Diketones are a class of organic compounds characterized by the presence of two ketone functional groups within their molecular structure. These compounds are often recognized for their distinct aromatic properties and flavor profiles, contributing to a variety of smells and tastes. This characteristic makes diketones valuable in several industrial applications.
Common Sources of Diketones
Diketones appear in both natural and artificially produced forms, contributing to flavors and aromas across many products. Naturally, these compounds arise from biological processes, such as the fermentation of certain foods and beverages. For instance, diacetyl, acetyl propionyl, and acetoin are found in products like butter, cream, cheese, coffee, and beer, where they are byproducts of microbial fermentation or roasting processes.
Beyond their natural occurrence, diketones are widely synthesized for use as artificial flavoring agents. These synthetic versions are incorporated into numerous processed foods to impart desirable tastes such as buttery, creamy, or caramel notes. Common examples include their use in microwave popcorn, baked goods, candies, and snack foods.
Inhalation Health Concerns
While diketones contribute to enjoyable flavors in food, inhaling them as aerosolized particles poses significant health risks. Prolonged exposure to these airborne compounds can lead to a severe and irreversible lung condition known as bronchiolitis obliterans, often referred to as “popcorn lung.” This disease involves the scarring and inflammation of the smallest airways in the lungs, called bronchioles, leading to their narrowing and obstruction.
The link between diacetyl inhalation and bronchiolitis obliterans was first identified in the early 2000s among workers in microwave popcorn manufacturing plants. These individuals developed severe respiratory symptoms after chronic exposure to high concentrations of diacetyl vapors used to create the buttery flavor. The damage to the bronchioles impairs the lungs’ ability to exchange air effectively, resulting in persistent coughing, wheezing, and shortness of breath. It is important to note that the danger lies specifically in inhaling these compounds, not in consuming foods that contain them.
The Role of Diketones in Vaping
Diketones, especially diacetyl and acetyl propionyl, are frequently added to e-liquids in vaping products to mimic popular dessert and sweet flavors. These compounds help create appealing tastes such as custard, caramel, and various fruit dessert profiles.
Studies have consistently detected diacetyl and acetyl propionyl in a substantial portion of flavored e-liquids, sometimes at levels comparable to those found in occupational settings linked to lung disease. For example, one study found diacetyl in 39 out of 51 tested e-cigarette flavors and acetyl propionyl in 23 out of 51. The heating process in vaping devices can aerosolize these chemicals, allowing them to be inhaled deep into the lungs, raising concerns about potential respiratory harm similar to that observed in industrial workers.
Regulatory Oversight and Safety Standards
The regulatory framework for diketones highlights a crucial distinction between safety for ingestion and safety for inhalation. The U.S. Food and Drug Administration (FDA) has designated diacetyl and other diketones as “Generally Recognized as Safe” (GRAS) for use as food additives, meaning they are considered safe to eat. However, this GRAS status applies only to consumption and does not extend to the inhalation of these substances.
The National Institute for Occupational Safety and Health (NIOSH) has recommended specific workplace exposure limits for diacetyl and acetyl propionyl to protect workers from respiratory diseases. These recommendations are based on studies showing adverse health effects from airborne exposure. While the FDA has begun to address ingredients in e-cigarette products, comprehensive federal regulations specifically limiting diketone levels in e-liquids are still evolving, leaving consumers potentially exposed to these inhalation hazards.