Synergistic Effects of Salicylic Acid and Calcium Oxide Nanoparticles on Physiological and Biochemical Quality of Fresh-Cut Lettuce During Cold Storage

Fresh-cut lettuce rapidly deteriorates during storage, and developing safe strategies to maintain its quality is critical. This study evaluated the effects of 2 mM salicylic acid (SA), 100 mg L−1 calcium oxide nanoparticles (CaNP), and their combination (CaNP + SA), and an untreated control on the physiological and biochemical quality of fresh-cut Lactuca sativa L. var. crispa stored for 18 days at 5 ± 1 °C. Treatments were assessed through measurements of total soluble phenolics (TSP), membrane stability index (MSI), chlorophyll components (Chl a, Chl b, Total Chl), chlorophyll stability index (CSI), relative chlorophyll content (SPAD), weight loss (WL), cutting resistance (CR), and color parameters. Both SA and CaNP + SA significantly delayed senescence and oxidative degradation compared with the control. The CaNP + SA combination showed the most comprehensive protection, exhibiting the lowest WL (3.91%) and the highest MSI and CSI values, indicating enhanced membrane integrity and pigment stability. SA alone maintained elevated TSP, SPAD, and chlorophyll contents, supporting its antioxidative and metabolic regulatory roles. Correlation analysis revealed strong positive relationships among MSI, CSI, SPAD, and chlorophyll variables, while WL and CR were negatively associated with these traits. PCA clearly separated treatments, with SA and CaNP + SA clustering with stability-related parameters. Overall, CaNP + SA effectively preserved membrane function, pigment structure, and water balance, representing a promising postharvest strategy for extending the shelf life of fresh-cut lettuce.