Phytochemical and Morphological Characterization of Hop (Humulus lupulus L.) Cones over Five Developmental Stages Using High Performance Liquid Chromatography Coupled to Time-of-Flight Mass Spectrometry, Ultrahigh Performance Liquid Chromatography Photodiode Array Detection, and Light Microscopy Techniques

Abstract

Hop (Humulus lupulus L.) inflorescences, commonly known as "hop cones", are prized for their terpenophenolic contents, used in beer production and, more recently, in biomedical applications. In this study we investigated morphological and phytochemical characteristics of hop cones over five developmental stages, using liquid chromatography coupled to time-of-flight mass spectrometry (LC-TOF-MS), and ultrahigh performance liquid chromatography photodiode array detection (UHPLC-PDA) methods to quantitate 21 polyphenolics and seven terpenophenolics. Additionally, we used light microscopy to correlate phytochemical quantities with changes in the morphology of the cones. Significant increases in terpenophenolics, concomitant with glandular trichome development and associated gross morphological changes, were mapped over development to fluctuations in contents of polyphenolic constituents and their metabolic precursor compounds. The methods reported here can be used for targeted metabolic profiling of flavonoids, phenolic acids, and terpenophenolics in hops, and are applicable to quantitation in other crops.

Italian hop germplasm: Characterization of wild Humulus lupulus L. genotypes from Northern Italy by means of phytochemical, morphological traits and multivariate data analysis

“…Hop strobiles, and hop leaves to a very lesser extent, display a substantial density of hop glandular trichomes (lupulin), mostly located in the outer lower surface of bracteoles and in the whole surface of the female perianth (Kavalier et al, 2011;Srecec et al, 2011). These glands store an unique and complex pool of secondary metabolites biosynthesized in the foliar mesophyll, comprising both prenylflavonoids (e.g., xanthohumol), prenylphloroglucinols (known as bitter ␣-and ␤-acids, prevailing in bitter hops) and a volatile terpenic fraction (prevailing in aromatic or finishing hops) that confers a characteristic fragrance, extremely valuable in the brewing process (Kishimoto et al, 2006;Wang et al, 2008;Zanoli and Zavatti, 2008;Srecec et al, 2012).…”

Transcriptome analysis of bitter acid biosynthesis and precursor pathways in hop (Humulus lupulus)

“…lupulone, colupulone and adlupulone), which differ from α-acids by the presence of an additional dimethylallyl prenyl group, are also abundant. Hop cultivars vary widely in their content and composition of bitter acids with some “super-alpha” cultivars containing greater than 20% humulone by dry weight in cones [4]. …”

Meta-Analysis Reveals a Critical Period for Management of Powdery Mildew on Hop Cones

“…A categorical variable was created for whether quinoxyfen was applied at least once during 20 July to 10 August or not. This time period corresponds approximately to stages I to 111 of cone de velopment (14), a period when powdery mildew can be particularly damaging to hop cones (7). To minimize potential confounding from plots that received quinoxyfen for the duration of the entire season grouped with treatments where quinoxyfen was utilized in a rotational program with other fungicides or biological control agents, an addi tional categorical variable was created that enabled evaluation of qui noxyfen only when this fungicide was applied in a rotational program with at least one other fungicide with a dissimilar FRAC code.…”