title: In vitro antioxidant activities of the novel pentapeptides Ser-His-Glu-Cys-Asn and Leu-Pro-Phe-Ala-Met and the relationship between activity and peptide secondary structure.
abstract: BACKGROUND
  Using high-performance liquid chromatography/tandem mass spectrometry, two novel antioxidant pentapeptides [Ser-His-Glu-Cys-Asn (SHECN) and Leu-Pro-Phe-Ala-Met (LPFAM)] were identified from 1-3-kDa soybean protein hydrolysates (SPH). The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was used to evaluate cytotoxicity in HepG2 cells. Antioxidant activity was measured using in vitro assays, including the cellular antioxidant activity assay (CAA), 2,2-diphenyl-1-picrylhydrazyl or 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) inhibition, and oxygen radical absorbance capacity (ORAC) assays. Finally, the secondary structure was determined using circular dichroism (CD).
  
  
  RESULTS
  The results revealed that two novel peptides were nontoxic and possessed antioxidant activity. SHECN had significantly higher antioxidant activity than LPFAM (P < 0.05). The CAA value of SHECN was 776.22 µmol QE 100 g-1. SHECN also showed significant DPPH inhibition (70.18 ± 4.06%) and ABTS inhibition (88.16 ± 0.76%). It had normalized ORAC values of 0.3000 ± 0.0070 µmol GE mg-1and 0.0900 ± 0.0020 µmol TE mg-1, respectively. The results of the CD analysis demonstrated that, compared to LPFAM, which had much lower antioxidant activity, SHECN had a high β-sheet content and reduced α-helix content.
  
  
  CONCLUSIONS
  The results indicated that SHECN possessed high antioxidant activity. A higher β-sheet content and lower content levels of α-helix appear to be correlated with antioxidant activity. © 2016 Society of Chemical Industry.
authors.affiliation: College of Food Science and Engineering, Jilin University, Changchun, 130062, P.R. China.
authors.forename: Ruiwen
authors.initials: R
authors.lastname: Yang
authors.affiliation: Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 30, DK-1958, Frederiksberg C, Denmark.
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.affiliation: College of Food Science and Engineering, Jilin University, Changchun, 130062, P.R. China.|School of Food Science and Technology, Dalian Polytechnic University, Engineering Research Center of Seafood of Ministry of Education, Dalian, 116034, P.R. China.
authors.forename: Songyi
authors.initials: S
authors.lastname: Lin
authors.affiliation: College of Food Science and Engineering, Jilin University, Changchun, 130062, P.R. China.
authors.forename: Haiqing
authors.initials: H
authors.lastname: Ye
authors.affiliation: Department of Food, Nutrition and Packaging Sciences, Clemson University, Clemson, SC, 29634, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D056945:Hep G2 Cells; D006801:Humans; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D010455:Peptides
keywords: 1-3-kDa soybean protein hydrolysates; 3-(4,5-dimethylthiazol-2-y1)-2,5-diphenyltetrazolium bromide assay; cellular antioxidant activity; circular dichroism; high-performance liquid chromatography/tandem mass spectrometry