Abstract
A new simultaneous method for determination of 16 heterocyclic compounds using SPE sample preparation and GC-MS determination was developed regarding increasing interest of the role of sensory active compounds in beer. LiChrolut® EN SPE columns proved to be optimal for both, a mixture of analytes with a different polarity and such complicated matrix as beer. Recoveries of individual analytes are about 100% except for three compounds (2-methylpyridine about 30%, maltol and furaneol about 50%); repeatability, uncertainty and LOQ are satisfactory for the method application. The method was used for monitoring of heterocyclic compounds formation during roasting, mashing, hop boiling and fermentation. To summarize, during roasting of malt, the concentration of oxygen heterocycle compounds (OHC) increases more rapidly in comparison with nitrogen heterocycles compounds (NHC) till a critical point where OHC starts to decrease and NHC starts to be formed sharper (with the exception of 2-acetylpyrrole which is similar to OHC). Finally, the total concentration of NHC during fermentation rapidly decreases whilst the OHC concentration is influenced by many factors, e.g., fermentation conditions and yeast strain.
Highlights
Organoleptic character of beer is influenced by various well-known compounds
The formation of heterocyclic compounds (HC) is caused by a generally known Maillard reaction, which was firstly reported by Louis-Camille Maillard (1878–1936) in 1912 (Nursten, 2005)
The aim of the study was (i) to collect information on HC in beer published so far including a method of extraction and determination, monitoring of HC origin of nitrogen heterocycles compounds (NHC) and oxygen heterocycle compounds (OHC) in the sequence of “malt–sweet wort– wort–beer”, (ii) to improve an extraction method which would have sufficient recovery and repeatability for all studied HC determined simultaneously, (iii) to validate the method of HC determination, (iv) to evaluate HC profiles in malts with an increasing colour, and (v) to study HC distribution in the sequence of “sweet wort– wort–beer”
Summary
There are still sensorially active compounds in beer, such as heterocyclic compounds (HC) which are not well described in literature yet. The formation of HC is caused by a generally known Maillard reaction, which was firstly reported by Louis-Camille Maillard (1878–1936) in 1912 (Nursten, 2005). This process, known as nonenzymatic browning, is based on a reaction between reducing sugars and proteins by the impact of heat (Bastos et al, 2012; Van Boekel, 1998). The reaction mechanisms responsible for formation of melanoidins involving active methylenes with heterocyclic structure and the structural characterization of the resulting products were published (Kanzler et al, 2019)
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