Characteristics of Bellamya purificata snail foot protein and enzymatic hydrolysates

The foot muscle protein of Bellamya purificata (mud snail, named Luosi in Chinese) was investigated. Its conformation change and increase in solubility were researched during enzymatic hydrolysis. The protein conformation was looser following an increase in pH (from 10 to 12), while the β-sheet was the main conformation at pH 12. Blending, ultrasonic extraction, ultradispersing and alkaline treatment increased the solubility of the foot muscle protein. The effects of several proteases on its hydrolysis were compared and Proleather FG-F was chosen. The relative molecular mass distribution, the free amino acids (FAA) content and the angiotensin-I converting enzyme (ACE) inhibitory activity of the hydrolysates were quantitatively analyzed and compared. In the Proleather FG-F hydrolysates, the percentage of the peptides with molecular weight between 150 and 2000 Da were 84.65%, much more than that in the Alcalase 2.4L hydrolysates (68.44%). Proleather FG-F released much less FAA (5.80%), than Alcalase 2.4L (17.01%). The IC50 of the Proleather FG-F hydrolysate was 0.69 mg/ml, whereas for the Alcalase 2.4L hydrolysate the value was 3.30 mg/ml. Finally, response surface methodology (RSM) was used to optimize the factors (pH, enzyme: substrate ratio- E/S- and temperature) affecting Proleather FG-F hydrolysis.