Semi-industrial scale upcycling strategy for hazelnut skin subcritical water extraction.

The current call for the advancement toward more sustainable and effective methodologies in waste minimization and valorisation can be addressed through the implementation of green extraction technologies. Recognised as so called “enabling technologies”, t hese methods encompass innovative approaches aimed at extracting primary and secondary metabolites from a wide range of biomass sources. Overall, the adoption of green extraction strategies provides a sustainable alternative to conventional practices, avoi ding the use of hazardous solvents, decreasing energy and time, enhancing extraction capacity, and mitigating operational risks. In this work, we assessed the efficacy of subcritical water extraction (SWE) for recovering bioactive compounds from hazelnut s kins. Initially, a preliminary investigation was conducted on laboratory scale, where different hazelnut skin samples were subjected to SWE. These samples were then evaluated for their polyphenol profile (total phenolic content, tannin content and monomeri c characterization), antioxidant (DPPH·, ORAC, metal chelating features), and antimicrobial activity , adopting as a benchmark an hydroalcoholic reflux maceration protocol. The promising results achieved on laboratory scale were replicated for one cultivar on a semi industrial scale to evaluate the process effectiveness, in terms of energy consumption and e xtract quality, under real plant production conditions. In detail, a pilot working with 150 L and 9 kg of matrix per batch was exploited, processing up to 200 kg of skins. In the scale up investigation, the optimal drying methods was assessed by comparing spray drying with freeze drying at the laboratory level, as well as with an industrial spray dryer. This study paves the way for the exploitation of green hazelnuts skins extracts as a feed ingredient, increasing the sustainability of both hazelnut production and animal farming. The significant growth of the hazelnut market highlights their residues as a potential negative cost source of bioactive compounds , while subcritical water extraction aligns with Circular Economy principles for waste valorisation.