Beer volatile analysis: optimization of HS/SPME coupled to GC/MS/FID

A powerful technique was developed for the identification and quantification of 9 volatile compounds of beer, using headspace solid phase micro-extraction (HS/SPME) and gas chromatograph coupled to a mass spectrometer and a flame ionization detector (GC/MS/FID). Optimized parameters included type of fiber, desorption time, and exposure time. Optimization was achieved with standard solutions of the target compounds. All samples were analyzed in triplicate. An exposure time of 45 min with PDMS fiber in the sample headspace was enough to reach equilibrium of the phases. A desorption time of 15 min in the gas chromatograph injector was enough for the fiber to desorb the target compounds. It was found that less polar compounds were more readily absorbed by the fiber (for example, isoamyl acetate) than more polar compounds (for example, acetaldehyde), under the extraction conditions, due to the nature of the fiber. Extraction conditions are important criteria to perform a good quantification of volatile compounds. Concentrations found in sampled beer, for the compounds of interest, ranged between 0.32 and 41.7 ppm. Results show that the reproducibility of the technique depends on the compounds. Esters have higher values (RSD mean value 5.05%) than higher alcohols (RSD mean value 2.5%) and aldehydes (RSD 3.7%). The simplicity of the validated methodology enables its use as a regular quality control procedure for beer flavor analysis.

This study describes a technique successfully used to identify and quantify volatiles of interest in beer that can be used for quality control purposes under normal brewery production conditions. The technique uses a gas chromatograph coupled to a mass spectrometer with a flame ionization detector.