Not Just an Aroma Compound: Expanding Perspectives on Diacetyl in Food Systems and Human Health.

Diacetyl has been a known key volatile compound for almost one century, a metabolite naturally produced by different microorganisms during fermentation processes, with traditional applications in food products preparations. Since its discovery, diacetyl has been recognized and actively explored regarding its buttery aroma, which is beneficial for a variety of fermented dairy foods. It is primarily synthesized by lactic acid bacteria (LAB) and other microbial groups through citrate metabolism, a pathway that is strain-dependent and strongly influenced by environmental conditions. Moreover, beyond its sensory relevance, diacetyl has attracted increasing scientific attention because of its antimicrobial activity, including synergistic interactions with bacteriocins and other microbial metabolites, which may enhance food preservation and biotechnological strategies. In contrast, its presence merits attention and needs to be carefully monitored in alcoholic beverages such as beer and wine, where excessive accumulation may compromise product quality. Some studies suggested that diacetyl may have negative health influences and presents safety concerns, as inhalation exposure was associated with pulmonary toxicity and occupational diseases, and was even suggested as one of the risk factors in electronic cigarettes. Emerging studies suggest that diacetyl may exhibit pharmacological potential, including antioxidant, antifungal, and even neuroprotective properties, although research is still in early stages and merits deeper scientific evaluation. Considering its dual nature, beneficial and harmful, this review provides an overview of diacetyl's properties, safety considerations, and promising applications in biotechnology, biomedicine, and fermented food systems, but with a focus on potential industrial and health hazards. In the current review, we have presented evidence for diacetyl's beneficial properties and discussed its hazards.