Zhang, X., et al. Preparation and identification of antioxidant peptides from protein hydrolysate of marine alga Gracilariopsis lemaneiformis. Journal of Applied Phycology. 1-12. 13/2/2019.

In this experiment, Gracilariopsis lemaneiformis proteins were hydrolyzed by different proteases (trypsin, pepsin, papain, α-chymotrypsin, alcalase) to prepare antioxidant peptides. Comparing with other hydrolysates, α-chymotrypsin hydrolysates displayed the highest antioxidant activity. The hydrolysis conditions of α-chymotrypsin were further optimized using response surface methodology (RSM), and the optimal conditions were as follows: substrate concentration 10 mg/mL, reaction time 2.0 h, enzyme/substrate ratio (E/S) 1.9%, temperature 46.4 °C, and pH 9.2. After fractionation and separation by ultrafiltration, gel exclusion chromatography, and reversed-phase high-performance liquid chromatography, an antioxidant peptide was purified and identified as Glu-Leu-Trp-Lys-Thr-Phe by UPLC-MS/MS. The results also confirmed that Glu-Leu-Trp-Lys-Thr-Phe could significantly scavenge DPPH free radicals with an EC50 value of 1.514 mg mL−1. It seems that the smaller molecular size and hydrophobic and/or aromatic amino acids in its sequence contributed to its antioxidant activity. Thus, G. lemaneiformis protein hydrolysate may be a good source of natural antioxidants.