How do sulfur dioxide and sulfites preserve dried fruits and fruit juices?

Sulfur dioxide and sulfites serve as vital inorganic chemical preservatives in dried fruits and fruit juices by acting as both antioxidants and antimicrobial agents.123

Their preservation mechanisms include:

• Antioxidant Effects: These compounds act as oxygen scavengers and enzyme inhibitors. By inactivating enzymes—such as phenolases that cause enzymatic browning—they prevent the formation of dark pigments like melanin in cut or bruised fruits. As reducing agents, they also help delay oxidative deterioration, which maintains the quality and appearance of the food.1456
• Antimicrobial Effects: Sulfur dioxide and sulfites inhibit the growth of spoilage microorganisms, including bacteria, yeasts, and molds. They function by forming addition compounds and inhibiting essential microbial enzymes, which helps extend the shelf life of products like wines and fruit juices.123

In the context of dehydration, fruits are often treated with sodium sulfite or sodium bisulfite prior to drying to ensure effective enzyme inactivation and to control browning during the process.5