Dielectric Barrier Discharge Cold Plasma Improves Storage Stability in Paddy Rice by Activating the Phenylpropanoid Biosynthesis Pathway

A nonthermal pretreatment using dielectric barrier discharge cold plasma (DBD-CP) was developed to improve the stress resistance of paddy rice during postharvest storage. The physicochemical properties, bioactive characteristics, and secondary metabolites of paddy rice were assessed after applying an optimized DBD-CP procedure, with enzyme activities and gene expression monitored over a 60 day storage period at 35 °C. A 17.06% reduction in the total color change index was noted in the DBD-CP group. Bioactive compounds, particularly gallic acid, were significantly increased, enhancing the defense mechanisms against high-temperature stress. Nontargeted metabolomics analysis indicated an upregulation of phenylpropanoid metabolism in DBD-CP-treated rice compared to controls, with notable increases in secondary metabolites such as coumaric acid, caffeic acid, and sinapic acid, suggesting potential biomarkers for stress resistance. Further verification showed significant enhancements in key enzymes of phenylpropanoid metabolism, including phenylalanine ammonia lyase (PAL), cinnamic acid-4-hydroxylase (C4H), plant coumaric acid-3-hydroxylase (C3H), and cinnamyl alcohol dehydrogenase (CAD), with increases ranging from 1.71 to 2.28 times. Gene expression levels of <i>OsPAL7</i>, <i>OsC4H4</i>, and <i>OsCAD2</i> aligned with these enzymatic changes post-DBD-CP treatment. In conclusion, DBD-CP treatment can modulate phenylpropanoid metabolism in paddy rice, thereby enhancing bioactive compound levels to reduce stress damage during high-temperature storage.