Identification of novel peptides from 3 to 10kDa pine nut (Pinus koraiensis) meal protein, with an exploration of the relationship between their antioxidant activities and secondary structure

In the present study, two novel peptides Lys-Trp-Phe-Cys-Thr (KWFCT) and Gln-Trp-Phe-Cys-Thr (QWFCT) were purified and identified from 3 to 10kDa pine nut (Pinus koraiensis) meal protein. Their cytotoxicity and antioxidant activities in vitro were determined. Additionally, pulsed electric field technology, antioxidant activities, and circular dichroism were used together to investigate the relationship between antioxidant activities and secondary structure. The results showed that neither peptide demonstrated cytotoxicity in HepG2 cells. KWFCT had higher values for 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition (67.43%±1.33%) and ferric-reducing antioxidant power (67.86±1.03mM Fe²⁺/mg), and Ac-QWFCT had higher values for 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) inhibition (74.9%±1.19%) and cellular antioxidant activity (916.32μmol of QE/100g) (P<0.05). The antioxidant activities reached their highest values when parameters of PEF were 5kV/cm and 2400Hz. An increase in antioxidant activities of Ac-QWFCT was correlated with a decrease in random coil content.