How deviations in the elemental profile of Humulus lupulus grown throughout the U.S. and Germany influence hop and beer quality.

Recently studies based on limited sample sizes procured from minor hop growing regions have speculated that the elemental profile of hops can possibly be used to authenticate the origin of a hop because changes in hop elemental profiles were realted to growing region and that these changes might also be related to beer quality. To explore this further, 205 hop samples (i.e. 203 whole cone hops and 2 pelletized samples) compromised of 19 varieties were procured from the major hop growing regions (i.e. the U.S. and Germany). These hops were digested with microwave digestion and analyzed for 25 elements using ICP-MS. Hops from most of the U.S. regions (mainly WA) had vastly different elemental profiles than hops from Germany. German hops had significantly lower concentrations for most of the elements except for Cu and K. Interestingly, high alpha varieties had significantly different elemental profiles than varieties bred for aroma purposes. Dry-hopping trials were then performed in an ale and a lager with the hops that had significantly different elemental profiles. Although heavy metals were extracted from hops into beer, at the 5 g/L dry-hopping load used in this study, beer concentrations of these elements remained below regulated water quality standards set by Germany, the U.S., and Canada. Based on electron paramagnetic resonance, dry-hopping had an antioxidant impact on beer regardless of the original elemental profile of the hops which was correlated to hop polyphenol and α/ ß - acid concentrations. Overall these results highlight that many factors including location have the potential to influence the elemental profile of hops and that changes in the elemental profiles of hops can be related to beer quality.

The Use of Metabolomics to Elucidate Resistance Markers against Damson-Hop Aphid.

Phorodon humuli (Damson-hop aphid) is one of the major pests of hops in the northern hemisphere. It causes significant yield losses and reduces hop quality and economic value. Damson-hop aphid is currently controlled with insecticides, but the number of approved pesticides is steadily decreasing. In addition, the use of insecticides almost inevitably results in the development of resistant aphid genotypes. An integrated approach to pest management in hop cultivation is therefore badly needed in order to break this cycle and to prevent the selection of strains resistant to the few remaining registered insecticides. The backbone of such an integrated strategy is the breeding of hop cultivars that are resistant to Damson-hop aphid. However, up to date mechanisms of hops resistance towards Damson-hop aphids have not yet been unraveled. In the experiments presented here, we used metabolite profiling followed by multivariate analysis and show that metabolites responsible for hop aroma and flavor (sesquiterpenes) in the cones can also be found in the leaves, long before the hop cones develop, and may play a role in resistance against aphids. In addition, aphid feeding induced a change in the metabolome of all hop genotypes particularly an increase in a number of oxidized compounds, which suggests this may be part of a resistance mechanism.