Liquid Chromatography-Diode Array and Electrospray High-Accuracy Mass Spectrometry of Iso-α-Acids in DCHA-Iso Standard and Beer

Abstract

Excellent liquid chromatographic (LC) separation of cis/trans stereoisomers of iso-␣-acids has been achieved with reversedphase sorbent XTerra MS C18. An isocratic alkaline mobile phase, consisting of a mixture of 5 mmol l -1 ammonium acetate (pH 8)-acetonitrile-methanol, 62:21:17 (v/v/v), was used. In the DCHA-Iso international calibration standard trans-isoposthumulone was identified combining photo diode array (PDA) spectra and electrospray high-accuracy mass spectrometric (MS) data. Moreover, the molecular mass of two degradation products resulting from the in-solution storage of the DCHA-Iso standard was determined. The presence of trans and cis isomers of isoposthumulone, isocohumulone, isoadhumulone and iso-n-humulone in beer samples was confirmed. The trans isomers of iso-␣-acids showed characteristic and reproducibly slightly different ultraviolet absorbance spectra with respect to cis isomers.

Determination of free amino acids in beers: A comparison of Czech and foreign brands

“…The presence of amino acids, vitamin B (esp. B6 and folic acid), minerals (in particular potassium, calcium and magnesium), protein derivates, organic acids, antioxidants and iso-a-acids (Hofta et al, 2007), makes beer a unique beverage due to its constitutive polymorphism (Briggs et al, 2006). The importance of amino acids in barley malting process and beer brewing is doubtless.…”

Relationship of iso-α-acid content and endogenous antioxidative potential during storage of lager beer

“…Reverse phase HPLC analyses with PDA (photodiode array) detection were performed using the slightly modified method previously described by Hofta et al . . Chromatographic determination was carried out on an Agilent 1100 series system (Agilent Technologies, Germany), equipped with an Agilent PDA detector.…”

“…Iso‐ α ‐acids are five‐membered ring structures that arise from the isomerization of α ‐acids during wort boiling , and are subjected to chemical transformation, especially during the storage of bottled beer. The reaction mechanisms are not fully understood, although several have been proposed .…”

Metabolism of Hop-Derived Bitter Acids

“…The interface settings were as follows: N 2 drying gas temperature, 250 °C; N 2 drying gas flow, 5 L/min; APCI vaporizer temperature, 150 °C; nebulizer pressure, 10 5 Pa; capillary voltage, 1000 V; corona current, 6 μA; charging voltage, 1000 V. In each analysis, qualitative identification was performed in the negative ion scan mode ( m / z 150–700) and quantitative data were obtained by reconstruction of the extracted ion chromatogram following measurement in the selected ion monitoring (SIM) mode. The [M – H] − m / z values, used for quantification of α-acids, β-acids, and iso-α-acids of the different compounds are presented in Table . − …”