Valorization of chestnut husks by non-isothermal hydrolysis

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.

► Hydrolytic processes to extract chestnut husks were evaluated.
► The highest phenolic release was performed with alkaline treatment.
► Antioxidant capacity of hydrolyzates was screened using scavengers, chelating and oil emulsion stabilizing assays.
► Ultrafiltration–diafiltration process with polymeric membranes increased the phenolic compounds in alkaline media.