For apple peel consumption matrix effects should be considered.The
apple peel is characterized by high fiber content. For quercetin release a
digestion of tissue prior to absorption is required.The plasma concen-
tration time curve is not different to the other treatments.But it appears
to consist of two peaks.Under this assumption the first peak (90min)
coincides with the time of the main peaks in the apple peel extract treat-
ment.Thus,for the first elevating peak the quercetin glycosides content
might be the main factor.But of the total 71 μmol quercetin equivalents
the apple peel consists only 5% of the well absorbed quercetin-3-O-glu-
coside,i.e.ca.1mg quercetin equivalents.It seems to be questionable
that quercetin-3-O-glucoside is exclusively responsible for the plasma
increase of the first peak.Also deglycosylation of quercetin derivatives
by the microbiota of the salvia as reported by Walle,Browning,Steed,
Reed,andWalle(2005) must be taken into account.The second peak
at 240 min — resulting in a broad plateau — was close to the cmax
of
the poor soluble quercetin dihydrate from capsules. In addition the
concentration time curves of the quercetin dihydrate capsule and
apple peel treatment were similar. This can be considered as an
indication for the poor digestibility of the peel matrix,which resulted
in a retardation of quercetin plasma concentration in crease.