Effect of pulsed electric field (PEF) on structures and antioxidant activity of soybean source peptides-SHCMN

Recently, high-intensity pulsed electric field (PEF) has successfully used in improvement of antioxidant activity. Ser-His-Cys-Met-Asn (SHCMN) obtained from soybean protein was chosen to investigate the phenomenon of antioxidant activity improvement. Effects of PEF treatment on antioxidant activity of SHCMN were evaluated by DPPH radical inhibition. Nuclear magnetic resonance (NMR), mid-infrared (MIR), circular dichroism (CD) were used to analyze structures of SHCMN. Two-factor-at-a-time results show that DPPH radical inhibition of SHCMN is significantly (P < 0.05) increased to 94.35 +/- 0.03% at conditions of electric field intensity of 5 kV/cm, pulse frequency of 2400 Hz, and retention time of 2 h. In addition, MIR and NMR spectra show that the basic structure of peptides SHCMN is stable by PEF treatment. But the secondary structures (alpha-helix, beta-turn, and random coil) can be affected and zeta potential of PEF-treated SHCNM was reduced to 0.59 +/- 0.03 mV. The antioxidant activity improvement of SHCMN might result from the changes of secondary structures and zeta potential. (C) 2016 Elsevier Ltd. All rights reserved.