Abstract This research describes an enhance‐fluidity liquid extraction process for extracting total phenolic compounds (TPC) from spent blackberry pulp (SBP) using a modified solvent (CO 2 –ethanol mixture). Effects of particle size (from 1,400 to 180 μm), pressure (150–300 bar), and cosolvent (ethanol)‐to‐solid ratio (64, 128, and 192 mL ethanol/32 g solid) on the extraction of TPC at 40°C were investigated. Experimental data was processed using the Sovova's model to obtain the solubility of TPC in the modified solvent. The Peng–Robinson equation of state was used to correlate the solubility of phenolic compounds at high pressures. Results indicated that particle sizes ranging from 600 to 850 μm and pressure of 300 bar allowed obtaining extracts with higher antioxidant activity (94.71% of inhibition) and TPC content (11.59 mg GA/g SBP). High pressure and the modified solvent increased the solubility up to 3.4 × 10 −4 (mol fraction).