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JOURNAL OF RESEARCH IN NATIONAL DEVELOPMENT VOLUME 7 NO 2, DECEMBER, 2009

THE PROXIMATE COMPOSITION AND THE ANTI-NUTRITIONAL FACTORS IN SEVEN VARIETIES OF COCOYAM (COLOCASIA AND XANTHOSOMA)
K.O. Amanze
Department of Chemistry, Alvan Ikoku Federal College of Education, Owerri, Nigeria
E-mail: amanzek@yahoo.com

Abstract
Flours produced from tubers of seven varieties of Colocasia and Xanthosoma were evaluated for proximate composition, some mineral constituents and phytochemicals. The results show that Xanthosoma contained (dry matter) 75.5 % carbohydrate, 10.95 % moisture, 6.93 % crude protein, 3.58 % ether extract and 2.1 % ash.  phytochemical analysis showed that caladium species had significantly higher levels (P < 0.05) of  Oxalate (10.10 %) and cyanogenic glycosides (5.20 %) than the rest of the samples.  The samples were found to be rich sources of macro minerals as well as some trace elements.
key words:  Colocasis, Xanthosoma, chemical composition, minerals, vitamins.

Keywords: Proximate composition; cocoyam; nutritional; organ


Introduction
Cocoyam belongs to the monocotyledonous family Araceae (the aroids) which contains several plants which are cultivated and used for food in various parts of the tropics (Onwueme, 1978).  They are mainly herbaceous plants, often with an enlarged rootstock, which acts as a storage organ.  Morphologically, the primary corm of the plants represent the main stem and the secondary corms or cornels, lateral branches.  The relative sizes of the two types of organ vary greatly between species and variety – the cornels are usually the more satisfactory item of food.

Colocasia and Xanthosoma species, after being processed in the local way is cherished by many people, especially in the rural areas of the Southern part of Nigeria.  It is roasted and eaten with palm oil, and as a condiment in soup especially Owerri soup ‘‘Ofe Owere’’.  Flour from Xanthosoma has potentials as an instant flour for ‘‘Fufu’’ in which regard it is necessary to blend it with cassava and maize to reduce stickiness (Ibe and Iwueke, 1984).  Although cocoyams are composed predominantly of starch, it is next only to certain varieties of yam in crude protein content among root crops.  It has appreciable quantities of calcium and phosphorus. Colocasia starch grains are among the smallest found in the plant kingdom, hence it is very easily digested and can form a good base for formulating infant food.

However, the nutritive value of the whole varieties and its contribution to human nutrition has not been thoroughly investigated.  A more detailed study of the proximate and mineral compositions of the food samples as well as the anti-nutritional factors was considered necessary to determine the nutritional value of the varieties and possible commercial uses of the food.  The usefulness of Colocasia and Xanthosoma varieties as a source of protein, vitamins, essential macro minerals necessary for the growth of man and animals is being investigated.

Materials and methods
Preparation of samples for analysis
All the samples used for this work were bought from local markets in and around Owerri, Imo State, Nigeria.  Their outer coverings were pealed off with knife, which exposed the fleshly edible portions.  These were sliced to pieces and dried in an oven (Memmert oven) at 600C.  The sample was powdered with a Victoria milling machine, packed in sealed polythene bags and kept at room temperature before use.

Proximate composition
Determination of the proximate composition of the sample was based on AOAC (1990) procedures, employing the micro-kjeldahl method for crude protein and Soxhlet extraction method for ether extract.  Moisture and ash

contents were determined as described by AOAC (1990).  The carbohydrate was determined by difference.

Mineral composition
The flour from the samples was wet-digested and corning flame photometer (Model 400) was used to estimate the amount of Sodium (Na) and Potassium(K).  The Phosphorus (P) content was determined by the standard spectrophotometric vanadomolybdate method as described by AOAC (1990).  Calcium (Ca) and Magnesium (Mg) were determined using atomic absorption spectrophotometer (Spectrophotometer 205).  Iron was determined spectrophotometrically by reading the absorbance at 535nm after pigmentation with thioglycollic acid.

 

Phytochemical composition
The saponin content was determined using methods described by AOAC (1984).  The percentage of Oxalates was determined using the method of Munroe and Bassir (1969) while the cyanide was determined by the modified alkaline picrate colorimetric method (Balagopalm et al, 1988).  The method of Griffith and Thomas (1981) was used for phytic acid (Phytate) extraction and then determined colorimetrically.  The cyanide content was obtained by alkaline titration method involving the use of 25 % Na0H, 6N NH40H solution, 5 % Potassium Iodidie and 0.02N Silver nitrate (A.O.A.C. 1990).

Result and discussion
The results of the proximate analysis of the varieties of cocoyam determined are presented in Table 1.


Table 1.  Proximate composition (%) of varieties of cocoyam


S/N

 

Varieties

 

Moisture
content

 

Crude fibre (C.F.)

 

Crude protein (C.P)

 

Ether extract (E.E)

 

Ash

 

Nitrogen free extract (N.F.E)

1

X.sagittifolium (Red cocyam)

          a
10.95+ 0.10

       a
1.40+ 0.28

       c
6.93+ 0.10

        b
3.58+ 0.28       

      a
2.05+ 0.07

      f
75.10+ 0.42

2

X. atrovirens (white cocoyam)

      C
14.45+ 0.71

      a
1.10 + 0.28

      b
4.74+ 0.23

     a
1.60 + 0.07

      a
2.35 + 0.21

      f
75.76 + 0.34

3

C.esculenta var. antiquorum

          e
18.25 + 0.28

     a
1.70+ 0.14

       b
5.89 + 0.28

     e
6.95 + 0.40

      b
2.70. + 0.21

      d
64. 51+ 0.42

4

C. esculenta var. esculenta

          f
19.85 + 0.21

       a
1.45 + 0.26

         d
8.19 + 0.58

        e
7.03 + 0.04

      b
3.0 + 0.17

         b
60.53 + 0.01

5

Colocasia Spp. (“Ede Anambe”)

     c
13.95 + 0.33

        b
5.70 + 0.00

         a
3.77 + 0.33

     b
2.95+ 0.07

      c
4.80+ 0.10

         e
68.83 + 0.24

6

Caladium Spp (C. hortinarum)

     c
14.35 + 0.28

     a
1.65+ 0.18

     c
7.52 + 0.03

      d
4.65 + 0.17

      a
2.70 + 0.050

     e
68.93+ 0.21

7

Alocasia Macrorrhiza

      d
15.90+ 0.82

     d
12.50+ 0.71

      b
5.60+ 0.21

      c
3.95+ 0.28

     d
7.70+ 0.17

      a
54.75+ 0.28


The values are mean ± S.D of three determinations. Values that are not showing a common superscript letter in a column are significantly different at P<0.05 as assessed by Duncan’s multiple range tests. The values obtained showed that the varieties are a rich, source of carbohydrates (i.e. N.F.E.), and protein.  Alocasia macrorrhiza has significant (P < 0.05) crude fibre Ash content as shown in tables 3 and 4.


Table 2. Phytochemical content of varieties of cocoyam
 

 

 


Varieties

 

Alkaloid

 

Saponin

 

Oxalate

 

Cyanide

 

Phytate

1

X.sagi ttifolium (Red cocyam)

          a
1.55 + 0.35

       a
1.40+ 0.28

      a
2.01 + 0.01

        b
3.46+ 0.30       

      a
1.6 + 0.20

2

X. atrovirens (white cocoyam)

     a
1.75 + 0.21

      a
2.05 + 0.10

      a
2.76 + 0.34

     a
2.59 + 0.13

      a
1.40 + 0.28

3

C.esculenta var. antiquorum

          b
2.40 + 0.14

     d
6.90+ 0.42

      a
2.07 + 0.10

     b
3.46 + 0.11

      b
240. + 0.14

4

C. esculenta var. esculenta (

         b
2.10 + 0.21

       a
1.30 + 0.14

        a
2.51 + 0.44

        c
3.89 + 0.28

      a
1.20 + 0.21

5

Colocasia Spp. (“Ede Anambe”)

     a
1.65 + 0.14

        d
7.05 + 0.07

         a
2.98 + 0.26

     b
3.45+ 0.64

      b
2.60+ 0.42

6

Caladium Spp (C. hortinarum)

     c
3.30 + 0.07

    b
2.80+ 0.00

     c
10.10 + 0.20

      d
5.20 + 0.12

      b
2.50 + 0.071

7

Alocasia Macrorrhiza

      d
1.90+ 0.82

     d
9.0+ 0.17

      b
5.24+ 0.34

      c
3.46+ 0.10

     d
1.6+ 0.56

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The values are mean ± S.D of three determinations.  Values not sharing a common superscript letter in a column are significantly different at P < 0.05 as assessed by Duncan’s multiple range test.
The phytochemicals and anti-nutritional factors contained in the samples are presented in Table 2.  They represent a high percentage of their dry matter.  With the exception of alkaloids, other phytochemicals are significant in most varieties.  Steroidal sapogenins in form of water soluble glycosides or saponins are responsible for the slimy nature of Colocasia species.  Colocasia and Xanthosoma species contain unpleasant amounts of Calcium oxalate in their corms and cormels.  African grown Colocasia has up to 2.6 % on dry weight basis of Oxallic acid (Coursey, 1968).  These agree with results obtained in table 2 above.  Oxalates exert an irritant effect when eaten (Okoro, 1992).


Table 3:    Mineral composition of varieties of cocoyam concentration in mg/100g

S/N

Samples

Ca

Mg

P

K

Fe

Na

1

X.sagi ttifolium (Red cocyam)

          A
17.0+ 0.14

       a
2.0+ 0.30

      e
27.0 + 0.21

        c
0.75 + 0.14       

     b
8.70+ 0.01

      b
150.0+ 1.41

2

X. atrovirens (white cocoyam)

       B
23.45+ 0.10

      a
4.0 + 0.60

      d
25.0 + 0.71

    c
0.83 + 0.04

     d
12.50 + 0.3

     c
231.30+ 0.35

3

C.esculenta var. antiquorum

       D
40 + 0.17

     a
2.0 + 0.20

       d
24.0 + 0.28

     c
0.83 + 0.10

      d
13.60 + 0.1

     c
231.30+ 0.0

4

C. esculenta var. esculenta

       B
25.0 + 0.14

       a
3.0 + 0.30

         e
28.0 + 1.41

        a
0.20 + 0.03

      e
19.80 + 0.3

         a
62.30 + 0.31

5

Colocasia Spp. (“Ede Anambe”)

       E
50..0 + 0.0

        a

5.0 + 0.70

         b
14.20 + 0.49

     b
0.34+ 0.09

     a
8.20+ 0.2

        d
550.0 + 1.41

6

Caladium Spp (C. hortinarum)

       F
55.0 + 0.28

     a
2.0+ 0.10

     C
18.0 + 0.00

      a
0.08+ 0.01

      e
16.30 + 0.10

     c
231.30+ 0.14

7

Alocasia Macrorrhiza

      G
70.0 + 0.42

     C
24 + 0.35

     A
11.90+ 0.35

      a
0.08+ 0.01

    f
42.40+ 0.10

      c
231.30+ 0.35

Values are mean+ S.D of three determinations. Values not sharing a common superscript letter in a column are significantly different at P< 0.05 as assessed by Duncan’s multiple range test.


The mineral content shows that Alocasia macrorrhiza contained 70.0±  28mg/100g, 24 ±0.35mg/100g and 42.40 ± 0.1mg/100g of Calcium, Sodium respectively.  The concentration of Potassium in the varieties is lowest (0.08-0.83mg/100g).  Thus they can be included in the diets of patients with renal failure.  Although, this analysis showed high contents of calcium and phosphorus.  However, investigations have shown that these are largely unavailable, owing to the presence of phytic acid.  Oxalates also reduce the availability of Calcium (Coursey, 1968).


Table 4: Heavy metal composition of varieties of cocoyam
                                    concentration in mg/100g

 



S/N

Varieties

Copper

Manganese

Zinc

Lead

Arsenic

1

X.sagi ttifolium (Red cocyam)

          b
0.07 0+ 0.01

       a
0.13 + 0.1

      b
0.28 + 0.10

 

Trace

 

Trace

2

X. atrovirens (white cocoyam)

      b
0.08 + 0.02

      a
0.09 + 0.07

      b
0.35 + 0.05

 

 

3

C.esculenta var. antiquorum (A)

         b
0.05  + 0.04

     c
0.33 + 0.06

       a
0.14 + 0.03

 

 

4

C. esculenta var. esculenta (1)

          b
0.09 + 0.01

      b
0.22 + 0.07

         b
0.36 + 0.12

 

 

5

Colocasia Spp. (“Ede Anambe”)

     b
0..07 + 0.02

       b
0.18 + 0.22

     d
1.79 + 0.20

 

 

6

Caladium Spp (C. hortinarum)

     b
0.11 + 0.01

     d
0.45 + 0.40

     c
1.28+ 0.40

 

 

7

Alocasia Macrorrhiza

      c
0.23 + 0.05

    b
0.88 + 0.20

      d
2.10 + 0.30

 

 

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Values are mean ± S.D of three determinations. Values not sharing a common superscript letter in a column are significantly different at     P < 0.05 as assessed by Duncan’s multiple range test.

The results show that, the varieties contain significant amount of Zn at an average of 0.70 mg/L of sample compared to 0.08 mg/L for copper in all the samples. These tubers can supply substantial portion of the manganese, Copper and zinc requirement of the adults in the tropics who cannot afford other rich sources of these minerals such as milk, cheese and eggs. (Samarajeewa et al 1988).

Conclusion
The results of this investigation have greatly shown the nutritive composition of the food items as quality food.  The result showed that the

cocoyam varieties contain a high percentage of carbohydrate, protein, fat, calcium, phosphorus, iron and sodium.  The starch grains of cocoyams are very small and easily digestible so cocoyam dishes are recommended for children, invalids and people with weak digestive system.  Cocoyam contains more protein than other root crops like cassava and sweet potato.  The protein is rich in most of the essential amino acids and the sulphur bearing amino acids is greater, in cocoyam than in other root crops.  The study shows that the levels of the trace heavy metals are generally within safe limits.  The levels of phytochemicals found can serve as potent nutritive food supplements and drugs.  The data obtained in this work will be valuable in complementing available food composition data and help in estimating dietary intakes of heavy metals in Nigeria.

References
AOAC (1984) Official methods of analysis (14th ed). Washing ton D . C.: Association
            of Official Analytical Chemists.

AOAC (1990). Official methods of analysis, Washington D.C.: Associated of Official Analytical Chemists 15th ed,

Coursey, D.G. (1968) The edible aroids, world crops. London: Grampian Press Ltd.

Coursey, D.G. (1976) Yams: In Simmonds, (ed): Evolution of crop plants London: Longmans.

Duncan, B.D. (1955). Multiple range and multiple F tests. Biomestrics 11, 1-42.

Griffiths, D. W. and Thomas, T.A. (1981) Phytate and total phosphorus content of field beans (Vicia faba) J. Sci Food Agric . 32: 187 – 192.

Ibe, M.U. and Iwueke, C.C. (1984) “Production and utilization of cocoyam” Extension Bulletin No. 14, NRCRI, Umudike. pp 10-11.

Munroe, A. and Bassir, O. (1969) Oxalate in Nigerian vegetables, W.A.J. Biol. Appl. Chem. 12 (1): 14-18.

Okoro, F.U. (1992) Tropical root and tuber crops, Tropical field crop production (hand book) for schools & colleges, Owerri, Nigeria: Totan Publishers Ltd Pg13-21, 32-35.

Onwueme, I.C. (1978) The tropical tuber crops: yams, cassava, sweet potato, cocoyams, Chichester, England :Wiley Publishers.

Samarajeewa, U., Suffiyan, M.I. and Gunasena, H.P.M (1988) Minerals and sapogenins of some yam species. ASEAN food Journal 4, 38-40.
Snedecor, G.W. and Cochran, W. (1987). Statistical methods 7th ed. Ames, I.A., USA: The Iowa State University Press