Preservation of Litchi Fruit with Nanosilver Composite Particles (Ag-NP) and Resistance against Peronophythora litchi

Litchi (Litchi chinensis Sonn.) is susceptible to infection by Peronophythora litchi post storage, which rapidly decreases the sensory and nutritional quality of the fruit. In this study, the effects of nanosilver (Ag-NP) solution treatment on the shelf life of litchi fruit and the inhibition of P. litchi were examined, and the underlying mechanisms were discussed. For investigations, we used one variety of litchi ('Feizixiao'), dipping it in different concentrations of Ag-NP solution after harvesting. Meanwhile, we treated P. litchi with different concentrations of Ag-NP solution. According to the data analysis, litchi treated with 400 μg/mL Ag-NPs and stored at 4 °C had the highest health rate and the lowest browning index among all the samples. In the same trend, treatment with 400 μg/mL Ag-NPs produced the best results for anthocyanin content, total soluble solids content, and titratable acidity content. Additionally, according to the results of the inhibition test, 800 μg/mL Ag-NP solution had a 94.97% inhibition rate against P. litchi. Within 2-10 h following exposure to 400 μg/mL Ag-NP solution, the contents of superoxide dismutase, peroxidase, and catalase in P. litchi gradually increased and peaked, followed by a gradual decline. At this time, the integrity of the cell membrane of P. litchi could be broken by Ag-NP solution, and the sporangia showed deformed germ tubes and abnormal shapes. Taken together, these results suggested that Ag-NP treatment inhibited respiration and P. litchi activity, which might attenuate litchi pericarp browning and prolong the shelf life of litchi. Accordingly, Ag-NPs could be used as an effective antistaling agent in litchi fruit and as an ecofriendly fungicide for the post-harvest control of litchi downy blight. This study provides new insights into the application of Ag-NP as an antistaling agent for fruit storage and as an ecofriendly fungicide.