Recently, pressurized hot water or subcritical water
has become of great interest as an alternative solvent
for extraction of natural active compounds. Water is
termed “subcritical” when its temperature is between its
boiling point (100 °C) and its critical temperature (374.15
°C), and its pressure is high enough to maintain it in the
liquid state. In this region, water’s dielectric constant is
greatly reduced from that at ambient conditions, thereby
decreasing its polarity.