Effect of carvacrol on postharvest quality, antioxidant system and volatile substance metabolism of peppers (Capsicum annuum L.)

Postharvest water loss and crumpling quality degradation in peppers were observed, and the changes in their volatile compounds warrant further investigation. This study examined the effects of carvacrol treatment on the metabolism of antioxidant flavonoids and volatile substances in post-harvest peppers using a combined transcriptome and GC-MS/LC-MS analysis. It has been demonstrated that carvacrol, at a concentration of 0.015 mg mL⁻¹, effectively delayed the decline in hardness, titratable acidity, capsaicin content, total phenolic compounds, and total flavonoids, while also mitigating the increase in weight loss, relative electrical conductivity, and decay rate in post-harvest peppers A total of 1304 differential genes were identified by transcription in this study, of which 143 differential genes were involved in flavonoid metabolism. Carvacrol increased 4-coumarate-CoA ligase (4CL), chalcone synthase (CHS), flavonoid synthase (FNS), and UDP-glucuronosyltransferase (UGT), transketolase (TK), azelate dehydrogenase (ADT), 1-deoxy-xylulose-5-phosphate synthase (DXS), 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), and isopentenyl phosphate kinase (IPK) gene expression. Carvacrol also downregulated the gene expression of chalcone-flavanone isomerase (CHI), flavonol synthase (FLS) and flavonoid 3-hydroxylase (F3H). Additionally, it increased the content of lignan-7-O-neohesperidin, kaempferol-3-O-rutinoside, and kaempferol-3-O-galactoside. Notably, the 72 differential volatiles in post-harvest peppers decreased over the storage period. However, after 40 days of storage, the levels of specific volatile aroma compounds, including 4-Hexen-3-one, (E)-2-Hexenal, 2-Furanmethanol, 1-Hexanol, 2-Methyl-2-pentanal, Copaene, 2-Methylbutyric acid, Methyl acetate, isovaleric acid, (E)-2-Methyl-2-butyraldehyde, and Phenylacetic acid propyl ester was up-regulated. Thus, it is illustrated that carvacrol affects flavonoid metabolism while maintaining the content of key postharvest volatile aroma substances, thus positively influencing the postharvest quality of pepper.