Industrial Crops and Products 21 (2005) 71–79

Composition and chemical variability of the oleoresin ofPinus nigrassp.laricio from Corsica

Serge Rezzi, Ange Bighelli∗, Vincent Castola, Joseph Casanova

UMR CNRS 6134, Equipe Chimie et Biomasse, Université de Corse, Route des Sanguinaires, 20000 Ajaccio, France

Received 15 April 2003; accepted 23 December 2003

Abstract

Eighteen samples of oleoresin ofPinus nigrassp.laricio were harvested in six locations in Corsica. Eight diterpene acids, sixneutral diterpenes and�-pinene were identified and their contents calculated by13C NMR spectroscopy, following a procedurerecently developed in our laboratories. The results were submitted to chemometric analysis (k-means and principal componentanalysis) and two clusters were distinguished with respect to the contents of levopimaric acid and dehydroabietic acid.© 2004 Elsevier B.V. All rights reserved.

Keywords: Pinus nigrassp.laricio; Oleoresin; Chemical composition; Chemical variability; Diterpenes;13C NMR

1. Introduction

Pine oleoresin is an important forestry product,which is traditionally obtained by tapping the bark(bark chipping) of pine tree and collection of the re-sulting exudate. Oleoresins are complex mixtures ofacidic and neutral diterpenes together with a more orless important fraction of volatile compounds (mono-and sesquiterpenes). In the industry, the crude ole-oresin is converted by steam distillation into gumturpentine (volatile compounds) and gum rosin (diter-penes), both gums in turn are processed into chemicalindustrial products such as food gums, adhesives,coatings, printing inks, disinfectants, cleaners, phar-maceuticals, fragrances and flavoring.

∗ Corresponding author. Tel.:+33-4955-24123;fax: +33-4955-24142.

E-mail address:ange.bighelli@univ-corse.fr (A. Bighelli).

Several studies have been carried out on the char-acterization of pine oleoresin. The main componentsare neutral monoterpenes (mostly�-pinene) andditerpene acids. Neutral diterpenes and sesquiter-penes are also present at appreciable to moderateamounts. Several compositions, exhibiting bicyclicditerpenes (labdanes), tricyclic diterpenes (abietanesand pimaranes) and macrocyclic diterpenes (cem-branes) as main components have been reported inthe literature depending on the pine species andthe geographical origins (Iconomou and Valkanas,1966; Tobolski and Zinkel, 1982; Hafizoglu, 1983;Walter et al., 1985; Weißmann and Lange, 1987;Lange and Weißmann, 1987, 1988, 1989; Fiebachand Kraemer, 1993; Lange and Stevanovic Janežic,1993; Lange et al., 1994a,b; Cheung et al., 1994;Lange and Spanoudaki, 1995; Song et al., 1995;Sunzel et al., 1997; Coppen et al., 1998; Arrabalet al., 2002).

0926-6690/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.indcrop.2003.12.008

72 S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79

Pinus nigra Arnold (European black pine) is na-tive to Europe and Asia. The species is divided intofive subspecies, among themP. nigra ssp. laricio(Poir.) Maire (=P. laricio Poir.), is widespread inCalabria and Sicily (Italy) and Corsica (France). InCorsica,P. nigra ssp.laricio constitutes forests cov-ering 22000 ha. It is a tree up to 50 m high with astraight trunk and grey to dark brown bark grow-ing on supramediterranean and mountainous terrainat altitudes of 900–1800 m (Gaussen et al., 1993;Gamisans and Marzocchi, 1996). This tree is ex-ploited for timber production under the control of theOffice National des Forets (ONF).

As part of our ongoing work on the chemical char-acterization of the extractives of species growing wildin Corsica (Castola et al., 2000, 2002; Rezzi et al.,2001a,b), the aim of this study was to characterize theoleoresin ofP. nigra ssp.laricio, to observe the ho-mogeneity or conversely the chemical variability ofits composition, and to compare the composition withthose of other species of pine.

2. Material and methods

2.1. Plant material

Eighteen samples of oleoresin ofP. nigra ssp.lar-icio, obtained by tapping the bark of individual adulttrees growing wild in the six most important forestsof Corsica (Aitone, Ghisoni, Melo, Valdoniellu, Verdeand Vizzavona, three samples per location) were col-lected in July and August 1999 (Fig. 1).

2.2. 13C NMR spectra

All the 13C NMR spectra were recorded on aBruker AC 200 Fourier Transform spectrometer op-erating at 50.323 MHz for13C, equipped with an As-pect 3000 computer and a 10 mm probe. The spectrawere recorded in deuteriochloroform, with all shifts(δ) referred to internal tetramethylsilane (TMS), withthe following parameters: pulse width (PW): 3�s(flip angle 30◦); acquisition time: 1.3 s and relaxationdelay D1: 0.1 s (total recycling time 1.4 s). The datawere zero filled from 32 to 64 K data table with aspectral width (SW) of 12,500 Hz (250 ppm); com-posite phase decoupling (CPD) of the proton band;

digital resolution of 0.382 Hz/pt; line broadening (LB)of 1 Hz was applied before Fourier transform. Thespectra of the resins were recorded with 200–250 mgof raw material diluted in 2 ml of CDCl3 added with10–12 mg (weighted at the precision of 0.1 mg) ofdiglyme (internal standard for quantitative determina-tions), 5000 acquisitions were accumulated for eachsample.

2.3. Identification and quantitative determinationof diterpenes

13C NMR was carried out on the whole samplewithout previous separation of the components. Iden-tification of the components was led according to anexperimental procedure and a computerized methoddeveloped in our laboratories and adapted toditerpenes (Rezzi et al., 2002). The components wereidentified by comparison of the values of the carbonchemical shifts in the mixture spectrum with thoseof reference spectra compiled in a computerized databank. Each compound is identified by taking intoaccount three parameters, directly available from thecomputer program: (i) the number of observed sig-nals with respect to that expected, (ii) the differencebetween the chemical shift of each signal in the mix-ture and in the reference (�δ), (iii) the number ofoverlapped signals of carbons belonging to two com-ponents which possess fortuitously the same chemicalshift.

The mass percentage (%mC) of each diterpenewas determined following the procedure recently de-veloped by our group which provided satisfactoryaccuracy and precision (Rezzi et al., 2002). From the13C NMR spectrum, the mean value of the area of theprotonated carbons of each diterpene (AC) was cal-culated and compared to that of the two methylenesof diglyme (AD) which was used as internal standard.The calculated amountmC (mg) of each diterpene,was determined using the formula (1) and its subse-quent mass percentage was then calculated.

mC = 2AC × MC × mD

AD × MD(1)

where mD is the amount (mg) of diglyme,MD themolecular weight of diglyme, andMC the molecularweight of the considered diterpene. The factor 2 isdue to the symmetry of diglyme.

S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79 73

Fig. 1. Sampling of the oleoresins ofPinus nigrassp. laricio from Corsica.

2.4. Chemometric analysis

Principal component analysis (PCA) was performedusing Statgraphics Plus 2.1 (Uniwin Plus, France),K-means clustering was performed usingK-meanspartitioning program (Pierre Legendre, Canada).

3. Results and discussion

Identification and quantitative determination of themajor components of 18 samples of oleoresin were

carried out by using a method recently developed inour laboratories and based on the computer aided anal-ysis of the 13C NMR spectrum of the crude oleo-resin (Rezzi et al., 2002). The results were submittedto chemometric analysis. In the 18 samples, we iden-tified and quantified, using13C NMR spectroscopy,15 compounds (Fig. 2), i.e. eight resinic acids (abi-etic acid1, dehydroabietic acid2, neoabietic acid3,palustric acid4, levopimaric acid5, isopimaric acid6,pimaric acid7a, and sandaracopimaric acid7b), sixneutral diterpenes (pimaral7c, pimarol7d, isopimaral8, isocembrol9a, 4-epi-isocembrol9b and cembrene

74 S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79

H

H

COOH 1

HCOOH

2

H

H

COOH 3

H

H

COOH5

H COOH

4

H

H

COOH 6

R1

R3

R2

7a-7d

H

H

H

CHO8

H

1110

R1 R2

9a-9b

Fig. 2. Compounds identified in the oleoresins ofP. nigrassp.laricio from Corsica.1: abietic acid,2: dehydroabietic acid,3: neoabietic acid,4:palustric acid,5: levopimaric acid,6: isopimaric acid,7a: pimaric acid (R1 = COOH, R2 = CH=CH2, R3 = CH3), 7b: sandaracopimaricacid (R1 = COOH, R2 = CH3, R3 = CH=CH2), 7c: pimaral (R1 = CHO, R2 = CH=CH2, R3 = CH3), 7d: pimarol (R1 = CH2OH,R2 = CH=CH2, R3 = CH3), 8: isopimaral,9a: isocembrol (R1 = OH, R2 = CH3), 9b: 4-epi-isocembrol (R1 = CH3, R2 = OH), 10:cembrene, and11: �-pinene.

10) and one monoterpene (�-pinene11), which repre-sented from 75.5 to 88.7% of the whole compositionof each resin (Table 1). According to the intensitiesof the unassigned signals in the13C NMR spectrum,all the unidentified compounds were minor compo-nents. The acidic fraction, which represented from 46to 66% of the identified compounds, was the majorone while neutral components accounted for 17–36%of the composition.

Seven diterpene acids, abietic acid (4.2–13.5%),dehydroabietic acid (2.3–17.8%), neoabietic acid(2.8–11.8%), levopimaric acid (2.7–26.0%), palustricacid (6.8–15.0%), pimaric acid (2.1–5.7%) and isopi-maric acid (1.8–7.6%) were present in the 18 samples.Similarly, the neutral oxygenated diterpenes isocem-brol (1.8–10.5%) and 4-epi-isocembrol (1.7–11.3%)and the monoterpene�-pinene (3.6–16.8%) were iden-tified in all samples. Conversely, sandaracopimaric

S.

Re

zzie

ta

l./Ind

ustria

lCro

ps

an

dP

rod

ucts

21

(20

05

)7

1–

79

75

Table 1Chemical composition of the 18 resins ofP. nigra ssp. laricio harvested in six locations of Corsica

Components Vizzavona Ghisoni Verde Melo Aitone Valdoniellu

1 (II)a 2 (II) 3 (I) 4 (I) 5 (II) 6 (II) 7 (I) 8 (I) 9 (II) 10 (II) 11 (I) 12 (I) 13 (II) 14 (I) 15 (II) 16 (II) 17 (II) 18 (II)

Abietic acid 1 5.5 9.2 4.2 6.7 8.8 8.7 7.7 5.6 7.5 4.3 6.5 4.6 9.5 4.7 7.0 13.5 8.3 9.7Dehydroabietic acid2 8.7 8.9 3.2 6.2 8.8 13.1 6.0 2.3 12.7 12.7 5.8 4.3 7.8 3.7 8.3 14.5 17.8 10.6Neoabietic acid3 9.0 7.0 8.2 11.8 11.0 7.0 8.2 10.9 7.3 6.7 9.2 9.9 5.3 8.9 7.1 3.6 2.8 9.0Palustric acid4 9.3 8.4 12.9 10.0 15.0 11.5 7.9 12.2 9.5 10.0 9.5 12.9 7.1 8.4 7.4 6.8 8.6 11.3Levopimaric acid5 12.8 7.3 26.0 19.5 11.7 13.2 15.9 21.0 12.7 9.8 22.7 24.9 8.7 17.0 10.0 2.7 4.9 10.8Isopimaric acid6 5.2 4.5 3.6 5.7 4.0 4.2 4.3 4.3 5.0 4.4 1.8 4.1 7.6 3.7 2.8 6.4 5.9 6.6Pimaric acid7a 5.5 5.7 3.6 4.2 4.6 2.8 4.5 5.1 5.4 4.9 2.3 5.0 4.6 2.6 2.6 2.1 4.9 5.6Sandaracopimaric acid7b 0.6 0.7 0.7 1.0 – 1.6 1.2 1.6 1.5 – – – 0.9 – 0.9 – – 1.2Pimaral7c 1.2 1.3 – 1.2 – 0.9 – 1.3 1.0 – – 1.3 0.8 0.8 – – 1.0 1.5Pimarol 7d – – – 0.7 – 0.9 – – – – – – – – – – – 0.8Isopimaral8 – 0.9 – 1.0 – 1.0 – 0.6 0.9 – – 1.7 – 0.7 – – – 0.8Isocembrol9a 10.5 6.2 1.8 6.6 4.5 4.0 5.0 5.0 4.4 10.5 4.8 5.8 6.4 8.9 9.9 8.6 4.8 4.24-epi-isocembrol9b 11.0 7.2 1.7 7.4 7.5 4.2 5.7 5.3 5.0 11.3 5.0 6.4 6.3 9.9 10.0 9.2 5.4 5.5Cembrene10 – – – – 1.6 – – – – – – – – – – – – –�-Pinene11 5.5 14.9 16.8 6.7 4.2 8.7 12.2 13.0 6.7 10.9 13.0 3.6 15.7 15.0 16.4 8.1 11.1 4.2

Total 84.8 82.2 82.7 88.7 81.7 81.8 78.6 88.2 79.6 85.5 80.6 84.5 80.7 84.3 82.4 75.5 75.5 81.8

a Sample (cluster).

76 S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79

-10

20

-10 30axis 1 (58,1%)

axis

2 (

20,4

%)

Cluster ICluster II

16 17

18 5

9 1

610

2 13

15

12

4

8117

143

Fig. 3. Principal component analysis scatterplot of 18 samples of resin ofPinus nigrassp. laricio from Corsica.

acid (0.6–1.6%), pimaral (0.8–1.5%), and isopimaral(0.6–1.7%) were identified respectively in 11, 11 and8 samples, while pimarol (0.7–0.9%) was detected inthree samples and cembrene (1.6%) was present onlyonce at a content observable by NMR.

The results of the 18 analyses were submitted tochemometric analysis in order to distinguish clusters.K-means analysis, taking into account the mass per-centages of the 14 diterpenes and�-pinene in the 18samples, suggested the existence of two principal clus-ters within the resins ofP. nigra. This partitioning wasthus corroborated by principal component analysis inwhich the first two axes accounted for 58.1 and 20.4%,respectively (Fig. 3).

Samples belonging to cluster I (seven samples)were characterized by a high content of levopimaricacid (mean:M = 21.0%, standard deviation: S.D. =3.8) (Fig. 4). The other important components were�-pinene (M = 11.5%, S.D. = 4.7), palustric acid(M = 10.5%, S.D. = 2.1), neoabietic acid (M =9.6%, S.D. = 1.4), 4-epi-isocembrol (M = 5.9%,S.D. = 2.5), abietic acid (M = 5.7%, S.D. = 1.3)and isocembrol (M = 5.4%, S.D. = 2.1). The contentof the remaining components did not exceed 5%.

In samples belonging to cluster II (11 samples), themean content of levopimaric acid (M = 9.5%, S.D. =3.4) is much less important than in cluster I (Fig. 4).It is of the same magnitude than those of other acids:dehydroabietic acid (M = 11.3%, S.D. = 3.2), palus-tric acid (M = 9.5%, S.D. = 2.4) and abietic acid(M = 8.4%, S.D. = 2.4). The contents of neutral

diterpenes 4-epi-isocembrol (M = 7.5%, S.D. = 2.5)and isocembrol (M = 6.7%, S.D. = 2.7) were a littlebit more important than in cluster I.�-Pinene was alsopresent at appreciable amount (M = 9.7%, S.D. =4.5). The proportion of the other products was lessthan 5% (Fig. 4).

Only a few studies reported the chemical com-position of resins ofP. nigra. They concerned: (i)the acidic fraction of the resin of pines from Greece(Iconomou and Valkanas, 1966), Spain and Yu-goslavia (Tobolski and Zinkel, 1982) and, Russia andBulgaria (Hafizoglu, 1983); and (ii) the neutral diter-pene fraction of resins ofP. nigra of Austrian origin(Lange and Weißmann, 1987, 1989).

It appears that, the chemical composition of sam-ples belonging to cluster I differs from most of thatreported in the literature. Indeed, in the samples fromYugoslavia and Spain (Tobolski and Zinkel, 1982),levopimaric acid represented 5–6% of the acidicfraction while, in our samples, this acid reached16–26% of the whole composition i.e. 27–43% ofthe identified acid diterpenes. In the samples fromGreece (Iconomou and Valkanas, 1966) and Russia(Hafizoglu, 1983), abietic acid and isopimaric acidrepresented, respectively, 16.7–23.0 and 9.6–20.0%of the composition of the acidic fraction while in oursamples, these two compounds reached only 4.2–7.7and 1.8–5.7% of the global composition i.e. 7.0–12.8and 3.0–9.5% of the acidic compounds. Conversely,the chemical composition of the acidic fraction ofsamples from Bulgaria is quite similar to that of our

S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79 77

Fig. 4. Mean chemical composition of samples of clusters I and II. Grey: mean, hachured: standard deviation.

samples belonging to cluster I (Hafizoglu, 1983).Concerning the samples of cluster II, they could bedistinguished from Greek, Spanish and Yugoslavianresins in which dehydroabietic acid was identifiedonly at very low concentrations, while this compoundwas present at higher contents (7.8–17.8% of thewhole composition) in our samples. However, thechemical composition of the acidic fraction of theresin of P. nigra from Russia (Hafizoglu, 1983) isclose to that of samples of cluster II.

The comparison of Corsican pine resin with theresin of P. nigra of Austrian origin is more diffi-cult since in the last one, only the chemical com-

position of the minor neutral diterpene fractions isreported (Lange and Weißmann, 1987, 1989). Nev-ertheless, samples from Corsica (clusters I and II) inwhich isocembrol and 4-epi-isocembrol represented1.8–10.5 and 1.7–11.3%, respectively, of the wholecomposition, differed from those of Austrian ori-gin in which these two diterpene alcohols were notreported.

Otherwise, a few studies concerning the chemicalcomposition of resins of several species ofPinushave been published. The resins ofP. nigra ssp.lar-icio of Corsica could be distinguished from thoseof P. pinaster(Arrabal et al., 2002) P. montezumae

78 S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79

(Lange and Spanoudaki, 1995), P. sylvestris(Langeand Weißmann, 1988; Lange and Stevanovic Janežic,1993), P. massoniana(Weißmann and Lange, 1987),P. merkusii(Weißmann and Lange, 1987), P. luchen-sis (Weißmann and Lange, 1987) by the occurrenceof isocembrol and 4-epi-isocembrol. They differedalso from the 22 species belonging to theStrobus,Parrya andPinussections from China (P. sibirica, P.bungeana, P. taiwanensis, etc.), in which these twomacrocyclic alcohols were not reported (Song et al.,1995). Conversely, isocembrol has been identifiedin the resins ofP. peuce(Lange et al., 1994a) andP. heldreichii (Lange et al., 1994b). However, thesetwo pine species can be differentiated fromP. nigrassp. laricio since their resins exhibited higher con-tents of cembrol and isopimaric acid (P. peuce) orlimonene (P. heldreichii).

From these results, we conclude that the oleoresinsof P. nigra ssp.laricio from Corsica can be classifiedinto two clusters in function of the contents of levopi-maric acid and dehydroabietic acid and both composi-tions could be distinguished from most of the otherP.nigra as well as those of otherPinusspecies reportedin the litterature.

Acknowledgements

We are indebted to Collectivité Territoriale de Corse(CTC) and Agence De l’Environnement et Maıtrise del’Energie (ADEME) for a research grant (SR).

References

Arrabal, C., Cortijo, M., Fernàndez de Simon, B., Garcia-Vallejo,M.C., Cadahia, E., 2002.Pinus pinasteroleoresin in plus trees.Holzforshung 56, 261–266.

Castola, V., Bighelli, A., Casanova, J., 2000. Intraspecific chemicalvariability of the essential oil ofPistacia lentiscusL. fromCorsica. Biochem. Syst. Ecol. 28, 79–88.

Castola, V., Bighelli, A., Rezzi, S., Melloni, G., Gladiali, S.,Desjobert, J.M., Casanova, J., 2002. Composition and chemicalvariability of the triterpene fraction of dichloromethane extractsof cork (Quercus suberL.). Ind. Crops Prod. 15, 15–22.

Cheung, H.T.A., Fu, S.L., Smal, M.A., 1994. Inhibition of plateletaggregation by diterpene acids fromPinus massonianaresin.Arzneimittel-Forschung 44, 17–25.

Coppen, J.J.W., James, D.J., Robinson, J.M., Subansenee, W.,1998. Variability in xylem resin composition amongst natural

populations of Thai and FilipinoPinus merkusiide Vriese.Flav. Fragr. J. 13, 33–39.

Fiebach, K., Kraemer, L.R., 1993. Resins, Natural in Ulmann’sEncyclopedia of Industrial Chemistry, vol. A23. VCHPublishers, Bremen, pp. 73–88..

Gamisans, J., Marzocchi, J.F., 1996. La Flore Endémique de laCorse. Edisud, Aix-en-Provence.

Gaussen, H., Heywood, D.H., Chater, A.O., 1993. In: Pinus, L.,Tutin, T.G., Burges, N.A., Chater, A.O. (Eds.), Flora Europaea,vol.1. Cambridge University Press, Cambridge.

Hafizoglu, H., 1983. Wood Extractives ofPinus silvestrisL., Pinusnigra Arn. and Pinus brutia Ten. with special reference tononpolar components. Holzforshung 37, 321–326.

Iconomou, N., Valkanas, G., 1966. Über die Zusammensetzung desharzbalsams einigerPinus-Arten Griechenlands. PharmaceuticaActa Helvetiae 41, 59–63.

Lange, W., Weißmann, G., 1987. Zusammensetzung derNeutralteile des Balsamkolophoniums vonPinus silvestrisL.,Pinus nigra austriacaEndl. undPinus pinasterAit. Holz alsRoh-und Werkstoff. 45, 345–349.

Lange, W., Wei�mann, G., 1988. Composition ofPinus sylvestrisL. gum oleoresin from different sources. Holz als Roh- undWerkstoff. 46, 157–161.

Lange, W., Weißmann, G., 1989. Die Zusammensetzung derDiterpenkohlenwasserstoffe des Harzbalsams vonPinus nigraaustriaca Endl., Pinus silvestrisL. und Pinus pinasterAit.Holzforshung 43, 359–362.

Lange, W., Stevanovic Janežic, T., 1993. Chemical compositionof somePinus sylvestrisL. oleoresins from southern Serbia,Bosnia and Makedonia. Holzforschung 47, 207–212.

Lange, W., Spanoudaki, M., Stevanovic Janežic, T., 1994a. Thecomposition of Balkan white pine (Pinus peuceGriseb.)oleoresin. Holzforschung 48, 368–370.

Lange, W., Stevanovic Janežic, T., Spanoudaki, M., 1994b.Cembratrienols and other components of white bark pine (Pinusheldreichii) oleoresin. Phytochemistry 36, 1277–1279.

Lange, M., Spanoudaki, M., 1995. The composition of an oleoresinof Pinus montezumaeLamb. from Guatemala. Holz als Roh-und Werkstoff 53, 68–71.

Rezzi, S., Bighelli, A., Mouillot, D., Casanova, J., 2001a.Composition and chemical variability of the needle essentialoil of Pinus nigrasubsp.laricio from Corsica. Flav. Fragr. J.16, 379–383.

Rezzi, S., Cavaleiro, C., Bighelli, A., Salgueiro, L., Proençada Cunha, A., Casanova, J., 2001b. Intraspecific chemicalvariability of the leaf essential oil ofJuniperus phoeniceasubsp. turbinata from Corsica. Biochem. Syst. Ecol. 29, 179–188.

Rezzi, S., Bighelli, A., Castola, V., Casanova, J., 2002. Directidentification and quantitative determination of acidic andneutral diterpenes using13C NMR spectroscopy. Applicationto the analysis of oleoresin ofPinus nigra. Appl. Spectrosc.56, 312–317.

Song, Z., Liang, Z., Liu, X., 1995. Chemical characteristics ofoleoresins from Chinese pine species. Biochem. Syst. Ecol.23, 517–522.

S. Rezzi et al. / Industrial Crops and Products 21 (2005) 71–79 79

Sunzel, B., Söderberg, T.A., Johansson, A., Hallmans, G., Gref,R., 1997. The protective effect of zinc on rosin and resin acidtoxicity in human polymorphonuclear leukocytes and humangingival fibroblasts in vitro. J. Biomed. Mater. Res. 37, 20–28.

Tobolski, J.J., Zinkel, D.F., 1982. Variation in needle and cortexresin acids during shoot development inPinus sylvestris, P.nigra, andP. strobus. Forest Sci. 28, 785–796.

Walter, J., Delmond, B., Pauly, G., 1985. Les acides résiniquesdes aiguilles et des tissus corticaux de pins maritimes (Pinus

pinaster Ait.) des Landes et de Corse: présence de l’acideanticopalique dans les aiguilles des pins d’origine Corse.Comptes Rendus de l’Académie des Sciences Paris série III301, 539–542.

Weißmann, G., Lange, W., 1987. Composition of neutralsfrom gum rosin of Pinus massoniaLamb., Pinus merkusiiJungh., andPinus luchuensisMayr. Holzforschung 41, 147–154.