Hop Science - March 2025

More light for isomerization!

Humulones (alpha-acids) consist of substituted phloroglucinols with two isoprenyl side chains, a carbonyl group and a quaternary ring carbon that is substituted with a hydroxyl group. When solutions of humulones are exposed to UV light, they go through stereoselective isomerization to become five-membered ring trans-isohumulones. These researchers looked into a controlled method for photochemical isomerization. For this a photoreactor was assembled from strip LEDs in close contact with UV-transparent tubing. The reactor allowed a chemical continuous-flow synthesis of the isohumulones. The yield, conversion and throughput were investigated for different wavelengths (visible, 400 nm, and 365 nm). By using an optimized continuous-flow reactor, a throughput of 0.43 g/h was obtained for trans-n-isohumulone.
This could become a scalable photochemical flow method with high yield isomerization of humulones to isohumulones. The continuous-flow approach avoids the inconsistent yields and conversions previously observed from batch photochemical reactions. In order to avoid decompositionproducts it is crucial to achieve the optimal emission of the light source and to control the  reaction of  residence time.

Hamper, B.C.; Gallow, B.; Giovine, G.; Smith, T. Continuous-Flow Photochemical Isomerization of Humulones to Isohumulones. Molecules 2025, 30, 1002. https://doi.org/10.3390/molecules30051002

Whats in the leaves?

In order to progress in sustainable farming, it is good to investigate every part of the plant for further valorization. In hops we only need the cones, but what about all the leaves? This group of researchers looked into the composition of hop leaves. Hop leaves, contain phenolic compounds of potential value for food or beverage applications. However, the abundant phenolics in hop leaves have been largely unquantified. This study has quantified phenolics in hop leaves over two crop years, for three commercially significant varieties, at different developmental stages post-flowering. They found that the  phenolic profile of hop leaves is significantly different from that of hop cones. Kaempferol/quercetin 3-O-glycosides and chlorogenic acids were the most abundant sub-groups with phenolic acids, procyanidins, prenylflavonoids, and bitter resins also being present. Phenolic profile was mainly variety-dependent with some crop year and developmental effects. Flavonol 3-O-glycosides were the main compounds driving varietal differences. So obviously the value is there, also in the leave.But what can we do with it?

Calvert D, Dew T, Gadon A, Gros J, Cook D. Valorisation of hop leaves for their bioactive compounds: Identification and quantification of phenolics across different varieties, crop years and stages of development. Food Chem. 2025 Feb 15;465(Pt 2):142005. doi: 10.1016/j.foodchem.2024.142005. Epub 2024 Nov 12. PMID: 3957726

Again only good news about Hops!

Xanthohumol (XN), a bioactive flavonoid found in hops, has emerged as a promising candidate for the prevention and treatment of neurodegenerative diseases. The experimental evidence highlights XN’s potent antioxidant capabilities, which play a crucial role in mitigating oxidative stress—a key factor in the pathogenesis of conditions such as Alzheimer’s, Parkinson’s, and Huntington’s diseases. By scavenging free radicals and upregulating the body’s endogenous antioxidant defenses, XN protects neurons from oxidative damage. Notably, in amyotrophic lateral sclerosis (ALS), preclinical studies suggest that XN can help preserve motor neurons. Moreover, XN exhibits significant anti-inflammatory properties, which are particularly important given the central role of neuroinflammation in many neurodegenerative disorders. By inhibiting pro-inflammatory mediators XN effectively reduces the chronic activation of microglia and astrocytes, thereby preventing further neuronal damage. This multifaceted anti-inflammatory action aligns with current trends emphasizing the importance of controlling inflammation to maintain neuronal health. In addition, XN influences key neuroprotective pathways, which is particularly relevant in Alzheimer’s disease, where the accumulation of amyloid-beta (Aβ) and hyperphosphorylated tau proteins contributes to cognitive decline. Experimental results indicate that XN reduces Aβ production and aggregation and inhibits tau hyperphosphorylation, thus potentially slowing the progression of the disease. Another critical aspect of XN’s action is its role in supporting mitochondrial function, a vital factor in neurodegenerative diseases. By maintaining ATP production, reducing mitochondrial oxidative damage, and promoting mitochondrial biogenesis, XN helps sustain neuronal energy metabolism, which is crucial for cognitive function and overall brain health. Finally, studies have demonstrated that XN positively impacts synaptic plasticity, enhances memory, and prevents cognitive impairment, which underscores its potential as a therapeutic agent. However, despite these promising findings, the bioavailability of XN in humans remains a challenge. Early clinical trials suggest that XN supplementation is safe and beneficial for gut microbiota and overall quality of life. So what is needed now are ways to optimize delivery methods and dosages to fully realize XN’s therapeutic potential.

Długosz A, Błaszak B, Czarnecki D, Szulc J. Mechanism of Action and Therapeutic Potential of Xanthohumol in Prevention of Selected Neurodegenerative Diseases. Molecules. 2025 Feb 5;30(3):694. doi: 10.3390/molecules30030694. PMID: 39942798; PMCID: PMC11821245