Obtained residues after free phenolics extraction were rewashed
with 20 mL of redistilled water to extract bound phenolic
compounds. Water was then separated off and samples were
blended twice with 25 mL of 0.4 M NaOH for 2 h in ultrasonic bath.
Both supernatants were combined and adjusted to pH 4.0–4.5
using 6 M HCl. After centrifugation at 3421 g for 25 min,
supernatant was used as bound phenolic extract