J. of Supercritical Fluids 70 (2012) 137–145 Contents lists available at SciVerse ScienceDirect The Journal of Supercritical Fluids jou rn al h om epage: www.elsevier.com/locate/supflu Supercritical fluid extraction of triterpenic acids from Eucalyptus globulus bark Marcelo M.R. de Melo, Eduardo L.G. Oliveira, Armando J.D. Silvestre, Carlos M. Silva ∗ CICECO, Department of Chemistry, University of Aveiro, Aveiro 3810-193, Portugal a r t i c l e i n f o Article history: Received 14 May 2012 Received in revised form 29 June 2012 Accepted 30 June 2012 Keywords: Supercritical fluid extraction Triterpenic acids Modeling Eucalyptus globulus Bark a b s t r a c t Eucalyptus globulus bark contains four significant families of compounds, namely triterpenic (TT) acids (betulinic, betulonic, oleanolic and ursolic acids, and the acetylated forms of the latter two), long chain aliphatic alcohols, fatty acids, and sterols. The first group is the most abundant and possesses demon- strated bioactivity, which raises the importance of this biomass. The supercritical fluid extraction (SFE) of E. globulus bark was carried out in this work with carbon dioxide at 100, 140 and 200 bar, and 40, 50 and 60 ◦ C, and the extracts were analyzed by GC–MS. The results are compared with those obtained by Soxhlet with dichloromethane, and the influence of the operating conditions upon the global yield and the indi- vidual yields of the triterpenic acids is discussed in detail. The acetylated TT acids imparted a large effect on the extraction yields, as they appeared in large concentrations on the extracts independently of their absolute loadings in the bark. The polarity of the free acids, higher than that of their acetyl derivatives, justifies this behavior. Modeling calculations were also performed for interpreting the SFE results. The experimental observations are in agreement with predictions accomplished for the solubilities and mass transfer fluxes of ursolic acid and 3-acetylursolic acid that were chosen as key TT acids in the process. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In a globalized world the competition drives the prices of prod- ucts down, forcing industries to look for alternatives to increase their profits. One possible path is to upgrade secondary low-value streams into new and high-value products. This idea, applied to industries that have natural raw materials as main raw materials, is the basis of the biorefinery concept [1,2]. Pulp and paper industry is one of the major industries of the agro-forestry sector. In production of paper the first step is to extract cellulose fibers from raw wood [3]. On arrival to the mill, the wood is debarked and the bark is burned for power generation. Eucalyptus species are the most important fiber sources for pulp and paper production in southwestern Europe (Portugal and Spain) and south America (Brazil and Chile), where this sector has observed a fast growing during the last few years [4]. The total Euca- lyptus planted area in Brazil, Chile, Portugal and Spain is around 5.7 million ha [5] and it was estimated that in 2010 they would be pro- ducing together around 14.7 million ton of Eucalyptus spp. pulp, representing 81% of the total Eucalyptus spp. wood pulp that will be produced worldwide [6]. In the Portuguese context, Eucalyptus globulus is the dominant species in terms of pulp and paper pro- duction, and the third in terms of forest area (about 672.000 ha), ∗ Corresponding author. Tel.: +351 234401549; fax: +351 234370084. E-mail addresses: marcelo.melo@ua.pt (M.M.R. de Melo), elgo@ua.pt (E.L.G. Oliveira), armsil@ua.pt (A.J.D. Silvestre), carlos.manuel@ua.pt (C.M. Silva). representing nearly 31% of the E. globulus area planted worldwide [7]. In a medium size pulp mill using E. globulus wood as feed- stock and producing 5 × 10 5 tons of bleached pulp per year, about 1 × 10 5 tons of bark are produced [8] indicating that there is a pos- sibility for upgrading this side stream if high value compounds are present in the bark. Freire et al. [9] and Domingues et al. [8] studied the com- position of E. globulus bark, the most used for papermaking in Portugal. Among the many compounds quantified by gas chromatography–mass spectrometry (GC–MS), several high-value triterpenic acids such as betulinic, betulonic, oleanolic and ursolic acids as well as the acetylated forms of the latter two were identi- fied. These triterpenic acids (Fig. 1) are powerful anti-oxidants and have anti-inflammatory and anti-cancer activities [10–13], making them considerably valuable and their extraction from the low-value bark worthwhile in terms of scale of the papermaking process. Some triterpenic acids have also been reported in extracts from dif- ferent raw materials, such as birch [14], alder [15], greater plantain [16], sea buckthorn [17] and quince [18]. Freire et al. [9] and Domingues et al. [8] reported also that the highest concentrations of extractives were found in the external part of E. globulus bark with about nine times the yield of the inner bark, despite the fraction of outer bark (1–3 mm) being much smaller than the inner bark (∼10 mm). Also, triterpenoids are the major constituents of the outer bark extractives obtained by Soxh- let dichloromethane extraction, making this part of the bark more interesting for an industrial valorization of this low-value stream from papermaking process. 0896-8446/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.supflu.2012.06.017