Moisture dynamics and flavor evolution in green Sichuan pepper during processing: An LF-NMR/MRI approach

This study hypothesized that specific moisture migration patterns during the dehydration-rehydration processes are intrinsically linked to the flavor profile evolution of green Sichuan pepper (Zanthoxylum armatum DC.). To test this, the study systematically evaluated the impacts of three dehydration methods - conveyor belt (WD), parallel-flow (PD), and natural drying (ZD) - and subsequent rehydration on the flavor profile, employing low-field nuclear magnetic resonance (LF-NMR) to elucidate water mobility. Findings revealed that all treatments significantly reduced L^⁎, a^⁎, and b^⁎ values compared to fresh samples (P < 0.05). Moisture content significantly dropped during dehydration (P < 0.05) and increased during rehydration (P < 0.05), with rehydrated samples (P60, Z60, W60) achieving moisture content (60.65 % - 61.69 %) closely resembling fresh samples. Total numbing substances content increased post-treatment, with dehydrated samples ranking natural drying for 6 days (Z6) > parallel-flow drying for 10 h (P10) > conveyor belt drying for 13 h (W13) and rehydrated samples ranking P60 > Z60 > W60. A total of 161 volatile aroma compounds were identified by GC-MS, comprising 22 shared and 139 unique compounds, accounting for the distinct aroma profiles across samples. The P10 dehydrated sample exhibited remarkable aroma similarity to fresh material. LF-NMR revealed progressive leftward T₂ peak migration during dehydration, while rehydration induced initial rightward shifts followed by leftward trends. MRI visualization confirmed superior water distribution uniformity in P60 rehydrated samples. Strong correlations (P < 0.01) were established among color parameters (a^⁎), moisture content, volatile oils, and numbing compounds. Principal component analysis demonstrated parallel-flow dehydration (PD) as the optimal method for flavor preservation. These results confirm our initial hypothesis, establishing critical structure-function relationships between water dynamics and flavor evolution in Z. armatum during dehydration-rehydration processes, and provide a theoretical foundation for optimizing industrial processing protocols.