Dynamic comparative analysis of moisture and flavour characteristics in green peppers (Piper nigrum L.) during thermal and non-thermal drying processes.

Dynamic changes in moisture and volatile organic compounds (VOCs) of green pepper (GP) during hot-air drying (HAD), far-infrared drying (FIRD), and freeze drying (FD) were investigated. Results showed HAD increased terpenoids peak area by 44.72 %, the drying time of FIRD was only 5 h, and the FD piperine retention was 135 %. LF-NMR results revealed a significant decrease in the peak area of free water, which positively correlated with 25 VOCs in dried GP as drying progressed. HS-SPME-GC-MS and HS-GC-IMS techniques further identified 1205 VOCs, with terpenoids (α-farnesene and β-myrcene) contributing 26.18 % to the overall flavour of dried GP, and being significantly upregulated by HAD. Notably, piperine showed strong correlations with three pyrazines containing heterocyclic structures (r ≥ 0.70). Moreover, the flavour-related metabolic pathways in dried GP include tyrosine metabolism, phenylalanine metabolism, microbial metabolism, and the biosynthesis of secondary metabolites, with the latter serving as the main pathway for GP flavour.