The revisited levels of free and bound phenolics in rice: Effects of the extraction procedure

• The phenolics recovery is influenced by the solvolytic solution.
• Three extraction steps increase up to 10% phenolics recovery.
• α-Amylase pre-treatment of the residue remarkably increased bound phenolics extraction.
• Phenolic acids extractability is favored by the reduction of matrix viscosity.

The effects of the type of solvolytic solution and number of extraction steps on the recovery of free phenolics, anthocyanins and proanthocyanidins from different rice samples were evaluated. Moreover, bound phenolic acids were determined as a function of enzymatic and/or alkaline hydrolysis treatment of the rice residue obtained after the extraction of free phenolics. The Acetone/Water (70:30 v/v) was the most effective solvolytic solution for extracting free phenolics from pigmented rice, as well as anthocyanins from black and wild rice, and proanthocyanidins from red rice. The application of three extraction steps increased the recovery of free phenolics up to 10%. The adoption of an enzymatic treatment, with α-amylase in order to reduce the paste viscosity of the residue, increased the extractability of bound phenolics. α-Amylase at 37 °C during 15 min followed by an alkaline hydrolysis at 37 °C was the best treatment for the recovery of bound phenolics.