Characterization and antioxidant activities of phenolic interactions identified in byproducts of soybean and flaxseed protein isolation

This study aimed to characterize the phenolic interactions generated from by-products of the protein isolation process from flaxseed and soybean flour. Protein isolates were removed from defatted and full-fat soybean and flaxseed using sodium hydroxide extraction and isoelectric precipitation. The residue and supernatant remaining after protein isolation were subjected to extraction of the free and bound phenolic compounds, which were evaluated for their phenolic profiles and interactions as related to their antioxidant activity. Analysis of residues obtained after isolation of the proteins showed the large phenolic contents of bound form in flaxseed (56-62%) and free form in soybean (59-85%). The supernatant remaining after precipitation of protein isolates of soybean and flaxseed revealed a relatively large proportion of phenolics in the free form ranging from 87 to 95%. The profile of free phenolics extracted from the residue and supernatant remaining after extraction and precipitation of protein from soybean and flaxseed differed from the profile of bound phenolic compounds. The measurement of degradation of a beta-carotene-linoleic acid emulsion showed that the extracted bound phenolics from residue remaining after protein extraction had antioxidant activities ranging from 27 to 34% for full-fat soybean residue and 18-24% for full-fat flaxseed residue. No antioxidant activities were noted following for bound phenolics extracted after base hydrolysis from the residue remaining after protein isolation from defatted soybean and flaxseed. The occurrence of protein-lipid-phenolic interactions in flaxseed protein residue and protein-phenolic interactions in soybean protein residue likely play a role in the observed antioxidant activities. (C) 2016 Elsevier Ltd. All rights reserved.