Naturally occurring low molecular peptides identified in egg white show antioxidant activity

Egg white is a rich source of bioactive proteins that are essential to provide protection to the embryo in yolk. There is an ongoing interest in identifying novel egg white proteins; it is not known however if peptides are also present in egg white. The objectives of the study were to identify low molecular peptides occurring naturally in egg white using a peptidomics approach and to determine their potential antioxidant activity. A total of 45 peptides were identified but surprisingly all are originated from egg white minor proteins (except ovotransferrin); three most abundant peptides, STDVPRDPWVWGSAHPQAQHTR, GDPSAWSWGAEAHS, and ALGEDIVDLDSFSEQH are derived from ovocleidin, zona pellucida glycoprotein C (ZPC), and sulfhydryl oxidase 1, respectively. Neuropeptide Y was identified for the first time in egg whites. The concentrations of eight most abundant peptides in egg white ranged from 0.004 to 0.292 mg/g, determined by triple quadrupole mass spectrometer in multiple-reaction monitoring (MRM) mode. Six peptides were found to have antioxidant activities based on reduced formation of superoxide and increased levels of superoxide dismutase (SOD) and catalase (CAT) in cells. Our study provided evidence on the presence of naturally occurring antioxidant peptides in egg white.