Vinegar soaked soybeans were authorized as functional food
status by China Food and Drug Administration (CFDA) (License
WEISHIJIANZI (1997) No. 823) mainly due to the presence of soy
isoflavones, particularly aglycone forms. However, little information
is available on the changes of isoflavone compositions and
the interconversion of soy isoflavones of soy germ during soaking
in vinegars. Yongchun Monascus aged vinegar, one of the four
famous China-style fermented vinegars, was brewed from sticky
rice in the traditional way and could be traced back to more than
2000 years ago (the early years of the North Song Dynasty).
Various b-glycosidases may be produced during the fermentation
process via microorganisms such as acetic acid bacteria
(Acetobacter sp.), lactic acid bacteria (Lactobacillus plantarum),
yeast (Dekkera sp.), Monascus purpureus. Additional, rare report
took full advantage of that soy germ was rich in endogenous b-glucosidase.
Therefore, the combination of endogenous b-glucosidase
and acid hydrolysis may facilitate the transformation of isoflavone
forms from glucosides to the aglycones.
Thus, the objectives of this study was to understand the conversion
of isoflavone forms of soy germ during the soaking by
Monascus aged vinegar, investigate the possible mechanism of
the transformation and provide a basis for developing functional
foods of soy germ.