Abstract:

Dihydro-iso-alpha-acids are the products of isomerization followed by hydrogenation of alpha-acids as one kind of the main soft resins in flower cone of hops (Humulus lupulus L.) and show a slightly bitter taste and the best solubility among all hydrogenation products of isomerizd alpha-acids. Single factor and orthogonal array design methods were used to deal with the effects of reaction temperature and time and amounts of added NaBH4 and KOH to iso-alpha-acids on dihydro-iso-alpha-acid yield. Results indicated that the above reaction conditions all exhibited an obvious effect on dihydro-iso-alpha-acid yield in the decreasing order: reaction temperature ＞ amount of added KOH ＞ amount of added NaBH4 ＞ reaction time and their optimal values were as follows: a reaction system composed of iso-alpha-acids, KOH and NaBH4 at 1:1:0.25 molar ratio left to react for 2 h at 100 ℃. Two-, 3- and 5- fold scale-up experiments carried out under such conditions all gave over 97% dihydro-iso-α- acids yields.

Key words: hops, dihydro-iso-alpha-acids, hydrogenation, reduction