Batch and continuous hydrolysis of ovine whey proteins

The aim of this work was to compare batch and continuous hydrolysis of ovine whey proteins in a membrane reactor and to evaluate influence of thermocalcic precipitation before hydrolysis. Reconstituted dried ovine whey from lump cheese production (a traditional Slovak cheese) was used as a substrate for hydrolysis by Promod 439L protease from Bacillus licheniformis. Initial substrate had 2% proteins and pH 8.5. Hydrolysis was performed directly (i) or after a pre-treatment (ii) comprising thermocalcic precipitation at 50 °C followed by microfiltration at 40 °C, batch-wise or in a membrane ultrafiltration (UF) reactor equipped with 8 kDa ceramic membrane. Mean residence time of 60 min was maintained after batch pre-hydrolysis of the substrate in the first 60 min period, during which the permeate was recirculated. During the subsequent UF, the reaction volume was kept constant by a continuous feeding of the substrate. After the pre-treatment (ii), crude protein decreased by 25%. Degree of hydrolysis was 9.2% (i) and 8.8% (ii) after 60 min at stand-alone batch hydrolysis, and 10.0% (i) and 9.0% (ii) after 60 min at batch-like pre-hydrolysis in the membrane reactor. After 180 min, the degree of hydrolysis (DH) in the UF permeate was 15.2% (i) and 13.0% (ii); the nitrogen content was comparable for (i) and (ii). Without the pre-treatment, (i) required three times higher pressure (0.3 MPa) in comparison with than (ii) to maintain residence time. The batch hydrolysis treatment resulted in 11.9% (i) and 14.6% (ii) DH after 180 min. At least 50% of enzyme can be saved using the membrane reactor in comparison with batch hydrolysis and the product does not contain enzyme and unhydrolyzed proteins.