Influence of Protein-Phenolic Complex on the Antioxidant Capacity of Flaxseed (Linum usitatissimum L.) Products.

Key Findings:

Several studies have shown the antioxidant potential of peptides released from enzymatic hydrolysis of different protein sources. This source of antioxidants has attractive characteristics for the food industry because it is nontoxic and has recognized nutritional value. Peptides can be an alternative to the use of synthetic antioxidants, preventing lipid peroxidation and maintaining the sensory characteristics of the products. A previous study carried out in this laboratory with flaxseed protein concentrates containing phenolic compounds have shown that simulated gastrointestinal digestion was equal or more effective than Alcalase hydrolysis to obtain antioxidant hydrolysates. This study showed that the presence of polyphenols contributed positively on the antioxidant capacity of the majority of protein samples. The presence of phenolic compounds led to an increase of about 80% on antioxidant capacity measured by ORAC and the FRAP assays. For the hydrolysate, the presence of phenolic compounds also led to an increase of nearly 80%, when measured by FRAP, but only of 15% when by ORAC. After simulated digestion, the influence of the phenolic compounds on the antioxidant capacity of the samples determined by the FRAP remained high.  In conclusion, the phenolic fraction showed the highest antioxidant capacity among the flaxseed products studied, which was enhanced by both alkaline hydrolysis and simulated gastrointestinal digestion, possibly by releasing SDG and pcoumaric, caffeic, and ferulic phenolic acids. The hydrolysis by both Alcalase and digestive enzymes also resulted in an increase of the antioxidant activity of protein concentrates with/without phenolic compounds. Flaxseed protein−phenolic complexes favored the exposure of protein moieties capable of acting as an antioxidant, which would complement the antioxidant potential of phenolics, with a positive relationship between these two classes of compounds. This would have a dual effect of phenolic protection against oxidative degradation along the gastrointestinal tract and establishment of a positive antioxidant environment.

 ABSTRACT

The impact of the naturally present phenolic compounds and/or proteins on the antioxidant capacity of flaxseed products (phenolic fraction, protein concentrates, and hydrolysates) before and after simulated gastrointestinal digestion was studied. For that, whole and phenolic reduced products were assessed. Four glycosylated phenolic compounds (secoisolariciresinol and ferulic, p-coumaric, and caffeic acids) were identified in flaxseed products. Phenolic fraction exerts the highest antioxidant capacity that increased by alkaline hydrolysis and by simulated gastrointestinal digestion. The action of Alcalase and digestive enzymes resulted in an increase of the antioxidant capacity of whole and phenolic reduced products. Principal component analysis showed that proteinaceous samples act as antioxidant is by H⁺ transfer, while those samples containing phenolic compounds exert their effects by both electron donation and H⁺ transfer mechanisms. Protein/peptide-phenolic complexation, confirmed by fluorescence spectra, exerted a positive effect on the antioxidant capacity, mainly in protein concentrates.