Abstract
In order to prepare reductive polypeptides from the placenta of dairy cows' fresh placentas from healthy Chinese Holstein cows were obtained and homogenized. Response surface model was established to optimize the hydrolysis condition for the extraction of the placental polypeptides. Specifically, the placental tissue homogenate was treated with both trypsin and pepsin for 348 min and 329 min; at 35.00% and 35.75% of substrate concentration; with an enzyme-substrate ratio of 3.33% and 3.92%, respectively, based on the models. The treated samples were then demineralized and freeze-dried to obtain the hydrolyzed polypeptides. In order to identify the molecular mass distribution and reducibility of polypeptides, matrix-assisted laser desorption ionization (MALDI) and Prussian blue methods were used. The concentrations of placental polypeptides after hydrolysis by trypsin or pepsin were 5.52% and 5.97%, respectively; the vitamin C (Vit C) equivalents were 36.26 μg mg(-1) or 61.15 μg mg(-1), respectively. Both groups showed intensity peaks of MALDI patterns in the range of 300 - 400 Da, and polypeptides hydrolyzed by pepsin had higher Vit C equivalent anti-oxidant activity than trypsin hydrolyzed polypeptide, suggesting that the proteins in the placental tissues were hydrolyzed to di-peptides and tri-peptides completely. In conclusion, both trypsin and pepsin hydrolysis performed well in preparation of reductive polypeptides from the fresh placentas of dairy cows; while, pepsin is more effective than trypsin. The primary reductive ingredients may be the oligopeptides with molecular mass less than 1000 Da.