Repurposing Hazelnut Waste Products for a Sustainable Economy: A Metabolomic Analysis of Cuticles and Shells to Highlight Their Antioxidant Potential and Inhibitory Activity against Verocytotoxic Escherichia coli

This study evaluated the functional components of hazelnut waste products (cuticles and shells) for potential use in the circular economy. HPLC-HRMS and ABTS assay were used to determine the molecules of waste products with functional properties and antioxidant capacity, respectively. The antioxidant capacity of hazelnut cuticles and shells was tested using two different methods of extraction (EtOH 50/50 and acetone 40/70) by ABTS radical cation decolorization assay. The growth inhibition effect of different extracts against porcine O138 E. coli F18+ was evaluated by the microdilution bacterial growth method and confirmed with the determination of minimal inhibitory concentration (MIC). The results showed that acetone extraction produced a higher yield of metabolites compared to ethanol extraction, and the cuticles exhibited higher antioxidant and antimicrobial potential. The acetone/water extraction led to the identification of 738 signals compared to 453 detected after EtOH/water extraction. Through metabolomic analysis, it was found that the cuticles presented a much higher quantitative and qualitative polyphenolic profile than did the shells. In addition, the ABTS assay revealed that the cuticles had a higher antioxidant capacity than did the shells. Thus, we believe that hazelnut-derived waste products show a high potential for use in a circular and sustainable economy.