Abstract
Hops is an almost unique source of the potent phytoestrogen 8-prenylnaringenin (8-PN). As hops contain only low levels of 8-PN, synthesis may be more attractive than extraction. A strain of the Gram-positive Eubacterium limosum was isolated previously for 8-PN production from more abundant precursor isoxanthohumol (IX) from hops. In this study, spent hops, an industrial side stream from the beer industry, was identified as interesting source of IX. Yet, hop-derived compounds are well-known antibacterial agents and the traces of a large variety of different compounds in spent hops interfered with growth and IX conversion. Critical factors to finally enable bacterial 8-PN production from spent hops, using a food and feed grade medium, were evaluated in this research. The use of bacterial resting cells and complex medium at a pH of 7.8–8 best fulfilled the requirements for 8-PN production and generated a solid basis for development of an economic process.
Highlights
The prenylated flavanone 8-prenylnaringenin (8-PN) is known as a very potent phytoestrogen (Milligan et al 1999; Schick and Schwack 2018) and is almost exclusively found in hops
Concentrations of 8-PN are only 0.025–0.060 g kg−1 in hop strobili (Rong et al 2000). This fact hampers commercially viable recovery of 8-PN through extraction and makes synthesis more attractive to obtain the compound at large quantities
IX conversion in food and feed grade bioconversion medium The rich brain heart infusion (BHI) medium was used to deliver the proof of concept for conversion of pure IX at 25 mg IX L−1 by Eubacterium limosum (Possemiers 2007)
Summary
The prenylated flavanone 8-prenylnaringenin (8-PN) is known as a very potent phytoestrogen (Milligan et al 1999; Schick and Schwack 2018) and is almost exclusively found in hops. Concentrations of 8-PN are only 0.025–0.060 g kg−1 in hop strobili (often called hop cones) (Rong et al 2000) This fact hampers commercially viable recovery of 8-PN through extraction and makes (bio-) synthesis more attractive to obtain the compound at large quantities. Moens et al AMB Expr (2020) 10:79 enantiospecific pharmacokinetics of IX in rat and monitored the appearance of 8-PN (Martinez and Davies 2015). As (S‐) 8-PN was found excreted in the urine in greater amounts than (R‐) 8-PN, further enantiospecific in vivo bioactivity studies are needed
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