Octanal incorporated in postharvest wax of Satsuma mandarin fruit as a botanical fungicide against Penicillium digitatum

The antifungal activity of octanal against Penicillium digitatum, the causal agent of citrus green mold, was assessed by in vitro and in vivo experiments. In vitro assays results showed that the minimum inhibitory concentration and minimum fungicidal concentration (MFC) of octanal were 500 and 1000 μL/L, respectively. In vivo test results demonstrated that wax + octanal (WO; 2 × MFC) treatment but not WO (1 × MFC) treatment effectively inhibited the growth of P. digitatum after 6 d of storage at 25 ± 2 °C. The WO treatment remarkably increased the activities of antioxidant enzymes, such as catalase and superoxide dismutase, in Satsuma mandarin fruit. However, this treatment evidently decreased phenylalanine ammonia lyase activity and malondialdehyde content. The WO treatment also inhibited peroxidase activity and prevented hydrogen peroxide accumulation. Furthermore, the WO treatment did not impair the fruit quality parameters (vitamin C content, pH, coloration index, and total soluble solid content) of the tested fruit. This study provided theoretical data for the practical application of octanal to improve citrus fruit quality during postharvest storage.