Fast Sampling, Analyses and Chemometrics for Plant Breeding: Bitter Acids, Xanthohumol and Terpenes in Lupulin Glands of Hops (Humulus lupulus).

Abstract

The valuable secondary metabolites in hops (bitter acids, xanthohumol, volatile monoterpenes and sesquiterpenes) are sequestered in lupulin glands (extracellular trichomes) which can be collected and analysed with little or no sample preparation. To determine whether high throughput screening of lupulin glands composition, by fast analyses and chemometrics, could be used for breeder selection of hops with key flavour attributes. Lupulin glands from 139 plants (39 cultivars/advanced selections) were analysed by Raman and 1 H NMR spectroscopy, and head-space solid-phase microextraction (HS-SPME) GC-FID. The digital X,Y-data were subjected to principal component analysis (PCA) and the results compared with conventional analyses of extracts of whole hops from the same plants. Quantitative 1 H NMR analyses were also done for the bitter acids. Raman spectroscopy rapidly identified hops cultivars with high xanthohumol concentrations and high α:β bitter acid ratios. 1 H NMR spectroscopy was slower, requiring a solvent extraction, but distinguished cultivars by cohumulone content as well as α:β acid ratios. HS-SPME-GC rapidly distinguished aroma hops with high myrcene and farnesene contents, and pinpointed a novel selection with unusual sesquiterpenes. The quantitative NMR analyses showed correlations between bitter acid concentrations related to biosynthetic pathways. Analysis of lupulin glands gave reliable results for the main quality indicators used by hops breeders, potentially avoiding harvesting, drying and solvent extracting whole hops. PCA of digital X,Y-data rapidly discriminated different hops chemotypes, and highlighted plants with potential for new flavourcultivars. Copyright © 2016 John Wiley & Sons, Ltd.