Hydrolysis of Native Starch of Some Wild Yam (Dioscorea) Species of Ivory Coast

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praehensilis; Dioscorea hirtiflora; Dioscorea burkilliana; Dioscorea dumetorum; Dioscorea bulbifera and Dioscorea minutiflora are studied according to their sensibility to the hydrolysis acid (HCl 2.2 N at 35?C).Hydrolysis curves have two parts, a part with strong slope and another part with weak slope. The form of these curves agrees with the physical structure of the starch granule which has an amorphous zone and a crystalline zone. The acid hydrolysis of the amorphous zone corresponds to the part of the curve with the strong slope and that of the crystalline zone corresponds to the part with weak slope.The intersection of the weak slope portion tangent with vertical axis (Y-axis) is the starch easily hydrolyzed fraction.Fractions easily hydrolyzable (HF) are 5% (Dioscorea burkilliana); 10% (Dioscorea praehensilis); 12 % (Dioscorea minutiflora); 22 % (Dioscorea bulbifera (tuber); 22 % (Dioscorea bulbifera bulbil); 30 % (Dioscorea hirtiflora) and 36 % (Dioscorea dumetorum). The sensibility to the acid hydrolysis of the starch extracted from the various wild yam species studied varies in the following order: Dioscorea dumetorum > Dioscorea hirtiflora > Dioscorea praehensilis > Dioscorea bulbifera bulbil > Dioscorea bulbifera to tuber > Dioscorea minutiflora > Dioscorea burkilliana.It would be related to the size and the chemical composition of the grain of the starch. The studied starch of wild yam species altogether resists to the acid hydrolysis.

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Agriculture Science Developments, 2(7) July 2013, Pages: 56-58

TI Journals
ISSN
2306-7527

Agriculture Science Developments
www.tijournals.com

Hydrolysis of Native Starch of Some Wild Yam (Dioscorea)
Species of Ivory Coast
Sahoré Drogba Alexis *1, Amani N’Guessan George 2
1,2

Food Sciences and Technology Department, University Nangui Abrogoua 02 BP 801 Abidjan 02 Ivory Coast.

AR TIC LE INF O

AB STR AC T

Keywords:

praehensilis; Dioscorea hirtiflora; Dioscorea burkilliana; Dioscorea dumetorum; Dioscorea
bulbifera and Dioscorea minutiflora are studied according to their sensibility to the hydrolysis acid
(HCl 2.2 N at 35°C).

Starch
Wild yam
Acid hydrolysis
Hydrolyzable fractions
Starch granules

Hydrolysis curves have two parts, a part with strong slope and another part with weak slope. The
form of these curves agrees with the physical structure of the starch granule which has an
amorphous zone and a crystalline zone. The acid hydrolysis of the amorphous zone corresponds to
the part of the curve with the strong slope and that of the crystalline zone corresponds to the part
with weak slope.
The intersection of the weak slope portion tangent with vertical axis (Y-axis) is the starch easily
hydrolyzed fraction.
Fractions easily hydrolyzable (HF) are 5% (Dioscorea burkilliana); 10% (Dioscorea praehensilis);
12 % (Dioscorea minutiflora); 22 % (Dioscorea bulbifera (tuber); 22 % (Dioscorea bulbifera
bulbil); 30 % (Dioscorea hirtiflora) and 36 % (Dioscorea dumetorum).
The sensibility to the acid hydrolysis of the starch extracted from the various wild yam species
studied varies in the following order: Dioscorea dumetorum > Dioscorea hirtiflora > Dioscorea
praehensilis > Dioscorea bulbifera bulbil > Dioscorea bulbifera to tuber > Dioscorea minutiflora >
Dioscorea burkilliana.
It would be related to the size and the chemical composition of the grain of the starch. The studied
starch of wild yam species altogether resists to the acid hydrolysis.

The starch extracted from the tubers of some
wild yam species Dioscorea
© 2013 Agric. sci. dev. All rights reserved for TI Journals.

1.

Introduction

The starch is an important raw material source in the food industry [1]. The modification of the starch physical-chemical properties permits
to manufacture some food, instantaneous flours and various diet products [1] [2]. The acid is used for a long time to modify the structure of
the starch granule and to produce the soluble starch [3]. Native starch resents higher temperatures, prolonged cookings, canning and it loses
its binding power in acid solution. Moreover, the phenomenon of the expulsion of a water molecule is all the more fast as the temperature is
low; what makes this starch not very suited to the manufacturing of the deep-frozen products. In order to these disadvantages, the modified
starches are used. The survey of less known starch, like this of the wild yam species is a way of research to be explored in the quest of good
quality native starch which could have the same properties like the modified starch. The starch extracted from some wild yam species of the
Ivory Coast forest zone has been studied by Sahoré et al [4]. Their surveys described some investigation on the starch properties. The
objective of this study is to know if starch extracted from these tubers get ready for the hydrolysis which remains an important stage in
numerous manufacturing processes of product with starch in the industry. This study is also a contribution to research on the polymers
derived from tropical products still little known.

2.

Material and Methods

2. 1. Vegetable material
Tubers, of the wild yam species: Dioscorea praehensilis, Dioscorea hirtiflora, Dioscorea burkilliana, Dioscorea dumetorum, Dioscorea
bulbifera and Dioscorea minutiflora are collected in July and August in the Ivory Coast forest zone. The specimens are identified at the
Cocody University Herbarium and their starch is extracted using the modified method of Banks and Greenwood [5]. - The tubers are
peeled, sliced and ground in a Warring blender (Moulinex). The paste of yam obtained is dispersed in 4% NaCl solution and then passed
successively through 500 µm and 100 µm sieves. The remaining solids are decanted and washed with distilled water at least four times and
then dried at 45°C for 48 hours”.

* Corresponding author.
Email address: [email protected]

Hydrolysis of Native Starch of Some Wild Yam (Dioscorea) Species of Ivory Coast

57

Agri culture Scienc e Developments , 2(7) July 2013

Shape and mean diameter of the starch granule extracted from wild yam species are: Dioscorea praehensilis: ovo triangular granule (Ф =34
µm), Dioscorea hirtiflora: ovo triangular granule (Ф = 25µm), Dioscorea burkilliana: ovo triangular granule (Ф = 44µm), Dioscorea
dumetorum: polyhedral granule (Ф = 3µm), Dioscorea bulbifera bulbil: triangular granule (Ф =31µm), Dioscorea bulbifera tuber :
triangular granule (Ф =32µm), Dioscorea minutiflora : ovo triangular granule (Ф = 40 µm) [4].

2. 2. Acid hydrolysis
Acid hydrolysis of the starch is performed as follows: “1 g of starch is put in 100 ml of a hydrochloric acid solution 2.2 N under the
ambient conditions at 35°C during 28 days [6]. Hydrolysis degree is followed regularly by takings of 1ml of the acid solution which is
diluted and titrated by Dinitrosalicylic Acid (DNS) [7]. The quantity of reducing sugar is dosed at the end of each time and converted into
starch with the factor 0.9 [8]”

3.

Results and Discussion

The acid hydrolysis kinetics of the starch extracted from wild yam tubers are expressed in a percentage of the starch degraded according to
the time (Fig. 1). The granule of starch is a heterogeneous structure physically amorphous and crystalline. This would explain the kinetic
process of the hydrolysis. During the first 16 days of hydrolysis noticed a rapid degradation of the starches followed by slow hydrolysis
until the 28th day.
Thus, the first phase of hydrolysis goes until the 16th day and the second phase of hydrolysis goes from the 16th day to the 28th day (Fig.
1). According to Hoover [6] the two phases of the hydrolysis kinetics corresponded to the two main states of the organization of the starch
granule structure. The first phase presenting a curve with a strong slope would correspond to the fast hydrolysis of the starch granules
amorphous zones and the second phase presenting a curve with a weak slope would correspond to the slow hydrolysis of the starch granule
crystalline matter zones. The difference in the kinetics and the extent of the hydrolysis would be allotted to the size of the granules, the
interactions of the starch chain and its chemical composition (Phosphor content, amylose content and the lipids-amylose complexes) [6],
[10]. These observations could explain also the resistance order to the acid hydrolysis of studied starch extracted from wild yam species.
The intersection of the curve weak slope portion tangent with vertical axis (Y-axis) is the starch easily hydrolyzed fraction. The easily
hydrolysable fractions (HF) values of the wild yam species starch studied range from 5 to 36% (Table. 1). They are lower than those of
other types of starch such as the starch of taro: 42.9%, corn: 51% and maize: 40% [9] [10]. Compared with these last starches we could say
that studied wild yam species starch has little sensibility to the acid hydrolysis. The sensibility to the acid hydrolysis, of the starch studied
extracted from wild yam species, seems to evolve in the following order:
Dioscorea dumetorum > Dioscorea hirtiflora > Dioscorea praehensilis > Dioscorea bulbifera (bulbil) > Dioscorea bulbifera (tuber) >
Dioscorea minutiflora > Dioscorea Burkilliana
It is noticed that starch extracted from Dioscorea dumetorum with small granules (Ф = 3 microns), is less resistant to acid hydrolysis than
starch with large granules of Dioscorea burkilliana (Ф = 44 µm) Dioscorea minutiflora (Ф = 40 µm), Dioscorea praehensilis (34 µm),
Dioscorea bulbifera tuber (32 µm), Dioscorea bulbifera bulbil (31 µm) and Dioscorea hirtiflora (25 µm) [4]. This could be explained by
the fact that the starch granule of Dioscorea dumetorum has a small surface area degradable.

70
D. praehensilis

%hydrolysis

60

D. hirtiflora

50

D. minutiflora

40

D. burkilliana
30
D. dumetorum
20

D. bulbifera (b)

10

D. bulbifera (t)

0
0

4

8

12

16

20

24

28

Day of hydrolysis

Figure 1. Acid Hydrolysis (HCl 2.2N; 35°C) Curves of Some Wild Yam Native Starch

Sahoré Drogba Alexis and Amani N’Guessan George

58

Agri culture Science Developme nts , 2(7) July 2013

Table 1. Characteristic of Acid Hydrolysis Curves of Native Starch
Samples

* [%]

Dioscorea praehensilis

10

Dioscorea hirtiflora

30

Dioscorea burkilliana

5

Dioscorea dumetorum

36

Dioscorea bulbifera (bulbil)

22

Dioscorea bulbifera (tuber)

22

Dioscorea minutiflora

12

*Easily hydrolysable fractions of starch

4.

Conclusion

Native starch easily loses its ability to bind in acidic solutions and is generally modified before being used in such environments. Native
starch is therefore preferred to modify starch. However, we note that native starch extracted from wild yam species is considered less
sensitive to acid hydrolysis. It could therefore be used, among others, as additives in acidic foods without being modified.

References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]

Mestres C. (1986) Thèse de Doctorat, Université de Nantes, 1986.
Grebault J. (1984) Cuisson extrusion des produits céréaliers. Ind. Céréales, 28. 7 – 12
Kirchoff G.S.S. (1871) Mémoires, Impériale des sciences de Sain Petersburg, 4, 27
Sahoré D.A., Amani N.G. and Kamenan A. (2007) Functional Properties of Wild Yam (Dioscorea spp.) Starches, Trop. Sci, 47 (1), 33 – 37
Banks W. and Greenwood C.I (1975) Starch and its component, Edingburg University Press,
Hoover R. (2000) Acid-treated starches. Food Rev. Int., 16, 3, 369 – 392
Bernfeld P. (1955) Amylase beta and alpha (assay method) in method in Enzymology (ed. I. Colowick and Kaplan), Academic press, New York,
149-154
J.O. L 248 /CEE n°900(2008) Règlement définissant les méthodes d’analyse et autres dispositions de caractère technique;
Amani N.G., Aboua F, Gnakri D., Kamenan A. (1993): Etudes des Propriétés Physico-chimiques de L’amidon de Taro (Xanthosoma sagittifolium),
I.A.A, vol. n°110 136 – 142
Robin J. P, Mercier C, Charbonnière R and Guilbot A (1974) Cereal Chem., 51. 389

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