Effects of different drying methods on phenolic metabolites and antioxidant activity in Paederia scandens

【Objective】The study aimed to analyze the changes in phenolic metabolites and differences in antioxidant activity of Paederia scandens after different drying methods，providing theoretical basis for the development and utilization of P. scandens.【Method】Two drying methods，freeze drying and heat drying，were used to treat P. scandens，and the antioxidant capacity of phenolic substances in P. scandens after different drying methods was compared. Non-targeted metabolomics was applied for the qualitative analysis of phenolic compounds in P. scandens. After screening for differential phenolic metabolites using partial least squares discriminant analysis（PLS-DA），hierarchical clustering analysis and KEGG metabolic pathway enrichment analysis were conducted. Additionally，the correlation between the differential metabolites and antioxidant activity of P. scandens after treatment with different drying methods was analyzed.【Result】 Freeze drying and heat drying had no significant effect on the total phenol and total flavonoid contents of P. scandens （P>0.05）. The 1,1-diphenyl-2-trinitrophenylhydrazine（DPPH）radical scavenging capacity，2,2-azino-bis（3-ethyl-benzothiazole-6-sulfonic acid）diammonium salt（ABTS）cation radical scavenging capacity and copper ion reduction capacity of freeze-dried P. scandens were all higher than those of the heat-dried samples. Using ultra-high-performance liquid chromatography coupled with Fourier transform mass spectrometry，99 phenolic compounds were identified in P. scandens treated with two drying methods，including 54 flavonoids，15 coumarins and their derivatives，13 cinnamic acids and their derivatives，9 phenolics，6 isoflavonoids，and 2 flavonols. The results of principal component analysis and hierarchical cluster analysis showed that the phenolic metabolites of P. scandens treated with different drying methods were significantly different（P<0.05，the same below）. The expression levels of 15 differential metabolites in the heat drying method were significantly higher than those in the freeze drying method. A total of 25 extremely significant differential metabolites were screened out using PLS-DA（P<0.01），among which 10 metabolites were up-regulated and 15 metabolites were down-regulated. Significant changes were mainly observed in flavonoids，phenols，and coumarins and their derivatives. KEGG metabolic pathway enrichment analysis revealed that there were 7 metabolic pathways enriched with differential metabolites of P. scandens under different drying methods. The top 5 most enriched pathways were flavonoid biosynthesis，phenylpropane biosynthesis，biosynthesis of multiple secondary metabolites 1，tyrosine metabolism，and biosynthesis of stilbenes，diarylheptanes and gingerol. The 25 phenolic differential metabolites showed significant correlations with both DPPH radical scavenging capacity and copper ion reduction capacity，with 10 phenolic differential metabolites exhibiting significant positive correlations with the two indicators and 15 phenolic differential metabolites showing significant negative correlations.【Conclusion】Different drying methods applied to P. scandens do not change the types of phenolic compounds，but they have obvious effect on the content of phenolic compounds and antioxidant activity. The functional activity of P. scandens is not the result of a single metabolite，but rather the synergistic effect of multiple metabolites.