Antioxidant activities and chemical profiles of pyroligneous acids from walnut shell

Three kinds of pyroligneous acids were prepared from walnut shell at different temperature ranges (low: 90–150 °C, SP1; middle: 151–310 °C, SP2; and high: 311–550 °C, SP3). The chemical profiles of the acids were established by GC–MS. Antioxidant activities of the acids were investigated from the aspects of DPPH free radical scavenging capacity, hydroxyl free radical scavenging capacity, superoxide anion radical scavenging capacity, reducing power, and anti-lipid peroxidation capacity. The results indicated that the chemical constituents of pyroligneous acids were similar, mainly phenols, organic acids, ketones, and furan derivatives. However, the contents of each constituent in three acids varied. All the pyroligneous acids exhibited antioxidant activity, but with different levels. The acid SP3 collected from high temperature range showed the strongest antioxidant activity, followed by those from middle (SP2) and low (SP1) temperature ranges. It was considered that the strongest antioxidant activity of SP3 was due to its highest content of phenols among the three acids. It is hopeful to develop food antioxidant from SP3.