Metabolomic and enzymatic markers reveal critical air exposure threshold for Crassostrea hongkongensis quality

Abstract

Post-harvest air exposure is unavoidable during oyster transportation and storage, yet the physiological tolerance limits and underlying metabolic responses of commercially important oyster species remain poorly understood. While previous studies have focused on immediate post-harvest quality changes, there is limited knowledge about the time-dependent metabolic adaptations that determine product quality during extended air exposure. This study investigated the physiological and metabolic responses of Crassostrea hongkongensis during air exposure at 4 °C, focusing on identifying the optimal period for quality preservation. Using a combination of survival analysis, enzyme activity assays, and metabolomic profiling, we examined oysters exposed to air for up to 18 days, with particular emphasis on the critical first three days. Survival analysis showed 100 % survival rate at 4 °C through day 7, with mortality beginning thereafter, compared to significant mortality observed at 25 °C (complete mortality by day 7) and 37 °C (complete mortality by day 2). Analysis of antioxidant enzyme activities revealed complex, time-dependent changes, with robust responses observed within the first three days, indicating effective stress management. Metabolomic analysis identified 38 differentially abundant metabolites throughout the exposure period. Notably, the metabolic profile at day 3 showed a tendency to revert towards the control state, suggesting a temporary adaptive response. Key findings included stability in total antioxidant capacity (T-AOC) levels during the initial three days and subtle changes in flavor-related compounds, such as slight decreases in glutamate and aspartate levels. Correlation analyses revealed intricate interactions between enzyme activities and metabolites, highlighting complex stress response mechanisms. The relationship between T-AOC and key osmolytes underscored their critical role in maintaining cellular redox balance during the initial exposure period. Our findings suggest that the optimal window for maintaining C. hongkongensis quality during air exposure at 4 °C is within the first three days. During this period, oysters demonstrate effective adaptive responses, maintaining key quality attributes and nutritional value. Beyond this timeframe, the risk of quality degradation increases significantly. These results have important implications for the oyster industry, providing evidence-based guidelines for post-harvest handling, transportation, and storage practices. We recommend limiting air exposure during cold storage to no more than 3 days to ensure optimal product quality and consumer satisfaction.