Untargeted Metabolomics Reveals the Effect of Carbon Dots on Improving the Shelf Life of Postharvest Goji Berries (Lycium barbarum L.)

<i>Lycium barbarum</i> L. (goji berry) undergoes rapid quality deterioration after harvest owing to its high water activity and abundant reactive oxygen species (ROS). Carbon-dot-mediated photodynamic treatment (CD-PDT) has recently been shown to extend shelf life by modulating ROS-scavenging and defense enzymes, yet the global metabolic reprogramming that supports this protection remains unresolved. Here, we applied ultra-high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)-based untargeted metabolomics to decode the metabolic footprint of CD-PDT in freshly harvested goji berries. Our results revealed a total of 17,603 differentially expressed metabolites between the treatment and control groups under both positive- and negative-ion modes. Principal component analysis indicated that CD-mediated PDT significantly altered the metabolic profile of fresh goji berries. The treatment activated the phenylpropanoid biosynthesis pathway, promoting the accumulation of compounds such as kaempferol-3-sophoroside, kaempferol-3-O-β-D-glucoside, and galactoside, thereby enhancing the antioxidant capacity of the fruit. Furthermore, CD-mediated PDT induced the tricarboxylic acid cycle, providing sufficient energy to support the phenylpropanoid biosynthesis pathway. In conclusion, these findings provide the systems-level evidence that CD-PDT orchestrates a coordinated activation of primary and secondary metabolism in postharvest goji berries, establishing a mechanistic framework for preservation of horticultural products.