Entrapment of α-amylase in alginate beads: Single step protocol for purification and thermal stabilization

Affinity precipitation could be a viable alternative to conventional protein purification techniques with advantages of easy scale-up, cost and time effectiveness. We have used alginate as the affinity matrix for entrapment of α-amylase and subsequent precipitation of the beads with calcium chloride. Amylase was recoverable by addition of 0.5 M NaCl containing 0.2 M Ca2+. The enzyme was found to be homogenous (recovery of 76%) with a specific activity of 1764 U/mg. The pH and temperature optima shifted (on entrapment) from 5.5 to 6.0 and 54 to 60 °C, respectively. The entrapped enzyme had higher thermal stability compared to the free enzyme. The midpoint of thermal inactivation for the enzyme increased by 6 ± 1 °C on entrapment. The entrapped enzyme had an Ea value of 51.7 compared to 40.9 kcal mol−1 for the free enzyme. The positive increase in Ea value as well as the half-life of the entrapped enzyme is indicative of increased stability. The reusability of the beads was dependent on bead size. Beads with <1 mm were stable and could be reused for six cycles with ∼30% loss in activity.