Sulfur Dioxide in Food: A Review of Its Preservative Mechanisms, Safety Concerns, and the Rise of Smart Detection Systems.

Sulfur dioxide (SO2) remains an indispensable food preservative, yet balancing preservation efficacy with residue safety continues to challenge both industry and regulators. The difficulty arises from the diverse chemical forms, dynamic release, and uneven distribution of SO2 in food matrices and package headspace, which hinder real-time monitoring and precise control. While progress has been made in preservation techniques, detection methods, and smart sensors, an integrated framework that unifies these threads to elucidate SO2 dynamics in complex food systems is still absent. This review provides an integrated perspective that draws together knowledge of SO2 chemical speciation, mechanism of action, safety thresholds, and controlled-release behavior. We trace the evolution of SO2 detection from traditional analytical methods and modern instrumental techniques to emerging smart detection platforms, with emphasis on active and intelligent packaging systems and on cold-chain monitoring challenges. Advances in smart detection technologies enable more precise monitoring of different SO2 forms in complex food systems and package atmospheres, improving the balance between quality preservation and safety control. Future research will prioritize real-time tracking of dynamic SO2 changes and localized residual levels throughout cold chains, alongside the integration of multimodal rapid sensing into smart packaging for synergistic food quality preservation and risk mitigation.