Use of Different Proteases to Obtain Flaxseed Protein Hydrolysates with Antioxidant Activity.

Key Findings

Defatted flaxseeds are rich in proteins, accounting for 31%–50% (w/w) with a relatively high content of aspartic acid, glutamic acid, leucine and arginine. Flaxseed protein hydrolysates using five proteases were produced and antioxidant activity in terms of radical scavenging activity, metal ion chelating activity and reducing power were assessed. The treatment of flaxseed proteins with proteases with high specificity (trypsin and papain) or enzymes with a broad range of action (pancreatin, Alcalase and Flavourzyme) produced hydrolysates with a high radical scavenging activity, ability to reduce ferric ions and ferrous ion chelation activity in comparison to the original proteins. Papain was the least effective in the release of peptides with antioxidant activity from flaxseed proteins among the enzymes applied. It was concluded that the type of enzyme used for the hydrolysis of flaxseed proteins determines the antioxidant activity of the respective hydrolysates.

Abstract

The antioxidant activity of flaxseed protein hydrolysates obtained using five different enzymes was evaluated. Proteins were isolated from flaxseed cake and were separately treated with papain, trypsin, pancreatin, Alcalase and Flavourzyme. The degree of hydrolysis (DH) was determined as the percentage of cleaved peptide bonds using a spectrophotometric method with o-phthaldialdehyde. The distribution of the molecular weights (MW) of the hydrolysis products was profiled using Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Tricine-SDS-PAGE) and size exclusion-high performance liquid chromatography (SE-HPLC) separations. The antioxidant activities of the protein isolate and hydrolysates were probed for their radical scavenging activity using 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS(•+)) and photochemiluminescence (PCL-ACL) assays, and for their ferric reducing antioxidant power (FRAP) and ability to bind Fe(2+). The hydrolysates were more effective as antioxidants than the protein isolate in all systems. The PCL-ACL values of the hydrolysates ranged from 7.2 to 35.7 μmol Trolox/g. Both the FRAP and ABTS(•+) scavenging activity differed among the hydrolysates to a lower extent, with the ranges of 0.20-0.24 mmol Fe(2+)/g and 0.17-0.22 mmol Trolox/g, respectively. The highest chelating activity (71.5%) was noted for the pancreatin hydrolysate. In general, the hydrolysates obtained using Alcalase and pancreatin had the highest antioxidant activity, even though their DH (15.4% and 29.3%, respectively) and the MW profiles of the peptides varied substantially. The O₂(•-) scavenging activity and the ability to chelate Fe(2+) of the Flavourzyme hydrolysate were lower than those of the Alcalase and pancreatin hydrolysates. Papain was the least effective in releasing the peptides with antioxidant activity. The study showed that the type of enzyme used for flaxseed protein hydrolysis determines the antioxidant activity of the hydrolysates.