Upgrading hazelnut skins: Green extraction of polyphenols from lab to semi-industrial scale

Hazelnut skins (HS) are usually managed as waste; however, this by-product is a source of bioactive compounds, with potential applications in feed and food sectors. Phenolic compounds can be extracted using green protocols combining enabling technologies and green solvents. This work investigates subcritical water extraction (SWE) of bioactive compounds from HS. A laboratory-scale study was performed on four different batches, with significant batch-to-batch heterogeneity. The evaluation of polyphenolic profiles and antioxidant activities afforded promising results compared to the benchmark of reflux maceration. To evaluate process effectiveness, the extraction protocol was replicated on a semi-industrial plant that processed 8 kg of matrix. Downstream processes have been optimized for scale-up, demonstrating the effectiveness of SWE in retaining product concentration and bioactivity avoiding excipients in spray-drying phase. Hazelnut extracts exhibited antibacterial properties against animal- and food-borne pathogens, supporting their potential use as sustainable feed ingredients for improved hazelnut production and animal farming practices.