Solid-state determination of hop bitter acids in beer by UV–MALDI–Orbitrap mass spectrometry

Abstract

Despite of the fact that the manufacturing of beer dated from many centuries, and nevertheless, of enormous analytical instrumental elaborations, developments and implementations for highly precise and accurate protocols for determination of foodstuffs, the quantitation of beer ingredients still represent significant challenge. It is caused by: (A) high complexity of the beer as foodstuffs matrix with significant proteins and maltooligosaccharide content as well as diversity of more than 57 low-molecular weight hop bitter acidic analytes and their oxidation products; (B) higher instability and variety of chemical oxidation processes typical for these ingredients; (C) easy isometrization and rearrangements, tautomerism and large number of different conformations of hop bitter acids; (D) structural similarity of the analytes; (E) photo-instability of the ingredients; and (F) still unavailable commercial standards for all hop acids, which difficult the analysis of major and minor components in crude hop extracts, during brewing process and storage of final food product. The diverse number of chemical and photochemical processes may be conducted at each these stages of beer manufacturing, which caused need of methodological elaborations and implementations of accurate analytical protocols for on-line analysis of beer components. For this reason the paper content encompasses quantitative solid-state analysis of hop bitter acids in different brands beer beverages employing UV–MALDI–Orbitrap MS method. Despite of its powerful instrumental capability, this mass spectrometric method has been scarce utilized in analysing of beer foodstuffs, limiting the scientific efforts and reports to mainly qualitative analysis and fingerprinting of proteins and maltooligosaccharides. In this respect the study provided novelty in the field of the quantitative analytical chemistry of low molecular weight analytes in beer demonstrating its capability for accurate determination of closely structural ingredients such as the large number of naturally occurring hop bitter acids.