Gas-phase volatilomic approaches for quality control of brewing hops based on simultaneous GC-MS-IMS and machine learnin
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RESEARCH PAPER
Gas-phase volatilomic approaches for quality control of brewing hops based on simultaneous GC-MS-IMS and machine learning Rebecca Brendel 1,2 & Sebastian Schwolow 1 & Sascha Rohn 2 & Philipp Weller 1 Received: 28 April 2020 / Revised: 7 July 2020 / Accepted: 22 July 2020 # The Author(s) 2020
Abstract For the first time, a prototype HS-GC-MS-IMS dual-detection system is presented for the analysis of volatile organic compounds (VOCs) in fields of quality control of brewing hop. With a soft ionization and drift time-based ion separation in IMS and a hard ionization and m/z-based separation in MS, substance identification in the case of co-elution was improved, substantially. Machine learning tools were used for a non-targeted screening of the complex VOC profiles of 65 different hop samples for similarity search by principal component analysis (PCA) followed by hierarchical cluster analysis (HCA). Partial least square regression (PLSR) was applied to investigate the observed correlation between the volatile profile and the α-acid content of hops and resulted in a standard error of prediction of only 1.04% α-acid. This promising volatilomic approach shows clearly the potential of HS-GC-MS-IMS in combination with machine learning for the enhancement of future quality assurance of hops. Keywords Simultaneous HS-GC-MS-IMS . Machine learning . Volatilomics . Brewing hops . Quality control . Partial least square regression (PLSR)
Introduction For centuries, hop (Humulus lupulus L.) has been used in the brewing process, due to its contents of secondary metabolites that give beer its typical flavor. Among those, the α- and β-acids (often referred to as bitter acids) formed in the lupulin glands of the hop cone are mainly responsible for bitter taste of beer [1]. In contrast, terpenes and terpenoids of the essential oil fraction and their oxygenated derivatives are responsible for the hoppy and spicy beer flavor [2]. Even today, the hop price and also the hop dosage mainly depend on the bitter acid level of the hop blossoms and, in particular, the α-acid content that mostly contribute to the bitterness during wort cooking [1]. With the Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00216-020-02842-y) contains supplementary material, which is available to authorized users. * Philipp Weller [email protected] 1
Institute for Instrumental Analytics and Bioanalytics, Mannheim University of Applied Sciences, Paul-Wittsack-Strasse 10, 68163 Mannheim, Germany
2
Institute of Food Chemistry, Hamburg School of Food Science, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany
increasing craft beer movement, special flavor hops currently gain great popularity. For those hop cultivars, the aroma yield or aroma potential is even more meaningful in terms of suitability and authenticity [3]. The bitter acid content as well as the essential oil composition is influenced by several factors, among of which the date of harvesting is of particular importance. α-
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