There is an article by Gerhard Liebig in Deutsches Imker-Journal, May 1990,
p. 104-106 making reference to a thesis "Versuche zur Anwendung von Mikro-
wellen zur Verfluessigung von kandiertem Honig" by A. Dettling (Diplomarbeit
Hohenheim, 1987, Landesanstalt fuer Bienenkunde und Institut fuer Lebens-
mitteltechnologie). According to G.L. this study contains information on
HMF changes in honey when liquified by microwaves, but he does not tell
these results in the article. He tells, however, that enzyme content is
reduced considerably, if the heating is done using with too high a power or
too long a treatment time.