from water or aqueous alcohols. With the temperature increase
from 60 ◦C to 90 ◦C, TPC in the alkaline extracts became slightly
reduced or not changed. It was supposed that the alkaline condition
at high temperature (90 ◦C) might induce the oxidative degrada-
tion of the phenolic compounds. Li et al. (2014) also reported
that the extraction yield reduced when alkaline solutions were
used.
Thermal treatment for extraction softens the chestnut inner
shells and thus the better facilitates the extraction of phenolic com-
pounds. However, excessive heating may decrease the recovery
yield by inducing oxidative degradation of the phenolic com-
pounds. The sensitivity to thermal treatment highly depends on
the inherent nature of the phenolic components. For anthocyanin,
thermal degradation occurred rapidly when the temperature was
higher than 70 ◦C (Havlikova and Mikova, 1985). Temperature
below 50 ◦C has been suggested for the conventional extraction
of phenolic components. In this study, however, a high temper-
ature up to 90 ◦C was used for the extraction, but no significant
decrease in the extraction efficiency was observed when water or
aqueous alcohols were used as the extraction solvent. Possibly,
the phenolic components in the chestnut inner shell were relatively stable to the thermal treatment unless alkaline solvent was
used.