Measurement of Diacetyl and 2,3-Pentanedione in the Coffee Industry Using Thermal Desorption Tubes and Gas Chromatography-Mass Spectrometry

Diacetyl is a potentially harmful chemical that is used as an artificial flavouring in the food industry and may also be generated during processing of some natural products including coffee. In Europe, an 8-h time weighted average occupational exposure limit (TWA-OEL) of 20 ppb has been adopted for diacetyl, together with a short-term exposure limit (STEL) of 100 ppb. A new measurement method involving sampling on thermal desorption tubes and analysis by gas chromatography-mass spectrometry has been used to investigate potential exposure to diacetyl, and the related compound 2,3-pentanedione, at eight companies involved in the coffee industry including large- and small-scale manufacturers and coffee shops. A total of 124 static and personal samples were collected. In the majority of personal samples airborne concentrations of diacetyl were <5 ppb, with those at coffee shops generally <1 ppb. However, diacetyl concentrations in ~40% of the long-term personal samples, mainly originating from one site, were found to be in excess of the newly adopted European TWA-OEL of 20 ppb. Diacetyl concentrations up to 400 ppb were detected on the static samples, with the highest values occurring during grinding of roasted coffee beans. 2,3-Pentanedione was also detected in most of the samples at airborne concentrations around half of those for diacetyl. A significant number of other volatile organic compounds (VOCs) were also detected at sub-ppm concentrations, including acetoin, aliphatic carboxylic acids, aldehydes, ketones and esters, methylfuran, furfural and furfuryl-based alcohols and ketones, and nitrogen containing compounds, such as pyridines and pyrazines. In laboratory tests, diacetyl emissions generated during heating of whole beans were found to be significantly lower than those from heating the same beans after grinding. Diacetyl emissions from both ground and whole beans were also found to be significantly dependent on temperature.