoilage. In this study, local varieties of D.
alata have lower moisture content than those
reported in the literature [5,8,20-22] Comparable
to our result, Udensi et al. [4] have reported
moisture content of 6.05% for local best variety
of D. alata. In the same study, five high yielding
and disease resistant water yam varieties gave
low moisture content. The moisture content of
Oko and Famurewa; BJAST, 6(2): 145-152, 2015; Article no.BJAST.2015.075
148
Table 1. Proximate composition of Dioscorea alata varieties (% dry weight)
*
Proximate
composition
Sample Varieties of Dioscorea alata (water yam)
A
B
D
E
D. purpurea
D. atropurpurea
D. vilgaris
D. villosa
Moisture content 9.90±0.14
b
9. 20±0.00
d
9. 90±0.14
10.30±0.14
a
9.5±0.14
c
Ash content 3. 40±0.14
a
3. 45±0.07
a
3. 53±0.04
2.48±0.04
c
3.14±0.04
b
Crude fibre content 3. 38±0.03
b
3.50±0.00
a
3.53±0.01
3.31±0.01
b
3.33±0.04
b
Fat content 1.99±0.01
d
2.15±0.07
c
2.39±0.01
1.62±0.03
e
2.41 ±0.01
a
Protein content 10.46±0.06
a
10.15±0.13
b
8.71±0.06
8.40±0.13
d
10.02±0.06
b
Carbohydrate
content
70.88±0.78
c
71.55±0.27
b
71.95±0.24
73.90±0. 04
a
71.57±0.15
b
*
Values are Mean±SD of triplicate determinations; means along a row with the same superscript are not
significantly different, P<.05
sweet potato, 8.72% and red cocoyam, 9.02%
corroborated the moisture content of D. alata
varieties in this study [20] These local varieties of
D. alata would be suitable for prolonged storage
and more stable for industrial food product
processing.
The crude fiber content ranged between 3.31 to
3.53% with a mean value of 3.41%. There was
no significant difference (P>.05) between D.
atropurpurea and D. liliopsida fibre contents,
however, significant difference (P<.05) was
observed between these varieties and others.
Fibers in foods are plant non-digestible
carbohydrate and lignin and have been shown to
have health benefits. Studies have shown that
increase in fiber consumption in foods reduces
the incidence of obesity, cardiovascular disease,
type 2 diabetes, digestive disorders and some
cancers [23]. Fiber consumption also softens
stools and lowers plasma cholesterol level in the
body [24]. The mean fiber content in the current
study is comparable to the 3.96% reported by
Shajeela et al. [25]. Lower values have been
reported for other varieties of D. alata [4], D.
rotundata(white yam) and Colocasia esculenta
(white cocoyam) [26]. The result indicates that
the local varieties of D. alata investigated could
be a source of dietary fiber with nutritional
benefits.
The range of crude protein content (8.40-
10.46%) was in agreement with the earlier
studies [4,5,21,25,27]. Strikingly, a study by
Alinnor and Akalezi, [26] reported crude protein
content of 0.087% for D. rotundata, a widely
cultivated and the most preferred specie of yam
in Nigeria and West Africa. In earlier study
carried out by Oyenuga [28], he found the protein
content of D. alata to be in the range of 7.26-8.10
while that of D. rotundata 4.42-5.87. This
suggests a higher nutritional potential for D.
alata, at least in terms of protein content than D.
rotunda. Intake of staple foods with low protein
content may lead to several impaired biological
processes in the body. This shows that D. alata
is rich in protein and can provide this nutrient to
the consumers.
The highest carbohydrate content in this study
was 73.90% with no significance difference
(P>.05) within the varieties. The result is in line
with the findings of studies [27,29] which
reported 76.57% and 75.65% respectively for D.
alata but lower when compared with the
carbohydrate contents reported for red cocoyam,
86.69% and sweet potato, 86.90% [29].
Improved varieties of D. alata contained a higher
carbohydrate content ranged between 81.53 to
87.64% [4]. However, lower carbohydrate
content has been reported for commonly
consumed root tubers in Nigeria. Alinnor and
Akalezi, [26] reported 40.61% and 57.78%
carbohydrate contents for white yam (D.
rotundata) and white cocoyam (Colocasia
esculenta) respectively. D.alata varieties in this
study may be considered as tolerable sources of
enegy and this may be related to the
recommendation of water yam and some other
cocoyam varieties for the diabetics.
3.2 Starch Characteristics of D. alata
Varieties
Table 2 presents the starch characteristics of the
yam varieties. The glycemic indices of D. alata
investigated ranged from 35.56 to 41.31, with
mean value of 38.62. The glycemic index (GI)
concept is based on the difference in blood
glucose response after ingestion of the same
amount of carbohydrates from different foods,
and possible implications of these differences for
health [30]. Based on this, previous studies have
been able to provide evidence for the
Oko and Famurewa; BJAST, 6(2): 145-152, 2015; Article no.BJAST.2015.075
149
classification of foods as low (≤ 55), intermediate
(56 to 59) and high (≥70) GI foods. The glycemic
index values of yam reported in literature ranged
from low to high and generally the species and
varieties were unspecified [30]. However, low GI
foods have been associated with reduced risk for
chronic and metabolic diseases including
diabetes [31-34]. The GI phenomenon expresses
the glycemic response to a food after ingestion of
50g of available carbohydrate and the possible
implications on health [30]. Foods that raise
blood glucose level quickly have high GI levels,
whereas foods with low GI will raise blood
glucose levels slowly [35,36]. The reported GI in
the current study is classified as low for the local
yam varieties specified in Table 2. A study
reported a GI of 67 for white yam (D. rotundata),
56 for three-leaved yam (D. domentorum) and 24
for water yam (D. alata) [21]. Among the Chinese
starch foods, a GI of 52 was obtained for yam,
although the specie unspecified [37]. It is
noteworthy that the D. alata varieties investigated
in the current study are low-GI foods.
Inconsistent in GI for yam may be due largely to
different species. The yam varieties may be
considered in diet and more importantly among
the diabetics who are concerned about their
postprandial blood glucose levels for effective
diet management.
The amylose content of the varieties varied
significantly (P<.05) and D. purpurea was found
to have the lowest amylose content
(12.42±0.03%) while D. vilgaris had the highest
(16.11±0.56%). A similar result was obtained in a
study that demonstrated inverse correlation
between amylose content and swelling power of
different food starches, reporting 12.24%
amylose for Dioscorea esculenta [38]. However,
previous studies have reported comparatively
higher values for amylose content in D. alata,
although varieties investigated were not specified
[39,40]. Riley et al. [41] analysed eight D. alata
cultivars grown in Jamaica and reported amylose
content that ranged from 20.117 to 23.001%.
The difference in amylose content observed may
be attributed to genetic variations among the
varieties, as it was found that the amylose
content of starches is affected by the expression
of the amylose extender gene [42]. The
gelatinization temperature range of starch in
the varieties was 85.00 to 87.00°C. The
gelatinization temperature obtained was
considerably higher than for wheat starch (55.6
to 63.0°C) according to Lineback and Ke [43].
This high temperature suggests slow swelling
property of the starch granules which may be
connected with protein-amylose formation [41]. In
biotechnological application of foods for value-
added products, starch with lower gelatinization
temperature to minimize energy cost and for
shorter cooking time may be more preferred.
3.3 Mineral Compositions of D. alata
Varieties
Minerals are biological components of diets
which perform biochemical and physiological
functions in living cells through synergistic
interactions and/or independent modulation of
biological reactions. The mineral levels of the D.
alata varieties are shown in Table 3. The low
mineral levels indicate that these varieties may
not be an important source of minerals to the
consumers. This may be due to the species and
the prevailing environmental factors. Considering
the specialized functions of minerals in the
human body, which include maintenance of acid-
base balance, neurotransmission, cofactors of
enzymes, bone and blood formation, energy
transduction among others, there is need for
improved varieties of D. alata for cultivation. The
sodium to potassium ratio in the body is of great
concern for the prevention of hypertension
[26,44]. According to the World Health
Organization [45], the sodium-to-potassium ratio
should be one. The consumption of the
varieties regarding sodium-to-potassium ratio
would not promote high blood pressure,
Table 2. Starch characteristics of Dioscorea alata varieties
Starch characteristics
Sample varieties of Dioscorea alata (water yam)
A
B
C
D
E
D. purpurea
D. atropurpurea
D. liliopsida
D. vilgaris
D. villosa
Glycemic index (%) 35.56±0.64
a
36.47±1.09
a
38.90± 1.09
a
40.88±0.45
a
41.31±1.77
a
Amylose content (%) 12.42±0.03
c
15.22±0.02
a
13.68±0.60
b
16.11±0.56
a
13.99±0.13
b
Gelatinization temp. (°C)
85.00±1.40
a
85.00±0. 00
a
85.50±2.10
a
87.00±1.40
a
87.00±1.40
a
Values are Mean±SD of triplicate determinations; means along a row with the same superscript are not
significantly different, P<.05
Oko and Famurewa; BJAST, 6(2): 145-152, 2015; Article no.BJAST.2015.075
150
Table 3. Mineral composition of Dioscorea alata varieties (mg/kg)*
Minerals
Sample varieties of Dioscorea alata (water yam)
A
B
C
D
E
D. purpurea
D. atropurpurea
D. liliopsida
D. vilgaris
D. villosa
Sodium 18.38±0.18
c
16.38±0.46
d
16.99±0.02
d
24.84±0.37
a
21.06±0.77
b
Potassium 134.68±1.38
b
141.14±1.35
a
127.04±2.74
c
111.30±1.06
d
97.78±2.58
e
Calcium 79.99±0.15
e
269.75±1.77
a
168.09±2.74
c
196.90±0.28
b
140.07±0.41
d
Magnesium 25.58±0.67
b
29.77±0.38
a
21.04±0.06
c
18.55±1.56
d
31.53±0.76
a
Phosphorus 114.65±0.43
d
211.63±2.02
a
117.10±0.64
b
205.10±7.78
a
169.76±1.05
c
Iron 20.61±0.09
b
19.25±0.64
c
16.86±0.23
d
30.86±0.29
a
15.18±0.61
e
*
Values are Mean±SD of triplicate determinations; means along a row with the same superscript are not
significantly different, P<.05
Table 4. Ratios of Na to K and Ca to P of Dioscorea alata varieties
Ratio
Sample varieties of
Dioscorea alata
(water yam)
A
B
C
D
E
D. purpurea
D. atropurpurea
D. liliopsida
D. vilgaris
D. villosa
Na/K
0.14 0.12 0.13 0.22 0.22
Ca/P
0.70 1.27 1.44 0.96 0.83
according to the ratios presented in Table 4.
Food is considered “good” if Ca/P ratio is above
one and “poor” if the ratio is less than 0.5, while
the Ca/P ratio above two helps to increase the
absorption of calcium in the intestine [46]. The
Ca/P ratios of D. atropurpurea and D. liliopsida
were above the recommended value of 1.00
Table 4. However, higher ratios have been
reported for Dioscorea rotundata and Colocasia
esculenta [26].
4. CONCLUSION
From the present study, it could be summarized
that D. alata varieties investigated had nutritional
proximate compositions with immense health
benefits. The average moisture content was
lower compared to the reported in the literature,
an important food property for long-term food
storage and industrial food processing. The
varieties are good sources of protein, fiber and
carbohydrate. D. purpurea, D. atropurpurea and
D. villosa in particular could be selected for high
protein level for intense cultivation in other parts
of Nigeria and other regions of the world growing
D. alata. Based on the standard criteria, D. alata
varieties with mean glycemic index of 38.62 in
this study are low GI foods. It is therefore
relevant, noting the health benefits of these
varieties to the consumers in prevention of
chronic diseases, including type 2 diabetes
mellitus. The tuber varieties had low mineral
levels. There is a need for intense breeding of
improved varieties for enhancing mineral quality
of these varieties without loosing the enviable
nutritional qualities. Taken together, D.
atropurpurea may be regarded as the best
variety according to the findings in this study.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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... The result revealed that that the moisture content is 10.08%, 10.11%, 10.19% for white yam, water yam and cocoyam respectively. The result obtained in this present study conforms to that of Oko and Famurewa [22] on their work on the estimation of nutritional and starch characteristics of water yam varieties commonly cultivated in the south-eastern Nigeria. Cocoyam has high protein content (8.86%) compared to water yam (5.07%) and white yam (2.48%) Oko and Famurewa [22] reported that the intake of stable foods with low protein content may result to several impaired biological processes in the body. ...
... The result obtained in this present study conforms to that of Oko and Famurewa [22] on their work on the estimation of nutritional and starch characteristics of water yam varieties commonly cultivated in the south-eastern Nigeria. Cocoyam has high protein content (8.86%) compared to water yam (5.07%) and white yam (2.48%) Oko and Famurewa [22] reported that the intake of stable foods with low protein content may result to several impaired biological processes in the body. With the high protein content recorded from cocoyam in this study, it is a good source of protein to consumers. ...
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... The crude fiber content showed significant differences (P ≤ 0.05) among the varieties, ranging from 0.61 to 2.07 %, with sample CEN/IB/97/AMA011 and the market sample having the lowest and highest value, respectively. Fibers such as the plant non-digestible carbohydrates and lignin found in food are known to have a lot of health benefits including the reduction of obesity tendencies, cardiovascular diseases, type II diabetes, digestive disorders, and some cancers [14]. The fibre content of the market sample falls within the crude fibre of 2.0 -2.5% which is recommended by the protein advisory group for weaning formulation [15]. ...
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... It seems it was first domesticated in the highlands of New Guinea. It competes with other important species like Dioscorea rotundata in terms of importance [3]. It is a tuberous root crop which belongs to the genus Dioscorea and contains starch between 70 and 80% of dry matter. ...
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... Greater yam has a high potential for increased yield and broader cultivation, with advantages compared with other roottuber-banana crops due to its superior nutritious content and low glycemic index 76,77 . Greater yam's ability to grow in tropical and sub-temperate regions around the world suggests that it is highly adaptable to its environment and that there may be adaptive traits (and associated alleles) that could be exploited in different global contexts. ...
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... Recently in the field of nutrition, there has been a tremendous interest in the assessment of nutrients, vitamins and mineral composition of staple foods such as yam, because they are considered to be economically, socially and culturally important in many tropic and subtropic regions of the world [26] . It is traditionally known that yam tuber of which D. bulbifera is not an exception, have potential ability to provide one of the cheapest sources of dietary energy in the form of carbohydrate [27] . ...
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This review presents different diseases associated with yam and the management strategies employed in combating its menace in Nigeria. The field and storage diseases are presented, anthracnose is regarded as the most widely spread of all the field diseases, while yam mosaic virus disease is considered to cause the most severe losses in yams. Dry rot is considered as the most devastating of all the storage diseases of yam. Dry rot of yams alone causes a marked reduction in the quantity, marketable value and edible portions of tubers and those reductions are more severe in stored yams. The management strategies adopted and advocated for combating the field diseases includes the use of crop rotation, fallowing, planting of healthy material, the destruction of infected crop cultivars and the use of resistant cultivars. With regards to the storage diseases, the use of Tecto (Thiabendazole), locally made dry gins or wood ash before storage has been found to protect yam tubers against fungal infection in storage. Finally, processing of yam tubers into chips or cubes increases its shelf live for a period of between 6 months and one year.