Thermal Volatile Generation in Barley Malt: Online MS Studies

Abstract

A novel mass spectrometry (MS) technique for measuring volatile formation during the thermal treatment of malt or barley has been developed that enables the effects of factors such as temperature and humidity on the pathways of flavor formation to be monitored in real time. Barley malt was treated at temperatures of 105, 130, 155, and 180°C under both dry and humid conditions. The principal MS ions monitored in each case were assigned to specific malt volatile compounds using an off-line solid-phase microextraction-trapping– and GC–dual-MS technique. Authentic standards of these compounds were injected into the apparatus singly and in groups over a range of concentrations. A linear response was obtained for calibrations of heterocyclic compounds (furans, pyrazines, pyranones, etc.) in complex mixtures at concentrations relevant to those monitored during online experiments. Hence, the technique can yield quantitative data on the formation of many compounds that are important to the character of roasted malt products. Data are presented illustrating the application of the technique, and results are discussed with respect to the underlying chemical pathways. At 180°C, dry conditions favored formation of pyrazines and 2-furaldehyde (furfural), whereas humidification of the purge gas resulted in higher concentrations of Strecker aldehydes relative to these compounds.