Static time is defined as the time the sample interacts with the
extraction solvent per cycle in the extraction cell under defined
extraction conditions in a pressurised liquid extractor (Luthria,
2008). Three static time settings (5, 15, and 30 min) were investigated
in order to determine the effects of static time on responses.
ASE 300 permits to extract samples with static time between 5 and
99 min. Although no statistical difference was observed between 5
and 15 min in terms of TPC (p > 0.05) (Fig. 1c), the maximum responses
as average value were observed with 5 min static time.
RSA% value for 5 min was higher and statistically important than
that of 15 min. Five minutes was selected as optimum for subsequent
experiments. It should be noted that TPC of the extracts
started to decrease when a static time longer than 5 min was applied
at 40 C. Even though the extraction temperature (40 C)
was mild, HPLC-DAD analysis showed the hydrolysing of punicalagin
found in pomegranate peel to some degree into ellagic acid
with an extended extraction time, and the longer the static time,
the higher the amount of ellagic acid formed. The decrease in
TPC with extended extraction time might be due to two possible
reasons. First, limited solubility of ellagic acid in water used as
extraction solvent might effect the TPC results negatively. Second,
differences between the reaction rates of ellagic acid and punicalagin
with Folin–Ciocalteu’s phenol reagent might result in the
underestimation of TPC of the extracts that of longer static time
treated.