Preparation and antioxidant properties of Maillard reaction products from Schizochytrium limacinum protein peptides

The Schizochytrium limacinum hydrolysate (SLH) was prepared from defatted S. limacinum residues, so as to analyze its Maillard reaction conditions. Besides, we explored the antioxidant activities of Maillard reaction products (MRPs) from the isolated fractions of SLH by ultrafiltration and sephadex gel column chromatography. The optimal Maillard reaction parameters were obtained as follows: mass ratio (ribose: peptide) of 1∶1, pH of 9, temperature of 100 ℃ and time of 6 h (the reducing power activity was 1.24 at 5 mg·mL⁻¹ and the DPPH radical scavenging rate was 88.62% at 12.5 mg·mL⁻¹). The SLH was ultra-filtered to obtain the fractions of SLH-1 (<5 kD), SLH-2 (<10 kD) and SLH-3 (<50 kD). It is found that the SLH-1 had the strongest antioxidant capacity before and after Maillard reaction. Then the SLH-1 was further separated by Sephadex G-25 gel column to obtain the fractions of SLH-1-I, SLH-1-II, SLH-1-III and SLH-1-IV. Higher molecular mass fraction of SLH-1-I had higher antioxidant activity after Maillard reaction (the reducing power activity was 0.741 at 2 mg·mL⁻¹ and the DPPH free radical scavenging rate was 79.41% at 5 mg·mL⁻¹). Amino acid composition analysis shows that Maillard reaction could decrease the contents of Tyr, Lys, His, Arg and Trp, etc. However, there was no obvious change in the content of essential amino acids after Maillard reaction.