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 (56e62%) and free form in soybean (59e85%). 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 b-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 18e24% 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
proteinelipidephenolic interactions in flaxseed protein residue and proteinephenolic interactions in soybean
protein residue likely play a role in the observed antioxidant activities.
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