Eucalyptus Globulus) Bark Extracts

industrial crops and products 29 (2009) 364–370

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Evaluation of potential applications for chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark extracts

G. Vázquez, J. González-Alvarez ∗, J. Santos, M.S. Freire, G. Antorrena

Department of Chemical Engineering, School of Engineering, University of Santiago de Compostela, Lope Gómez de Marzoa s/n, 15782 Santiago de Compostela, Spain article info abstract

Article history: The potential of chestnut shell and eucalyptus bark extracts as phenol substitutes in the Received 21 May 2008 formulation of adhesives, as chrome substitutes in leather tanning and as a source of Received in revised form 8 July 2008 antioxidants compounds has been studied. The inﬂuence of extraction conditions, type

Accepted 9 July 2008 and concentration of alkaline compounds (NaOH, Na2SO3 and Na2CO3) and temperature, on extraction yield and on extract characteristics: Stiasny number, tannin content, total phenols content, FRAP (ferric reducing/antioxidant power) antioxidant capacity and Keywords: molecular weight distribution was analysed. Chestnut shell extracts had much better Chestnut (Castanea sativa) shell properties than eucalyptus bark extracts and signiﬁcantly higher extraction yields were ◦ Eucalyptus (Eucalyptus globulus) bark obtained. The increase of temperature from 70 to 90 C not only increased the extrac- Tannins tion yield but also improved the quality of the extracts. For both materials, the 2.5% ◦ ◦ Antioxidants Na2SO3–90 C extract, together with the 2.5% NaOH–2.5% Na2SO3–90 C extract for chest- Adhesives nut shell, showed high extraction yields and the best properties for all the applications Leather tanning proposed. © 2008 Elsevier B.V. All rights reserved.

1. Introduction Tannin extracts from chestnut wood (Pasch and Pizzi, 2002), bark (Garro-Gálvez et al., 1997) and ﬂesh (Hwang et al., 2001) Castanea sativa and Eucalyptus spp. represent 5 and 27% (in have been characterized as hydrolyzable tannins; however, m3 with bark), respectively, of the total wood stock in Galicia no literature has been found about chestnut shell tannin (NW of Spain). The Galician food industry uses ∼7000 t/year of composition. Eucalyptus globulus bark extracts from different chestnuts in the production of different derivatives, such as Spanish provenances were characterized by the abundance of marron glacé and chestnut purée. The shell, which represents total phenols, polymeric proanthocyanidins and ellagitannins around 10% by weight of the chestnut, is removed in the peel- (Conde et al., 1996; Cadahía et al., 1997a). ing process and used as fuel. Eucalyptus wood is used mainly Chestnut wood tannins are of the most common hydrolyz- to produce cellulose pulp and, secondly, panels and boards. able tannins used in the leather industry. Tannins from the In both cases, eucalyptus bark is separated as a waste prod- bark of various eucalyptus species (E. grandis, E. citriodora and E. uct and also used as fuel. The aim is the development of new urophylla) were used in the formulation of adhesives for wood technologies for the valorisation of both renewable industrial derivatives (Mori et al., 2001). The shell and hull of various residues as raw materials for high-value products. nuts, such as almond (Prunus amygdalus)(Pinelo et al., 2004;

∗ Corresponding author. Tel.: +34 981 563100x16758; fax: +34 981 528050. E-mail address: [email protected] (J. González-Alvarez). 0926-6690/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2008.07.004 industrial crops and products 29 (2009) 364–370 365

Moure et al., 2007) or hazelnut (Gevuina avellana)(Moure et 2.3. Antioxidant capacity al., 2000), and the bark of several tree species (Kähkönen et al., 1999) have been evaluated as sources of antioxidant com- The antioxidant capacity of the extracts was determined by pounds. means of the FRAP assay, in which the antioxidants present in In this work, tannins extracted from chestnut shell and the sample reduce the Fe(III)/tripyridyltriazine (TPTZ) complex eucalyptus bark under different conditions (type and con- to the blue ferrous form with an increase in absorbance at centration of alkaline chemicals in aqueous solution and 593 nm. temperature) were analysed in order to establish their proper- The FRAP assay was done according to Szöllösi and ties for different potential applications including: their use as Szöllösi-Varga (2002): 0.1 mL of an aqueous solution of the phenol substitutes in the formulation of adhesives for wood extracts was transferred to a test tube and 3.0 mL of freshly derivatives, as chrome substitutes in leather tanning and as prepared FRAP reagent (25 mL acetate buffer, 300 mmol/L, pH a source of antioxidants compounds. The inﬂuence of extrac- 3.6; 2.5 mL, 10 mmol TPTZ in 40 mmol/L HCl; 2.5 mL, 20 mmol/L tion conditions on extraction yield and on Stiasny number, FeCl3·6H2O) was added. The absorbance was recorded after tannin content (hide-powder test), total phenols content, FRAP 5 min at 593 nm. The relative activities of samples were (ferric reducing/antioxidant power) antioxidant capacity and calculated from the calibration curve of l-ascorbic acid molecular weight (MW) distribution of the extracts was anal- (0.1–1 mmol/L) and the results were expressed as nmol ascor- ysed. bic acid equivalent (AAE) per mg of extract (on dried basis) (Maksimovic et al., 2005).

2. Materials and methods 2.4. Total phenols content 2.1. Raw materials Total phenols content was determined by the Folin–Ciocalteu Chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus method (Singleton and Rossi, 1965): to 0.5 mL of an aque- globulus) bark were supplied by a food and a pulp factory, ous solution of the extract, 2.5 mL of Folin–Ciocalteu reactive, respectively, both in Galicia. previously diluted with water (1:10, v/v) and 2 mL of a 75 g/L Both wastes were air-dried till equilibrium moisture con- sodium carbonate aqueous solution were added. The mixture tent, ground in a hammer mill, sieved and the fraction of waskept5minat50◦C and, after cooling, the absorbance at particle size between 0.1 and 2 mm was selected. Chemical 760 nm was measured. The phenols content was calculated composition of chestnut shell and eucalyptus bark was deter- as a gallic acid equivalent (GAE) from the calibration curve of mined in a previous work (Vázquez et al., 2008). gallic acid standard solutions (2–40 ␮g/mL) and expressed as g GAE/100 g of extract (on dry basis). 2.2. Extraction and concentration

The extraction experiments were carried out in a 2-L Pyrex 2.5. Tannin content (hide-powder test) glass reactor with mechanical stirring and temperature con- trol. Chestnut shell or eucalyptus bark and water were mixed An aqueous solution of extract (100 mL) previously vacuum fil- at room temperature, heated and, once the selected temper- tered through a 0.45 ␮m filter (to determine the soluble solids ature was attained, the alkali was added and contact time of the extract) was added to 6.25 g of hide-powder. The suspen- begun to run. After 1 h the suspension was vacuum filtered, sion was stirred for 20 min, then left 10 min at rest and finally the solid residue was washed with water and the extract filtered through a sintered glass filter. Fifty milliliters of filtrate together with the first water washings were concentrated by were evaporated to determine the non-tannins. The tannins spray-drying. The solid was dried at room temperature in (%) were obtained as the difference between the soluble solids order to calculate the extraction yield as the percentage weight (%) and the non-tannins (%). The tannin concentration in the loss of the starting raw material. aqueous solution of the extract must be between 3.75 and Solid/liquid ratio was maintained constant at 1/10 (w/w) 4.25 g/L. Otherwise the analysis should be repeated adjusting for chestnut shell and 1/15 (w/w) for eucalyptus bark. Water the extract concentration. and different alkaline chemicals such as sodium hydroxide, sodium sulphite and sodium carbonate (alone or combined) in aqueous solution were used as extraction agents at 2.6. Stiasny number different concentrations and temperature was 70 or 90 ◦C (Tables 1 and 2). The Stiasny number of the extracts, a measure of their The extraction experiments and the analysis of the extracts formaldehyde condensable polyphenols content, was deter- obtained (antioxidant capacity, total phenols content, tannin mined according to the procedure proposed by Yazaki and and non-tannin contents, Stiasny number and gel permeation Hillis (1980). The extract (0.25 mg) was dissolved in distilled chromatography (GPC) analysis) were made in duplicate and water (100 mL) and 2.5 mL of 10 M HCl and 5 mL of 37% the results averaged. formaldehyde were added. The mixture was heated under The crude extracts were redissolved in water and the reflux for 30 min. The suspension was filtered through a sin- UV–vis spectra were recorded in a Milton Roy Spectronic 1201 tered glass filter, the precipitate washed with hot water and spectrophotometer using water as a reference. then dried at 105 ◦C until constant weight. Download English Version: https://daneshyari.com/en/article/4514966

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