ACCELERATED LABORATORY TEST OF THREE AMAZONIAN WOOD SPECIES CALLED TAUARI, EXPOSED TO WHITE- AND BROWN-ROT FUNGI AND COLOR RESPONSE ACCORDING TO CIE L* A* B* SYSTEM

ENSAIO ACELERADO DE LABORATÓRIO DE TRÊS ESPÉCIES DE MADEIRAS DA AMAZÔNIA CHAMADAS DE TAUARI, EXPOSTAS AOS FUNGOS DE PODRIDÃO-BRANCA E PARDA E RESPOSTA COLORIMÉTRICA DE ACORDO COM O SISTEMA CIE L* A* B*

ABSTRACT

The purposes of this study were to: evaluate de natural durability of three species of tauari (Couratari guianensis Aublet, Couratari oblongifolia Ducke & R.Knuth and Couratari stellata A.C.Smith), report the colorimetric parameters according to CIE L*a*b* 1976 system and also show the appearance of control and attacked wood blocks. Two brown-rot [Gloeophyllum trabeum (Persoon ex Fries) Murril. and Lentinus lepideus Fr.] and two white-rot [Trametes versicolor (Linnaeus ex Fries) Pilat and Ganoderma applanatum (Pers. ex Wallr.)] fungi were used.Tauari wood was classed as "moderately resistant" to "resistant" when exposed toGloeophyllum trabeum, Trametes versicolor andGanoderma applanatum fungi. All extractives' contents of attacked samples decreased when compared with the control (sound wood), exceptCouratari stellata exposed to Ganoderma applanatum.Conversely, all ash contents increased when compared with the control, except Couratari stellata exposed to Gloeophyllum trabeum. All attacked wood blocks and wood meal samples were darker, except wood meal from Couratari stellata exposed toTrametes versicolor, and redder than the control. The∆E* mean value in attacked wood blocks and wood meal samples attained 29.5 and 14.3, respectively.

Keywords:
natural durability; extractives; ashes; Couratari sp.; colorimetry

RESUMO

Os objetivos deste estudo foram: avaliar a durabilidade natural de três espécies de tauari (Couratari guianensis Aublet, Couratari oblongifolia Ducke & Knuth R. e Couratari stellata A.C.Smith), relatar os parâmetros colorimétricos de acordo com o sistema CIE L * a * b * 1976 assim como mostrar a aparência dos blocos de madeira antes e após o ataque. Dois fungos de podridão-parda [Gloeophyllum trabeum (Persoon ex Fries) Murril. e Lentinus lepideus Fr.] e dois de podridão-branca [Trametes versicolor (Linnaeus ex Fries) Pilat e Ganoderma applanatum (Pers. ex Wallr.)] foram utilizados. A madeira de tauari foi classificada como "moderadamente resistente" a "resistente" quando exposta aos fungos Gloeophyllum trabeum, Trametes versicolor e Ganoderma applanatum. O conteúdo de extrativos das amostras atacadas diminuiu quando comparado com o controle, exceto Couratari stellata expostos a Ganoderma applanatum. Por outro lado, os conteúdos de cinzas aumentaram quando comparados com o controle, exceto para a madeira de Couratari stellata exposto ao Gloeophyllum trabeum. Todos os blocos de madeira atacados e as serragens tornaram-se mais escuras, exceto para a serragem de Couratari stellata exposto ao fungoTrametes versicolor, e mais vermelho do que a amostra sem ataque. O ΔE * médio do bloco de madeira e serragem, atacados, atingiram 29,5 e 14,3, respectivamente.

Palavras-chave:
durabilidade natural, extrativos; cinzas; Couratari sp.; colorimetria

INTRODUCTION

Wood holds a special place in the traditional culture because of its impressive range of attractive qualities, including aesthetic appearance, low density, low thermal expansion, and desirable mechanical strength. Among these properties, color is of considerable importance in wood used for decorative purposes (CHANG and CHENG, 2001).

The family Lecythidaceae is composed of medium size trees, occurring in tropical rain forests, especially in the neotropical region. The stands predominate in low lands and preferably occupy the canopy, although Couratari guianensisAublet and Couratari stellata A.C.Smith are emerging species (MORI and PRANCE, 1979). This family comprises approximately 400 genera and 22 species, distributed in all over the tropics.

According to Bernal et al (2011) "Tauari" is a tropical timber very commonly harvested (commercialized and exported) in the Amazon Basin due to its good physical and mechanical properties and easy workability. However, woods from several species and different origin are grouped under the name "tauari" and marketable lots are usually composed of a mixture of species. So, a species called by one name in a region might not be the same in another; moreover, one common name might be used in multiple regions but referring to different species. Also grouping of several species under same name results in an overexploitation of this "individual pseudospecies" inventories, Therefore a logger company could harvest a species that surpasses its capacity to natural regeneration. According to the literature there are 18 plant species called "tauari" within four Neotropical genera belonging to the Lecythidaceae: Allantoma (3 spp.), Cariniana (4 spp.), Couratari (9 spp.) andEschweilera (2 spp.). They reported that wood colour was very useful and helped to separate Couratari (white, yellowish or grayish) from Allantoma and Cariniana (pink, reddish or brownish).

The main natural diversity of the genus Couratari occurs in the Central Amazon, with 53% of their species. The group named tauari includesCouratari guianensis, Couratari oblongifolia, andCouratari stellata, which are among the more marketable wood species. Work carried out by the Brazilian Institute of Forestry Development - IBDF (1981, 1988), Fedalto et al. (1989), andSouza et al. (1997) presented macroscopic and microscopic descriptions, data of physical and mechanical properties, general characteristics and end uses. More information, fast and free, about these species may be retrieved from the Database of Brazilian Woods (http://sistemas.florestal.gov.br/madeirasdobrasil/), Garzón (2004), and Procópio and Secco (2008).

Natural durability, or alternatively decay resistance, is defined as the ability of wood to resist biological degradation. It is generally low in the sapwood and high in the heartwood of some species (EATON and HALE, 1993). Heartwood formation is associated with cell death, the disappearance of storage material and an increase in extractive content (BAMBER, 1976). Heartwood extractives comprise terpenoids, tropolones, flavonoids, stilbenes, and other aromatic compounds (SCHEFFER and COWLING, 1966). Extractives can protect wood from decay, add color and odor, specific grain pattern and enhance strength properties. Extractives may also inhibit setting of concrete, glues and finishes, cause problems in papermaking, contribute to corrosion of metals in contact with wood, present health hazards and affect wood color stability to light (ROWE and CONNER, 1979).

The tristimulus spectrocolorimetry technique was developed for color quality control and finds application in paints, textiles, and plastic (BILLMEYER and SATZMAN, 1981).

According to Nelson and Heather (1970), probably the color of dark-colored wood is largely controlled by extractives absorbed on and within cell walls, while textural properties (e.g. lumen diameter and wall thickness distribution) probably significantly affect the color of light-colored woods. The color of wood depends on chemical components interacting with light, i.e. the presence or absence of extractives (HON and MINEMURA, 2001). Furthermore, for the amount of heartwood extractives, there is a huge variability within and among trees, across sites, species, provenances and tree age (GIERLINGER et al., 2004; WINDEISEN et al., 2002)

There are several intrinsic factors of the wood contributing for the formation of the gross features such as figure and the color, such as the anatomical elements (BURGER and RICHTER, 1991), and still there are the chemical factors that influence the natural durability and the extractives forming chromophores compounds.

According to Janin (1988), the color of wood, mainly of heartwood, comes from gradual deposit of the degeneration of protoplasmic vegetal cell along time and from chemical substances that are found inside the fiber wall, wooden rays that selectively absorb the light in different spectral wavelengths.

The changes in wood color is more frequently measured by the CIEL*a*b* system, in accordance with the axial variation∆a* and ∆b*, which correspond to the pair of color coordinates red-green and yellow-blue, respectively, and the luminosity∆L* (MAZET et al., 1993). The luminance, which is the lightness or intensity of the color, defines the gray scale where "0" is black and "100" is white, also refers to the darkness of the wood, where darker wood usually have lower luminance than light-colored wood. Purity is related to hue and is the amount in the total color of an object. This parameter is used to characterize the color of an object both quantitatively and objectively in a physical sense.

Nishino et al. (1998), studying the colorimetry of 97 wood species from French Guiana, reported values of 69.83, 6.99, 25.63, 26.57 and 74.76 to Couratari guianensis Aubl., respectively, for L*, a*, b*, C and h*, in the radial surface, while for the tangential the values were respectively 70.53, 6.81, 24.57, 25.49 and 74.50.

With the aim of supplying more technical data information of the well marketed tauari species, the present work evaluates the natural resistance of the Couratari guianensis, Couratari oblongifolia, and Couratari stellata species exposed to brown-rot Gloeophyllum trabeumand Lentinus lepideus fungi and the white-rotTrametes versicolor and Ganoderma applanatum.It also reports alcohol-toluene extractive, ash, and color characteristics in wood meal and blocks.

MATERIAL AND METHODS

The material used was collected in Santarém- PA, and the voucher has been deposited in FPBw - Xylarium from Setor de Anatomia e Morfologia Florestal LPF/SFB according to the following numbers 000467 (Couratari oblongifolia Ducke & R.Knuth.), 001135 (Couratari guianensis Aublet.) and 001132 (Couratari stellata A.C.Smith).

The material in wood disc-shaped or wedges-shaped was used to prepare 2.5 x 2.5 x 0.9 cm wood blocks. Accelerated laboratory test was conducted according to ASTM D 2017-05 (2005) which establishes that specimen should be conditioned, before and after fungi attack in an air-forced at (50 ± 1°C), weighed, sterilized and submitted to fungus attack, in controlled environment at (27± 1)°C temperature and (70 ± 4)% relative humidity.

The brown-rot Gloeophyllum trabeum (Persoon ex Fries) Murril. andLentinus lepideus Fr. fungi and the white-rot Trametes versicolor (Linnaeus ex Fries) Pilat and Ganoderma applanatum (Pers. ex Wallr.) fungi were used. The wooden feeder used was Cecropia sp. for white-rot fungi and Pinus sp. for brown-rot.

The experimental design is shown in Table 1, consisted of three wood species, four types of fungi, with 12 samples per treatment, totaling 180 specimens. It was also conducted a blank treatment plus 36 samples as reference blocks.

Tabela 1
Número de amostras de madeira utilizadas no bioensaio
Table 1
Numbers of wood samples used in the bioassay test

Wood species	Number of wood samples
	Gloeophyllum trabeum	Lentinus lepideus	Trametes versicolor	Ganoderma applanatum	Control (blank)
Couratari oblongifolia	12	12	12	12	12
Couratari guianensis	12	12	12	12	12
Couratari stellata	12	12	12	12	12
Reference blocks	9	9	9	9	-

The mean value of colorimetric parameters were submitted to an analysis of variance (ANOVA), and to the Tukey test at 5% of significance level to evaluate the differences between color parameters of the control and attacked samples, pairwise. Further, stepwise regression analysis was conducted using color parameters and weight loss as predictors. The software used was the Statistical Program for Social Science (SPSS), version 13.0 for Windows.

The wood susceptibility to fungi attack was evaluated throughout the percentage of weight loss - WL, before and after exposure to decay, and reported as resistance classes according to ASTM D 2017-05 (2005).

Illustrations

The cross section photomacrography of the wood blocks, in stabilized condition, to control and attacked specimens was made using the binocular microscope Olympus BH2 and the stereo digital camera Olympus SZ4. Preview binning 2, exposure time of 5 milisec and 0.67 magnifying lenz were used. None surface processing was applied to the samples, except for the control to illustrate and show details of the transversal surface, which was smoothed by using a sequence of 150, 320 and 400 grit sandpaper.

Spectrocolorimetry

Percent reflectance data were collected at 10 nm intervals over the visible light spectrum (400 to 700 nm) by using a spectrophotometer Datacolor International Microflash 200D equipped with a diffuse reflectance integrator sphere. Spectral curves with resolution of 3 nm were obtained. The illuminant was D65 daylight type (xenon light), as required by Commission Internationale de Enluminure (CIE) in 1976. When measuring, a 10° standard observer and a 6 mm sensor head diameter were used, with the specular component included. Before measuring the color parameters, the equipment was calibrated following the supplier recommendations. Three measures for each sample were made and averaged as mean values.

The color variations were calculated as the difference between the samples, either woods blocks or wood meal, and the reference. To evaluate the effect of the fungi attack in the color parameters, in both surfaces of the wood blocks, the parameters a* and b* were calculated as the difference between each of the attacked block and the paired control.

For wood meal the effects of extractives withdrawal and also fungi attack were evaluated. In the first case, the color variations were calculated as the difference between control wood meals extractive-free minus unextracted. The effects of fungi were calculated between attacked wood meals minus control, both unextracted, using equations described in a previous study reported by Okino et al. (2009).

To avoid possible alteration in the color, samples were kept in darkness to reduce photo-induced or other alteration. The wood blocks were prior stabilized and oven-dried at 50°C. Then, the color parameters were measured before and after fungal attack. The same procedure was applied to the wood meal, after the preparation process.

General analysis

As to the methodology, two different faces were adopted to measure the color, referred now as the upper and the lower surfaces of the attacked specimens. After conditioning, the colorimetric parameters of the wood blocks were measured before and after fungal attack.

The sample preparation for the chemical analysis was conducted according to TAPPI T 264 om-82 (TAPPI, 1996a) with few modifications. Only the surfaces degraded by fungi were removed from the wood blocks and screened. It was collected the material that passed the 42 mesh sieve and was retained on the 80 mesh, resulting in the wood meal sample. This material was conditioned at room temperature reaching 6% to 9% moisture content.

The extractive contents in alcohol-toluene (1:2, v/v) were gravimetrically determined, in control and attacked samples, according to TAPPI T 204 om-88 (TAPPI, 1996b).

Ash content was obtained according to TAPPI T 211 om-93 (TAPPI, 1996c) for control and attacked wood meal samples.

RESULTS AND DISCUSSIONS

The used Couratari guianensis Aublet. species had medium basic specific mass (0.52 g/cm³⁾; yellowish to yellowish-gray heartwood indistinct from sapwood; imperceptible smell. Couratari oblongifolia Ducke & R.Knuth. wood had medium basic specific mass (0.49 g/cm³⁾; whitish-yellow heartwood indistinct from sapwood; characteristic smell. Couratari stellata A.C.Sm. wood had medium basic specific mass (0.65 g/cm³⁾; yellow-pale heartwood indistinct from sapwood; imperceptible smell (FEDALTO et al., 1989; IBDF, 1981).

Table 2 shows the mean values of percentage weight loss, to the three tauari woods exposed to fungi, in the accelerate laboratory test.

Tabela 2
Porcentagem de perda de peso das espécies de tauari expostos aos fungos de podridão-parda e de podridão-branca, após 12 semanas de ensaio acelerado de laboratório
Table 2
Percentage weight loss of tauari wood species exposed to brown-rot and white-rot fungi, after 12 weeks in accelerated laboratory test

Species	Brown-rot percentage weight lossa
	Gloeophyllum trabeum	Resistance class b	Lentinus lepideus	Resistance class
Couratari oblongifolia	34.58 (9.85) c	MR	6.31 (0.24)	HR
Couratari guianensis	25.01(5.17)	MR	1.93 (1.28)	HR
Couratari stellata	21.04 (4.53)	R	0.93 (0.59)	HR
	White-rot percentage weight lossa
	Trametes versicolor	Resistance class	Ganoderma applanatum	Resistance class
Couratari oblongifolia	32.34 (9.71)	MR	19.36 (4.02)	R
Couratari guianensis	28.44 (6.83)	MR	26.94 (4.09)	MR
Couratari stellata	18.46 (4.19)	R	16.74 (2.60)	R

• Where in: ^aMean values of 12 samples per fungus.^b HR = highly resistant, MR = moderately resistant and R = resistant. ^cValues in parentheses are standard deviations.

According to the data listed in Table 2,Couratari stellata was the least susceptible wood against the attack of the three out of four fungi and ranked as "resistant class". The resistance classes determined to tauari varied from "moderately resistant" to "resistant" when exposed to Gloeophyllum trabeum, Trametes versicolorand Ganoderma applanatum, and "highly resistant" toLentinus lepideus.

According to Kartal and Green III (2003), all three wood species were below the weigh loss limit of 25% to be classified as "resistant" according to the ASTM D 2017-05 standard (Figure 1). The ANOVA, taking into account only the wood species, showed that Couratari stellata suffered the lowest weight loss (15.7%). The analysis by type of fungus alone shows that Gloeophyllum trabeum and Trametes versicolor provoked the higher wood decay, above the 25% limit, and was not significantly different. Also, there is a tendency to an inverse correlation between basic specific mass and the percentage of weight loss.

Figura 1
Mean values of weight loss by fungus type (each value represents the means of 36 replications) and by wood species (each value represents the means of 48 replications). Specimens with weight loss of ≤ 25% is classified as resistant (Bars represent means of weight loss, and error bars represent standard deviations). Letters represent homogeneous groups in the Tukey test at 5% significance level.
Figure 1
Valores médios de perda de peso por tipo de fungo (cada valor representa a média de 36 repetições) e por espécies de madeira (cada valor representa a média de 48 repetições). As amostras com perda de peso ≤ 25% é classificada como resistentes (Barras representam perda de peso médio, e barras de erros representam os desvios padrão). Letras representam grupos homogêneos no teste de Tukey a nível de significância de 5%.

Special care must be taken if the wood of tauari will be exposed to environments under fluctuations and prone to the attack of Gloeophyllum trabeumor Trametes versicolor.

Figure 2 shows that the color of control sample (Couratari oblongifolia) is lighter than Couratari guianensis and Couratari stellata. Figures 3 and 4 show that specimens exposed to the white-rot Trametes versicolor fungus were clearer in color than the brown-rot Gloeophyllum trabeum. In Figure 4a the Couratari oblongifolia wood blocks attacked by Gloeophyllum trabeum, besides great wood color changes, showed clean and larger pores, whereas Couratari guianensis (4b) and Couratari stellata (4c) showed protuberant areas and cracks near the pores.

Figura 2
Photomacrography of transversal section of the control hardwood samples a: Couratari oblongifolia; b:Couratari guianensis and c: Couratari stellata. Scale bars = 1000μm.
Figure 2
Fotomacrografia da seção transversal das amostras controles de madeira a: Couratari oblongifolia; b:Couratari guianensis e c: Couratari stellata. Barra de escala = 1000μm.

Figura 3
Photomacrography of transversal section of hardwood attacked by Trametes versicolor. a: Couratari oblongifolia; b: Couratari guianensisand c: Couratari stellata. Scale bars = 1000μm.
Figure 3
Fotomacrografia da seção transversal da madeira de tauari atacada por Trametes versicolor. a: Couratari oblongifolia; b: Couratari guianensise c: Couratari stellata. Barra de escala = 1000μm.

Figura 4
Photomacrography of transversal section of hardwood attacked by Gloeophyllum trabeum. a: Couratari oblongifolia; b: Couratari guianensisand c: Couratari stellata. Scale bars = 1000μm.
Figure 4
Fotomacrografia da seção transversal de madeira de tauari atacada por Gloeophyllum trabeum. a: Couratari oblongifolia; b: Couratari guianensise c: Couratari stellata. Barra de escala = 1000μm.

According to Bernal et al. (2011) the vessels in Couratari stellata are wider than in Couratari guianensis, as shown in Figures 2a and 2c. Their SEM micrography study showed silica grains in body ray cells in the irregular form, so it may have affected positively in decay resistance as observed in the lower weight loss percentage.

The morphology of decay exhibits different pattern of structural and ultrastructural changes along the decay process. Levin and Castro (1998) reported that hyphae colonize the lumen of vessel elements, fibres and parenchyma cells causing cell wall thinning and erosion. Hyphal penetration was mainly through pits, whose inner apertures were enlarged enzymatically, this is, large holes in the wood were evident during biodeterioration. It is known that decay is not uniform, and practically unaltered tissues coexist with seriously damaged ones.

In general the white-rot fungus degrades the lignin polymer, leaving almost intact the hemicelluloses and cellulose resulting in the whitish surface of the wood. On the other hand, the brown-rot fungus attacks the polysaccharides leaving the lignin modified, thus darkening the surface of the wood.

Results in Table 3 show that Couratari stellata presented the lower extractives and ash contents. Generally, there is an inverse correlation between extractives content and weight loss. This discrepancy may be partially explained not by the amount of the extractives, but mainly by the chemical structure, where dual synergism plays a fundamental role in inhibiting fungi attack. Couratari oblongifolia andCouratari guianensis showed similar amounts of extractives and ash contents. Attacked samples showed lower extractive content values than control, except for Couratari stellata exposed to Ganoderma applanatum. It is not a common behavior, once the cleavage of the cell wall wood polymers constituents into small fragments takes place, remaining a modified lignin residuum and increasing solubility of the "extractive" component of wood (McGINNES and ROSEN, 1984). It is known that carbohydrate polymer is source of nourishment of xilophagon organisms, it is a possible explaining the decline in the extractive content of the attacked samples. The extractives content in tauari wood is in accordance with that one described in the literature for tropical hardwoods. Santana and Okino (2007) reported the extractives' content of Couratari multiflora (Sm.) Eyma, Couratari sp. andCouratari stellata A.C.Sm., of 1.1%, 1.4% and 1.0%, respectively, quite below that one obtained in this study, while for ashes the contents were 2.0%, 1.6% and 1.8%, respectively. Although the last species is the same one used in this study, the material was from a different site, tree, age and place of harvesting, explaining possible deviation in extractives' and ash contents.

Tabela 3
Percentagem média de umidade, extrativos em etanol-tolueno e cinzas em madeiras de tauari-controle e atacadas por fungos
Table 3
Percentage of moisture content, extractives in ethanol-toluene and ashes in control and attacked tauari wood samples

Percentagea		Attacked by fungi
	Control	Gloeophyllum trabeum	Lentinus lepideus	Trametes versicolor	Ganoderma applanatum
Couratari oblongifolia
Moisture content	8.18 (0.02) b	7.00 (0.16)	6.61 (0.09)	7.16 (0.10)	6.64 (0.06)
Extractives	3.17 (0.06)	2.26 (0.04)	1.65 (0.21)	2.43 (0.05)	2.17 (0.04)
Ash	0.52 (0.02)	0.63 (0.04)	0.55 (0.00)	0.60 (0.03)	0.54 (0.01)
Couratari guianensis
Moisture content	8.49 (0.04)	6.13 (0.01)	6.69 (0.40)	7.04 (0.04)	7.47 (0.31)
Extractives	3.24 (0.12)	2.40 (0.10)	1.72 (0.03)	2.09 (0.22)	2.72 (0.08)
Ash	0.52 (0.01)	0.58 (0.09)	0.57 (0.01)	0.59 (0.02)	0.57 (0.08)
Couratari stellata
Moisture content	7.59 (0.04)	6.58 (0.25)	6.45 (0.17)	7.18 (0.01)	5.80 (0.10)
Extractives	1.70 (0.11)	1.57 (0.10)	1.25 (0.13)	1.27 (0.18)	1.89 (0.13)
Ash	0.34 (0.05)	0.25 (0.08)	0.48 (0.02)	0.50 (0.01)	0.56 (0.02)

• Where in: ^a Mean values of two repetitions. ^bValues in parentheses are standard deviations.

The ash contents of the attacked samples increased when compared to control, except for Couratari stellata exposed to Gloeophyllum trabeum. Green III et al. (1997)reported a significant increment in the amount of iron, aluminum, magnesium, manganese and copper in southern pine wood inoculated with four brown-rot fungi, and maple inoculated with Trametes versicolor. Since the wood ashes are formed by oxides of these metals, a proportional increment of the ash content was expected.

Table 4 list the mean values of color parameters due to fungi effects and wood species, either in upper and lower surface of the wood blocks.

Tabela 4
Efeito dos fungos e espécies de madeira nos parâmetros colorimétricos de blocos de madeira de tauari expostos aos fungos de podridão-parda e podridão-branca, após 12 semanas em ensaio acelerado de laboratório
Table 4
Effect of fungi and wood species in colorimetric parameters of tauari woods block exposed to brown-rot and white-rot fungi, after 12 weeks in accelerated laboratory test

	CIE L*a*b*	L*	a*	b*	L*	a*	b*	∆L*	∆a*	∆b*	∆E*
		Control			Attacked			Color variations
Fungus		Upper surface wood blocksa
	Gloeophyllum trabeum	65.5 A	6.3 A	21.0 A	36.3 A	10.1 B	21.5 A	-29.3 A	3.8 A	0.5 A	29.5 C
	Lentinus lepideus	68.2 A	5.5 A	21.0 A	57.6 B	7.9 A	24.3 B	-10.6 B	2.4 A	3.3 A	11.4 A
	Trametes versicolor	67.4 A	5.4 A	20.3 A	59.2 B	13.8 C	37.5 C	-8.1 B	8.3 B	17.2 B	20.7 B
	Ganoderma applanatum	66.3 A	5.8 A	20.1 A	55.3 B	15.0 C	36.8 C	-11.0 B	9.2 B	16.8 B	22.1 B
		Lower surface wood blocks
	Gloeophyllum trabeum	66.4 A	5.8 A	21.7 A	37.5 A	9.8 B	21.0 A	-28.9 A	4.0 B	-0.7 A	29.2 C
	Lentinus lepideus	68.4 A	5.4 A	21.2 A	59.4 B	7.0 A	23.2 A	-9.0 B	1.6 A	2.0 B	9.4 A
	Trametes versicolor	67.2 A	5.4 A	20.0 A	63.3 B	12.0 C	35.1 B	-3.9 C	6.5 C	15.1 C	17.0 B
	Ganoderma applanatum	68.1 A	5.2 A	19.7 A	61.2 B	13.6 D	37.5 B	-6.9 BC	8.3 D	17.8 D	20.8 B
		Upper surface wood blocksb
Wood species		L*	a*	b*	L*	a*	b*	∆L*	Da*	Db*	∆E*
	Couratari oblongifolia	70.4 C	5.9 A	23.0 A	55.9 A	12.0 A	32.0 A	-14.4 A	6.0 A	9.0 A	18.0 A
	Couratari guianensis	67.0 B	5.8 A	19.6 A	53.2 A	11.7 A	30.3 A	-13.8 A	5.9 A	10.7 A	18.4 A
	Couratari stellata	61.7 A	5.3 A	17.6 A	50.0 A	12.1 A	29.9 A	-11.7 A	6.9 A	12.3 A	18.3 A
		Lower surface wood blocks
	Couratari oblongifolia	70.7 C	5.7 B	23.1 A	58.8 C	10.7 A	31.2 A	-11.9 A	5.0 A	8.1 A	15.2 A
	Couratari guianensis	67.3 B	5.6 A	19.7 AB	56.5 B	10.1 A	28.3 A	-10.8 A	4.5 A	8.6 A	14.5 A
Couratari stellata	63.2 A	4.9 A	17.4 A	54.4 A	11.3 A	30.1 A	-8.8 A	6.4 A	12.7 A	16.7 A

• Where in: ^a Mean values of 36 measurements (12 for each of the three wood specimens). ^b Mean values of 48 measurements (12 for each fungus). Capital letters represent homogeneous group in the Tukey test at 5% significance level. Chromaticity coordinates _a* = (along the X axis red to green) and _b* = (along the Y axis yellow to blue); _L* = lightness; ∆E* = [(∆L*)²+(∆a*)² + (∆b*)²]^1/2 is the color difference, where ∆L*, ∆a*, ∆b* is given by measured value of the attacked sample minus measured value of non-attacked sample.

In Table 4, statistical analysis was applied to observe the effects of fungi and also the wood species.

Statistically there was some correlation (R² = 0.767) between weight loss - WL and _^a* (after fungi exposure) and ∆E* as given by Eq. 1.

WL = -12.861 + 0.533∆E*_upper+ 0.265∆E*_lower + (0.243 a*_lower + 1.105 a*_upper)_attacked Equation 1

If by any means ∆E* of tauari can be estimated, this equation can be used to estimate the percent weight loss of the attacked sample.The correlation (R = 0.239) between weight loss and the parameters ^{_{a*, b*}} and ^_L* of the control samples was very low, so it is not a good estimate of the weight loss. This low correlation may be partially explained because wood is highly anisotropic or else the area of measurement was very restrict.

The colorimetric parameters did not vary extensively between upper or lower surfaces. The direct contact of the sample with soil did not restrain fungus settlement, so there was no need to worry about which sample surface is to be measured.

Camargos (1999) stated that chromatic coordinates fit the first quadrant for major reported tropical hardwood species, which were corroborated in this study. He classified the wood color ofCouratari oblongifolia as yellow-whitish and theCouratari guianensis and Couratari stellata as gray-yellowish. In this study, once lightness mean values were higher than 54 woods are considered as light color. Silva et al. (2007) reported to Couratari sp. the color parameters ^_L*, ^_a*, ^_b* of 50.4, 5.7 and 15.6, respectively. These values are similar to those found in Couratari stellata wood. Although it belongs to the same genera, the color suffers influences of samples, site, age and anatomical characteristics. Souza (1997) reported for Couratari sp. indistinct heartwood and yellowish-white to light yellowish-brown sapwood, as characterized by the Munsel color chart. Gonçalez et al. (2006) reported for wood of tauari (Allantoma lineata) the following values 57.7, 7.2 and 14.4 to ^_L*, ^_a* and ^_b*, respectively, classifying it as clear wood, gray-pinkish color.

No statistical significant difference was observed in the color parameters of the control samples at 5% significance level. The effects of brown-rot and white-rot fungi in the results of ∆a* and ∆b* increases in the upper surface, showing two homogeneous groups, while in the lower surface there were two to three homogeneous groups. The ∆E* mean value also showed that white-rot fungi belong to an intermediate group, and each brown-rot fungus fit the extreme sub-set.

Color differences (∆E*) were higher in all samples attacked by brown-rot Gloeophyllum trabeum fungus, reaching up to 29.5, decreasing in the following sequence Ganoderma applanatum, Trametes versicolor and Lentinus lepideus. The∆E* values of brown-rot fungi specimens were mainly caused by variation in the mean values of lightness (∆L*), whereas to white-rot fungi were dominantly caused by variation in ∆b*. Specimens attacked by Gloeophyllum trabeum fungus indicated a color change towards reddish, while both specimens attacked by Trametes versicolorand Ganoderma applanatum fungi indicated a color change towards yellowish. This same trend can also be observed in Figures 3 and 4.

Wood blocks attacked by both fungi types, wether in upper or lower surfaces, showed the highest perception levels (∆E*), surpassing the maximum class range reported by Cui et al. (2004), which is 6.0 - 12.0 as very appreciable, although their study was carried out only in weathered wood samples. Nelson et al. (1969) evaluated black walnut and suggested that differences of 3.5% in luminance, 4 nm in dominant wavelength and 5% in purity would be visually detectable by a normal observer. Some of this changes occurred in tauari sample, allowing visible color differences under naked eyes.

Mean values of yellow and red hue increased considerably when compared to control samples. These changes may be attributed to lignin oxidation besides others compounds plus exposure of the specimens at high moisture and longer time. Extractives should have an important role in color changes as reported by Ishiguri et al. (2003), since their constituents can also be chemically changed. As reported by Chang et al. (2000) and Chang and Cheng (2001), specimens exposed under high moisture conditions had the color darkened and eventually turned to brownish black, this effect may also strengthened the Gloeophyllum trabeum decay pattern in this study.

Despite brown-rot or white-rot, both fungi decreased the lightness of the samples, that is, all attacked samples were darker than the control. This trend was also reported by Ferraz et al. (2007), who evaluated Eucalyptus grandis wood chips biotreated byCeriporiopsis subvermispora, where final lightness of the biopulps was always slightly lower than the control pulps. However, the cause for the darkening observed in biopulps remains unclear. They also commented that aspen wood, biotreated by Phanerochaete chrysosporium followed by refiner mechanical pulping the biopulps were darker than control pulps.

After 12 weeks of exposure, no statistical difference of color parameters among the wood species was observed.

The results of the color parameters of the wood meal taking into account the effects of the extractives withdrawal and fungi exposure are presented in Table 5.

Tabela 5
Parâmetros colorimétricos em serragem de madeira de tauari expostos aos fungos de podridão-parda e de podridão-branca, após 12 semanas em ensaio acelerado de laboratório
Table 5
Color parameters in wood meal of tauari exposed to brown-rot and white-rot fungi, after 12 weeks in accelerated laboratory test

Sample	Colorimetric parametersa of wood meal
	Effect of extractives withdrawal
	Unextracted			Extractive-free				Color variations
Control	L*		a*		b*	L*		a*		b*		∆L*	∆a*	∆b*	∆E*
Couratari oblongifolia	53.6		8.1		25.9	55.5		9.2		27.3		2.0	1.1	1.4	2.7
Couratari guianensis	51.0		9.2		24.5	51.3		9.7		25.8		0.3	0.5	1.2	1.6
Couratari stellata	51.1		8.4		24.4	50.4		8.3		24.7		-0.7	-0.1	0.3	0.8
	Effect of fungus in color parameters
	Couratari oblongifolia			Couratari guianensis				Couratari stellata
Attacked by	L*		a*		b*	L*		a*		b*		L*		a*	b*
Gloeophyllum trabeum	44.4		7.7		22.3	41.6		8.4		21.7		37.4		7.9	20.6
Lentinus lepideus	48.5		7.7		23.6	48.2		8.0		22.9		50.2		6.9	23.3
Trametes versicolor	49.4		10.1		28.5	48.5		9.7		26.7		53.2		8.7	28.1
Ganoderma applanatum	49.1		10.1		28.1	45.1		10.0		26.0		49.9		8.6	27.0
	Couratari oblongifolia			Couratari guianensis				Couratari stellata
Attacked by	∆L*	∆a*	∆b*	∆E*	∆L*	∆a*	∆b*	∆E*	∆L*	∆a*	∆b*	∆E*
Gloeophyllum trabeum	-9.2	-0.4	-3.6	9.9	-9.3	-0.8	-2.9	9.8	-13.8	-0.5	-3.8	14.3
Lentinus lepideus	-5.1	-0.4	-2.3	5.6	-2.7	-1.2	-1.7	3.4	-0.9	-1.5	-1.1	2.1
Trametes versicolor	-4.2	2.0	2.6	5.3	-2.5	0.5	2.1	3.3	2.1	0.3	3.7	4.3
Ganoderma applanatum	-4.4	2.0	2.2	5.3	-5.9	0.8	1.5	6.1	-1.2	0.2	2.5	2.8

• Where in: ^a Mean values of 3 repetitions.

Unextracted wood samples of Couratari oblongifolia are brighter more yellowish than Couratari guianensis and Couratari stellata, thus matching the pattern of the control blocks in Figure 2. From these colorimetric mean values the tauari wood color was quantitatively specified, although the differences among them were quite small.

The ethanol-toluene (1:3, v/v) extracting process caused an increment in ^_L*, ^_a*and ^_b* mean values and consequently in ∆E* parameters for wood of Couratari oblongifolia and Couratari guianensis. Even in comminuted form, the Couratari oblongifoliasamples showed to be brighter and with higher color difference (∆E* = 2.7). The withdrawal of the extractives from Couratari stellata samples caused darkening, but this phenomenon is not discrepant. McGinnes and Dingeldein (1971)found that acetone extraction significantly lightened the redcedar (Juniperus virginiana L.) heartwood samples, conversely to water extraction. McGinnes Jr. (1975) reported that redcedar samples were least affected by the extraction procedure, with slight darkening of samples in the violet-blue zones of the spectrum. Also Dellus et al. (1997a) applied various treatments to the Douglas fir heartwood, and in the case of extracted wood powder by acetone/water, a good extractant for polyphenols, the red tint of heartwood (a* value) was not affected by this extraction and the lightness (L*) value did not increase. This show that even with these solvents (DELLUS et al., 1997b) a major fraction remains bound to the matrix. Extraction with the same aqueous solvent but at a higher temperature similarly failed to significantly increase the lightness of Douglas fir heartwood (ZIMMER and WEGENER, 1992).

All mean values of attacked wood meal showed a decrease in ΔL*, except for Couratari stellata sample exposed to Trametes versicolor. All mean values Δa* and Δb* increased when exposed to the white-rot fungi, conversely to the brown-rot for Δa* and Δb*. This behavior is well known by means of fungi biochemistry. Major samples were classified as appreciable (3.0 - 6.0) in terms of ∆E*, according to Cui et al. (2004), while samples exposed toGloeophyllum trabeum fungus attained the highest∆E* from ca. 10 to 14.

The lightness of the control wood meal was lower than the wood block, while ^_a*and ^_b* mean values were higher. The difference in the color measurement between wood meal and wood blocks was clear, with preference to the second form, due to no additional sample preparation and also due to higher total color difference.

Although extra care was taken to get these measurements, still some diffuse light beam may have been lost. Future recommendation is the use of a wood meal in pellet form, although this type works well as unextracted lignocellulosic material (more cohesion) than extractive-free. The acquisition of an integrator sphere equipped with smaller aperture is also well recommended.

CONCLUSIONS

The tauari wood species Couratari oblongifolia and Couratari guianensis were ranked as"resistant" to "moderately resistant" when exposed to the Gloeophyllum trabeum, Trametes versicolor andGanoderma applanatum fungi.

The wood of Couratari stellata showed the lowest extractives and ash contents. Almost all extractives' content of attacked wood samples showed a lower value than the control, conversely to almost all ash contents.

All studied specimens altered its color significantly under this experimental condition.

Wood blocks of Couratari oblongifolia were the lighter, andCouratari stellata the darker. Colorimetric parameter responses of the attacked wood blocks matched the patterns of white- or brown-rot fungus.

The attacked wood blocks showed high perception, in term of ∆E*levels, when exposed to Gloeophyllum trabeum. Ganoderma applanatumand Trametes versicolor showed no statistical difference in∆E* parameter.

The color parameters of the three wood species exposed to fungi were not statistically different.

Wood blocks showed higher total color differences than wood meal, involving less sample preparation.

The best correlation was obtained between weight loss and ∆E*and a*.

ACKNOWLEDGEMENTS

The authors are grateful to the colleagues Luiz Fernando Marques, Maria Eliete de Sousa, Hugulino de A. Dias, Júlio C. Mendes, Maria H. M. G. de Figueiredo for their technical support; Theodora R. Fischli for English revision and also the technicians Getúlio F. de Almeida, Luiz D. Santana and Ricardo P. dos Santos for their collaboration.

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Publication Dates

• Publication in this collection
  Sept 2015

History

• Received
  23 Aug 2011
• Accepted
  07 Apr 2013