Hop (Humulus lupulus L.) volatiles variation during storage

Storage conditions play an important role in maintaining the integrity of hop products during processing, transport and storage, and their ultimate quality when used to brew beer. Several groups have investigated variation in alpha acids, beta acids and polyphenols under different storage conditions, but there are few studies directly linking changes in hop acid composition under pro-oxidative conditions, to either: (i) industry standard measures of the oxidative quality of hop alpha acids (hop storage index [HSI]); or (ii) changes in the volatile composition of hops. The aim of this work was to present useful information regarding the variation in hop acids and volatiles in different storage conditions, such as temperature and exposure to ambient air. A comparison between pellets and pressed hop flowers was investigated. Long term storage in oxidizing conditions can lead not only to a decrease in the essential oil content, in particular at the expense of the more volatile fraction, but also to the degradation and/or transformation of some of the main compounds to their oxidized forms. With this work, we hope to give some insight into the inter-relationship of measurable hop quality parameters (such as HSI, hop acid chemistry and volatile chemistry), as well as demonstrate how easily hop chemistry can be affected by improper storage conditions

Prebiotic and probiotic supplementation and the tryptophan-kynurenine pathway:A systematic review and meta analysis

This systematic review aimed to synthesise the results from studies investigating the effects of prebiotics and probiotics on kynurenine pathway metabolism. Thirteen studies were identified for inclusion, comprising 12 probiotic and two prebiotic arms. Participants included healthy individuals and individuals with various clinical conditions. Twelve metabolites were examined across the studies, using a range of biological samples. Across all interventions, 11 reported an effect on ≤ metabolite. Although limited by clinical and methodological heterogeneity, pooled analysis (n = 253) found probiotics to significantly affect serum kynurenine (g = 0.315, CI = 0.070 to 0.560, p = 0.012, 4 studies, I2 = 0%) and the kynurenine:tryptophan ratio (g = 0.442, CI = 0.074 to 0.810, p = 0.018, 4 studies, I2 = 42 %). Risk of bias across the studies was generally low. The results provide preliminary evidence that probiotics can modulate kynurenine pathway metabolism, with less evidence available regarding prebiotics. Future studies which further consider methodological confounds and sample characteristics are required, to establish intervention efficacy. PROSPERO registration #CRD42019154677