Electronic nose combined with HS-SPME/GC-MS for characterization of volatile substances in pepper fruits treated with exogenous 2,4-epibrassinolide and its inhibitor brassinazole across different developmental stages

The aroma quality is a key factor determining the market value of peppers ( Capsicum annuum L.). In this study, the effects of different concentrations of 24-epinobrassinolide (EBR, 0.05–1.0 mg/L) and its specific biosynthesis inhibitor (BRZ, 0.5–2.0 mg/L) on volatile compounds in pepper fruits were comprehensively evaluated by using electronic nose (PEN3) and HS-SPME/GC-MS technology. Differential metabolites were identified through multivariate statistical analysis and odor activity value (OAV) calculation. The results showed that the peak of volatiles accumulation occurred at the green maturity stage (36 DPA). Treatment with low-concentration EBR (0.05–0.1 mg/L) significantly increased the accumulation of nitrogen oxides, aromatic substances and sulfides, elevated the total volatile content, and increased the aldehyde (by 25.5%) and alcohol (by 24.8%) compounds. On the contrary, the B3 treatment (1.5 mg/L) resulted in a 19.8% reduction in total volatile matter. Among the 99 identified compounds, 14 exhibited an odor activity value (OAV) greater than 1, with the E1 treatment (0.05 mg/L) exhibited the highest total OAVs. In addition, VIP analysis identified 15 different volatiles as characteristic biomarkers associated with EBR/BRZ treatment. In conclusion, the exogenous application of low concentrations of EBR (0.05–0.1 mg/L) could promote the accumulation of substances such as aldehydes, (e.g., hexanal), alcohols (e.g., (2Z) -2-hexene-1-alcohol, leaf alcohols,) and nitrogen-containing heterocyclic compounds (e.g., 2-Isobutyl-3-methoxypyrazine), thereby significantly improving the aromatic quality of pepper fruit. These findings provide a theoretical foundation for the enhancement of chili fruit flavor mediated by BR.