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

## TL;DR

This study explores how heat and humidity during transportation affect rice quality by analyzing microbial changes and flavor shifts.

## Contribution

The study identifies specific microbial and volatile markers that indicate rice spoilage under high-temperature and humidity conditions.

## Key findings

- Prolonged transportation under high temperature and humidity leads to significant rice quality deterioration.
- Microbial community shifts from bacteria to fungi, with Lichtheimia becoming dominant, correlate with flavor changes.
- Volatile compounds like 1-octen-3-ol and ethyl acetate accumulate, signaling a transition to moldy and fermented odors.

## Abstract

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, Lichtheimia surged from <0.01% to 23.95%, becoming the dominant genus, while Aspergillus increased from 0.03% to 4.57%. Correlation analysis indicated that while Pseudomonas 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.