Pergamon

0308-1978(95)00085-Z

Biochemiwl S)stematics and Ecolow. Vol 23, No. 710, pp. 843-848.1988 Copyright 0 1885 Elsevier Science Ltd

Printed in Great Britain. All rights reserved 0305-1978/95 69.50+0.00

Composition and Properties of Albizia lebbeck Gum Exudate

MARITZA MARTINEZ,” GLADYS LE6N DE PINTO,? SOFiA ALVAREZ,’ NOLA GONZALEZ DE TROCONIS,” EDGAR OCANDOS and

CARLOS RIVASS ‘Centro de lnvestigaciones en Quimica de 10s Productos Naturales, Facultad de Humanidades y Educaci6n.

Universidad del Zulia, Maracaibo, Venezuela; SCentro de Quimica, lnstituto Venezolano de lnvestogaciones Cientlficas (IVIC), Caracas 1010, Venezuela

Key Word Index-Albizia lebbeck; Leguminosae; gums; uranic acid materials; 13C-NMR spectroscopy; chemotaxonomy.

Abstract-An analytical study has been made of six gum specimens from Albiziia lebbeck, Lagumin- osae. Galactose, mannose, arabinose, glucuronic acid and its 4-O-a-methyl analogue are present in all the specimens studied. Rhamnose was not detected according to sugar analysis and spectral data. The absence of this sugar, the high acidity and the relatively low limit viscosity number contrast with the values reported previously for one African sample of A. lebbeck. The lead content is much higher than that recorded for other Albizia gums. 13C-NMR spectrum of this gum, in deuterium oxide, shows good resolution.

Introduction Albizia Durazzini is a complicated genus according to botanical observation (Allen and Allen, 1981). This contention is supported by the analytical data now available for Albizia gums. This paper presents data of six gum specimens of A. lebbeck (L.) Benth. This gum has been reported as a gum arabic substitute (U.S. National Academy of Sciences, 1979).

Materials and Methods Origin end pudfication of tie gum samples. Gum samples, light yellow in colour, were collected in November 1983 by MSc. Sofla Alv&ez after 2 weeks of an incision being made at the trunk level. Gum specimens l-5, Table 1, were collected in the Municipio Maracaibo, Zulia State, Venezuela. These specimens were located closely. Sample 6 was collected in Cabimas, east of Lake Maracaibo, Zulia State. Sample 5 was collected from a tree infected by fungus. The identification of voucher specimens was confirmed by Lit. Carmen Clamens, a botanical taxonomist of Univenidad del Zulia, Venezuela. The gum exudates were purified as described previously (Anderson et al., 1984; Martinez et al., 1992).

Ana&ical methods. The standard methods for the analysis of gum exudates have been described (Anderson and Cree, 1968; Anderson and Bell, 1975). Sugar composition was determined by the phenokulphuric acid method (Dubois et al, 1956). Optical rotations at equilibrium were measured in water at 30°C. Nitrogen contents were determined with a Parkin-Elmer 240 Elemental Analyser. Metals were determined by atomic absorption, using a Perkin-Elmer 3100 spectrophotometer. Methylation (Purdie and Irvine, 1903; Haworth, 1915) and methanolysis of the gum were done and the methylglycosides were studied by GLC (Lebn de Pinto et al., 1993). 13C-NMR spectra (Figs 1 and 2) were recorded with a Bruker AM-300 spectrometer. Data points (6000-7000) were accumulated overnight at 37°C and with complete proton decoupling. The spectra width was 5000 Hz and they were calibrated by the addition of 1,4-dioxane to the samples (666.67 ppm). The sample (150 mg) was dissolved in deuterium oxide (1 ml).

tAuthor to whom correspondence should be addressed.

(Received 5 October 1994; accepted 11 ./u/y 1995)

843

844

TABLE 1 . ANALYTICAL DATA FOR GUM SPECIMENS FROM ALBIZIA LEBBECK

M. MARTiNF_.Z ETAL.

Samples

Maracaibo Cabimas Africa*

1 2 3 4 5 6 7

Moisture (%) 10.30 13.41 11.91 14.57 14.50 1 6.13 11.9 Ash (%)1" 2.20 5.30 4.48 4.89 1.70 5.40 6.0

Nitrogen (%)1 0.18 0.19 0.18 ND 0.18 0.23 0.24 Hence protein (%)t 1.12 1.18 1.12 ND 1.12 1,43 1.60

[~]D in H 2 0 (°)1" +45 +44 4-44 +45 +50 +50 +6

Intrinsic viscosity (ml g 1)t 38 40 37 66.5 41.0 67 142 Equivalent weight (g)t 1173 1 248 1199 1178 1197 1130 1 970

Hence uronic acids (%)1" 1 5 14 14 1 5 1 5 1 6 9

NeutTal sugar composition after hydrolysis (%)1" Galactose 49 50 50 50 52 58 55 Arabinose 32 32 32 32 29 23 21 Mannose 4 4 4 3 4 3 6 Rhamnose 0 0 0 0 0 0 9

"Anderson and Morrison, 1990.

tCorrected for moisture.

~1~ I 1 i r I ~ I I [ I i ¢ i I I I I i I l ~ i i I I

2 0 0 f 5 0 I O0 5 0 © ppm

FIG. 1.13C-NMR SPECTRUM OFALBIZIA LEBBECK GUM, IN DEUTERIUM OXIDE. U = uronic acids.

Results The data obtained for the analytical parameters are presented in Table 1. The cationic composition of the ash, obtained at 550°C, is shown in Table 2. The methylation analysis of the gum is observed in Table 3. Tables 4 and 5 contain the interpretation of 13C-NMR spectra of A. lebbeck gum, which are exhibited in Figs 1 and 2.

Discussion Albizia lebbeck, widespread in Venezuela, exudes a clear gum, in contrast with the red brown colour reported for this gum from the African species (Anderson and Morrison, 1990). The gum specimens studied are soluble in cold water. It has been confirmed in this species and in many bearing gum species, by the authors, that the

COMPOSITION OF GUM EXUDATE

a - A r o f -1 ~

845

A

I I i I I 0

G - t '

i I i I I I ' I i 108 106 104 102 I OO

ppm

a - A r a f - 3 '

B

. . . . . . . . so' . . . . . . . . . . . . 7 o . . . . 6o' . . . . ppm

FIG. 2. EXPANSION OF 13C-NMR SPECTRUM OF ALBIZlA LEBBECK GUM, IN THE RANGE 99-110 PPM (2A) AND IN THE RANGE 60-85 PPM (2B). Araf =arabinofuranose. Arap= arabinopyranose. G =~8-D-galactopyranose. U==4-O-methyl-~- D-glucuronic acid. U = J~-o-glucuronic acid.

gum has the highest solubility when collected from the tree as soon as the gum is exuded and air-dried (Lebn de Pinto, 1990).

The analytical data, Table 1, of the gum from the six Venezuelan specimens of A. lebbeck reveal that they are very similar. They all have low nitrogen contents. The limit viscosity number (39 ml g- l ) is comparable to A. harveyi and A. adianthifolia but lower than the value reported for an African A. lebbeck gum sample (Anderson and Morrison, 1990). The relatively high positive specific rotation, the low acidity and the absence of rhamnose in Venezuelan samples contrast with the results published for the African sample and for otherAIbizia gums (Anderson and Morrison, 1990).

The presence of mannosa, as has been reported in otherAIbizia gums (Anderson and Morrison, 1990), is of greater diagnostic significance. This sugar was also observed in some Anacardiaceae (Anderson et aL, 1974; Lebn de Pinto et al., 1994a) and Combretaceae gums (Anderson and Bell, 1977). The calcium content is

846 M. MARTiNEZ ETAL.

TABLE 2. CATIONIC COMPOSITION OF THE ASH FROM ALBIZIA LEBBECK

Cations I~g g 1 ash; 550°C

Aluminium 1500 Cadmium 20 Calcium 307 400 Chromium 0 Cobalt 70 Copper 22 Iron 95 Lead 2100 Magnesium 31 400 Manganese 80 Nickel 230 Potassium 56 400 Sodium 108 600 Silicon 9900 Titanium 0 Zinc 100

TABLE 3. METHYLATION ANALYSIS OFALBIZIA LEBBECK GUM

Methyl ethers T ° (min) Linkage

2,3,5-Mes-L-Ara 0.67 L-Araf (1 --* 2,3,4-Mes-L-Ara 0.98 L Arap (1 2,4-Me2-L-Ara (2.25); 2.36 --*3) L-Arap (1 2,5-Me2-L-Ara (2.25), 3.21 ~3) L-Araf (1 2,4,6-Me3-D-Gal 3.96; 4.26 ~3) o-Galp (1 2,3,4-Me3-D-Gal 5.71; 6.02 ~6) D-Galp (1 2,4-Me2-o-Gal 1 2.33; 14.04 ~3,8) o-Galp (1 2,3,4-Me3-o-GIcA? 2.42; 2.82 D-GIcA (1-4

*Relative to methyl-2,3,4,6-tetra-O-methyl-~- D-glucopyranoside. tAs methyl ester methyl glycoside.

TABLE 4.13C-NMR SPECTRAL DATA" OF NEUTRAL SUGARS IN ALBIZIA LEBBECK GUM EXUDATE

Type of linkage C-1 C=2 C-3 C-4 C-5 C-6

-*3) J]-D-Galp (1 ~ 1 03.84 71.06 82.07 68.78 75.33 (Le6n de Pinto, 1993) 69.01

105.00 71.20 83.00 69.30 75.37

~6 ) [3=D-Galp (1 ~ 1 03.84 70.28 72.06 67.78 73.60 (Cartier et aL, 1987) 103.30 70.40 72.80 67.80 73.00

eL- L-Araf (1 ~ 109.48 82.07 76.45 84.11 61.40 (Beck and Pedersen, 1983) 110.90 82.30 76.50 84.90 62.00

~3 ) ~-L-Araf (1 ~ 1 08.11 81.20 84.11 84.11 61.40 (Odonmazig et aL, 1994) 109.50 81.45 85.22 84.10 62.31

~3 ) JS-L-Arap 1 01.50 67.78 74.21 --= 62.84 (J6ao et aL, 1988) 101.70 62.97

1 01.20t 67.58 74.48 65.85 62.76

13-L-Arap (1 --, 100.82 69.37 69.94 69.94 63.34 (Beck and Pedersen, 1 983) 101.00 69.40 69.90 70.00 63.80

61.27

61.80

68.29 68.10

"Values relative to the signal of 1,4*dioxane (866.5 ppm). "~Joseleau, 1 977.

COMPOSITION OF GUM EXUDATE

TABLE 5. ~3C-NMR SPECTRAL DATA* OF URONIC ACID RESIDUES IN A. LEBBECK GUM EXUDATE

847

Type of linkage C-1 C-2 C-3 C-4 C-5 C-6 4-O-Me

4-O-Me-cc-o-GIcA (1 -, 99.27 72.06 73.60 82.83 70.28 59.85 (Utille et aL, 1986) 99.44 60.21

99.73 99.70 72.20 73.30 82.70 70.80 61.10

~-D-GIcA (1-* 104.34 75.33 76.45 73.60 76.67 176.83 (Hamer and Perlin, 1986) 104.00 75.50 77.10 73.30 77.50 177.50

"Values relative to the signal of 1,4-dioxane (866.5 ppm).

comparable to that reported for gums from Pereskia guamacho (Le6n de Pinto et aL, 1994b), Cercidium praecox (Lebn de Pinto et aL, 1994c) and some Anacardiaceae (Lebn de Pinto et aL, 1994a) while the sodium content is relatively high in comparison with the values reported for other Leguminosae gums (Anderson et aL, 1990). The lead content is much higher than recorded previously (Anderson and Morrison, 1990; Anderson et aL, 1990; Le6n de Pinto et aL, 1994a). The cationic content of a gum depends on the composition of the soil upon which the trees grew. The results support the assumption that Albizia gums must be avoided as food additives (Anderson and Morrison, 1990).

Albizia lebbeck gum shows, in deuterium oxide, a very well resolved 13C-NMR spectrum (Figs 1 and 2). Chemical studies of this gum, Tables 1 and 3, and previous results of this gum (Lebn de Pinto et aL, 1989) and of analogous polymers (Lebn de Pinto, 1991; Le6n de Pinto et aL, 1993) led to unequivocal signal assignments. The spectrum shown in Fig. 1 contains resonances due to galactose, arabinose and uronic acid residues, (Tables 4 and 5). The expansion of the anomeric region (99- 110 ppm), Fig. 2a, reveals the presence of at least five different linkages. These resonances are attributed to 4-O-methyl-¢-o-glucuronic acid (99.73 ppm) (Utille et aL, 1986; Lebn de Pinto et aL, 1994c), I~-L-arabinopyranose (101.54 ppm) (Bock and Pedersen, 1983; Odonmazig et aL, 1994), I~-o-galactopyranose (103.84 ppm) (Defaye and Wong, 1986; Lebn de Pinto, 1991;), I~-D-glucuronic acid (104.35 ppm) (Hamer and Perlin, 1976; /e6n de Pinto et aL, 1994c) and ¢-L-arabinofuranose residues (108.11; 109.48 ppm) (Lebn de Pinto, 1991; Lebn de Pinto et aL, 1993). The expansion in the range 60-85 ppm, Fig. 2b, shows, in addition to hydroxyl secondary carbon atoms, the presence of 3-O- (82.07 ppm) (Lebn de Pinto et aL, 1993), 4-O- (79.54 ppm) and 6-O-galactose (68.29 ppm) (Lebn de Pinto et aL, 1994d), 3-O-Cc-L- arabinofuranose residues (84.10 ppm) (Joseleau et aL, 1977; Le6n de Pinto, 1991; Odonmazig et aL, 1994). On the other hand there are signals attributed to B-D- glucuronic acid and its 0~-4-O-methyl derivative, Table 5.

The sugar and methylation analyses and the spectral evidence reveal that interesting structural features are involved in the complex molecular structure of A. lebbeck gum.

Acknowledgement--The authors thank the University of Zulia, Consejo de Desarrollo Cientlfico y Humanistico (CONDES) for financial support.

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848 M. MARTINEZ ETAL

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