Low phenolic sunflower protein isolates and their potential antioxidant action in vitro

Oxidative stress, caused by the deregulation between the formation of pro-oxidant and antioxidant substances, is associated with increase incidence of chronic non-transmissible diseases (type II diabetes, Parkinson's disease, and some types of cancer). Sunflower meal, a co-product of biodiesel production, is rich in proteins with unknown functionality. Studies show that peptides, generated after a hydrolysis process, may have antioxidant action beneficial to health. In view of the above, the present work aims to evaluate physical-chemical properties and the potential antioxidant action of sunflower proteins after hydrolyzation. From defatted flour, the phenolic compounds were removed by alcoholic extraction (70%) and the proteins precipitated in isoelectric pH (4.5). The sunflower protein isolates (SI) was hydrolyzed by enzyme alkalase, in pH start (pH 9, at 50ºC/90 min). Then, the material was ultrafiltered on <5kDa membrane, generating sunflower hydrolysate filtered (SHF) and retented (SHR) fraction. In the physical chemical analysis SI, SHF and SHR showed 94, 71 and 56 % of protein content on dry basis, respectively. The molecular size of the fractions was determined by Fast Protein Liquid Chromatography (FPLC) by size exclusion. The molecular size of the peptides among the fractions were SI: >7, SHF: <3 and SHR: >7 and <3 KDa. The amino acid profile was determined by reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with a UV detector using a wavelength of 254 nm. It was observed that both fractions are rich in glutamic and aspartic acids, but limited on lysine. The in vitro antioxidant potential was evaluated by ABTS, DPPH and ORAC in different concentrations (0.3 to 2.5 mg/mL). The hydrolyzed fractions had a higher antioxidant potential than the isolated fractionin the ABTS and DPPH assay. The increase in antioxidant activity was dose-dependent. These data show for the first time that peptides derived from sunflower isolates show antioxidant activity even with the reduction of phenolic compounds. This industrial residue can be a promising source for obtaining foods derived from vegetable proteins, with antioxidant activity.