Total antioxidant activity of hazelnut skin (Nocciola Piemonte PGI): Impact of different roasting conditions

The thin brown perisperm (skin) that envelops hazelnut kernels is usually removed after roasting process, leading a phenolic-rich by-product. Principal aim of this work was to characterise the total antioxidant activity of phenolic extracts obtained from roasted "Nocciola Piemonte PGI" hazelnuts skin. Different extraction solvents (methanol, acidified methanol, ethanol, acidified ethanol, and acetone/water) and different protocols (cold solvent-assisted extraction and semi-automated Soxhlet extraction) were employed. The influence of different roasting degree (180 °C/10 min and 180 °C/20 min) was also investigated. DPPH ^{{radical dot}} and ABTS ^{{radical dot}+} radical-scavenging methods, ferrous ions chelation activity and inhibition of lipid peroxidation investigated in this study demonstrated significant antioxidant properties for hazelnut skin phenolics. The main mechanism involved appeared the antiradical activity, strictly related to the total phenolic content (r = -0.8798 and -0.8285 for DPPH ^{{radical dot}} and ABTS ^{{radical dot}+} assays, respectively). The acidification of extraction solvents led to a significant decrease of antiradical activity, whilst the different roasting conditions significantly influenced the chelation activity and the inhibition of lipid peroxidation, showing higher effectiveness for high-roasted hazelnut skin extracts. Conversely, the direct measure of the antioxidant capacity of defatted hazelnut skins revealed higher ABTS ^{{radical dot}+} scavenging properties for medium-roasted sample.