Antioxidant activity and functional properties of porcine plasma protein hydrolysate as influenced by the degree of hydrolysis

Antioxidant activity and functional properties of porcine blood plasma protein hydrolysates (PPH) prepared with Alcalase at 6.2%, 12.7% and 17.6% of degree of hydrolysis (DH) were investigated. The PPH showed stronger radical-scavenging ability and possessed stronger Cu²⁺-chelation ability and a reducing power compared to non-hydrolysed plasma protein (P < 0.05). The antioxidant activity of PPH, indicated by thiobarbituric acid-reactive substance (TBARS) values in a liposome-oxidising system, increased with increasing DH (P < 0.05). The Alcalase hydrolysis increased protein solubility from its original 68.46–81.79% (non-hydrolysed) to 82.95–94.94% (hydrolysed) over a broad pH range (3.0–8.0). However, hydrolysis decreased surface hydrophobicity and suppressed emulsifying and foaming capacity of the plasma protein. To identify antioxidant peptide, PPH was subjected to ultrafiltration, ion-exchange chromatography and reverse-phase high performance liquid chromatography (RP-HPLC), and the amino acid sequences of isolated peptides were determined by liquid chromatography/tendem mass spectrometry (LC–MS/MS). The peptide with the strongest antioxidant activity had the amino acid sequence of His-Asn-Gly-Asn. The results indicated that PPH could be used as a novel antioxidant but may be of limited utility as an emulsifying or foaming agent.