Hops are the flowers (also called seed cones or strobiles) of the hop plant Humulus lupulus. They are used primarily as a bittering, flavouring, and stability agent in beer. In addition to bitterness, they impart floral, fruity, or citrus flavours and aromas. Hops are also used for various purposes in other beverages and herbal medicine containing such as resins, volatile oils, polyphenols, and polysaccharides.
Hop resins mainly refer to the soft resins, the most important hop component from brewing point of view, that can be dissolved in hexane primarily consist of alpha-acids (α-acids) and β-acids.The main compounds in hops oxidize or degrade not only during ripening but also during processing and storage. These compounds are active, unstable, easily oxidized or reduced, and may change when exposed to different pHs. Particularly, hop β-acids, a blend of different analogues of lupulone, colupulone, adlupulone, prelupulone and postlupulone, are easily oxidized. β-acids are hydrophobic due to extra isoprenyl side chain, making them practically insoluble in aqueous media.
Gu and Liu prepared the HPBCD complex of β-acids by the cogrinding method in order to improve the solubility and stability of β-acids. Water solubility was increased (up to 1.73 mg/mL) and the inclusion complexes showed increased photostability, thermostability, and pH stability.
Stabilization and solubilization of hop extracts by cyclodextrin have been explored in various patents:
- Cheng, W. (2017) Preparing method of hop–
oil sustained- release microcapsule and application of hop– oil sustained- release microcapsule to beer brewing. CN106753942
- Peng, X. &Tan, Z. (2016) Application of hop acid-
beta-cyclodextrin inclusion compound in preparation of animal feed additives. CN105360623
- Dragan, L. (2014) Solid dosage form of the drug with sedative and hypnotic effects. UA88462
- βIshida, H. et al. (2013) Method for producing a composition containing xanthohumol/cyclodextrin inclusion complex. JP2013066459
- Wada, K. & Yamamoto, T. (2012) Method for producing clathrate of the components of derived from hop and cyclodextrin. JP2012019695
- Yoshikoshi, T. & Amano, H. (2005) Method for correcting meat odor and meat processed food by cyclodextrin and hop extract. JP2005295988
- Wilson et al. (2004) Method of improving the stability of hop extracts and hop flavoured beverages. WO2006065131
 Gu, W., & Liu, Y. (2019). Characterization and stability of beta-acids/hydroxypropyl-β-cyclodextrin inclusion complex. Journal of Molecular Structure, 127159. doi:10.1016/j.molstruc.2019.127159