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Preparation of immobilized β‐galactosidase by poly(vinylpyrrolidone) and the continuous hydrolysis of lactose in acid whey

Immobilized β‐galactosidase gel was prepared using poly(vinylpyrrolidone) (PVP) under β‐ray irradiation. In contrast to the gelation of N‐vinylpyrrolidone monomer–enzyme solution, the gelation of PVP‐β‐galactosidase solution (PVP content: 10%) was almost completely uneffected by the dose rate and amount of phosphate present. PVP‐enzyme solution was gelled by irradiation with 3.0 Mrad. The expressed activity of the PVP‐enzyme gel was about 30% of the initial activity and added activity was almost totally entrapped. No leakage of enzyme from these gels could be detected. Leakage was, however, detected in the case of the gelation of PVP‐enzyme solution containing more than 1% of enzyme protein. When the general properties of the gel were compared with those of the native enzyme, the gel proved to be slightly inferior to the native enzyme with respect to optimum temperature, heat stability, pH activity, and pH stability. Continuous hydrolysis of lactose in acid whey could be carried out at 50°C using a column packed with the gel and sawdust and the degree of hydrolysis was found to be almost, constant for 12 days. The merits of using PVP in the immobilization of enzymes include the simplicity of the procedure and the fact that the PVP‐enzyme gel can be used in the food industry without anxiety because of its high degree of compatibility with living organisms.