Industrial Crops and Products 36 (2012) 172–176 Contents lists available at SciVerse ScienceDirect Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop Valorization of chestnut husks by non-isothermal hydrolysis Noelia González López, Andrés Moure ∗ , Herminia Domínguez, Juan C. Parajó Departamento de Enxe˜ nería Química, Facultade de Ciencias de Ourense, Universidade de Vigo, Edificio Politécnico, As Lagoas, 32004 Ourense, Spain article info Article history: Received 23 June 2011 Received in revised form 31 August 2011 Accepted 6 September 2011 Available online 20 October 2011 Keywords: Chestnut husks Autohydrolysis Alkaline hydrolysis Ethyl acetate Antioxidants Membranes abstract Chestnut is a valuable fruit with traditional food applications due to its nutritional value. The shell accounts for around 10% of the fruit weight and have no commercial applications, so they are destined for fuel. The development of alternative applications for the shells could contribute to valorization of the major constituents and to an integral utilization of renewable resources of low cost and residual origin according to a sustainable development philosophy. Husks come from two different peeling treatments, a dry dehusking process and a wet dehusking process. Husks from the dry process contained more lipophilic compounds as those hulls coming from the wet dehusking process. Treatments of chestnut husks were performed to release tannins and hemicelluloses components. High temperature extraction (HTE) was the selected technology, and aqueous and alkaline media were the solvents chosen. Treatments allowed the solubilisation of 37.7% of the chestnut husks, with maximum values of 55.5% of phenolic compounds solubilisation at treatment temperature of 180 ◦ C. The higher antioxidant activity had a maximum value of 1.87 g Trolox/gram of extract at 160 ◦ C. The extract produced under the optimal processing alkaline conditions was processed by membrane technology and the phenolic concentration in the final product was about 15% higher than the initial phenolic concentration in the hydrolyzates. This product showed an antioxidant activity comparable to that of synthetic antioxidants. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Chestnut (Castanea sativa) is a valuable fruit with traditional food applications due to its nutritional value. The shell accounts for around 10% of the fruit weight and in the industrial manufacture of marron glacé and chestnut purée the chestnut shell is removed during the peeling stage. At present, shells have no commercial applications and are destined for fuel. The development of alterna- tive applications for the shells could contribute to valorization of the major constituents and to an integral utilization of renewable resources of low cost and residual origin according to a sustainable development philosophy. The extraction of phenolic compounds from chestnut hulls using organic solvents (Vázquez et al., 2008) and the extraction with alkaline aqueous solutions (sodium sulfite, sodium carbonate and sodium hydroxide) were reported (Vázquez et al., 2009, 2010). These authors proposed the application of the extracted pheno- lics as phenol substitutes in the formulation of adhesives for wood derivatives, as chrome substitutes in leather tanning and as antiox- idants. During the alkaline extraction of phenolic compounds the temperature selected was 70–90 ◦ C, in the range of those used in ∗ Corresponding author. Tel.: +34 988368892; fax: +34 988387001. E-mail address: amoure@uvigo.es (A. Moure). industrial scale for the extraction of tannins for wood adhesives and leather tanners. However, the need for chemical free processes and the successful utilization of high pressure water extraction pro- cesses for the extraction of food antioxidants (Garrote et al., 2003, 2004, 2008; Conde et al., 2008, 2011) could suggest the suitabil- ity of trying higher temperatures in the absence of chemicals; an alternative not previously reported for this material. Autohydrolyis is an environmentally friendly technology for biomass fractionation. The catalytic species responsible for the hydrolytic degradation of hemicelluloses are the hydronium ions from water autoionisation and the organic acids generated in the process. The resulting liquors contain a mixture of sugar oligomers, monosaccharides, sugar-decomposition products and acetic acid. The solid phase from treatments is enriched in cellulose, which is hardly altered during autohydrolysis, enabling its further uti- lization for a variety of purposes. The autohydrolysis processing of chestnut shells has not been studied and it could be advantageous not only due to operational and environmental reasons. Despite the higher phenolics extraction yield at higher pH, the extraction selec- tivity was enhanced at lower pH, allowing higher purity, Stiasny number and antioxidant activity of the tannin extract (Vázquez et al., 2009). The present work is aimed at assessing the feasibility of a non isothermal treatment to solubilise the hemicelluloses and tannin fractions of chestnut husks and to recover fractions with 0926-6690/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2011.09.002