Transcriptome analysis revealed the effects of preharvest carvacrol spraying on postharvest antioxidant activity and cell wall metabolism in peppers

Pepper is susceptible to softening and decay during storage and transportation, resulting in loss of fruit quality and severely affecting the commercial value of peppers. To investigate the effects of preharvest carvacrol spraying on postharvest antioxidant capacity and fruit softening in peppers, we applied a 0.015 mg/mL carvacrol solution to the peppers and evaluated its influence on antioxidant activity and cell wall metabolism during storage. The results demonstrated that treatment with 0.015 mg/mL carvacrol significantly (P < 0.05) reduced the weight loss rate by 48.51%, increased titratable acid (TA) content by 47.30%, and effectively maintained chlorophyll levels Additionally, there was a significant reduction in firmness by 13.2%. Carvacrol enhanced the antioxidant capacity of peppers during postharvest storage by augmenting the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and chalcone isomerase (CHI) enzymes, and retarding the accumulation of H₂O₂ and O₂^•- contents. The application of carvacrol retarded the softening of pepper fruits by delaying the reduction of the pectin, protopectin, soluble pectin, and cellulose content, inhibiting the β-galactosidase (β-Gal), polygalacturonase (PG), pectin methyl esterase (PME), cellulase (Cx), and glucosidase (GLU) enzyme activities, and reducing the rate of cell wall metabolism during postharvest storage. In the transcriptome WGCNA analysis, a total of 11 distinct modules were identified. Notably, genes associated with antioxidant functions and cell wall metabolism were significantly enriched in the blue-green, blue, green, and brown modules. In conclusion, it can be posited that carvacrol may enhance the antioxidant system of pepper fruits and maintain postharvest storage quality by increasing antioxidant activity and delaying the cell wall metabolism pathways.