Maltotriose syrup preparation from pullulan using pullulanase

摘要

Pullulan production was carried out at shake-flask level and purified with isopropanol precipitation using single-step purification strategy. Purified pullulan obtained was used for preparing maltotriose syrup using pullulanase. Pullulanase was subjected to kinetic and thermodynamic characterization before its use for pullulan hydrolysis. Pullulanase exhibited considerable activity between pH 5 and 6, with an optimum pH of 5.0. It remained stable (100%) for 6 h at optimum temperature of 50 °C. Mn~(2+) and Ca~(2+) showed 1.8 and 2.1 times increase in pullulanase activity. Pullulanase effectively hydrolyzed pullulan, soluble starch and dextran. Decimal reduction time (D value) was 76.77 h at 50 °C and Z value was 12.5 °C for pullulanase. Thermodynamic parameters (ΔH*, ΔG*, ΔS*) for irreversible inactivation of free pullulanase at different temperatures (50-70 °C) were also determined. In a batch system, pullulanase hydrolyzed 94.25 ± 1.83% of purified pullulan and the resultant syrup contained 3.77 ± 0.07 mg/mL of maltotriose. Thus far, there is no report on thermodynamics of irreversible inactivation of pullulanase for the hydrolysis of pullulan.