88. Comparison of the aroma profiles of hops by TD-GC-TOF MS and soft electron ionization

Laura McGregor (1), Wade Bontempo (2); (1) Markes International, Llantrisant, U.K.; (2) Markes International, Fort Collins, CO, U.S.A.


Beer contains hundreds of organic ingredients, with concentrations spanning many orders of magnitude. Mono- and sesquiterpenes (C10, C15 respectively) are aromatic hydrocarbons found in the essential oils of various plants and, most notably for the brewing industry, in hops. Hops provide much of the characteristic flavoring of the finished beer, so the terpenes content has a major impact on the final aroma and flavor. These compounds have very low odor thresholds, making them challenging to detect analytically. The ability to apply quality control to the raw ingredients and the finished product offers desirable cost and time savings to breweries. This study investigates the use of micro-chamber/thermal extractor (µ-CTE) for direct desorption of both whole and chopped hop cones. Hop samples were placed in individually sealed and temperature-controlled pots within the µ-CTE. Volatiles were then extracted by a dynamic headspace process and retained on a sorbent tube for subsequent analysis by thermal desorption (TD)-GC-TOF MS. The aroma profiles of three different types of hops cone, as well as two hops oils, were compared by this analytical approach. Distinct differences were observed in the ratios of key (high-loading) aroma compounds and in the trace components. Novel data processing software was used to extract as much information as possible from the resulting data files. The use of TD offers pre-concentration of the aroma compounds, while coupling to highly sensitive time-of-flight MS detection with novel soft ionization technology ensures that a comprehensive flavor profile can be collected in a single sequence.

Laura McGregor gained her Ph.D. in environmental forensics from the University of Strathclyde in Glasgow, where she used two-dimensional gas chromatography with time-of-flight MS to “chemically fingerprint” environmental contaminants. She joined Markes International in 2013 as a sales support specialist and is now the product marketing manager for Markes’ time-of-flight mass spectrometry products.