Comparison of α and ß-acid isomerization in hops and beer using HPLC, confocal microscopy, spectrofluorimetry and chemical analysis of metabolites and essential oils in flowers of different hop cultivars produced in Brazil.

We used confocal microscopy and spectrofluorescence to characterize the emission spectra in hop flowers, to follow the isomerization processes in different hop preparations, and beers, to compare with HPLC extracted samples. Flowers of different hop cultivars produced in three regions of Brazil, were quantitated by HPLC and GC-MS. The fluorescence spectra showed two characteristic emission bands evaluated from different preparations. The isomerization process leads to a gradual decrease in fluorescence intensity as the reaction progresses. This demonstrates the valuable use of confocal microscopy and fluorescence spectroscopy for analysis of the correlation between bitter acid indices with fluorescence intensity and lifetime microscopy. Such techniques can be used directly in the flowers allowing rapid monitoring of the brewing process. Twenty-nine substances were characterized in the essential oils and some cultivars presented quantities of bitter acids and essential oil levels close to those expected for plants after more than three years of cultivation.

QuEChERS extraction for quantitation of bitter acids and xanthohumol in hops by HPLC-UV.

We hypothesised that QuEChERS could be successfully applied to the extraction of bitter acids and xanthohumol from hops, which would be less time consuming, cheaper, and more eco-friendly by the severe reduction of solvent use. High performance liquid chromatography was used to separate the compounds after extraction and quantitation was evaluated against standard calibration curves for bitter acids prepared from an International calibration extract (ICE-4) and an authentic standard of xanthohumol. The standard QuEChERS method was compared to mini and micro-versions including clean-up and spiking procedures. The quantitative analyzes indicate the applicability of the QuEChERS method for the quantitation of bitter acids compared to Soxhlet extraction. The statistical data confirm reproducibility of the total alpha- and beta- acids measured by the standard method and the modified mini- and micro-QuEChERS procedures. Our hypothesis is supported by the data described and is consistent with other previous methods described in the literature.