Ozone Micro–Nano Bubbles Application Controls Disease Development and Maintains Quality of Fresh Radix astragali

Ozone micro–nano bubbles (OMNBs) are an emerging preservation technology. However, there are few reports regarding their application in controlling postharvest diseases of agricultural products. Radix astragali, as a medicinal and edible plant, is particularly vulnerable to pathogenic microorganisms during postharvest storage, which leads to diminishing the quality and commercial value. In this study, fresh R. astragali inoculated with Penicillium polonicum was treated with different concentrations (2, 3, 4, 5, 6, 8 mg/L) of OMNBs and stored at room temperature for 28 days. The results indicate that 3 mg/L OMNBs application for 8 min effectively inhibited the development of blue mold in fresh R. astragali and preserved its quality. Then, we compared the three different treatments of micro–nano bubbles (MNBs), 3 mg/L O3, and 3 mg/L OMNBs on physiological and pathological parameters of un-inoculated fresh R. astragali during storage and analyzed the changes in the active ingredients by liquid chromatography and metabolomics. The results indicate that the 3 mg/L OMNBs treatment effectively inhibited the decline in weight loss rate, respiratory rate, firmness, browning index, and ABTS and DPPH radical-scavenging rates, as well as reduced the incidence rate and disease index of fresh R. astragali during storage. The metabolomics results suggest that the 3 mg/L OMNBs application activated the mevalonate pathway (MVA), the methylerythritol phosphate pathway (MEP), and the phenylpropanoid biosynthesis pathway to maintain the content of active ingredients such as terpenoids and flavonoids, and these findings are consistent with the results of HPLC-MS analysis.