Multivariate analysis of chemical and genetic diversity of wild Humulus lupulus L. (hop) collected in situ in northern France.

The hop plant (Humulus lupulus L.) has been exploited for a long time for both its brewing and medicinal uses, due in particular to its specific chemical composition. These last years, hop cultivation that was in decline has been experiencing a renewal for several reasons, such as a craze for strongly hopped aromatic beers. In this context, the present work aims at investigating the genetic and chemical diversity of fifty wild hops collected from different locations in Northern France. These wild hops were compared to ten commercial varieties and three heirloom varieties cultivated in the same sampled geographical area. Genetic analysis relying on genome fingerprinting using 11 microsatellite markers showed a high level of diversity. A total of 56 alleles were determined with an average of 10.9 alleles per locus and assessed a significant population structure (mean pairwise FST = 0.29). Phytochemical characterization of hops was based on volatile compound analysis by HS-SPME GC-MS, quantification of the main prenylated phenolic compounds by UHPLC-UV as well as untargeted metabolomics by UHPLC-HRMS and revealed a high level of chemical diversity among the assessed wild accessions. In particular, analysis of volatile compounds revealed the presence of some minor but original compounds, such as aromadendrene, allo-aromadendrene, isoledene, ß-guaiene, α-ylangene and ß-pinene in some wild accessions; while analysis of phenolic compounds showed high content of ß-acids in these wild accessions, up to 2.37% of colupulone. Genetic diversity of wild hops previously observed was hence supported by their chemical diversity. Sample soil analysis was also performed to get a pedological classification of these different collection sites. Results of the multivariate statistical analysis suggest that wild hops constitute a huge pool of chemical and genetic diversity of this species.

Portuguese wild hop diversity assessment by fast SNP genotyping using high-resolution melting.

A set of seven SNP markers was used to evaluate the genetic diversity of wild Portuguese hops in comparison with commercial cultivars. A collection of 110 wild genotypes and 33 cultivars was characterized by a high-resolution melting analysis of short amplicons targeting SNP loci. Most of the 143 genotypes (75%) could be differentiated. Phylogenetic analysis showed three main clusters, one included almost exclusively (98%) wild accessions, being the others constituted of both wild and commercial genotypes. The study of population genetic structure placed the accessions into three genetic units, being one exclusively of Portuguese genotypes. The study showed the great biodiversity of the Portuguese hop germplasm and the notable differences (FST = 0.163, p<0.00001) from commercial hops. Results support the usefulness of the use of these seven markers for hop discrimination, with the fast and high-throughput HRMA technique for allele calling and contribute to the affirmation of the high richness breeding potential of Portuguese wild hops.

Sensory and Olfactometry Chemometrics as Valuable Tools for Assessing Hops' Aroma Impact on Dry-Hopped Beers: A Study with Wild Portuguese Genotypes.

Sensory, olfactometry (using the sums of odour intensities for each class of compounds) and chemometric analyses were used to evaluate Portuguese wild hops' sensory characteristics and the aroma that those hops impart to dry-hopped beer. CATA analysis and agglomerative hierarchical clustering was applied for the sensory characterization of 15 wild hops of Portuguese genotypes, clustering them in two groups: one more sulphurous, floral, and fruity, and another more earthy, resinous, floral, and non-citrus fruits. Two hops representative of each group were selected for the production of four dry-hopped beers using the same base beer style (Munich Helles). Beers were analysed by quantitative descriptive analyses and quantification of hop-derived key volatile compounds. Multivariate statistical treatment of the data was performed. Results indicate significant differences (p < 0.05) in fruity, resinous, earthy, floral, and sulphurous attributes of hops, but the dry-hopped beers only have a significant increase (p < 0.05) in fruity and spicy notes when compared with non-dry-hopped Munich-style Helles beer. Hop olfactometry explained the sensory perception that the 11 hops not used for brewing (employed as supplementary observations) are placed into the space of the odour-active compounds profile of the four hops selected for brewing. These 11 hop samples have more spiciness than fruitiness potential.

Differences in Leaf Chemistry and Glandular Trichome Density between Wild Southwestern American Hop (Humulus neomexicanus) and Commercial Hop Cultivars.

The female flowers ("cones") of the hop plant (Humulus L.) produce compounds that contribute to the flavor and other properties of beer. Hop leaves and cones produce many of the same compounds, which also confer agronomic traits such as insect and disease resistance. Targeted and untargeted ultraperformance liquid chromatography-quadrupole time-of-flight-mass spectrometry with Waters MSE technology (UPLC-QTof-MSE) metabolomics were used to compare leaf phytochemical compositions of greenhouse-grown southwestern American wild Humulus neomexicanus (A. Nelson and Cockerell) Rydb. against a group of commercial hop cultivars consisting of both pure European Humulus lupulus L. and European-North American hybrids. Principal component analysis showed a clear distinction in chemical profiles between the two groups. H. neomexicanus leaves had a significantly higher content of total α acids (p = 4.4 × 10-9), total bitter acids (p = 2.6 × 10-6), cohumulone (p = 1.0 × 10-13), humulone + adhumulone (p = 9.1 × 10-4), and the prenylflavonoids xanthohumol (p = 0.013) and desmethylxanthohumol (p = 0.029) as well as significantly higher densities of glandular trichomes (p = 1.3 × 10-6), the biosynthetic site of those compounds. Most flavonol glycosides measured were also significantly more abundant in H. neomexicanus (p = 1.5 × 10-22 to 0.0027), whereas phenolic acids were consistently, but generally nonsignificantly (p > 0.05), more abundant in the cultivars. The higher bitter acid, prenylflavonoid, and flavonol glycoside content of H. neomexicanus leaves may help to confer more favorable insect and disease-resistance properties.

Phytochemical Characterization of Wild Hops (Humulus lupulus ssp. lupuloides) Germplasm Resources From the Maritimes Region of Canada.

A survey was conducted in the Maritimes region of eastern Canada to measure the phytochemical diversity of prenylchalcone, soft resins (alpha & beta acids), and flavonol constituents from 30 unique wild-growing populations of hops (Humulus lupulus L.). Based on cone chemometrics, the majority of accessions (63.3%) are native Humulus lupulus ssp. lupoloides, with cones containing both xanthogalenol and 4'-O-methyl xanthohumol as chemotaxonomic indicator molecules. Interestingly, the leaves of all verified Humulus lupulus ssp. lupulus accessions accumulated high proportions (>0.20 total flavonols) of two acylated flavonol derivatives (kaempferol-3-O-(6''-O-malonyl)-ß-D-glucopyranoside; quercetin-3-O-(6''-O-malonyl)-ß-D-glucopyranoside), both previously unreported from hops leaves. The native lupuloides accessions examined possess only trace amounts of this compound in their leaves (<0.10 total flavonols), suggesting its potential utility as a novel, leaf-derived chemotaxonomic marker for subspecies identification purposes. A leaf-derived taxonomic marker is useful for identifying wild-growing accessions, as leaves are present throughout the entire growing season, whereas cones are only produced late in summer. Additionally, the collection of cones from 10-meter tall wild plants in overgrown riparian habitats is often difficult. The total levels of alpha acids, beta acids, and prenylchalcones in wild-collected Maritimes lupuloides cones are markedly higher than those previously reported for lupuloides individuals in the westernmost extent of its native range and show potentially valuable traits for future cultivar development, while some may be worthy of immediate commercial release. The accessions will be maintained as a core germplasm resource for future cultivar development.