Is colour an indicator for phenolic content in Tectona grandis from plantation of Côte d'Ivoire?

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T

ls

co1our an indicator for P.henolic

·

ectona grandis

from

EAK is

o,1e

of the most valuable timber widely used in the world. lt is prized for

Florence Bobelé Niamké'·'·'·'·', Nadine Amusant', Gilles Chaix', Kadio Adjumané3

, Kati-Koulibaly',

Augustin Amissa Adima', Christian Jay-Allemand'

· its colour,

aesthetic

and natural durability. A variability has

been

observed in

1 CIRAD: Unité de Recherche cl de V.alorisalion des Bois Tropinux, 34398 Montpellier Ccdu 5, Fro1nce

.· wood pr,Jperties with consequences for Forest

managers

and end-users.

1 _{CIRAD: Unité de RC"chcrchc Oiveuité Génétique et Amë:lior;ation} dei Espèces Forestières, 34398 Montpellier Cedex S, France Determir.ing

some

attributes for

earlier

characterization of wood quality may

be

useful. Wood co/nur is an important criterion of wood quality

and

depends on the chemical components of wood (HON and M1NEMURA, 2001 ).

We

assessed the use of

colorimetry to de termine the content of phenolics in the wood.

1 _{SOOEFOR, 01 BP 3770 Abidj;i.n 01} 4 UFR, Bioscicnces, Université d'Abldj.an Cocody,

01 BPV H, Abidj.m 01, CôtC" d'Ivoire \ INPHB: Unité de Chimie des E,ux et des Subst.ances Naturelles

(LACESNA)1 8.P. 1313, Yamouuoukro, Côte d'Ivoire

9 trees of teak were collected in Agboville (Séguié). Samples were taken from sapwood (5), outer heartwood (OH), middle heartwood (MH) and inner heartwood (IH).

Colorimetric values of the CIELAB system: lightness (L *), redness (a*) and yellowness (b*l were measured with a spectrocolorimeler Datacolor 200. Phenolics werc analyzed with a HPLC system coupling to a DAO detector.

OH MH IH Wm dtype OH MH IH Wood type

Pith

OH MH IH Wood type

a'

Teak sap'-' ood is lighter, less red than heartwood. The heartwood is rcddcr with di·;tancc from pith. Tcak wood is evcntly yellow through the stem. Heartwo )d of lvorian teak is red as teak from Togo but redder than leak from lndia (KOKUSTE ET Al., 2006; THULASIDAS ET AL., 2006).

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c ~

• UM2: Laboratoire de Biochimie et de Physioloci, Vécé1al,s, UMR 188 (DIAPC),

- - · · - -Eq_u-ip~ ·i·~-•g_•_•è_,._. ,_•0_9!~~-~,llie._,_c._d_«_o_s_F,_•"_'_' _ _ _,) 7 6 Phenolic content 5 (mg.eq.S·metoxy -4 Oavone.g OW 1) 3 DW = Dl)I Weight

I

OH

I

MH IH OQl OQ2 OPl

I'

Threc major cornpounds wcrc characlcrized as tcctoquinone (Q1), 2-hydroxymethylanthraquinone (Q2) and an unidentiiied compound named P1. Q·I was present in sapwood and accumulated in heartwood. Q2 and P1 appeared and accumulated only in heartwood. Phenolics increased from the outer to the middle heartwood and decreased in the inner heartwood. The change in colour of wood was conspicuous with the darkening and the reddening of wood.

EJe

~;~;~99

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5 0 Elenlo.!oU97 R10.69 RMSfP258 V,IIUC pri:!clic1cd Ql

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1: . DO

(,

r53

Q

.

.

2 0 0 20 40 10 20

X-value measured X-value measured

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---·-·--·---'

The relationships between T x and

Ql

contents and colour coordinates follow the equations: Tx

=

101

.1 -1.2L* -1.18a*. 0.2b*;

R2

=

₀

_.

_78;

_{P <}

_0.0001

Ql

=

56.3 - 0.68L

•

- 1.07a*; R

2

=

₀

_.

_{69; P}

_<

_0.0001

. . l'LS regression shows high correlations between colour

coordinates and contents of total soluble phenolics (TX) and Q1: it suggests that more phenolics accumulated in teak wood, darker the wood is.

j

Accumulation of phenolics were found to coincide with the change in colour of wood. Therefore, colour measurement could be used as a lool for determining phenolics content of wood. Total soluble phenolics were predicted using L •, a • and b* (78% of total variation). More investigations are required for optimal calibration using a large scale of samples Lo perform the prediction.

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The authors thank SOOEFOR for its technical support during sampling for this study.

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