There was no correlation with the mole percent of
conjugated phenols and total phenol concentration in
the vegetables analyzed in Table 1. For instance, beets
that had the highest dry weight phenol concentrations
had the lowest percent conjugated, only 23.2%. Absorption
of flavonoids from the human diet was long
considered to be negligible since only free aglycons were
thought to be absorbed from the gut wall, and no
enzymes are present to split the â-glycosidic bonds
(Kuhnau, 1976). However, they can be hydrolyzed in
the large intestine by the bacterial flora enzymes and
be absorbed (Bokkenhueser et al., 1987). Quercetin
from onions, which is mostly present in the conjugated
form, is well absorbed in humans (Hollmann et al.,
1996).
The quality of the phenol antioxidants was determined
by the IC50 values shown in Table 2. The IC50
values are the same for both wet or dry weight phenol
of a vegetable. A low IC50 indicates strong antioxidants
in a vegetable. Yellow onions had the best antioxidants