Antioxidant capacity of caseinophosphopeptides prepared from sodium caseinate using Alcalase

The antioxidant capacity of caseinophosphopeptide prepared at different pH from casein hydrolysate with Alcalase was evaluated using oxygen radical absorbance capacity (ORAC), reduction capacity and metal chelating activity. The yield of CPP production was dependent on the pH of supernatant from pH 4.6 clarified Alcalase hydrolysate of sodium caseinate. CPP of pH 3 had higher content of cysteine, aspartic acid, glycine, histidine, proline, tyrosine, and leucine, and less content of glutamic acid, serine, and isoleucine than those of other pH. The phosphate contents of all CPP were relatively similar, 5.0–5.4% (w/w) except at pH 3. The ORAC against peroxyl radical (ORACROO${\text{ORAC}}_{{\text{ROO}}^{\text{<glyph name="rad"></glyph>}}}$) of CPP decreased with increasing pH (3–8) in concentrations tested and was positively correlated with its reduction capacity. The ORAC against hydroxyl radical (ORACOH${\text{ORAC}}_{{\text{OH}}^{\text{<glyph name="rad"></glyph>}}}$) of CPP at 50 μg/ml increased with increasing pH to 7 and then decreased, and its metal chelating activity on ferrous ion increased linearly with increasing pH from 3 to 5, then slowly increased until pH 8, indicating that the ORACOH${\text{ORAC}}_{{\text{OH}}^{\text{<glyph name="rad"></glyph>}}}$ activity of CPP might be attributed to the scavenging activity on hydroxyl radical itself as well as the chelating activity of transition metals.