Agbor-Egbé, T.

Trèche, Serge

Horizon / Pleins textes

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3 food hases. 1982. 
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5, I 
VARIABILITY IN THE CHEMICAL COMPOSITION OF YAMS 
GROWN LN CAMEROON 
T. AGBOR EGBE AND S .  TRECHE] 
~~ 
We analyzed 98 cultivars belonging to eight gam species for mineral. protein. lipid. sugar. and 
cell-wall constituents. For most of the nutrients. intraspecific variability was as high as interspecific 
variability, but significant differences in the average values per species were found between 
Dioscorea alata, D. dumetorum, and the D. cayenensis-D. rotundara complex. 
Several workers have shown the great vari- 
ability that can exist between yams of different 
species. Busson (1965) compared the chemical 
composition of eight species of yam collected in 
different parts of West Africa. He  observed im- 
portant differences in the contents of crude pro- 
tein (5.3-11.9 gll00 g), total carbohydrates 
(53.3-91.0 g/lOO g). nondigestible carbohydrates 
(4.9-51.7 gllOO g), and calcium (0.014-0.024 @ 
100 g). Martin and Thompson (1971) insisted on 
the differences in  crude protein content. 
Other workers have been interested not only 
in the interspecific but also in the intraspecific 
variability in the chemical composition of yams. 
Baquar and Oke (1976.1977) determined crude 
protein and mineral contents of about 60 sam- 
ples belonging to 6 different yam species; the 
samples were collected from markets in Nigeria 
but were not well classified into different 
cultivars. Results showcd ihat important varia- 
tions. though not statistically tested, probably 
exist between species, and, in addition. that vari- 
ations between samples within a species are also 
high. Similarly. using principal-component anal- 
ysis based on amino-acid composition of 46 
cultivars belonging to 5 yam species. Splitt- 
stoesser et  al. (1973a) demonstrated wide intra- 
and interspecific diversity in amino-acid 
composition. 
Earlier studies in our laboratory (Treche and 
Guion 1980) were dedicated to the differences in 
nutritional potentialities of the main yam species 
grown in Cameroon. This paper contains part of 
the results of a study on 98 cultivars agro- 
nomically classified (Lyonga and Ayuk-Takem 
Food Studies Laboratory. Centre of Nutrition. 
General Delegation for Scientific and Technical Re- 
search. Yaounde. Cameroon. ? 
- n,. 
153 
1982) belonging to 8 species. The objectives of 
our study were to compare intra- and inter- 
specific variability in chemical composition, to 
assess nutritional value of cultivars, and to give 
references for clonal selection. 
MATERIALS AND METHODS 
From 1977 to 1982. we collected 98 samples 
from multiplication plots of the Institute of 
Agronomic Research throughout Cameroon. 
The samples corresponded to the descriptions 
by Lyonga and Ayuk-Takem (1982): D. alata. 23 
samples; D. bulbifera. 11; D. cayenensis, 18; D. 
dumetorum. 23; D. esculenta. 6; D. liebredit- 
siana. 2; D. rotundata. 9; and D. schimperiana. 
6. For each sample, stored less than a week. 
tubers were weighed. peeled, washed. dried in 
vucuo at < 60"C, and ground in a "whiley" mill 
to pass through a 0.5-mm sieve. 
We noted flesh colour and conducted chemi- 
cal analyses to determine the contents of dry 
matter, ash, and crude protein; lipid by soxhlet 
extraction with petroIeum ether; starch by the 
glucoamplase method (Thivend et al. 1965); 
total soluble sugars colorimetrically by the an- 
thron method (Loewus 1952) after two hot ex- 
tractions and one cold extraction by 80% 
ethanol; free glucose, fructose, and sucrose in 
8GQ ethanol extract as proposed by Johnson et 
al. (1964); nondigestible carbohydrates by the 
formic-acid technique of Guillemet and Jacquot 
(1943); acid detergent fibre (lignocellulose) and 
neutral detergent fibre (lignocellulose and 
hemicellulose) by the procedures of van Soest 
(1963) and van Soest and Wine (1967); pentosans 
by the aniline-acetate colorimetric method of 
-- "Ea- -:<- 
.Er .. . 
"bble 1. Dty matter, starch, cell-wall constituents, minerals, protein, lipids, and energy content of eight yam species. 
D. ritara , , D. bulbifira D. cayenem& D. dumeforum D. uculenta D. liebmhnirvra D. "doIn D. srhhpenona 
23 11 18 23 
27.2 f 0.6 
70.5 f 0.7 
19.0 - 28.3 
61.7 - 75.5 
5.5 f 0.3 
3.4 - 7.6 
5.2 t 0.4 
3.0 - 8.4 
0.161 t 0.005 
0.118 - 0.201 
0.042 -c 0.003 
o.nu - 0.073 
1.05 -+ 0.07 
0.49 - 2.03 
57.1 f 2.7 
30.9 - 114.5 
6.85 f 0.85 
2.1ß - 18.7 
1.R8 f O.OR 
O.ß9 - 2.98 
1.02 f 0.10 
0.61 - 2.18 
15.9 f 0.9 
8.1 - 23.4 
9.64 f 0.30 
7.36 - 13.21 
6 2 9 6 
24.4 i 1.2 , h.8 & 0.9 
14.1 - 35.1 
72.6 2 1.4 72.9 f 0.7 
60.2 - 82.1 
24.8 - 35.1 
69.8 - 78.6 
. . . - . 
32.6 t 1.0 
23.5 - 40.2 
80.0 5 0.7 
76.9 -85.3 
29.7 5 1.2 
24.5 - 30.8 
70.4 rt 1.2 
66.3 - 73.4 
36.1 
35.9 - 36.3 
80.4 
79.7 - 81.1 
33.4 t 1.5 
26.3 - 39.5 
80.2 f 0.9 
77.4 - 84.1 
23.0 IT 0.9 
19.4 - 25.6 
71.1 IT 3.2 
56.3 - 78.1 
3.4 f 1.0 3.5 f 0.6 
2.1 - 5.0 3.0 - 5.0 
4.9 & 1.5 3.5 f 0.7 
2.8 - 8.8 2.9.- 5.2 
0.116 f 0.685 0.128 & 0.006 
0.068 - 0.193 
0.029 f O.Ob5 
0.014 - 0.049 
0.100 - 0.154 
0.&3 f 0.007 
0.020 - 0.m 
1.35 f. 0.06 1.17 f 0.03 
27.2 & 0.9 fi.5 f 1.5 
4.30 rt 0.78 
1.4 i 0.12 
0.87 f 0.04 
0.85 - 1.91 0.99 - 1.36 
19.5 - 35.5 22.4 - 25.8 
4.39 f 0.48 
1,76 f 0.07 
1.47 f 0.05 
0.94 - 17.6 2.01 - 7.53 
0.68 - 2.47 1.40 - 2.12 
0.53 - 1.78 1.25 - 1.79 
2.6 k 0.7 
1.2 - 4.1 
2.7 f 0.1 
2.3 - 3.1 2.0 1.9 - 2.1 2.4 f 0.1 2.1 - 2.7 3.5 IT 0.5 2.4 - 5.8 
2.6 f 0.2 
2.4 - 3.2 
0.089 f 0.008 
0.063 - 0.114 
0.0'25 f 0.003 
0.019 - 0.032 
1.26 f 0.05 
1.15 - 1.48 
37.4 t 2.4 
28.9 - 44.6 
3.00 f 0.34 
1.69 - 3.83 
2.11 f 0.19 
1.63 - 2.65 
1.14 f 0.06 
o m  - 1.30 
3.9 f. 0.9 
3.8 - 4.0 
2.4 
2.4 - 2.5 
4.6 t?: 1.0 
2.0 - R.6 
0.112 t?: 0.010 
0.061 - 0.140 
0.045 -c 0.010 
0.020 - n.0~4 
1.213 0.05 
40.8 f 4.6 
1.15 - 1.45 
30.1 - 5R.4 
3.42 2 0.34 
2.6R - 4.75 
2 . 3 ~  t?: 0.32 
1.65 2 0.14 
1.42 - 3.48 
I . !Q - 2.13 
2.0 -c 0.2 
1.4 - 3.0 
3.3 f 1.0 
1.7 - 5.0 
0.093 f 0.004 
0.065 - 0.125 
0.015 1: 0.001 
O.OOR - 0.m 
0.087 t 0.05 
0.57 - 1.45 
23.4 f 0.7 
19.6 - 29.4 
2.92 .c 0.32 
0.70 - 5.90 
2.6 f 0.4 
1.6 - 4.4 
0.094 f 0.005 
0.067 - 0.114 
0.018 -c 0.003 
0.011 - 0 . m  
1.07 t?: 0.10 
0.73 - 1.74 
52.8 2 5.0 
26.7 - 72.5 
5.47 f 0.82 
2.46 - 10.27 
1.30 -c 0.16 
1.14 e 0.17 
0.78 - 2.16 
0.73 - 2.16 
12.9 t 1.5 
11.0 - 16.7 
0.052 
0.050 - 0.053 
C8klum @,!l00 8)  
Average f SE 
Rnnge 
h+malnm (gllba I) 
Average f SE 
Rnnge 
M n w l a m  (n/lM &) 
Averogc f SE 
Averngc f SE 
Rnnge 
ZlIlC (dl86 8) 
Average f SE 
Range 
COPPCr ($100 R) 
AvernBc f SE 
RnnRe 
Satlum (glliW g) 
Average * SE ' 
Ran&e 
hnl (dfm K) 
0.023 
0.020 - 0.026 
0.76 
0.70 - 0.82 
29.0 
27.9 - 30.1 
4.89 
333 - 5.94 
2.71 
2.59 - 2.83 
O.% 
0.96 - 0.96 
2.7 
2.4 - 2.9 
1.39 A 0.08 
0.73 - 2.02 
0.94 -L 0.06. 
0.43 - 1.36 
13.0 f 0.9 
7.3 - 18.8 
6.08 f 0.33 
3.55 - 8.35 
8.8 f 1.6 13.9 f 1.7 
3.9 - 19.3 11.6 - 21.6 
5.10 2 0.41 
4.06 - 6.46 3.17 3.12 - 3.22 7.02 f 0.54 4.31 - 8.8R 7.66 t?: 0.55 5.94 - 8.87 
h 
J - -&> 
Cerning and Giulbot (1973); phosphorus color- 
imetrically bp the phosphovanadomolybdate 
ammonium method; iron by the orthophe- 
nanthrolene colorimetric method; calcium. po- 
tassium, sodium by Eppendorf flame photome- 
ter (Gueguen and Rombauts 1961); magnesium, 
zinc, and copper by Varian atomic absorption 
spectrometer. 
RESULTS AND DISCUSSION 
Average weight of tubers from the eight spe- 
cies differed markedly. In fact, we could dis- 
tinguish species by the number of tubers per 
plant -one or two: D. alata, D. cayenensis, D. 
liebrechtsiana, D. rotundata, D. schimperiana; 
several tubers jointly attached per plant: D. 
dumetorum; and distinct small tubers: D. es- 
culenfa; or bulbils: D. bulbifera. 
Average peeling losses varied between 17.1% 
and 33.3%, depending on the species. Within 
o n e  spec ies ,  var ia t ions  were very high 
(11.8-51.3% for D. dumetorum yam samples). 
The flesh was most commonly white or yellow, 
but some cultivars of D. alata were distinctly 
violet and those of D. schimperiana orange. 
The species could be divided into those with 
low (23-25%) dry-matter content (D. alata, D. 
dumetorum,  D. schimperiana) and high 
(32-37%) dry-matter content (D. cayenensis, 
D. liebrechtsiana, D. rorundata), with D. es- 
culenta and D. bulbifera having intermediate 
values (Table 1). Within D. cayenensis, cultivar 
C169, which has been selected as agronomically 
elite (Lyonga and Ayuk-Takem 1982). was the 
only one with low dry-matter content. Varia- 
tions within D. alata were more important than 
those within the other species. 
ïn  mineral contents, ratios between the lowest 
and highest average by species varied between 
1 : 2 and 1 : 3 except for sodium with a ratio of 
1 : 8 found between several species (Table 1). 
Within one species, the ratio did not exceed 1 : 4 
€or most of the minerals Intraspecific variability 
for P was lower than for other minerals, whereas 
Na and Fe had higher variability. The highest Fe 
values were probably caused by contamination 
of the samples during drying. Our results on K 
and Zn contents ìn D. alata, D. dumetorum, and 
. .D. roiundata were similar to those of Baquar and 
O k e  (1977), bu t  o t h e r  values differed 
systematically. 
Starch contents were within the range 
70.4-72.9% except for D. cayenensis, D. 
liebrechtsiana, and D. rotundata, which had val- 
AGBOR EGBE AND TRECHE 155 
ues greater than 80.0% (Table 1). The intra- 
specific variability in the low-starch species was 
higher than in the others. 
Dioscorea esculenta and D. liebrechrsiana had 
comparatively high soluble sugars. The other 
species did not differ markedly from one an- 
other, but there was a high intraspecific vari- 
ability, mostly within D. alara species. 
For all the cell-wall constituents studied (Ta- 
ble l), D. dumetorum had the highest average 
values, then D. alata and D. schimperiana. The 
lowest were peculiar to D. rotundara and D. 
liebrechfsiana. The high values for some D. 
dumetorum cultivars probably reflected the 
hardening phenomenon (Treche and Delpeuche 
1982), which can occur just hours after harvest. 
As has been shown by Brillouet et al. (1981). the 
proportions of different cell-wall constituents, 
especially lignocellulose and hemicellulose, 
were not the same in all the yam species. Aver- 
age hemicellulose content was unnoticeable for 
D. dumetorum tubers, whereas i t  reached 0.7% 
and 1.6% for D. cayenensis and D. alata, 
respectively. 
Dioscorea dumetorum and D. alata had the 
highest average crude protein (Table 1); D. 
liebrechfsiana and D. esculenta, the lowest. High 
crude-protein content seems to be characteristic 
of D. dumetorum tubers, as the average value of 
24 new varieties bred in Cameroon attained 
10.2% (Pfeiffer and Treche. unpublished data). 
Nevertheless, intraspecific variability of crude 
protein seems to be at least as high as inter- 
specific variability. On a fresh-weight basis, D. 
rotundata, D. dumetorum, D. alata, and D. cay- 
enensis were distinct from the others by having a 
protein content more than or equal to 2.0%. 
Lipid content was low except in D. liebrecht- 
siana and some cultivars of D. dumetorum. The 
range of ash content was not wide. 
The energy content (Table 1) did not vary 
much because of the small absolute variation in 
lipid and ash, with D. rotundata, D. cayenensis, 
and D. liebzchtsiana having the highest calorific 
value. 
CONCLUSrON 
Diascoreu cayenenrk and D. rotundata were 
shown to be closely related. In fact, certain re- 
searchers (Martin and Rhodes 1978; Miege 
1982) have grouped cultivars of these species into 
a D. cayenensix-D. rotundata complex. Using 
the Student’s t-test €or each nutrient, we found 
no significant differences between the two spe- 
c i  
. .-- Y .  . Y Z  -- -- 
J I y 
. .  
156 . ROOT CROPS: PRODUCTION AND USES 
cies except for total soluble sugars, nondigesti- 
ble carbohydrates. Fe. and Mg. 
especially the dry-matter content, we belim 
that ccltivars of the D. cayenensis-D. rom& 
complex a re  best for consumption fresh, 
whereas D. dumeforum and perhaps D. & 
could be used in yam flouf 
Taking into account the characteristics in the 
chemical composition of the different species, 
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TROPICAL ROOT CROPS: - 
PRODUCTION A D USES m AFRICA 
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PROCEEDINGS O F  THE SECOND TRIEh'NIAL SYMPOSIUM OF THE Ih'TERNATIONAL 
SOCIETY FOR TROPICAL R O O T  C R O P S  - AFRICA B R A N C H  HELD IN DOUALA, 
CAMEROON, 14 -19 Au~usr1983 
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Variability in the chemical composition of yams grown in Cameroon

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