Impacts of high-temperature and humidity transportation on rice quality: an integrated analysis of microbial community succession and flavor compound alterations

This study investigated the dynamic changes in rice quality, microbial communities, and volatile compound profiles during simulated summer transportation (35 °C, 70% RH, 15 days). Indica rice samples were systematically collected every 3 days and analyzed using HS-SPME-GC-MS/MS, HS-GC-IMS, and metagenomic sequencing. Prolonged transportation significantly altered the physicochemical properties of the rice. Moisture content plateaued on day 12, while germination rates declined significantly starting from day 6. Furthermore, fatty acid values increased continuously due to accelerated lipid hydrolysis and oxidation. Visible mold growth became evident on day 12, marking a critical tipping point for quality deterioration. The odor activity value (OAV) and relative odor activity value (ROAV) analyses revealed that the decline in unsaturated fatty aldehydes such as (E)-2-nonenal and the significant accumulation of alcohols, ketones, and short-chain esters, including 1-octen-3-ol and ethyl acetate, drove the transition from a "fresh and fatty" aroma to one characterized by moldy, fermented, and pungent notes. Metagenomic analysis demonstrated a profound ecosystem shift from bacterial dominance (Proteobacteria, Actinobacteria) to fungal dominance. Notably, <i>Lichtheimia</i> surged from <0.01% to 23.95%, becoming the dominant genus, while <i>Aspergillus</i> increased from 0.03% to 4.57%. Correlation analysis indicated that while <i>Pseudomonas</i> was associated with elevated fatty acid levels, the flavor shift was primarily linked to microbial succession. These findings provide insights into the synergistic mechanisms of rice spoilage and suggest that specific volatile markers could serve as early warning indicators for quality control in real-world grain logistics.