Lactose Hydrolysis in Ultrafiltration-Treated Cottage Cheese Whey with Various Whey Protein Concentrations

Lactose hydrolysis by soluble Aspergillus oryzaeβ-galactosidase was studied in (a) ultrafiltration (UF) permeate containing varying concentrations of isolated β-lactoglobulin or serum albumin; (b) UF retentate at four protein levels; and (c) cottage cheese whey during the UF treatment in an Amicon stirred cell unit. The rate and extent of lactose hydrolysis achieved in all the conditions studied was independent of protein concentration in the whey preparations used. After 6 hr of the simultaneous UF-lactose hydrolysis process at room temperature, similar hydrolysis level was achieved in the retentate as in the batch hydrolysis process. The average degree of hydrolysis in the permeate was 52.6%. The retentate added to milk at room temperature hydrolysed 93% of the lactose in 15 hr.