Optimum Method of Analyzing Hop Derived Aroma Compounds in Beer by Headspace Solid-Phase Microextraction (SPME) with GC/MS and Their Evolutions during Chinese Lager Brewing Process

Abstract

A simple and sensitive headspace solid-phase microextraction (SPME) and gas chromatography with mass spectrometer detection (GC/MS) method was developed for simultaneous determination of 19 key hop derived aroma compounds at trace levels in beer. Nineteen hop derived aroma compounds were classified into four groups: esters, terpenes, terpenols, and ketones. A PDMS-coated fiber was found to be the most effective with optimum extraction temperature (50°C) and time (60 min). Degassed beer matrix was found to yield better recovery and possess greater reliability with calibration standards than a 5% ethanol/H2O solution. This method is advantageous over conventional extraction methods because it allows for lower detection limits, higher reproducibility and accuracy, and offers simple manipulation. The integration of effective enrichment, qualification, and accurate quantification of a wide variety of compounds in one injection is made possible. Thus, this method promises to be suitable for a routine beer hop-aroma analysis and applicable for quality control of aroma hop usage and hop aroma assessment during the brewing process and finished beer. The result of evolution of them during Chinese lager brewing process suggests that the esters and free terpenols derived from the yeast metabolism and biotransformation of glycosidically bound terpenols play more important roles.