The depletion of the fossil resources entails that the modern society must face two important challenges: the substitution of fossil-based products by biomass-based ones and the change from a linear economy towards a circular model, which could allow establishing a global sustainable bio-economy. To accomplish these great challenges, in the last decades the employment of by-products and residues from the agro-food industry to manufacture added-value products has been explored. This would constitute an important step towards economically sustainable and environmentally friendly industrial processes. In this scenario, waste products of lignocellulosic nature represent an attractive, inexpensive and renewable feedstock for the manufacture of biofuels, energy, chemicals and polymers. Chestnut shells are rejected lignocellulosic residues from the agro-food industry with promising possibilities as a suitable feedstock to be used under a biorefinery perspective. These by-products have been employed as a source of antioxidants, mono- and oligosaccharides and to prepare adsorbents for pollutants removal. The development of alternative applications for the chestnut shells could contribute to the integral valorisation of their main constituents. In this work, the hydrothermal treatment of chestnut shells was proposed with a double purpose: to assess its suitability for the solubilisation of the hemicellulosic fraction and phenolic compounds and to determine the optimal conditions that allow the obtaining of the maximum concentration of hemicellulosic oligosaccharides with the minimum amount of monosaccharides and degradation products in the liquid phase. The yield in hemicellulosic oligosaccharides and phenolic compounds is a key parameter for the economic evaluation of the hydrothermal process. This process would permit a selective fractionation of the feedstock as it is designed to solubilise a high percentage of hemicelluloses and phenolic compounds leaving a solid enriched in cellulose and lignin. The obtained results showed that the temperature that enabled the obtaining of the highest concentration of total oligosaccharides and the maximum total phenolic compounds was 180 ºC.
