Binary ethanol–water solvents affect phenolic profile and antioxidant capacity of flaxseed extracts

Flaxseed extracts are in focus because of their potential application as a food ingredient. Ethanol–water mixtures are recommended for preparation of plant extracts due to their acceptability for human consumption. However, there is a lack of comprehensive studies concerning solvent effect on phenolic profile (phenolic composition and content) and its impact on flaxseed extract antioxidant capacity. This study investigated the effect of ethanol concentration in ethanol–water extraction solvent on the changes in phenolic profile (HPLC analysis after alkaline or alkaline-acid hydrolysis) and the antioxidant activity (DPPH· and ORAC_FL assays) of flaxseed extracts; various ethanol concentrations were investigated to prepare a suitable extract that could be safely introduced into food. The results showed relationships between the tested factors, i.e. the ethanol concentration and the phenolic content or the antioxidant capacity of flaxseed extracts. The content of phenolic compounds in extracts, including secoisolariciresinol diglucoside, phenolic acids and their glucosides, decreased with increasing concentration of the ethanol from 60 to 90 % in extraction solvent (total phenolics after alkaline hydrolysis were 106.5 and 7.7 mg g−1, respectively). On the contrary, the content of phenolic acid esters was the highest in the 90 % ethanol flaxseed extract. Changes in the phenolic profile with ethanol increase in extraction solvent impacted negatively the radical scavenging activity of the extracts. This study indicates that the mixture of ethanol and water in proportion of 60:40 (v/v) is the most suitable to obtain flaxseed extract with the high content of phenolic compounds and antioxidant activity.