Enhancement of postharvest longan fruit quality through chitosan (CTS)-induced modulation of energy and proline metabolism

Chitosan (CTS), a biologically safe preservative, is crucial for post-harvest treatment of fruit and vegetables, yet its regulatory mechanisms remain poorly understood. Our research on various CTS concentrations in longan fruit post-harvest showed that 1.5% CTS curtailed Weight loss and malondialdehyde content while enhancing soluble solid content, carotenoids, ascorbic acid, total phenols, and flavonoids. Transcript-level analysis revealed that 1.5% CTS maintains longan fruit quality by modulating energy and amino acid metabolism pathways. Further evaluations demonstrated increased energy charge, adenosine triphosphate (ATP), and adenosine diphosphate (ADP) levels, alongside elevated activities of H⁺-ATPase, Ca²⁺-ATPase, cytochrome C oxidase, and succinate dehydrogenase in CTS-treated fruit. CTS also upregulated genes like H⁺-ATPase1, SDH1, SDH6, CCO5b-2, and CCO6b-2, boosted proline content, and enhanced activities of proline-metabolizing enzymes Δ1-pyrroline-5-carboxylic acid synthase (P5CS) and ornithine-ծ-aminotransferase (OAT), while reducing pyruvate dehydrogenase (PDH) activity. These results suggest that CTS effectively modulates gene expression and enzymatic functions related to energy and proline metabolism, enhancing the preservation of longan fruit freshness during storage.