Nonanal

Nonanal is a nine-carbon straight-chain aldehyde that ranks among the important aroma volatiles of many foods. With a fatty, citrusy, slightly waxy character, it arises from oxidation of oleic acid and contributes to the fresh scent of citrus fruits, cucumbers, and cooked meats, while at elevated levels it betrays lipid oxidation and staleness. Flavourists dose it into citrus and floral formulations, and lipid chemists watch it as a marker of oxidative deterioration in edible oils. Its double identity, prized aroma compound at trace levels and warning signal of rancidity at higher ones, makes concentration and context decisive when judging quality.