Bioaffinity based immobilization of almond (Amygdalus communis) β-galactosidase on Con A-layered calcium alginate-cellulose beads: Its application in lactose hydrolysis in batch and continuous mode

In this study, immobilization of partially purified almond (Amygdalus communis) β-galactosidase on Con A layered calcium alginate-cellulose beads was investigated. Immobilized β-galactosidase retained 72% of the
initial activity after crosslinking by glutaraldehyde. Both soluble and immobilized enzyme exhibited the same
pH and temperature optima at pH 5.5 and 50ºC, respectively. However, the immobilized enzyme
showed a remarkable broadening in pH and temperature-activity profiles as compared to the native
enzyme. Immobilized enzyme was significantly more stable against thermal denaturation at 60ºC.
Immobilized β-galactosidase exhibited 67% residual activity in the presence of 5% D-galactose while its soluble counterpart retained only 35% activity under identical conditions. Soluble enzyme showed 69% residual
activity after exposure to pepsin (0.15 mg/ml) for 1 h whereas the immobilized β-galactosidase was more
stable and retained nearly 84% activity under identical experimental conditions. The activity of immobilized
enzyme was enhanced to 156% whereas soluble β-galactosidase showed an enhancement upto 134%
when exposed to trypsin (0.1 mg/ml) for 1 h. Moreover, immobilized β-galactosidase exhibited greater
enhancement in enzyme activity against exposure to various ions present in milk such as Na+, K+, Ca+2,
Mg+2 and citrate ions. The higher concentration of lactose was hydrolyzed from whey as compared to the
hydrolysis from milk by immobilized enzyme at 50ºC and 60ºC in batch processes. Lactose was hydrolyzed
to 86% and 78% after 20 days continuous operation of reactors at the flow rates of 20 ml/h and 30 ml/h,
respectively. In view of its stability and utility in batch and continuous processes, such preparation could be
exploited for the hydrolysis of lactose from milk and whey in a more convenient and cheaper way in dairy
industries.